180 replies to this topic

[manolis]

Hello.

The advantages of the tooth belts for the transmission of power (as in the final transmission of motorcycles, for instance) and for the synchronization of shafts (like: crankshaft to camshaft) are well known: efficient, reliable, lightweight, simple, cheap, quiet, smooth, lubricant free and maintenance free.

In the typical case, a belt having teeth at one side engages a pair of pulleys (or sprockets).
A limitation of this transmission: the two sprockets (and the shafts wherein they are secured) rotate necessarily at the same direction.

In several applications, however, the two shafts must rotate at opposite direction. For instance: in order the two crankshafts (disposed at a distance from each other) of an opposed piston engine (click here) to counter-rotate in synchronization, a tooth belt would be preferable than a series of gear wheels (or than four bevel gears and a shaft); but the "same direction" limitation is not allowing the use of a tooth belt.

In the following image:



At (a) a conventional tooth belt is engaging a pair of tooth belt sprockets at 1:1 transmission ratio. The two sprockets rotate at the same direction.

At (b) the conventional tooth belt of the (a) arrangement is utilised in a different way: the two sprockets rotate at opposite direction with the same 1:1 transmission ratio. The distance of the two sprockets is smaller. The tooth belt forms a big "X" between the two sprockets, with the teeth, at the center of the "X", facing each other.
In order to avoid the touching / wear / friction of the teeth, the two "crossing" parts of the belt (at the center of the "X") must be kept at a safety distance by spacers, rollers, tensioners etc.

At © an unconventional, as explained in the following, tooth belt interconnects the two sprockets; the sprockets rotate at opposite direction with the same 1:1 transmission ratio.
In comparison to the (b) arrangement, at the center of the "X" of the © arrangement the backsides of the tooth belt face each other, leaving (and protecting this way) the teeth at the other "external" sides.
Even if the backsides of the tooth belt are left free to touch each other at the middle of the "X", the system works reliably:
besides keeping the teethed sides away from each other,
it is also the smaller height, measureded from the "belt pitch line", of the backside of the tooth belt (as compared to the height of the front side with the teeth), allowing a wider angle of the belt at the center of the "X".
If necessary, the surface of the backside of the tooth belt can be covered / coated with a Nylon, or other antifriction / wear-resisting, "film".
If desired, a slim spacer (made of Teflon, for instance), or rollers etc, can keep, at the center of the "X", the backsides of the tooth belt from touching each other.


Starting with a conventional tooth belt:



the following images show the steps for "making" (actually for explaining the structure of) an unconventional tooth belt like the one shown in the © arrangement.

The conventional tooth belt is properly cut (the "arrow" at the one end of the band shows how this end is to be twisted):



Keeping the one end immovable, the other end of the band is twisted for two complete turns (720 degrees):



The two ends of the twisted band are rejoined forming an unconventional / twisted tooth belt:



like that used in the © arrangement.


Unlike the Mobius belt / strip wherein there is not front-side and back-side, here the belt has a back-side rid of teeth and a front-side wherein the teeth are mounted.


Applications:
For the transmission of power between, and for the synchronization of, shafts rotating at opposite direction.
For instance, for the synchronization of the two crankshafts of the PatATi Portable Flyer at http://www.pattakon....pattakonFly.htm


For a tooth belt manufacturer the cost for making either a conventional or this unconventional toothed belt is the same.


Thoughts?

Objections?

Thanks
Manolis Pattakos

[kikiturbo2]

two objections..

 

first... you can't manufacture it... not in a mass production sense anyway...

 

second... by introducing a twist in the continuous belt, even if you can make it, you will introduce compliance which might be ok for power transfer purpose, but not for timing belt usage..

[Kelpiecross]

An interesting idea - but the disadvantages may outweigh any advantages. Hard to tension, may not work well at high loads or RPM etc. Main problem may be that rubber belts in general do not last all that well - especially not as well as a chain or gear drive.

The gear drive on your normal engine is fairly simple anyhow - and would be a lot more reliable.

It is not uncommon to see in old (1920s or thereabouts) books on engineering to see described crossed belt or chain drives to reverse direction. The Wright Flyer used a crossed chain to reverse one of its propellers direction.

[manolis]

Hello Kikiturbo2.

You write:
“by introducing a twist in the continuous belt, even if you can make it, you will introduce compliance which might be ok for power transfer purpose, but not for timing belt usage..”

The twisting is distributed along the whole tooth belt.

All the teeth are identical. If an ant or bug “walks along the belt from tooth to tooth”, it cannot say whether it is a twisted tooth belt or a conventional tooth belt.

This makes the twisted tooth belt proper for power transmission and for timing / synchronization usage.



Hello Kelpiecross.

Quote from bmw-motorrad:

Toothed belt drive F 800 S/ F 800 ST



The innovative rear wheel drive of the F 800 S/ST, in which a toothed belt transfers engine power to the rear wheel, ensures clean and maintenance-free power transmission. Together with the single-sided swing arm in light alloy, it is an entirely new concept in motorcycle design. With this combination, the secondary drive of the F 800 S/ST can be regarded as the equivalent of the clean and low-maintenance shaft drive of the R and K series. Specially developed for BMW Motorrad, the toothed belt not only runs extremely quietly, but it is also extremely durable due to its Aramide fibre reinforcement. Once the correct tension has been set during the first service, it is checked every 10,000 km, with a routine replacement being carried out at 40,000 km. The toothed belt is tightened over the bearing which guides the rear wheel in the single-sided swing arm. The mono swing arm ensures that the rear wheel is always positioned perfectly.

Since the belt is constantly under tension, possible load change reactions are minimised. This is a great advantage when compared to conventional chain drive. The load change reactions are additionally reduced by means of a jerk damper fitted with four elastomer blocks. The durability of the drive system is ensured by the toothed belt wheel in stainless steel and the output pinion gear which has a steel inner core; the sprocket consists of a sintered metal alloy. This combination ensures minimum wear. Due to the weight saving compared to chain drive, centrifugal forces are also reduced, thus improving the efficiency of power transmission.

End of quote


The power output of the BMW F800S/ST engine is 85bhp/8,000rpm.
They don’t use conventional tensioner for the alignment of the tooth belt.


In comparison, a twisted tooth belt in the PatATi Portable Flyer



runs rid of load: the two crankshaft rotate in phase, with their respective pistons sharing the same combustion chamber.

