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suspension pushrod angle in plan view?


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#101 Fat Boy

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Posted 12 August 2015 - 18:01

I'm going to advise you otherwise on M.R. Keep it simple. Pick a motion ratio and make it a linear. There may be situations where a rising rate is faster, but it's always tricker to set up. Your wheel rate right now doubles as it goes through the range. Can you see how that might cause some problems?



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#102 gruntguru

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Posted 13 August 2015 - 05:45

Agreed, and don't forget you need to produce similar rate curves at each end of the car.



#103 Fat Boy

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Posted 14 August 2015 - 04:33

Agreed, and don't forget you need to produce similar rate curves at each end of the car.

 

 

I have less of an opinion on that point, but I'm interested in your logic. What are you going for?


Edited by Fat Boy, 14 August 2015 - 04:34.


#104 gruntguru

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Posted 14 August 2015 - 05:24

I mean MR plots ie fixed MR both ends or equal rising-rate both ends - but do not mix.



#105 Greg Locock

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Posted 14 August 2015 - 07:56

We often use jounce and rebound bumpers to upset one end of the car as it approaches the limit, to encourage limit understeer. I suppose you could think about doing the same with the MR.



#106 NeilR

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Posted 14 August 2015 - 09:40

Equal mild rising rates both ends is the aim at this stage.



#107 Fat Boy

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Posted 14 August 2015 - 18:37

Equal mild rising rates both ends is the aim at this stage.

What's mild? I would say wheel rate changing no more than 15% through the range.



#108 NeilR

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Posted 27 May 2016 - 04:47

Well I can revive and old thread here with some good news: my car is on it's wheels.

 

Front suspension (note not the bellcrank that will be used).

20160527_110038_zpsgro1get3.jpg

 

Full view

20160527_103138_zpsmj0n0fbs.jpg



#109 Greg Locock

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Posted 27 May 2016 - 05:39

Looking very neat and, um, sturdy. 



#110 NeilR

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Posted 27 May 2016 - 07:14

Oh hell yes!

Could almost off road in this! But then first single seat car ever and it's a learning exp in design and driving. So it needs to be sturdy so I can enter with friends and also drive interstate (it on a trailer) and have it continue to function with minimal risk of failure/breakage. Besides who am I trying to kid...I'm 6' 8" and 250lbs - I'm nver going to be competitive I just want to have a good time and enjoy the challenge and be a little safe!


Edited by NeilR, 27 May 2016 - 12:41.


#111 Kelpiecross

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Posted 28 May 2016 - 05:45


Is it going to have bodywork?

#112 NeilR

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Posted 28 May 2016 - 12:56

Yes, will have bodywork, under-floor aero and front and rear wings. Initial runs will not have official bodywork. The rules say you must run with some, so we'll wrap the car in black plastic flim used for pallets and cut and tape the cockpit.



#113 Greg Locock

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Posted 28 May 2016 - 22:19

There'll be plenty of corflute available soon!



#114 gruntguru

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Posted 29 May 2016 - 05:00

Sturdy yes, but I am guessing still under 250kg (under 300kg when complete) and with 150+ hp, pretty exciting to drive.



#115 rachael

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Posted 29 May 2016 - 09:32

Only part that doesn't look sturdy are those front rockers - any out of plane force from the pushrod is going to bend those plates very easily.  Can you weld or bolt in a plate to stiffen them up?

 

Nice job in all other respects though,

 

rachael



#116 NeilR

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Posted 29 May 2016 - 11:29

Rockers are just a mockup plate - will have a very different design with a substantial lip. We needed something to check motion rations and also to get the thing on it's wheels and with a big O2 laser it's simpler to just cut a mockup plate as you see.

We think the weight to be around 220-230kg as you see it. In fact I will check just for interest sake.



#117 NeilR

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Posted 30 May 2016 - 11:54

Greg that would be coreflute with smiling happy faces on it? For those not in this country we are blighted by a national election and lots of coreflute is used for signs.



#118 Greg Locock

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Posted 31 May 2016 - 06:56

Well, the ones that aren't riddled with bullet holes might be useful.



