How did this happen? Too much cowbell?
-Nick
I think by cowbell, we mean what was the motor setup + gear ratio into this wheel? Also, how did the wheel stall?
The outer rims of the wheel seem like a really odd way for this wheel to shear. Wouldn’t the bolt holes loosen, the sprocket bend, etc. before the outer part of the wheel broke? How does that relieve the stress?
Pretty interesting failure. Definitely not typical from what I’ve seen out of the kit wheels in the past.
Still looks like it was due to the robot being pushed sideways in some manner.
-Brando
Sure looks like a side-loading failure to me. A rotational-loading failure would more likely manifest itself in shattering spokes, or breaking the holes in the hub.
Team RUSH had a couple wheels go like that during the past season, those bumps were pretty rough, but we did add reinforcements to them by cutting pieces of what I believe was 1/16" aluminum and placing them between each set of spokes.
I don’t fully understand what you mean by side-loading, so I’m not sure if that’s the same as this, but I think the general belief is that our failures were due to the forces of impact on the wheels when they hit the ground.
The distorted shape of the wheel doesn’t look like what I’d expect from either a rotational or side load. It looks like a simple impact to me. The robot might have taken a hard bounce, or it might have run the wheel into a proverbial brick wall at high speed.
Then again, the wheels were redesigned to handle greater side loads without breaking the spokes, and this might just be how they react now.
A force parallel to the wheel’s axis I presume.
**
That’s what I assumed, I was just thinking that an impact force would be more likely to have this effect on the wheel, since it reflects what we saw happen in our own wheels this year.
“load” can include impact loads.
You get hit hard in the side, the impact creates a momentary side load (especially if the bottom of the wheel is against the bump or the goal ramp)
**
Neat picture. As others say, my guess is not torque but a thump coming down of a ramp etc.
I will add for fun–possible plastic “creep”. *If *that robot has been strapped in real tight to a shipping crate for what? 7 months now…that could cause some high stress points that now show up after standard use.
Troy
The odd thing about this is that 2200 had an omnidrectional robot that could not cross the bump. Perhaps their preseason prototype has enough power to break wheels by pushing?
Correct:
Axle-Wheel-Load
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Woot ASCII Art
EDIT: It messes up my spacing…
Correct:
Axle Wheel Load
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Fixed art above.
1178 had something kind of like this happen at an off-season event (any Venturing Scouts might know about the Fall Fun Rally held in St. Louis, Boeing always asks us to come out to their events and show off a competition bot). After several hours of driving on asphalt, a scout drove the robot off the road, where one wheel got stuck. The scout proceeded to show the joystick all the way forward, and bent the sprocket and sheared off all the bolst holding the sprocket to the wheel. Needless to say, we were done driving that day.
Thats exactly what happened a simple impact, this happened on our 2009 robot. We had 6 similar wheels like this one on the robot. This was caused by going forward then reversing fairly quickly. The front four wheels then came off the ground then quickly back down crushing this wheel.
Aha! So the subject line is correct. Too much torque on the other wheels caused this one to break, because the robot did a wheelie. 