The lightweightness, the simplicity, the smoothness, the lubricant free operation of a twisted tooth belt are significant advantages for a Flyer.

Thanks
Manolis Pattakos

[Kelpiecross]

There have been both primary and final drive cogged belts for motorcycles for many years. This doesn't mean a twisted belt will work satisfactorily - it should not be difficult or expensive to test your crossed belt idea.

[kikiturbo2]

when I talk about compliance I am not talking about teeth pitch.. I am talking about stiffness, module of elasticity of a twisted belt vs. its straight counter part... take a piece of flat textile band and compare its elasticity when it is stratight and twisted.

Also, cambelts are made by cutting individual belts from a wide piece, IIRC, and the production of your twisted one would require a whole new process..

[kikiturbo2]

also, the drive of counter rotating shafts has allready ben done using traditional methods, by using toothed belts with theeth on both side... Fiat 2.0 16V comes to mind (the old one based on lampredi engine)

 

Edited by kikiturbo2, 02 November 2014 - 14:32.

[bigleagueslider]

If you consider how a synchronous timing belt transmits torque between the driving and driven sprockets the problems of putting a 180deg twist in the loaded section of the belt body become apparent. Think about the fact that these belts only transmit force in the section of the belt loaded in tension. They have a circumferential arrangement of parallel fibers that are very stiff in tension that allow the belt to handle high tension forces while also having sufficient out-of-plane compliance to conform to a small diameter pulley. If you put a 180deg twist along the belt span loaded in tension, the outer edges of the belt will have to travel a longer distance than the center of the belt, and this will result in the outer edges of the belt taking most of the loads. The problem becomes worse as the belt gets wider and/or the span between the sprockets gets shorter.

 

If you plan to use this belt arrangement to synchronize the crankshafts of an opposed piston 2-stroke engine, you should also consider that there will likely be reversing torque oscillations between the intake and exhaust cranks. And these load reversals will present a serious problem for a belt drive.

[manolis]

Hello Kelpiecross.

The twisted tooth belt is to be tested in the PatATi Portable Flyer.



Hello Kikiturbo2

Mass production:

You are right about the manufacturing.
The twisted tooth belt cannot be made, in mass production, as the conventional tooth belts, i.e. by cutting in several pieces a wide toothed belt.


Stiffness issue:

For a belt with a "free opening" of 530mm (it is the length of the belt between the two sprockets / pulleys of the PatATi Portable Flyer) and a width of 20mm, the stiffness of the straight belt and of the twisted is substantially the same.
The ratio of the length of the outmost fibers to the length of the center fibers is 1.0007 ( 1.0007 = 530 / (530^2+20^2)^0.5 )

That is the central fibers contribute a little less than the external ones to the stiffness of the belt (in other words: the central fibers of the “skeleton” of the timing tooth belt run a little bit less tighten).

If you take into account that flexible material surrounds the fibers (the reinforcing fibers are "swimming" inside the elastic basic material of the belt), there is no measurable difference in the stiffness of the straight and of the twisted timing tooth belt.

20mm width is more than necessary for the PatATi Portable Flyer (it transfers no loads, it just keeps the two crankshafts synchronized).

For power transmission, a 40mm width for 530mm “free length” is more realistic. In this case the ratio of the length of the “external” fibers to the length of the central fibers is 1.0028. The elastic material of the belt – wherein the fibers "swim" - smoothes out even this small difference. It is also the fact that the external fibrers is the majority.


Teeth at both sides of the tooth belt:

In the PatATi Portable Flyer there are two well supported (by roller bearings) crankshafts.
How many additional sprockets, shafts and roller bearings does it takes a “double sided tooth belt”? Where to support them? How much weight they add?

From a different viewpoint: if the one 2nd order balance shaft of the FIAT 2.0 was driven - through a twisted tooth belt - by the other 2nd order balance shaft, wouldn't it be a better solution than the existing with the double sided tooth belt?

An interesting application of the twisted toothed belt: the driving of the 1st order balance shaft of the cross-plane straight-four engines.



Hello Biflegueslider.

I think the response to Kikiturbo answers the issue of the unevenly tighten fibers.


You also write:
"If you plan to use this belt arrangement to synchronize the crankshafts of an opposed piston 2-stroke engine, you should also consider that there will likely be reversing torque oscillations between the intake and exhaust cranks. And these load reversals will present a serious problem for a belt drive."

Read in my last post how much better – according BMW – a tooth belt receives the load reversals than a chain.
If there were reversal loads, it would not be an issue for the twisted toothed belt.

However, in the PatATi Portable Flyer there are no load reversals, at all.

The PatATi Opposed Piston engine has no intake crankshaft and exhaust crankshaft. The two crankshafts are equivalent and share the same combustion chamber. Their pistons feel / see the same instant pressure.

It is a perfectly symmetrical engine, with lots of built-in asymmetry of the intake and transfer processes like:



Take a look at http://www.pattakon....ttakonPatAT.htm



So, the question remains:

Is there a more lightweight and simple way to keep the two counter-rotating crankshafts of the PatATi Portable Flyer synchronized ?

Thanks
Manolis Pattakos

[kikiturbo2]

toothed belt with a planetary gearbox on one side?

[DaBeRa]

This is the 500 4cyl König 2stroke with a very smart drive for the 2portet discvalve. Flat contrerotating boxer.

Edited by DaBeRa, 03 November 2014 - 10:51.

[manolis]

Hello DaBeRa.

Thanks for the photo (and for the story behind the photo at http://www.odd-bike....d-underdog.html )


The 500cc 4cyl König 2stroke had a power of 85bhp at 10,000 rpm.

Its tooth belt twists by 90 degrees from the crankshaft to the first "tensioner" and by another 90 degrees from the 1st tensioner to the disk valve. The same from the disk valve to the 2nd tensioner and back to the crankshaft.
If you add the twist angles, this tooth belt is equivalent with the PatBelt, the twisted tooth belt presented in this thread.

Besides twisting, the toothed belt of the 500cc 4cyl König 2stroke also bends (changes direction) for 90 degrees at the one tensioner, it also bends for 90 degrees at the other tensioner). This "bending" is at the opposite direction than the direction the belt normally bends at the toothed sprockets.

Despite the twisting and the consequence "uneven tightening" of the "skeleton" fibers, despite the bending, despite the 10,000+ rpm wherein it was working, despite the poor quality of the materials used for the toothed belts 50 years ago, the toothed belt of the 500cc 4cyl König 2stroke was working reliably and the engine was a GP-500 winner.