#119 thegforcemaybewithyou

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Posted 31 May 2016 - 11:24

Well I can revive and old thread here with some good news: my car is on it's wheels.

 

Front suspension (note not the bellcrank that will be used).

20160527_110038_zpsgro1get3.jpg

 

Full view

20160527_103138_zpsmj0n0fbs.jpg

 

Do the lower front wishbones touch the chassis when the chassis travels down too much?



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#120 NeilR

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Posted 31 May 2016 - 11:37

They will touch with around 90-100mm of travel. Expected to use about half of this.



#121 thegforcemaybewithyou

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Posted 31 May 2016 - 11:42

Ok, so there is some safety in your calculations. Have you considered bumps that lead to high chassis travel or will the spring definitely stop the movement at one point?



#122 mariner

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Posted 31 May 2016 - 20:12

One question which has interested me is how much applying the suspension vertical loads into a chassis well back from the axle centre line helps torsional stiffness.

 

It seems to me ( but I am quite likely to be wrong!) that if you react the torsional loads into the chassis back from the axle line you get a pro rata gain in effective chassis stiffnes as the loads are over a distance less than the wheelbase.

 

Obviously the mountings must be rigid and the sloping back of the push rods ( as in your design ) causes fore and aft loads on bump but those loads are easier to react than torsional loads across the chasis.

 

Is my logic valid please?


Edited by mariner, 31 May 2016 - 20:12.


#123 Kelpiecross

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Posted 01 June 2016 - 05:21

One question which has interested me is how much applying the suspension vertical loads into a chassis well back from the axle centre line helps torsional stiffness.
 
It seems to me ( but I am quite likely to be wrong!) that if you react the torsional loads into the chassis back from the axle line you get a pro rata gain in effective chassis stiffnes as the loads are over a distance less than the wheelbase.
 
Obviously the mountings must be rigid and the sloping back of the push rods ( as in your design ) causes fore and aft loads on bump but those loads are easier to react than torsional loads across the chasis.
 
Is my logic valid please?


I did wonder the same thing about fore and aft loads on the front suspension. No F1 car has sloping-back pushrods - but that doesn't mean that they are right of course.

#124 Greg Locock

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Posted 01 June 2016 - 06:07

No free lunch there, the same moment across the axle has to be reacted whatever the linkage geometry.



#125 kikiturbo2

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Posted 01 June 2016 - 07:05

also, one has to be careful about effective wheel rate because sloping pushrods will lead to falling rate..



#126 NeilR

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Posted 01 June 2016 - 12:36

Kiki that is the advantage of going for bellcranks in that you can vary geometry in so many ways.

Were we to make a Mk2 we would not angle the pushrods so and we'd follow the advice and example of many and have them inline with the axle.

MaytheG "Ok, so there is some safety in your calculations. Have you considered bumps that lead to high chassis travel or will the spring definitely stop the movement at one point?" The car will be soft on the bumstops at 50mm and full-hard on at 60mm of wheel travel. Give the front suspension design we can actually raise the chassis on the front suspension by spacing the lower arms and dropping the top suspension points. However I have ensured that there is a minimum working clearance for all suspension components through full movement and at the most extreme of suspension setups. It's probably a bit of overkill as we're basing the current suspension setup on an early 1990's Formula Ford, which used the same tyres, so I doubt we'll use all of the available adjustment.



#127 NeilR

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Posted 03 June 2016 - 12:20

I checked the chassis today and the measurements I gave were pretty much spot on. The centre of the lower bearing is 28mm below the bottom of the chassis, supported by a conical steel mount welded to the bottom of the chassis tube, with a 'tail' section going through the top surface of the SHS. Clearance should not be a problem. Will weigh it next week.



#128 bigleagueslider

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Posted 04 June 2016 - 04:13

Looked thru your photos. Seems like a fun project. Do you have any provisions for using a roll bar in your F/R suspensions? Would not seem to be too difficult with your rocker arm/damper arrangement.



#129 mariner

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Posted 04 June 2016 - 14:37

No free lunch there, the same moment across the axle has to be reacted whatever the linkage geometry.

