Wheel Expanding Under A "Few" Gs

RoboLoCo Post


And THAT is why nobody should be using AM compliant wheels for a shooter…


Once did that with a Lego for fun to see what would happen. I stuck one of the flat tire hub tires (see below) on a 6000rpm (I think) motor. The tire itself expanded to about double it’s original diameter and then proceeded to pop off, roll about 75ft, and put a black mark on my wall. It may have been higher than 6000rpm, I can’t remember exactly as this was about 5 years ago. Fun times.

The wheels:

This would be awesome to see. Wheels blowing apart. Wheels expanding greatly. Much better than boring Fairlanes.

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as Jeremy Clarkson always says… SPEED AND POWER


It’s worth mentioning that my team’s CAD group was finalizing our shooter design a few days ago when I noticed what appeared to be a Compliant wheel on the screen… Obviously I put a stop to this real fast, but not even we’re free from foolish mistakes.

I almost let them try it, but it’s just a little too much of a safety concern for me.

… and by a few, you mean a couple thousand, correct?

Can you spare a few dollars?


Actually, we found they were quite good at shooting the ball and only aren’t going with them because programming wanted a consistent wheel diameter for PID Tuning. Unless you are doing something fancy with controls, I would definitely suggest trying them out. (We were using green compliant wheels)

Edit: Unless people really think there is a safety concern, technically not my specialty, I just was part of the group testing it.

RoboLoCo opted to use a different wheel for various reasons. In any case, I do agree with Fletch1373 that it’s probably not safe in the long run; that much physical stress is bound to take a toll pretty quick.

I can spare a few dollars for you if you can spare a “few” for me :wink:

I’ve heard horror stories of those wheels disintegrating at high enough velocities. After seeing how they behave under relatively low velocities, I’m inclined to believe the horror stories.


Good to know, thanks for the heads up.

For typical shooter speeds on a 4 inch wheel it will be experiencing well over 100 G’s

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We found that the green compliant wheels degraded quite a bit from high RPM shots. Another reason not to use them for a shooter.

Relative centripetal force in g is given by:

g-force = radius x RPM^2 x 1.118e-5

As an example: a 4 inch shooter wheel at 4200 RPM sees about 1000 g RCF.

Another example: laundry spinning at 1000 RPM in a front-load washing machine with 28 inch drum diameter sees about 400 g RCF.

Extra trivia: that load of laundry has about the same kinetic energy as my station wagon cruising at 80 MPH; i.e., about a million Joule. The shooter wheel has a lot less, but still enough to do damage. See some of the earlier posts in this topic.

So you are suggesting using a wash drum for the shooter wheel?


Only if you don’t plan on running the trench. :wink: