8mm too small?

[URracing]

We plan to run 8mm rod ends on our wishbones. I wasn't the one to purchase them but as far as I know they are a pretty good quality, but not quite aircraft grade I don't think.

We plan to run them in-line with the a-arm so no transverse forces are applied on the shank. Along with that, we plan to use 8mm spherical bearings on the upright mount. Just need to know if 8mm is gettin a little small for both spherical bearings and rod ends. Most bigger Formula race cars I've seen run closer to 10 or even 12 mm but they also weigh twice as much as a FSAE car.

By running a bolt horizontally through a steel clevis tab and then through the rod end bearing on the side of the frame, is this a viable solution for adjusting caster? By placing washers or spacers between the clevis and the bearing, this allows the whole a-arm assembly to move fore/aft as needed when adjusting your caster. That way, camber can be adjusted using shims behind these clevis tabs and threading 8mm bolts through the frame. By the way, do we need anti-intrusion bars on the a-arms or is that still optional? We plan to use glued aluminum a-arms so placing a bar in between the rod ends might be a little tricky.

I would attach a JPEG of what I'm talking about but haven't figured out how to upload images from my computer, just URL's from what I can see.

Thanks for your opinions. Unfortunately for us Formula SAE cars don't run in -40 deg C weather, even with beer. Otherwise we'd organize some ice races for those interested (and have some old tires they wish to put studs in for that matter).

[URracing]

We plan to run 8mm rod ends on our wishbones. I wasn't the one to purchase them but as far as I know they are a pretty good quality, but not quite aircraft grade I don't think.

We plan to run them in-line with the a-arm so no transverse forces are applied on the shank. Along with that, we plan to use 8mm spherical bearings on the upright mount. Just need to know if 8mm is gettin a little small for both spherical bearings and rod ends. Most bigger Formula race cars I've seen run closer to 10 or even 12 mm but they also weigh twice as much as a FSAE car.

By running a bolt horizontally through a steel clevis tab and then through the rod end bearing on the side of the frame, is this a viable solution for adjusting caster? By placing washers or spacers between the clevis and the bearing, this allows the whole a-arm assembly to move fore/aft as needed when adjusting your caster. That way, camber can be adjusted using shims behind these clevis tabs and threading 8mm bolts through the frame. By the way, do we need anti-intrusion bars on the a-arms or is that still optional? We plan to use glued aluminum a-arms so placing a bar in between the rod ends might be a little tricky.

I would attach a JPEG of what I'm talking about but haven't figured out how to upload images from my computer, just URL's from what I can see.

Thanks for your opinions. Unfortunately for us Formula SAE cars don't run in -40 deg C weather, even with beer. Otherwise we'd organize some ice races for those interested (and have some old tires they wish to put studs in for that matter).

[exFSAE]

First of all.. I dunno about this metric malarky.

You can run AN 4-series (1/4" dia) hardware all around and be just fine.

Believe thats 6.35mm for those of you stuck on the metric fad.

Not exactly envisioning you're caster adjustment thing. Would need a picture. Try imagebucket or whatever it is for uploading pictures. Keep in mind adjustability is good, but anything that adds compliance to your system = bad.

[Brett Neale]

8mm would be plenty fine. We had sphericals all round last year, with 8mm sphericals on the upper and lower upright joints, and 6mm sphericals on the inboard side. As far as rodends go, we used inboard M8's on the 2006 car with no problems. Using shims behind the clevises for camber adjustment is a good idea, and judges like it too apparently.

[ben]

We used 1/4" Aurora rod ends all round. M6 is pretty much the same size so I wouldn't have thought it would be a problem.

When we won the electrical award at FS in 2003 the trophy was a Jaguar Racing Pushrod load cell mounted on a plinth. It used an M6 aerospace grade spherical. If the load path's good you don't need big joints.

Ben

[Frank]

dunno about this inches garbage... but

it depends on the heat treatment of the rodends

if they are not much better than mild steel, then use 8mm

if they are quality heat treated low alloy, medium carbon steel then 6mm should be fine (Aurora AM-6M, and AB-6M)

5mm would be pushing it for the A-arms, but maybe ok for steering links and push/pullrods

We usually used 1/4" (AM-4) all round, but only because they are the common ones aurora stock

Only problem is you then have to use silly inch series nuts and bolts, and make dumb sized parts with rediculous inch holes, etc to mount the rubbish things

[fade]

the castor adjustment method you described should work fine.