The twisted tooth belt of the PatATi Portable Flyer has a much easier life.
The rev limit is only 5,000 rpm; this limit is imposed by the (1m diameter) propeller tip speed which, at 5,000rpm, is 80% of the sound velocity.
It bends only at one direction and only around the toothed pulleys.

Thanks again DaBeRa.



Hello Kikiturbo2.

You write: "toothed belt with a planetary gearbox on one side?"

What I am looking for, is "a more lightweight and simple way to keep the two counter-rotating crankshafts of the PatATi Portable Flyer synchronized".

What you describe is heavier, more expensive, more complicate, it introduces asymmetry to a completely symmetrical structure etc.

Believe it or not, one more lb (0.5 more Kp) on your shoulders is too much in the case of a Portable Flyer.

Thanks
Manolis Pattakos

[Greg Locock]

I think you'd be better off using a cord at each edge of the belt rather than the traditional belt of fibres. If you use a flat belt of fibres the centre ones are relatively unstressed compared with the outer ones, which i think will cause problems. Another option would be a pair of belts with a spacer between them

 

http://www.mulco.net...res/34282-6.pdf

 

may be helpful

[Wuzak]

I think there is a reason why aero engines tend to not use belts and chains for important timing functions.

 

Now, say your belt fails or skips a few teeth. What are the consquences - to the engine and pilot?

 

If the pilot runs out of fuel, or the engine stops working for any other reason, will the Portable Flyer autorotate?

[Lee Nicolle]

I am sort of a fan of toothbelts. But bending them like you show to me seems damn dangerous. 

My experience with them  is that if they are not aligned properly they will try to run off the gear. That with dry sump pumps running at 50% of crank speed. I know someone that tried a chain drive. It lasted about 15 min literally. Supposedly self lubricating industrial chain. probably ok at a 1000 rpm, not 7000 divided by two. It spat off and through the radiator.

For cam timing to me they are far superior than chains, far less harmonics put into the crank, and they last a lot better without the large amount of stretching that happens with chains.  And ofcourse do not require large amounts of oil, that has to be kept in the engine.

Thatt Conti cattledog that Greg has put up does show 90 deg of bend. I suspect very expensive belts in very limited sizing. Probably with quite a short life. And do have to be very long.

I have seen the double sided belts, driving a one off OHC engine, they are quite functional BUT it appears the service life is quite limited. Eg about 20 hours. Though the engine was running at up to 7000 rpm. Though realistically that is probably all I ever got from dry sump belts. They started to look distressed and were replaced every 4 or 5 meetings. I still have half a dozen used ones in the spares box! Rubbish really as I always carried a new spare anyway. Though the stones and road muck did most of the damage.

That motorcycle engine to me is an accident waiting to happen. That poor belt will be destroying itself very rapidly, yet alone the propensity to jump off. or jump teeth. A bit like a tyre underinflated, destroys itself with heat.

 I have seen V belts crossed like that on agricultural equipment, though again not going very fast though they were driving quite a lot. Evidently they wore out the pullies quite quickly with all the belt thrust on one side. eg a 100 hours or so.

Edited by Lee Nicolle, 03 November 2014 - 23:48.

[DaBeRa]

@Lee Nicolle: The König Mc engine sure had its issues with its discvalvebelt, Non the less Kim N posthumed did 2. WC 1972. Later this PU had succes in sidecar racing. But in my POW this engine is a stroke of beauty...

Edited by DaBeRa, 04 November 2014 - 00:54.

[manolis]

Hello Greg Locock.

Thanks for the link.
Having the central fibers (or tension members) slightly less tighten is a better solution than replacing the tooth belt by a pair with a spacer between them: with a single tooth belt, the central part can be regarded as the spacer.



Hello Wuzak.

The PatATi Portable Flyer can perform a lot of tests without going high.
When flying no higher than 1m above the ground (or, even better, no higher than a few meters above the sea) a falling (due to a malfunction or due to an error of the rider) is no more dangerous than falling with a motorcycle.

The autorotation is an option for the future.



Hello Lee Nicille.

You write:
"I am sort of a fan of toothbelts. But bending them like you show to me seems damn dangerous."

It is not bending, it is twisting.
And it is not dangerous at all.
On the contrary, it seems it complies with manufacturers’ specifications:

Quote from Greg Lockok’s link:



As you see, according Continental you can twist their synchroflex toothed belts (made of a cast polyurethane shell and a high grade steel cord tension member):

"No power reductions or special measures are necessary at a "span length to belt width" ratio >= 20.
At a required "span length to belt width" ratio < 20 please contact our technical department for advice"

At top right it is the arrangement used in the 500cc 4cyl König 2stroke, with the "tensioners" at an angle and with the "span length to belt width" ratio well below 10 (strange that in Conti-Flex arrangemrnt the "tensioners" are not touching the toothed belt at the backside).

As you see, the theory, the practice (Konig GP-500) and the manufacturers say that this unconventional twisted toothed belt works reliably.

By the way, the camshaft pulleys from a Honda VTEC (and a compatible Twisted tooth belt) are to be used in the PatATi.
The pulleys/ belt operate reliably at least till 9,000 rpm on the Honda VVA-roller prototype:



see the youtube video at https://www.youtube....h?v=-zzW8YkReLU ,

which means 4,500 rpm for the camshafts.

In the case of the Honda VVA roller prototype the timing belt transfers nearly a couple of KW (12mm intake valve lift, 11mm exhaust valve lift, 9,000 rpm, egg-shape Toda valve springs), while in the case of the PatATi Portable Flyer the tooth belt transfers no power.


As you see, an unconventional solution of a problem is not necessarily “a damn dangerous” solution.


And the question remains:
"Is there a more lightweight, efficient and simple way to keep the two counter-rotating crankshafts of the PatATi Portable Flyer synchronized ?"

Thanks
Manolis Pattakos

Edited by manolis, 04 November 2014 - 06:55.

[Greg Locock]

Well, you could try:

 

1) Use crank angle sensors and a motor-generator on each crank, to feed power from the fast crank to the slow one

 

2) Use bevel gears and a quill shaft

 

3) a governor on each cylinder

 

4) pitch control on the blade, so reduce the pitch on the slow one 

 

All of those sound horrific, admittedly. VF22 uses (2), WW2 bombers used (3 or 4), (1) is just traction control

Edited by Greg Locock, 04 November 2014 - 08:03.

