Single shear Uprights

[LU-Bolton]

What do you guys think about placing the Lower and Upper ball Joints in single shear at the upright? Would judges cringe just as they do at teams running outboard rodends? The biggest problem here being that you're putting bolt threads in bending.

[LU-Bolton]

What do you guys think about placing the Lower and Upper ball Joints in single shear at the upright? Would judges cringe just as they do at teams running outboard rodends? The biggest problem here being that you're putting bolt threads in bending.

[Jersey Tom]

There have been a lot of threads re: uprights already, might want to check one of those.

Its bad practice in my opinion, though I believe some teams do it. If youre gonna do it, you better have a really good reason that you can back up.

[Garlic]

Judges won't cringe at a single shear upright.

But they will choke at threads in bending! Don't put threads in bending if you consider yourself an engineer!

Passenger cars have single shear uprights all the time but definitely won't have threads in bending.

[Denny Trimble]

Learn to use the "find" feature (http://fsae.com/eve/forums/a/tpc/f/125607348/m/23310401721/r/16610311721#16610311721)

Several top teams use single shear in their LBJs, even those who have won design. Just avoid threads carrying shear / bending loads.

[Jersey Tom]

I would think it would be difficult to avoid putting those threads in bending in a purely single shear mount.

You're basically screwing the bolt into something and its cantelevered into the air. To avoid putting the threads in bending you'd drill your hole (say this is for a 1/4-28 bolt), tapped at the bottom and drilled straight 1/4" above it. Thus the threads are full "submerged" in the part and only the grip comes out of the hole.

I've never actually measured the grip diameter on standard bolts, but I'd imagine the tolerancing isn't all that amazing. Its a bolt after all, not a dowel pin. Let's say its .245

Your clearance hole likewise, even if you drill it with a 1/4" drill, is gonna have some tolerance associated with it. Lets say it comes out oversize, .253

Depending on how your threads are centered in the hole, you'll have anywhere between .000 and .008" of room for that bolt to bend around in the hole, with the shear and bending loads being supported by the junction of the grip and the thread, until the whole bolt bends to the point that the grip comes fully in contact with the inside of the hole. And if you're using something soft for your upright, like aluminum with no hard surface treatment on it, it can enlarge the top of the hole and compound the problem.

.008" doesn't seem like much but it can be a lot or a little depending on the size of the bolt and how far down your threads are submerged. And every time you go into a corner you're adding another bending fatigue cycle on that bolt, in addition to whatever tensile load there is. Theyre strong bolts and all, but hell working in a machine shop I've sheared old, hardened 1/4-20 cap screws by hand, which still confuses the hell outta me but I'd imagine its from continued cyclic loading over the years.

Just some thoughts. I could be crazy.

[Denny Trimble]

Don't use a bolt, use a stud that you make yourself to whatever tolerances you care about.

It can be pressed and welded into the bottom plate of your boxed upright. Then, you have no threads in bending.

Don't forget about the washers required by the rules to retain the spherical housing if the ball pulls out.

[Foote]

So why not use a dowel pin?
make it slightly oversized, then drill and tap the centre of it. Some people have told me that this would be stiffer per unit weight than a double shear joint. I'm not entirely convinced, but it's worth studying. I guess it probably depends on how the rest of your corner is designed.
I know several teams (including us) have used studs in single shear. see the lower heim in this picture.
http://dot.etec.wwu.edu/fsae/v30/image024.jpg
These also load rod ends in bending, and the upper mount is a good example of how not to use single shear.
Either system can work, and can be very strong and light. I would just be sure to have lots of numbers to back up your single shear design, because i think most of the judges share carrol smith's perspective on them.

[Travis Garrison]

Justin,

V30's upright uses a single shear bolt...not stud right?...that's what you want to avoid. As far as using dowels, wouldn't you just be changing where you put your threads? so now instead of a nylock nut you have to use a bolt of some kind, which would mean safety wire.

[PatClarke]

Hi Justin,
The pic you posted is one that has made it into my 'Rogues Gallery' a selection of pictures I show to new teams when I am doing my "Don't do this" talk =].
The outer loaded rod end in this application is actually the upper one (look closely, you can see where the pullrod is). This rod end is certainly loaded in bending on the threaded shank.
The Allen screw threaded into the upright is scary enough, but in this application the thread on the Allen screw is also loaded in bending.
Other things I point out are the offset pullrod loading, the cantilevered caliper, the inside out brake, the bottom outer rod end.

How do you change a wheel? Remove the caliper?
What effect does feeding the brake temperature directly into the rim have on tyre temp and pressure?
And finally, how did you steer it with that amount of scrub?
This seems like a poor set of compromises made to try adapt 10" wheels.
When one remembers the high points of the V8, one tends to forget this aspect of the car.
Im not bagging it, just pointing out the obvious.
Regards
Pat

[Marshall Grice]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Don't use a bolt, use a stud that you make yourself to whatever tolerances you care about.
</div></BLOCKQUOTE>

i thought about going this route but was thrown off by the rule that says all critical hardware must be grade 8 or higher. Besides, tolerance on a NAS bolt is .001", and can get reamers with even closer tolerances. Good enough for me to design to.

[Jersey Tom]

Good discussion..

I dunno about drilling and tapping dowel pins. Hardened steel, no thanks.

NAS bolt tolerance is that good? Reamer will definately do the trick. Interesting. Might have to take note of this..

[Marshall Grice]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> NAS bolt tolerance is that good? </div></BLOCKQUOTE>

look (http://www.coastfab.com/pdf/1103%20gen%20specs.pdf) for yourself.

[Denny Trimble]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Marshall Grice:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Don't use a bolt, use a stud that you make yourself to whatever tolerances you care about.
</div></BLOCKQUOTE>

i thought about going this route but was thrown off by the rule that says all critical hardware must be grade 8 or higher. Besides, tolerance on a NAS bolt is .001", and can get reamers with even closer tolerances. Good enough for me to design to. </div></BLOCKQUOTE>

Don't let that stop you. Our '05 car had student-machined studs as I described above, and the front live axle nuts were made in-house as well, out of aluminum. No problems (with these things) in tech.

The "lift the car by the battery to check the tie down" test caught us off guard, though.

[Foote]

Sudenlee
You are absolutely right about 'don't do this'. The upper and lower rod ends are in bending during braking, and the upper gets suspension loads passed through it.
I was pointing out that the upper joint in that picture is how not to use single shear upright joints. But the lower joint (which is not shown very well) is an example of how they can be used correctly.

Yes, you must remove the caliper during wheel changes, but it's really not very hard.
To be honest, there hasn't been enough testing to find out exactly what effect the brake temp has on the tire temp. I've always made the argument that we have trouble getting our tire temps high enough anyway, so the brakes are probably actually helping.
The steering geometry is the way that it is because of the spool. I haven't ever driven that car at speed, but sitting still it is one of the lightest steering cars we have.

The team that built that car was very small, even for WWU standards, and what they did acomplish was astonishing. There are definetely some areas of the car that are not entirely thought out, though. The powertrain took so much of their time, that i think some of the other systems sort of fell through the cracks.
Still, i wish i could have come to school one year earlier and built it with them.