[Austin]

We just use some caution now if we go down to 6mm on the upright side, we had shit quality sphericals on our 06 car and had the pushrod mounted to the wishbone, the axial force into the bottom joint caused the ball to be bashed out of the housing, our bearings came out in two pieces. We had to replace them 3 times in only 4 days of testing. We now use good quality 1/4in chassis side and 5/16 upright side with no problems

[Fyhr]

Delft use 5mm rodends inboard http://fsae.com/groupee_common/emoticons/icon_smile.gif

[murpia]

Surely you can do this analysis properly?

If you've stressed your suspension with vehicle load cases, you'll KNOW how much load is in your joints and therefore what factor of safety you are operating them at, based on the manufacturers data.

If you don't have manufacturers data and have to rely on an internet forum, I would question your choice of supplier...

Regards, Ian

[js10coastr]

"8mm too small" ...that's what she said.

[Raphaël Rochette]

Rod-ends or spherical bearing are like any other component on your car, aren't they? So as murpia said, define the set of load cases on your suspension then get the corresponding loads in each member and you'll be able to size your joints. Be carefull when you compare with what other teams use, it depends on a whole bunch of factors (suspension geometry, weight, weight distribution, load cases, etc...). I am sure you did not make your driver seat based on someone else's car...

Good luck!

[URracing]

http://s268.photobucket.com/albums/jj16/cdnbacon85/?act...uspensiontopview.jpg (http://s268.photobucket.com/albums/jj16/cdnbacon85/?action=view&current=frontsuspensiontopview.jpg)

[The AFX Master]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">First of all.. I dunno about this metric malarky.
You can run AN 4-series (1/4" dia) hardware all around and be just fine.
Believe thats 6.35mm for those of you stuck on the metric fad. </div></BLOCKQUOTE>

On what century do you live?? all the world is going to metrics.. the auto and aerospace industry is based on metrics!!!.
So who is hiding on the imperial fade?.

How many fingers do you have?.. 3/8 or 5/16

[B Hise]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">How many fingers do you have?.. 3/8 or 5/16 </div></BLOCKQUOTE>

you really only need 1/8 of your fingers to communicate.

[Kirk Feldkamp]

Yikes. That's a lot of misalignment for that "left" inboard rod end based on the photobucket picture. Do you actually have this modeled up yet?

-Kirk

[Drew Price]

Also, make sure you find the radial force component with the bearings mounted with their axis parallel to the frame tube, you will get a force trying to push the ball out of it's housing.

I seem to remember hearing that the radial capacity of the aurora sphericals was only 10% of the static axial capacity?

Best,
Drew

[URracing]

Haha, I hope I don't start any wars over metric vs imperial, otherwise it'd be the US against the rest of the world - except Canada cuz we're just peace keepers with our canoes n all http://fsae.com/groupee_common/emoticons/icon_smile.gif

But ya, we have these CM-M8 Aurora rod ends that are 28 deg offset misalignment angle. The purpose is because we would like to design our frame a little wider on the front so it fits bigger people (like me) so at least we get to drive the thing when it's done. I hopped into our last FSAE car and almost didn't get out - very uncomfortable to drive (especially turning with the paddle shifters). We probably won't use the total 28 deg but stick around 25 or so - or try to.

http://aurora.thomasnet.com/item/all-products-commercia...onomy/cm-m8?&seo=110 (http://aurora.thomasnet.com/item/all-products-commercial-male-rod-ends-metric-units/eries-male-rod-ends-metric-general-purpose-economy/cm-m8?&seo=110)

Keeping our track to a minimal width around 50" or so is key, while at the same time giving the a-arms a wide enough stance over the frame to properly disperse the forces of braking/acceleration through the wishbones.

Speaking of which - has anyone used aluminum a-arms and still use an anti-intrusion bar between the frame mounts? We plan to use aircraft epoxy to glue all the a-arm components together so that is why I'm curious.

I'm also curious as to find out the easiest way to incorporate anti-dive and anti-squat into the suspension. From what I've seen the most practical way is just angling the front a-arms up a little so the fore mount is a little higher up than the aft mount on both top and bottom. Vise-versa with the rear a-arms. Correct?

Thanks for the replies. It's good to get the input from other members to make sure we are thoroughly understanding the concepts we are after. I'm workin on a model so that will give a much clearer image of what we are doing.