 

I think I understand but can I test the argument a bit?

 

Imagine a chassis which is a large tube from spring base point to spring base point,so its degree of flex is linear and therefore torsional rotation is proportional to the spring base

 

Now assume all roll resistance is provided by an anti roll bar at each end with drop links of infinite length ( please humour me)

 

In case one the A/R bar mounts through which all roll load is absorbed by the chassis are at the wheel centres , so chassis stiffness length equals wheelbase, say 2.5 metres.

 

In case two the A/R mounts are both 0.25 metres towards the car centre line so the springbase is 2 metres.

 

The roll stiffness load is the same in each case but in case two it only distorts 2 metres of tube whereas in case one it is 2.5 metres of tube.

 

So why isn't the chassis stiffness in case two 20% better please?



#130 Greg Locock

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Posted 04 June 2016 - 22:11

You are right. Imagine extending the antiroll bar arms so far that they each half the length of the car.In effect you've built 3 chassis'. Tongue sticking out emoticon goes here!

 

What I meant was that in the practical range of pushrod angles the torque exerted on the rest of the chassis is still going to be track*difference in wheel load, whatever the bellcrank location, assuming no arb.


Edited by Greg Locock, 04 June 2016 - 22:29.


#131 NeilR

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Posted 05 June 2016 - 03:44

Looked thru your photos. Seems like a fun project. Do you have any provisions for using a roll bar in your F/R suspensions? Would not seem to be too difficult with your rocker arm/damper arrangement.

I do have a set of blade adjusters from an Indycar that should mount to the front bulkhead, but I'm heading towards a simpler arrangement - a solid bar with two links from the bellcranks to the bar ends. Adjustment by varying the lever just as you would expect.


Edited by NeilR, 05 June 2016 - 12:56.


#132 NeilR

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Posted 07 June 2016 - 12:34

Has anyone see a neat sway-bar arrangement on a single seat car? Please exclude blade adjusters.



#133 Fat Boy

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Posted 08 June 2016 - 02:23

Has anyone see a neat sway-bar arrangement on a single seat car? Please exclude blade adjusters.

 

Make up your mind. Do you want a neat single seater anti-roll bar arrangement or do you want one without blades? Why no blade love?



#134 NeilR

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Posted 20 June 2016 - 10:20

OK we weighed the car albeit with two 180kg bathroom scales, one each end with a plank under the tyres ... so not too scientific. Anyway there is 50kg on each front tyre and 75 kg on each rear tyre for a grand total of 250kg. Weight of components (diff/carrier, fluids, panels, wing mounts) to add is around 25kg and mostly at the back, plus wings. So we could scrape in at under 300kg plus driver. So perhaps a little lighter than many FF cars on the same rubber.

Why not blade adjusters? I've been given the impression that they are not linear in use and I think I need simple above all.



#135 Lee Nicolle

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Posted 21 June 2016 - 10:10

Well I can revive and old thread here with some good news: my car is on it's wheels.

 

Front suspension (note not the bellcrank that will be used).

20160527_110038_zpsgro1get3.jpg

 

Full view

20160527_103138_zpsmj0n0fbs.jpg

My thought [and you say not the rockers to be used] is that the rocker at that height is very close to binding. especially once some droop is taken into account.



#136 NeilR

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Posted 21 June 2016 - 10:47

reweighed with four scales - weight 245KG and around .5-1kg cross weighted FR/LR. Lee there is no droop planned on the front suspension at this stage, which is the usual setup on bike-engined hillclimb Formula Libre cars I am familiar with.



#137 NeilR

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Posted 18 September 2016 - 07:03

Gear linkage took some thought: Machined two grooved rollers to encase the shaft half way down. They proved all around support and minimal friction - the gear change is very clean and accurate:

20160916_135718_zpshq1zdeky.jpg

 

Bike dash in place:

20160912_102943_zpsfzspff2g.jpg

 

Made better rack ends:

20160912_103122_zpsxngn0xgk.jpg


Edited by NeilR, 18 September 2016 - 07:03.