Wheel Expanding Under A "Few" Gs

RoboLoCo Post

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

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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:
image

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

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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?

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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.

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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?

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