And by the way, for you genius' south of the border, I am 2.11 yards tall http://fsae.com/groupee_common/emoticons/icon_wink.gif lol

[Fyhr]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by URracing:
Haha, I hope I don't start any wars over metric vs imperial, otherwise it'd be the US against the rest of the world - except Canada cuz we're just peace keepers with our canoes n all http://fsae.com/groupee_common/emoticons/icon_smile.gif

But ya, we have these CM-M8 Aurora rod ends that are 28 deg offset misalignment angle. The purpose is because we would like to design our frame a little wider on the front so it fits bigger people (like me) so at least we get to drive the thing when it's done. I hopped into our last FSAE car and almost didn't get out - very uncomfortable to drive (especially turning with the paddle shifters). We probably won't use the total 28 deg but stick around 25 or so - or try to.

http://aurora.thomasnet.com/item/all-products-commercia...onomy/cm-m8?&seo=110 (http://aurora.thomasnet.com/item/all-products-commercial-male-rod-ends-metric-units/eries-male-rod-ends-metric-general-purpose-economy/cm-m8?&seo=110)

Keeping our track to a minimal width around 50" or so is key, while at the same time giving the a-arms a wide enough stance over the frame to properly disperse the forces of braking/acceleration through the wishbones.

Speaking of which - has anyone used aluminum a-arms and still use an anti-intrusion bar between the frame mounts? We plan to use aircraft epoxy to glue all the a-arm components together so that is why I'm curious.

I'm also curious as to find out the easiest way to incorporate anti-dive and anti-squat into the suspension. From what I've seen the most practical way is just angling the front a-arms up a little so the fore mount is a little higher up than the aft mount on both top and bottom. Vise-versa with the rear a-arms. Correct?

Thanks for the replies. It's good to get the input from other members to make sure we are thoroughly understanding the concepts we are after. I'm workin on a model so that will give a much clearer image of what we are doing.

And by the way, for you genius' south of the border, I am 2.11 yards tall http://fsae.com/groupee_common/emoticons/icon_wink.gif lol </div></BLOCKQUOTE>

Where to start, for load carrying, if you have bearings that can take 28deg offset, turn them 90 degrees and brackets will be easy as pie to make even if aligned with the frame. However do tilt them upwards to your "static A-arm rideheight angle" if you follow my drift. We did run quite long a-arms last year, but total angle deflection from max bump to max rebound was ~5deg. Thus you don't have to take as much axial force on your rodends.

Second, Aluminum, with a Young's modulus of about 70 GPa vs steel of about 200 Gpa will give you apprixmately the same specific stiffness, however for buckling (would be euler 3, 2.15EIpi^2/L^2 (just off the top of my head, do check)) will give you aloooot larger a-arms if made from alu, which will in turn affect your much needed steeringclearance (unless you messed up your suspension with tons of KPI, huge scrub or a not tall enough upright) if you do want to glue stuff, get some pulltruded carbon tubing and stick alu ends to it.

As for antisquat, this clears it up a bit: http://en.wikipedia.org/wiki/Suspension_(vehicle)#Anti-dive_and_anti-squat
But better to look at a picture in any suspension book. RCVD is always nice.

[The AFX Master]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by B Hise:
you really only need 1/8 of your fingers to communicate. </div></BLOCKQUOTE>.

Nice one, i'll try to use 1/4 of my fingers so i can use both hands to do the universal greeting http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
Back in topic, M6's or 1/4's UNF are just fine for almost any FSAE. I think that youll have more flexural compliance issues with your wishbone than rodend axial compliance (And loading in that way is that's supposed to be done).And putting those inboard rodends horizontal instead of vertical frees you from the axial loads on the ball housing
If you use rodends on your upright kingpin points you'll get bending loads on them no matter of what kind of suspension do you have (due to braking loads), use balljoints instead

[URracing]

Well we can say I'm 19 hands high, but I 'm not a horse.

Okay, so here's a couple of models I quickly pulled from my suspension geometry sims I did in our Solid Edge CAD software. To answer all of your questions in regards to it, yes, we are planning to use a COM-M8 spherical bearing on the upright end, both top and bottom. The upright has zero KPI and about 1" of scrub radius since the guys wanted to design the car with equal length a-arms like the last car, but I said no no to that and bought them OptimumK so they can learn something on vehicle dynamics. And yes, I do understand the concept of angling the suspension tabs upwards a little to compensate for less load tavel that is put on the rod end under bump/rebound, thanks for the tip. I figured by turning the rod ends vertical like this, it would offer a VERY simple and easy way to adjust caster. To me there are too many variables using the shims behind the clevis tabs to adjust your caster, plus having to rotate your rod end either in or out depending on the a-arm radial travel when doing so. By the way, how many design points do we lose for NO caster adjustment? I'm thinking of going that route too.

