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Rocker arm inboard suspension


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#1 carlt

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Posted 01 August 2015 - 11:02

http://www.jaytorbor...pension 600.jpg

 

Comment please,

I'm particularly looking at the rod end/rose joint link from rocker arm to upright 

 

 

link to the constructor

http://www.jblmotor.com/car1.htm



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#2 saudoso

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Posted 01 August 2015 - 11:37

jbl%20front%20suspension%20600.jpg

Just putting it inline



#3 Greg Locock

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Posted 01 August 2015 - 11:45

Yeah, Carroll Smith would say that's horrible. Size wise, a 5/8" thread (by eye) in bending is OK there, in an if it looks right it is right sort of way These things are calculable after all, and the guys who manufacture ball joints and rod ends are actually pretty helpful.



#4 mariner

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Posted 01 August 2015 - 15:25

The ball joint shank looks strong but I would worry about the vertical load pushing the insert clean out.Ball joints dont like radial load as only the staking keeps it in place.

 

The trouble is you can't really predict the vertical force as its straight from the contact patch and it could be very heavy.


Edited by mariner, 01 August 2015 - 15:27.


#5 Widefoot2

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Posted 01 August 2015 - 18:37

I looked at some of the other chassis build pics, they have their front rotors mounted backwards (vane orientation).  Not a big deal if it was just thrown together for pictures, but if that's the way they intend it it doesn't say good things about their design skills.



#6 Bloggsworth

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Posted 01 August 2015 - 22:22

I wouldn't drive it...



#7 bigleagueslider

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Posted 02 August 2015 - 02:48

Threads in bending/shear are never a good idea. That upper rod end is also designed to primarily take radial loads, and only minimal axial loads.



#8 Greg Locock

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Posted 02 August 2015 - 05:46

Axial capacity of an 5/8 thread rod end is 830 lbs, for a cheapy. 

 

http://www.ewp.rpi.e... Connectors.pdf

 

surprised me.


Edited by Greg Locock, 02 August 2015 - 05:49.


#9 mariner

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Posted 02 August 2015 - 09:01

The car kerb weight is quoted as 2350lb. With two people, fuel etc about 3,000lb laden. With a 50/50 weight distribution thats 750lb per corner static versus Greg's 830lb axial load for a 5/8" rod end.

 

Hmmmm...



#10 carlt

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Posted 02 August 2015 - 10:28

what about instantaneous shock loads , would assume they would be much higher [kerbing etc or rumble strips if competing]

 

have also found that rod end balls soon become loose with use [ hence short lifeing for competition?], that must impact dramatically on axial loading figures 


Edited by carlt, 02 August 2015 - 10:31.


#11 saudoso

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Posted 02 August 2015 - 10:34

Is there anything to be gained from merging a rocker arm and a wishbone? Besides having less nuts and bolts to handle?

 

Two structures dealing with forces directed roughly 90 degrees apart? You can't even gain weight doing that. A weight supporting wishbone should weight more than a regular one and a rocker. You carrying the load over a way longer lever.



#12 Greg Locock

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Posted 02 August 2015 - 12:19

You can see how meaty they've made the upper arm, that tends to support your theory. I've never really got into the idea of inboard suspensions, it seems to me that if you want progressive springing use a rising rate spring (or ride aid), and I'm not really sure that the second order effect of having ride height dependent damping is tunable in the average weekend.

 

Mariner and carlt, yes in retrospect I agree, given that it has to react ALL the vertical loads, say 3g at least, it does look like a bad detail. I missed that.



#13 carlt

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Posted 02 August 2015 - 14:18

That was my first thought on seeing this - massive top arm/rocker with a rod end stuck on the end 

why not use the conventional ball joint designed for this application - other than it doesn't look so sexy/racy 



#14 Bloggsworth

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Posted 02 August 2015 - 21:47

Quite frankly, they've made a pig's ear of it. I would guess that the rocker arm could handle 10 times the load that the rod end could, so why so beefy - If they couldn't think of anything better, which this is not, they would have been better of with an old-fashioned Triumph top joint, which would have handled the load and been much easier to design for.



#15 saudoso

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Posted 02 August 2015 - 22:09

Quite frankly, they've made a pig's ear of it. I would guess that the rocker arm could handle 10 times the load that the rod end could, so why so beefy - If they couldn't think of anything better, which this is not, they would have been better of with an old-fashioned Triumph top joint, which would have handled the load and been much easier to design for.

Well, at least when it fails they'll be sure what to bring to fix it.


Edited by saudoso, 02 August 2015 - 23:15.


#16 gruntguru

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Posted 04 August 2015 - 07:46

Ambulance? Orthopaedic surgeon?



#17 Lee Nicolle

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Posted 05 August 2015 - 23:59

Without doubt there should be a ball joint in that top arm. It would be a bit better mounted at 90 deg to what it is to put the load on the cage and not on the swedge holding the ball.That is what they are for! You will probably get away with it on the bottom but really a ball joint should be used top and bottom.  And make the LOWER arm adjustable for camber not the top.

That great fabricated upright really is weaker than a factory one too and then there is a range of aftermarket drop spindle forged steel uprights. Corvette ones have been used by racecar fabricators for a long time. Meanwhile small Formula cars still use triumph Herald!

A heim joint is not very strong that way and the liner will pound out really quickly too. The thread too is a weak point to break used on that angle. I have had a heim break  the cage used as an inner lower wishbone pivot and that was a good 3/4" one. Unusual to be fair but the cage was still copping some of the spring load. And yes it was at 90 deg too that set up

A small formula car without the rocker may  be ok though the ones you see too me are often too small. 3/8 where they should be 1/2 and 1/2 where the should be 5/8. If nothing else the bigger size gives more angle. And when they fall off the road they all bind and then break.


Edited by Lee Nicolle, 06 August 2015 - 00:06.


#18 Kelpiecross

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Posted 06 August 2015 - 04:12


I notice in the detail pictures of the front suspension they use a large flat washer over the top of the joint - at least it would stop the top arm breaking away completely from the upright.

#19 kikiturbo2

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Posted 09 August 2015 - 21:40

The car kerb weight is quoted as 2350lb. With two people, fuel etc about 3,000lb laden. With a 50/50 weight distribution thats 750lb per corner static versus Greg's 830lb axial load for a 5/8" rod end.

 

Hmmmm...

 

 

what about instantaneous shock loads , would assume they would be much higher [kerbing etc or rumble strips if competing]

 

have also found that rod end balls soon become loose with use [ hence short lifeing for competition?], that must impact dramatically on axial loading figures 

 

yeah... add in a 3 G bump, which is not severe, and you are in a serious problem... that design is flawed on many levels.. They should have used a pressed in spherical, direct in the rocker/suspension arm, with a nice lip to hold it in place + propperly sized bearing..


Edited by kikiturbo2, 09 August 2015 - 21:40.


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#20 Fat Boy

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Posted 12 August 2015 - 17:50

Yeah, Carroll Smith would say that's horrible. Size wise, a 5/8" thread (by eye) in bending is OK there, in an if it looks right it is right sort of way These things are calculable after all, and the guys who manufacture ball joints and rod ends are actually pretty helpful.

 

Even if it's sized correctly, it's sloppy.



#21 Fat Boy

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Posted 12 August 2015 - 20:31

Further thoughts.

 

1. It's got chrome springs. Does it even matter?

2. It's a convertible. Does it even matter?

3. It's a Cobra replica. Does it even matter?