[kikiturbo2]

5. Use a single or twin cyl engine of classic design with a signe crank, mount it vertically and then use two toothed belts in an angular drive setup to drive the twin blades..

[Wuzak]

Well, you could try:

 

1) Use crank angle sensors and a motor-generator on each crank, to feed power from the fast crank to the slow one

 

2) Use bevel gears and a quill shaft

 

3) a governor on each cylinder

 

4) pitch control on the blade, so reduce the pitch on the slow one 

 

All of those sound horrific, admittedly. VF22 uses (2), WW2 bombers used (3), (1) is just traction control

 

Not sure if you are talking of propellers or timing systems.

 

Most in-line engines of WW2 used bevel gears and shafts for their cam shaft drive.

 

 

 

The Jumo 205 opposed piston 2 stroke Diesels used spur gears to maintain teh timing between the two cranks.

 

 

[Greg Locock]

Ah, you've provided the solution. Synchronise the sparks, then they can never get more than 10 degrees out of position. Until the engine fails, in which case you are toast anyway.

[manolis]

Hello and thanks for the replies and for the proposed solutions and “solutions”.

I wrote in my last post:
“strange that in Conti-Flex arrangement (it is the arrangement at top right of the Conti-SynchroFlex brochure) "tensioners" are not touching the toothed belt at the backside”

Thinking again, the reason for this set-up seems to be that the tooth belt bends exclusively at one direction.

If Kim Newcombe:



had chosen this setup for his 500 4cyl König 2stroke GP500 (i.e. to put the tooth belt “upside-down” on the tesnioners), his toothed belt would be even more reliable.

The PatBelt (i.e. the twisted tooth belt we are discussing here) bends exclusively at one direction.

As for the gear wheels for the crankshafts synchronization, there is experience with the OPRE prototype engines built so far:



youtube video at http://www.youtube.c...h?v=64TY-x2Cj6Y

however, a twisted tooth belt between the two crankshafts is more lightweight, needs not additional bearings or support, is simpler, is more quiet, is smoother, needs not lubricant.

So the question remains unanswered.

Thanks
Manolis Pattakos

Edited by manolis, 05 November 2014 - 04:26.

[Kelpiecross]

In the case of the Konig engine the belt would be transmitting very little power.

I still think the original gear setup is best for the OP engine. How much heavier would gears be compared to the cogged belt arrangement? - maybe one kilo or so?

That You Tube video - although very impressive it just looks diabolically dangerous - both to the pilot and any bystanders.

[bigleagueslider]

The OEM data shown notes a limit of 20:1 for belt width and span length with a 90deg twist. A 180deg twist would likely require twice that amount. That would mean a 50mm wide belt would require a 2000mm (or 6.5 foot) span between the crank pulleys for your OP engine.

[Wuzak]

Wouldn't there also have to be a tensioner in there somehwere?

 

The spur gears shown could have a lot of material removed?

[manolis]

Hello Biglequeslider.

You write:
"The OEM data shown notes a limit of 20:1 for belt width and span length with a 90deg twist. A 180deg twist would likely require twice that amount. That would mean a 50mm wide belt would require a 2000mm (or 6.5 foot) span between the crank pulleys for your OP engine."


Quote from ContiSynchroFlex brochure
"No power reductions or special measures are necessary at a "span length to belt width" ratio >= 20.
At a required "span length to belt width" ratio < 20 please contact our technical department for advice"

According this, you can go bellow the 20:1 twist limit, provided you reduce the power transferred or the expected life of the belt (for instance, Kim Newcombe’s tooth belt twist ratio seems as being near to 5:1).

Besides, the Conti-SynchroFlex belts of the brochure are not the most elastic tooth belts. They are made of a cast polyurethane shell and a high grade steel cord tension member. The allowable twist ratio of the normal toothed belts (those used in the final transmission of motorcycles, for instance, or those used in the crankshaft to camshaft synchronization) is, reasonably, higher.

Besides, the toothed belt for the PatATi Portable Flyer is not transferring power, because the two crankshafts share the same combustion chamber and operate without phase difference. And the load is symmetrical (a pair of symmetricall counter-rotating propellers, each secured on its own crankshaft).
On this reasoning the 50mm wide tooth belt you mention is, by far, more than what the PatATi Portable Flyer needs.
Unless I am wrong, the toothed belt of the final transmission of the 85bhp BMW 800F is only 35mm wide. Think that F800 toothed belt is much heavily loaded by the inertia loads during a deceleration using the engine as brake, than by the transferring of the 85bhp. The expected life of this belt is over 40,000Km

If you divide the 530mm span length by 40 (40=2*20), the result is 13.25mm. If the width of the twisted tooth belt is 13.25mm (or less) it is OK with the specifications of Continental, that is, you can use it at full power without any reduction of its expected life. 13.25mm is OK.
A 19mm ( 3/4’’ ) width is very common for timing belts. If we use it in the PatATi Portable Flyer, the twist ratio becomes: 28. Reasonably the power capacity should reduce somewhat. But think that the belt of the PatATI PortAable Flyer transfers no power at all.



Hello Wuzak.

You write:
"Wouldn't there also have to be a tensioner in there somehwere? "

It is preferable to use the twisted tooth belt without a tensioner. The distance of the crankshafts can be set so that the belt to be properly tighten without tensioners.
But if you want a tesnioner, it can be located near the center of the "X", at the right orientation.



Hello Kelpiecross/

You write:
"In the case of the Konig engine the belt would be transmitting very little power."

Similarly in the PatATi Portable Flyer the PatBelt transfers very little power. The PatATi engine is completely symmetrical. As long as the two crankshafts have no phase difference, the PatBelt transfers no power at all. It transfers less power than what a timing belt transfers from the crankshaft of an car engine to the camshaft. The PatBelt just keeps the two crankshafts synchronized.


You write:
"I still think the original gear setup is best for the OP engine. How much heavier would gears be compared to the cogged belt arrangement? - maybe one kilo or so? "

It is more than one kilo. But let’s suppose it is only one kilo.
Isn’t it preferable to have one more kilo of fuel with you, than carrying one more kilo of "transmission"?
With one more kilo of fuel (about 1.5 lt) the range extends for some 20 Km.


You write:
"That You Tube video - although very impressive it just looks diabolically dangerous - both to the pilot and any bystanders."

