Can a 4" Omni and LS gear fit in 3 holes?

So when I was designing my base for this years game in CAD, It seems that I can’t quite fit a 4" omni and a LS gear in a 3 hole wide space.
As you can see, the rollers hit the side of the channel and the gears. I can’t really move the inner channels out easily, as they will mess up my mogo lift spacing, either.
Can anyone confirm that this does actually work, or am I stuck with a larger space in between?

That is not possible in your current setup. what you could do however, is turn the c channels so that the flanges are facing inwards. That should give you barely enough space, or if not you can file down the flanges where the wheel/gear hits it without hurting your drive’s integrity too much.


Remember, CAD is more precise than real life.

In reality, you have more wiggle room/slop to work with.
If you use normal screws rather than shoulder screws, you can get ~1/16’’ of extra space from the fact that the screw’s diameter is less than the square hole size. If you need more, just drill out the hole in the aluminum a little more. A quick but unadvised solution is to just bend the channels apart like prying apart disposable chopsticks.

Real life is much more flexible than CAD. You should ditch the mentality that CAD is meant to ensure super precise spacing/building. CAD is only a model, a reflection of reality and should only be a general guideline for your building. Almost zero vex robots would be possible if we strictly followed a 0.5’’ grid of bolting channels together. The c-channel itself is has very imperfect dimensions that mess spacing up which is why VEX purposely used smaller diameter screws with extra slop.

Here is an example implementation of a 3-hole wide drive for reference (4411S Turning Point)


4411S did drill out the holes in the c channel slightly to make it work tho


Another question about this drive: As you can see in the picture below, the wheel gets in the way of putting a shaft all the way through this gear:
Should I round out the hole in the inside and use a screw joint there?

It’s best to avoid issues like this when possible, by using larger sized idler gears. But if you must, you could theoretically use a cantilevered screw joint, but be aware of the risks of friction and fragility using cantilevered gears on your drive could have.

add this issue to the list of why 3.25" wheels are superior I guess.


I’m using 4" because they can climb better and are faster. I don’t know that I can really rearrange my spacing easily, so I may just have to

climbing isn’t really that big an issue since the platform when down forms a near-perfect ramp that requires no additional ground clearance to drive up. And as far as speed goes 4" wheels are only faster on the same ratio, you can make 3.25" wheels just as or faster with a faster gear ratio.

But I mean there’s nothing bad about 4" wheels, they’re plenty good, I just think 3.25" wheels are objectively superior.


This is, probably, the best you can do:


Edit: But in the year with heavy defense the less metal there is the more you risk it to be too fragile to survive the pushing.


That is a bad idea. The drive train should be built to endure an entire season (ideally) of wear and tear. You might get away with that for remote competition, but I don’t expect that to last even one full competition. At the very least, the wheel will experience large amounts of friction if the outer c channel bends in the slightest because it’s supporting the weakest part of the drive train. Once the metal deforms, it will create friction with the spacer (which is contacting the wheel) and also the axle if it becomes slightly un-level.

Instead, you could cut small notches in the flanges only where the rollers of the omni-wheel pass through. So, the flange will sort of dig-in to the cavity where the wheel spokes are recessed. This way, the structural integrity of the chassis is preserved as much possible and even then, I don’t think it’s worthwhile in order to save roughly 1" of space from adding a hole of spacing to each side of the drivetrain.


So I am actually not going to have this problem- I want to go 257 rpm on 4" wheels, but I was going a 36-60 instead of a 36-84, which would have given me 360 rpm, which is not what I want. So that was just my mistake, sorry about that.

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