Quick Question about wheel placement

I am remaking my robot in CAD and I want to put the 4 inch omni wheel on the 4th middle hole. I am putting a brace behind the wheel that is elevated by two full spacers. Is there any risk at all that the wheel will be hitting the brace? There is very little space between the wheel and brace
Screen Shot 2020-06-02 at 4.03.59 PM
(Ignore the bottom brace, I didn’t want to fix it until I was sure about the top)

Well, according to your CAD, no. However, in real life your build will have a bit of wiggle. Just be sure when you build it that the wheel can spin freely.


Yes I agree with Josh, I would see if you can measure the space in CAD, and if it is more than about 3 millimeters I would say you are fine. When you build it make sure things aren’t shifting around of course.

Okay great, and I guess I could just add a couple metal spacers if things aren’t working


Washers could work, but you will probably want to connect something else to that brace and since that will be thrown off by the washers, just try to get it right the first time.

Here was our clearance which never negatively impacted our robot during TT.

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so in theory that brace is safe, but in practice the wheel probably will be able to rub against it if it has enough wiggle. I would move the wheel forward by one hole just to be safe, it shouldn’t effect your robot too much.

yeah thats what I was wondering if I should do but I am hesitant to do it because then the middle friction wheels wouldn’t be centered anymore because there are only 24 middle holes and that could affect the turning on autonomous

it will effect turning, but not a lot. your center of rotation will still be a fixed point between your middle wheels, and it won’t really cause any issues.

you could also do away with the middle wheels all together, it makes things simpler. you could lock just the front omnis if you want, which will make your center of rotation at the front of your robot, which often is continent, and you won’t be able to be pushed as easily.

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I’m gonna have to disagree here. Tight clearances are fine in Vex given you use proper types of bracing. In order to ensure that brace won’t bend over time, run it through a box bolt. Otherwise, you should be fine. All my robots were made with really tight clearances because it maximizes rigidity and compactness. The less distance a part has to span, the more rigid it will be. For example, try bending a 12" shaft, then try bending a 2" shaft. One of the shafts is much more resistant to bending. That general concept can and should be applied throughout the whole robot [imo].


well that gap looks really tight, and there is no garuntee that real omni wheels will fit there. the ones in cad could be a tiny bit smaller, and manufacturing tolerances could mess stuff up.

personally that tolerance looks too close for comfort.

you could easily test it though, just build a little thing with those dimensions, and see if an omni wheel fits.


I will definitely test it. I know that the little rubber pieces stick out a bit, so the wheel could definitely hit the brace. Plus CAD is using a perfect omni wheel and in practice wheels aren’t perfect. If I decide to use a couple metal washers will that be fine or will it screw up my spacing when I attach c channels to that brace?

I would build it but first test by rotating the wheel to its tightest spot in CAD and measure the clearance there.

Can’t disagree with you there, but at that point @Athan is better of just raising the brace slightly with a few washers, no big deal. A lot better than shifting the whole wheel forward

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Okay cool because I’ll probably be adding a couple metal washers just to be safe. I don’t want the wheel to ever be scuffing on the brace

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That is killing me that there is no box bracing

haha is it really that important?

it’s pretty important yeah. people often underestimate the power of box bolts.


Sorry to put you on the spot but how much box bolt’s should I put on one aluminum c channel? I assume box bolting steel is unnecessary.

its not really a set amount, really you should use them whenever you have a place that a screw can go all the way through.

I would box bolt on steel as well, steel really isn’t that much stronger than aluminum.

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I would box bolt where any bracing is. Not only will it help make sure the metal doesn’t bend but also it can make the bracing a lot more sturdy.

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