The engine in the video is to be secured at the nose of an ultralight (or small) airplane and drive it without loading the airplane frame with reaction torque (even at extreme changes of the load) and without tranfering inertia and combustion vibration to the rest structure.

Why is it dangerous in this case? Is the pilot in more danger than with a conventional engine? Are the bystanders?

Now think of the, say, PatTilt Portable Flyer. The pilot – rider cannot approach the propellers, no matter how hard he tries.
The bystanders are in the same danger as if they were standing besides the rotating propeller of an airplane.
Similarly with the PatATi Portable Flyer: being secured on pilot body, it cannot injure the pilot. The bystanders should stand away, as with an airplane.

Thanks
Manolis Pattakos

Edited by manolis, 06 November 2014 - 06:25.

[Wuzak]

Manolis, since the power transmitted is low the gears in a gear train can be very light weight too. And even made from lighter materials than steel.

 

Will there ever be a situation where one of the cranks can make less power than the other? Say in the case of piston failure - or would that effect both equally?

 

If so the drive system needs to transmit the power equally between the two rotors.

[kikiturbo2]

Similarly in the PatATi Portable Flyer the PatBelt transfers very little power. The PatATi engine is completely symmetrical. As long as the two crankshafts have no phase difference, the PatBelt transfers no power at all. It transfers less power than what a timing belt transfers from the crankshaft of an car engine to the camshaft. The PatBelt just keeps the two crankshafts synchronized.

 

 

If the belt is to transmit little power the simplest and lightest solution for you is to use a double sided tooted belt and have two extra idlers on one side which will guide the belt around 1/2 of one sprocket so that it has enough contact between the sprocket and the outer side of the belt... All in all, you need those two extra idlers + maybe one more as a tensioner... It is not perfectly simetric but is the lightest solution available..

 

 

http://img.photobuck...mac/manolis.jpg

Edited by kikiturbo2, 06 November 2014 - 10:03.

[Kelpiecross]

Interesting point about the belt not having to transmit much power.

[manolis]

Hello Wuzak.

You write: "Manolis, since the power transmitted is low the gears in a gear train can be very light weight too. And even made from lighter materials than steel."

Imagine a more than 0.5m long casing full of gearwheels, roller bearings and pins.


You write: "Will there ever be a situation where one of the cranks can make less power than the other? Say in the case of piston failure - or would that effect both equally?"

No.
See the animations at post #4. The one side of the common combustion chamber is sealed by the one piston, the other side is sealed by the other piston.

If you want to run the PatATi Opposed Piston engine as a single cylinder, you can. All you have to do is to secure the one crankshaft at – or near – its TDC and to remove the synchronizing mechanism. With the immovable crankshaft at TDC the compression ratio drops to nearly half, yet the engine can still operate. Depending on the angle you fix the immovable crankshaft, the compression ratio varies (like in a VCR).

On the other hand, imagine having an 800cc engine secured on your shoulders / body. It has to be lightweight, it has to be reaction-free, it has to be vibration-free (including both: combustion and inertia vibrations), it has to be of zero (or near zero) gyroscopic rigidity (otherwise you cannot vector the thrust force quickly in order to control your flight).
These are the characteristics of the fully symmetrical PatATi Opposed Piston Portable Flyer.
The twisted tooth belt is a quite simple, reliable and lightweight synchronizing mechanism.



Hello Kikiturbo2 and thanks for the drawing.

The problem with the arrangement you propose is that it uses a substantially longer (than the PatBelt) double-sided (and expensive, I think) tooth belt, it also uses a pair of additional pulleys (with roller bearings at their hubs?) and a basis wherein these additional pulleys are to be secured.
All these add weight and cost.
It is also the loading of the double-sided belt: after the left sprocket it straightens, then it bends counterclockwise around the small diameter lower pulley at right, then it straightens again, then it bends clockwise around the right toothed pulley, then it straightens again, then it bends counterclockwise around the right-top small diameter pulley, then straightens again and finally bends counterclockwise around the left tooth pulley.
By the way, the additional pulleys cannot be so small in diameter (it is bad for the belt).
Compare the stressing of the double-sided tooth belt with that of the PatBelt at © of post #1.



Hello Kelpiecross.

You write: "Interesting point about the belt not having to transmit much power."

The actual load of the Twisted toothed belt is its initial tightening.
With the divided load (either it is a pair of counter-rotating symmetrical propellers, or it is a pair of counter-rotating symmetrical electric generators etc) the synchronizing mechanism runs unloaded.

Thanks
Manolis Pattakos

[bigleagueslider]

The configuration Manolis shows is unique since the power is taken out at each crankshaft by a pair of propellors. In this case the belt would only be required to transfer enough torque to keep the crankshafts synchronized. With other OP engines the belt or gear drive would need to transfer a much larger amount of torque. Typically the amount of torque would be something like 40% or more of that at the engine PTO.

[PJGD]

BLS: Not completely unique.  Earlier last century, Van Auken built a family of opposed piston 2-stroke SI engines for boats - see below.

There were flywheels at the non-driving end, while at the driving end there were bevel gears and cross shaft joining the two cranks to maintain synchronization.

Downstream of the cross shaft were clutches on both shafts which both drove the boat propellors. Clutching one or other propellor gave enhanced maneuverability.

 

PJGD

 

Edited by PJGD, 08 November 2014 - 02:22.

[manolis]

Hello PJGD.

Here are the drawings from Van Auken US Patent.





The mixture is compressed in the two crankcases.
It uses through scavenging (transfer ports at one end of the cylinder, exhaust ports at the other end of the cylinder).
With symmetrical timing (and symmetrical load at both crankshafts) the synchronizing mechanism runs unloaded, as you correctly write.

In the Junkers Jumo Diesel Opposed Piston, the crankshafts are at some 10 degrees phase difference from each other, providing a substantial asymmetry between the transfer and the exhaust (significant for the “volumetric efficiency”). In this case, the exhaust crankshaft (which is the first that passes the TDC) receives about 2/3 of the engine power (the propeller is typically driven by the first gear after the exhaust crankshaft). The synchronizing mechanism is heavily loaded, as Biglegueslider writes.


The PatATi Opposed Piston engine combines advantages of both schools.

It has asymmetric timing (as the Junkers Jumo Opposed Piston) :



however the two crankshafts have no phase difference at all (as the Van Awken Opposed Piston).

