Wheel shaft inserts not the right size

[Jaydynite]

I’m currently cadding my drivetrain, but the wheel’s shaft insert creates a tiny space in between that’s about 0.07 inches wide. Anyone else having this problem? Should I just ignore it?

[9210KAbsoluteHack]

You should just ignore it because lots of cad software do the same thing also in real life it won’t do it it not like your building the physical bot the cad is just to help invision it will get its message across

[nenik]

Do you mean this gap?

Well, that’s not a CAD problem, that’s a wobbly wheel problem.
On the real robot, the tolerances might stack in different ways and you don’t want the wheel too tight, but 0.07" is quite a lot of play, perhaps enough to get the omni rollers hit the C-channel.
On a real robot, you’d likely use a teflon washer in that space. You can drop one such in the CAD as well and leave the rest of the space empty.
But on a real robot, you wouldn’t use those plastic inserts over a screw, as they are way usually too tight. You’d rather use the the brass inserts (276-8034) and then your spacing would be somewhat different (likely 1/8").

[VexThirteen]

@nenik

But on a real robot, you wouldn’t use those plastic inserts over a screw, as they are way usually too tight.

Is this really true? Do most teams use the brass inserts? I’ve always used plastic inserts and I generally have about 10-11 seconds of free spin on my wheels.

For teams that have used both, was there any significant improvement with the brass inserts?

[Charles-8889A]

plastic inserts work fine and are also lighter

[nenik]

Measured in OnShape, the brass insert has the nominal inner diameter of 0.165", while the round plastic insert only 0.160". It also shows screws as having 0.164" outer diameter, which is the nominal outer diameter of standard 8-32 screws.
By the way, 0.160" is also nominal diameter of the 1/8" shaft, since it has the corners rounded for that.

So far for the theory. I have also measured (using cdtools digital caliper) few specimens I had at hand:
Old green round plastic insert ID: 0.162"
Newer gray round plastic insert ID: 0.1625"
Robosource violet color coded screw: OD: 0.160"
1/8" shaft diagonally: 0.159"
Those two particular inserts have rotated reasonably well on that particular screw, but still had tendency to follow the thread. The gray one would even keep spinning without any additional mass for about a second when spun up, while the green one had a tad more friction and would just stop immediately.

Note that I have also observed that they are sometimes little too tight to fit into the HS hole, so when pressed in, they shrink a little and become very bad.