http://s268.photobucket.com/albums/jj16/cdnbacon85/?act...Dview-suspension.jpg (http://s268.photobucket.com/albums/jj16/cdnbacon85/?action=view&current=3Dview-suspension.jpg)

http://s268.photobucket.com/albums/jj16/cdnbacon85/?act...pview-suspension.jpg (http://s268.photobucket.com/albums/jj16/cdnbacon85/?action=view&current=topview-suspension.jpg)

I will admit, it is pretty tight. I would like to clarify my understanding of the misalignment angle on the rod-end. If it is speculated at 28 degrees, then wouldn't that angle (marked by the red arrow) be 62 degrees? I set that angle at 65 degrees so that should have given me a total of 25 degrees misalignment - well within my limit of 28 degrees. I have a feeling though (from looking at the diagram on the Aurora website) that the 28 degree misalignment angle is an INCLUDED angle. Please feel free to enlighten me on that, please. I realized that after modelling the rod end into CAD and figuring out that it does indeed collide with the pin that is ran through the clevis.

I don't think I am understanding the idea of the rod end tending to push the bearing out with the more angle you put the force on. The reason for the spherical bearing inside is to evenly distribute the load over the race, just as long as the bearing housing doesn't collide with the pin being ran through it (from TOO much angle) causing it to buckle.

MY original plan was to use chromoly tubes from the start since they are easy to weld, will be less weight than all that hunky thick-walled aluminum garbage, and plus - if you break an a-arm then chances are you broke somethin else more vital so there's no sense in being able to quickly replace it by drilling and what not. Although the aluminum tubing is a bit cheaper than chromoly, the manufacturing costs of welding steel a-arms is much less than milling billet aluminum. Just gotta make spare steel wishbone frames I guess.

Lastly, what might be a realistic angle for that marked by the red arrow? Keep in mind we would like to keep our frame wider (530mm to outside of 1" tubes) so that bigger people actually have a chance of fitting in the car. Having a wider frame and narrow track will increase that angle but I'm just curious as to what most teams run for the width of their frame in that area.

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by URracing:
I don't think I am understanding the idea of the rod end tending to push the bearing out with the more angle you put the force on. The reason for the spherical bearing inside is to evenly distribute the load over the race, just as long as the bearing housing doesn't collide with the pin being ran through it (from TOO much angle) causing it to buckle. </div></BLOCKQUOTE>
Just think about the surface area of contact and the resultant of the force vector(s)...

Regards, Ian

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by URracing:
http://s268.photobucket.com/albums/jj16/cdnbacon85/?act...Dview-suspension.jpg (http://s268.photobucket.com/albums/jj16/cdnbacon85/?action=view&current=3Dview-suspension.jpg)

http://s268.photobucket.com/albums/jj16/cdnbacon85/?act...pview-suspension.jpg (http://s268.photobucket.com/albums/jj16/cdnbacon85/?action=view&current=topview-suspension.jpg) </div></BLOCKQUOTE>
There's a lot that could be commented on in those models, but you'll solve most of them by rotating the rod ends 90deg so they actually work properly...

If caster adjustment is your thing, try offset inboard clevises that can be 'flipped'.

I think I'll repeat my earlier advice, calculate the loads in all the suspension members and joints, based on your geometry, car weight, expected performance etc. etc. then you can make informed decisions as to materials, tube sizes, joint sizes, bolt sizes etc.

Regards, Ian

[D J Yates]

You should turn your rod ends through 90 degrees as Fhyr suggested; for several reasons:

1. Misalignent - exactly as Fyhr pointed out.
2. Friction - Clamp the ball in a vice and try individually rotating and misaligning the race. I expect it require more effort to rotate.
3. you'll be able use a narrower clevis - the bending moment in the bolt running through the ball is hideous. Unless you change this, expect the bolt to fail before the bearing.

To answer your original question. The radial load capacity of an M6 is ample, on the upper wishbones (or lower if using a pull-rod) you could use even smaller. However, the limiting factor is more likely to be the female thread in your tube-insert, for which M8 coarse will be fine, but anything much smaller may cause problems (depending on material, thread length, etc).

[Biggy72]

I have read other places and it makes sense, that the friction induced by the sphericals/rod ends is negligible once you look at the moment arm being applied to it.

The outboards should be much more important friction wise because there is not much if any of a moment arm, but they should be aligned a particular way just for loading purposes and steer angle so you don't have much of a choice there.