The loop scavenging allows a more compact combustion chamber: in the PatATi prototype the space among the two cylinder liners (79.5mm bore) is narrower (60mm diameter), with the two spark plugs more centrally located.
For the same dead volume, the “height” (along the cylinder axis) of the combustion chamber of the PatATi prototype is 75% taller as compared to the case without narrowing between the two cylinder liners). It is also the squeeze.

In the PatATi prototype there are, per piston, two Schnuerle transfer ports, two asymmetrical transfer ports (those controlled by the upper end of the connecting rod) and a power transfer port.

The middle area of the connecting rod controls asymmetrically the intake ports.

The PatATi is a completely symmetrical engine. The basis of the engine is perfectly rid of inertia vibrations.
The PatATi has a substantially asymmetric transfer process and a substantially asymmetric intake process.
Avoiding any transmission of the power (the propellers are the flywheels of the engine), the overall efficiency improves and the overall weight is the minimum.
With symmetrically divided load (the two counter-rotating propellers) the basis of the engine is perfectly rid of combustion vibrations, too.
Beside, the basis of the engine does not need to provide any reaction torque.

With the symmetrical engine structure and the symmetrical load (the two counter-rotating propellers), the overall gyroscopic rigidity of the system is zero, which means the thrust can “instantly” be vectored to the desirable direction (flight control).

The Twisted Tooth belt keeps the two crankshafts synchronized without transferring loads, and seems the most lightweight solution for the required synchronization.

Thanks
Manolis Pattakos

Edited by manolis, 08 November 2014 - 10:30.

[imaginesix]

At the risk of ending up with a head-shaped hole in one of my walls, here are my 2c...

 

Hello Wuzak.

You write:
"Wouldn't there also have to be a tensioner in there somehwere? "

It is preferable to use the twisted tooth belt without a tensioner. The distance of the crankshafts can be set so that the belt to be properly tighten without tensioners.
But if you want a tesnioner, it can be located near the center of the "X", at the right orientation.

 

Unless you can adjust the distance between the two crankshafts after installing the belt, then you can't tension using just the crankshafts, you need a tensioner. If you put a tensioner in the middle of the X then it will will put some side load on the belt where it runs on and off each crankshaft pulley.

 

Regardless of your tensioning mechanism, I don't understand why you can't just use a standard belt with a 1/2 twist? Since you can't let the belt rub against itself in the middle of the X, then it doesn't matter of the teeth on one side are facing the inside of the loop since they will need to be separated by a belt guide either way.

[imaginesix]

OK, here's an idea that I think solves all the issues.

The planetary gearset reverses the rotation of the drive. The asymmetric satellite gears can be adjusted on their carrier (blue) causing the annular gear to be displaced relative to the opposing crankshaft (it would move up and down in this image). This would give you your adjustable tensioner. The tension forces would have to run through the frame of the gearset so that the gears are free to turn without binding, but I think it's possible.

Edited by imaginesix, 08 November 2014 - 22:48.

[kikiturbo2]

I changed a cambelt today... tried to introduce a 1/2 twist in the belt... it just flat out doesnt work.. nor can you introduce a twist along the single belt as per ilustration C at the begining of this topic. Toothed belts that are needed for sznchronisation need to be very stiff along 2 dimensions... that doesnt go along with introducing twists..

[kikiturbo2]

I really like the eccentric planetary drive idea.. cool..

[manolis]

Hello Imaginesix and thanks for your drawing / mechanism proposed.

The tightening by aligning the distance of the two crankshafts is the simplest way.

With the PatBelt connecting the two counter-rotating toothed pulleys to be used in the PatATi Opposed Piston, and tighten as necessary, the center to center distance D between the two toothed pulleys is measured.

The crankshaft axis to crankshaft axis distance for the PatATi Opposed Piston is selected equal to D.
The structure of the combustion chamber allows the alignment of the compression ratio to the desirable value.

Till now I did not see anything more lightweight or simple.

After several flights the twisted toothed belt is to be replaced by a new one (in BMW F800 every 10,000Km - say every year - the toothed belt of the final transmission is re-aligned, every 40,000Km it is replaced).


Regarding your mechanism with the planetary set of gear-wheels: it is heavier, more expensive, more complicate, it needs lubricant, it needs several additional bearings – not shown - , it introduces asymmetry to a perfectly symmetrical structure etc; it is also not functional as it is:



If the above figure is not explanatory, just let me know to further explain.
In a few words, while the upper crankshaft does counter-rotate, it rotates with much higher angular velocity than the lower crankshaft / toothed pulley.

To correct the problem, you have to add gear wheels (like the red one). In this case the two other gear-wheels at the apexes of the triangle cannot cooperate.

Another better solution – in order to make your mechanism functional – is to make the upper toothed pulley some 2.5 times bigger in diameter than the lower toothed pulley (the ratio depends on the gear-wheels selected).

Clever idea.

However, the PatBelt does the same being by far simpler, lightweight, symmetrical, cheap etc.

Thanks
Manolis Pattakos

Edited by manolis, 09 November 2014 - 08:18.

[imaginesix]

Manolis,

 

It seems to me that it may be useful for you to elaborate very clearly what your goal is in the creation of this device. As best as I can guess from your replies, you seem to be approaching this as though it is a mechanically functional work of art rather than an item of mass production, for the following reasons;

 

1- You seem to be reliant on a mechanism (the belt) which cannot be mass produced, and AT BEST can only be produced in a small batch with much effort.

2- The assembly method you describe would be unsuitable for production and maintenance over the serviceable life of the device.

3- You seem to have a strong concern for maintaining a "perfectly symmetrical structure".

 

But that's just a guess. Please feel free to clarify your goals for us, because I think all the responses you have been getting are based on the assumption that at the end of the line this device is intended to be a production item seeking to achieve the maximum number of sales.

 

These are two very distinct purposes, either of which would lead to their own unique set of solutions through the course of discussion here.

Edited by imaginesix, 09 November 2014 - 15:01.

[RogerGraham]

The tightening by aligning the distance of the two crankshafts is the simplest way.

 

Sort of following on from imaginesix's post - I'm far from being an engineer, and I may be misunderstanding your meaning here, but this strikes me as unusual.  Presumably a tensioner keeps the belt at the correct tension with virtually no maintenance all of the time - including during the rather critical period when the engine is actually being used.  How practical is it to require the crankshaft-crankshaft distance to be changed to keep the belt tensioned?  Wouldn't such changes affect the combustion chamber? Etc...

Edited by RogerGraham, 10 November 2014 - 03:31.

[manolis]

Hello Imaginesix.

You write:
"It seems to me that it may be useful for you to elaborate very clearly what your goal is in the creation of this device."


I don’t know why, but a couple of days ago I received an e-mail from Pal-V.

It starts with a photo of their flying vehicle:



It continues with their logo:

"It drives, it flies, it works like a charm!"

Later it presents Pal-V pricing:

Though we do not have a detailed price list yet, we can give you a rough estimate. The prices will be comparable to fast but non flying sports cars ranging from app. € 300,000.- for the sports edition to € 500,000.- for the exclusive limited Pioneers Edition (only a few are available per region).


Martin’s JetPack cost is comparable to Pal-V: unless I am wrong, their last estimation for the simple version is 200,000$ . The range is about 30 Km, the fuel tank is about 40 lit.


Quote from the Internet about the flying cost of the Peroxide JetPacks ( youtube video at https://m.youtube.co...h?v=E81KQ7u3-7s ) :

"According to Tecaeromex's Juan Lozano "The flight time is very limited, but it is a great business for shows, special events and sport events because you charge about $25,000 for each flight. So the business is great.""


Recently they have been published several articles about the drones for "medicine delivery in roadless areas". Quote from one of them:

"Right now, Matternet’s drones weigh well under 5 kilograms, can carry cargo over 0.5 kilograms, and fly over 25 kilometers on a battery charge."



You write:
"It seems to me that it may be useful for you to elaborate very clearly what your goal is in the creation of this device."


A “true portable” (say 15Kp / 33lb) Flyer on the shoulders of a man, capable to go fast (say, with 250Km/h), at really long distances (say, 300Km range), fuel efficiently (high mileage), changes the world.

Is it now obvious what is the goal of the pattakon Portable Flyers?

Another reading at http://www.pattakon....pattakonFly.htm may be useful.

Thanks
Manolis Pattakos

[Wuzak]

How much fuel do you estimate it will take to get that 300km range? Bearing in mind that rotary wing craft are not generally fuel efficient.

 

Is the 250km/h an estimated/calculated figure, or a goal? What angle does a man have to be to get to that 250km/h?

 

What do you do when you get to the other end? With the Pal V when you get to the other end you land and you have a 3 wheel bike/car in which to drive around. 

 

Are you going to provide a container like a suitcase so the operator can put the Portable Flyer away and wheel it around, rather than having to carry it wherever he goes?

[kikiturbo2]

The tightening by aligning the distance of the two crankshafts is the simplest way.
 

 

I may not understand this completely, but won't this change the CR?

[manolis]

Hello RogerGraham

With a given toothed belt, the distance of the two crankshaft centers is defined. The PatATi Opposed Piston is then designed with this crankshaft to crankshaft distance.
The optimum compression ratio results by the selected diameter of the central narrowing of the combustion chamber.
The toothed belt of the BMW F800 has to be aligned every 10,000Km.


Hello Kikiturbo2.

You write:
I may not understand this completely, but won't this change the CR?

No.
Read what I wrote to RogerGraham.

But even if you have to put another 1 mm in the combustion chamber, the change of the compression ratio is not a big deal. For instance, you go from 10:1 to 9.5:1.
And 1mm longer combustion chamber means 2mm more tight tooth belt.

Thanks
Manolis Pattakos

[manolis]

Hello Wuzak and thanks for your questions.

You write:
"How much fuel do you estimate it will take to get that 300km range? Bearing in mind that rotary wing craft are not generally fuel efficient."

The estimation is:
less than 20lt for 300Km at 160Km/h (100mph),
and less than 35lt for 300Km at 250Km/h (~160mph)

The reasoning behind this figures is below.

The glide ratio of a wingsuiter moving with 160Km/h (100mph) is about 3.
If the total weight (rider plus equipment) is 75Kp (165lb), with a glide ratio 3 and a speed of 160Km/h (100mph) the power consumed during the flight of the wingsuiter is calculated as:
P = 75Kp*160Km/h*(1/3) = 10.9KW = 15bhp

I.e. in order the above wingsuiter to fly horizontally (i.e. without falling) at 160Km/h (100mph), someone has to provide the 15bhp above calculated.

A power loss at the rotors is inevitable.
It is also the additional weight of the Flyer and of the fuel.
A reasonable assumption is that with the PatATi OP engine providing 25bhp, the wingsuiter moving with 160Km/h (100mph) keeps his height for as long as there is fuel to consume.

Assuming a 0.35Kg/KWh (0.25Kg/bhp/h, 0.35lt/bhp/h) specific fuel consumption (it is a low friction two stroke engine, it has a compact combustion chamber, it avoids the loss of unburned fuel to the exhaust, it is optimised for the specific revs it operates, there is no transmission, etc), the fuel consumption for providing 25bhp is 25*0.35 = 8.8lt/h.

(0.35Kg/KWh specific fuel consumption means some 23% BTE (Brake Thermal Efficiency))

For 300Km you need (300/160)*8.8= 16.5lt.

At higher speeds, the increased aerodynamic resistance decreases the mileage.


You write:
"Is the 250km/h an estimated/calculated figure, or a goal? What angle does a man have to be to get to that 250km/h?"

With more than 70bhp from the engine, and a substantially smaller front area than a motorcycle / rider, the 250Km/h is a pessimistic estimation.
70bhp at 5,000rpm from an 800cc (49cu.in.) two-stroke engine means a torque of:
M=(70/1.4)/5 = 10mKp (~70lbft). A tuned 800cc two-stoke makes almost two times this torque.

The angle of the body of the rider / pilot at 250Km/h will be some 5 to 10 degrees (dependant on the suit and on the rider).
Worth mentioning: the front area is adjustable; at high speeds the rider / pilot retracts his hands / legs because he no longer needs all the area to provide aerodynamic lift.
Worth mentioning: the direction the propellers rotate is important (Zimmerman).


You write:
"What do you do when you get to the other end? With the Pal V when you get to the other end you land and you have a 3 wheel bike/car in which to drive around."

The rider reduces speed and turns progressively perpendicular, then he lands vertically; then he puts-off the Portable Flyer and leaves it down; then he walk and does what he wants to do; then he returns to the Portable Flyer; then he puts-on the Portable Flyer; then he checks it and takes off vertically.

Since he can take-off and land anywhere (two “clean” square meters on the roof of a building or on the deck of a boat, or 3 “clean” meters between two trees at a road side is all he needs, or 0.5m2 on the top of a rock in the sea), he can go anywhere and needs not a second vehicle. See the youtube video of the JetPack GoFast in my post #41.


You write:
"Are you going to provide a container like a suitcase so the operator can put the Portable Flyer away and wheel it around, rather than having to carry it wherever he goes?"

No.
A casing is not essential. You can keep it by the “casing” as a suitcase and put it in the port baggage of a car or in a storehouse.

Thanks
Manolis Pattakos

[imaginesix]

Is it now obvious what is the goal of the pattakon Portable Flyers?

 

Not entirely, no. What you've provided are a set of performance objectives, which is fine, but to what end?

 

Let's imagine the day comes when you complete your Flyer with the necessary performance, you need to know what you do after that. Do you pack it all up into bins and then move on to your next project, maybe a Portable Submarine or Space Capsule for example? Do you fly around the world? Do you start a production line? Do you sell off the patented bits of it to the highest bidder? This is a big part of the purpose of your work, which will have a strong influence on your choice of technical solutions. I think you need to clarify that to help find the best answers to the questions you are asking.

[kikiturbo2]

Hello Wuzak and thanks for your questions.

You write:
"How much fuel do you estimate it will take to get that 300km range? Bearing in mind that rotary wing craft are not generally fuel efficient."

The estimation is:
less than 20lt for 300Km at 160Km/h (100mph),
and less than 35lt for 300Km at 250Km/h (~160mph)

The reasoning behind this figures is below.

The glide ratio of a wingsuiter moving with 160Km/h (100mph) is about 3.
If the total weight (rider plus equipment) is 75Kp (165lb), with a glide ratio 3 and a speed of 160Km/h (100mph) the power consumed during the flight of the wingsuiter is calculated as:
P = 75Kp*160Km/h*(1/3) = 10.9KW = 15bhp

 

 

Total weight of rider + equippment of 75 Kg???? and that is with your engine, props and 16.5 litres of fuel for your 300 km journey??? Good god, I must be really fat..

[manolis]

Hello Imaginesix.

You write:
"Let's imagine the day comes when you complete your Flyer with the necessary performance, you need to know what you do after that."


After completing the tests and after demonstrating the Flyer to the mass media, we will calm down (say for a couple of months) trying to see the whole project / idea from a distance and to evaluate it from various viewpoints.

Depending on the demand, we will examine all options as you describe them: from putting the project aside, to putting it in mass production at an affordable price.

Judging from the millions invested so far in projects like the Pal-V and the Martin JetPack, the World seems more than thirsty for a transportation means / tool like the Portable Flyers.

Besides, think that when you are making a low-budget proof-of-project prototype, the main goal, the first priority, is to complete it and to be functional.

With a functional prototype at his hands, any engine maker can easily adjust the design for mass production.

So, first thing first.



Hello Kikiturbo2.

You write:
"Total weight of rider + equippment of 75 Kg???? and that is with your engine, props and 16.5 litres of fuel for your 300 km journey??? Good god, I must be really fat.."

Wrong.
Read again the post.

The 75Kg refers to the wingsuiter.
A wingsuiter wears a wing-suit and a “landing” parachute at his back. This is all.
By the way, with the PatATi Portable Flyer added / secured on the shoulders / body of a wingsuiter, the parachute is optional.



At post #9 I write:

"Hello Kikiturbo2
You are right about the manufacturing.
The twisted tooth belt cannot be made, in mass production, as the conventional tooth belts, i.e. by cutting in several pieces a wide toothed belt."

This doesn’t mean the twisted tooth belt cannot be made in mass production.
Besides the approach of making a wide belt and cutting is in pieces, there are other approaches, too.
Think about it.
Instead of cutting you can union. The basic material of a toothed belt is ideal for such a process.

On the other hand, with the existing solutions (Pal-V, Martin-JetPack, Malloy-Hoverbike, GoFast-JetPack etc) being so much expensive, what is wrong if the twisted tooth belt ( PatBelt ) costs two or three times more than a conventional tooth belt?

Does the PatBelt solve the synchronization problem?
Is it reliable?
Is it simple?
Is it lightweight?

Do you know a better solution?

Thanks
Manolis Pattakos

[Kelpiecross]

You demonstrated in this video the system appears to work well mechanically - maybe it is time you made a simple test rig to discover just how much thrust it can produce? Endless speculation and calculation about the system's performance is not really enough.

[RogerGraham]

Does the PatBelt solve the synchronization problem?
Is it reliable?
Is it simple?
Is it lightweight?
 

 

Hi Manolis,

If these four questions are the only criteria we should use, then maybe it is indeed the "best" solution.  

 

However, I think you may be missing the point of the other posts, which is that (a) this list of criteria is far from complete, and (b) we don't really even know what questions to ask unless we know what the purpose/market/volumes/etc for the unit is, which imaginesix alludes to.

 

But in my mind at least, additional questions would include:

1. is it cheap (enough) (compared to other solutions)?
2. is it easy (enough) to manufacture (compared to other solutions)?
3. is it easy (enough) to maintain (compared to other solutions)?
4. is it safe (enough) (compared to other solutions)?

 

And so on.  

 

To take one example, and with reference to points 3 and 4 above, you say that to adjust the belt tension you simply adjust the crankshaft-crankshaft spacing.  But:

• you haven't shown how you would achieve this.  A mechanism to allow movement of the crankshafts relative to each other must, to some extent:
  • add weight and complexity and cost and maintenance effort, and
  • reduce reliability and safety
  • (and how do you mount the engine, if its length changes each time it needs adjusting?) 
• even assuming it is possible, you say that the resulting change in CR isn't very large.  Yet it will have real effects on the performance/economy/emissions/etc of the engine, which you apparently haven't allowed for in the calculations above

• you haven't shown how this would impact safety of a device for which safety must be the Number 1 criteria.  What happens if the best loses tightness during the course of a flight?  I don't think I'd want to be using it at that time...  A normal belt-tensioning system has no such worries.

 

In other words, it's far from clear that this is the best solution for the intended purpose, as opposed to being simply the lightest / simplest / etc.

 

Cheers,

Roger

Edited by RogerGraham, 11 November 2014 - 07:18.