So how do I put this back inside? :ahh:
I think we all know these have been pretty reliable motors. In fact, I don’t think we’ve failed any at Team 4926. But this one spit out a brush last night! I found it 10 ft away. I assume the fan blades threw it, although I wasn’t there to see it.
One of my favorite memories this year was when our electronics team was freaking out about a brush getting broken and completely sucked into the motor when we were testing it- dont worry about it honestly it should still work. I wouldnt expect an easy way to reattach it since basically you break it after opening it.
EDIT: okay I though that was a fan piece or brush casing… my bad!
This kills the motor.
There’s no coming back from that. It’s probably dead already if that fell out. My team burned like 2 775 when that happened so yeah…¯_(ツ)_/¯
A question: is this motor still legal to use per R34? Additionally, if you somehow fixed it and got the brush back in, would it be legal then?
I don’t think there’s anything in the rules about components modifying themselves…
Even if it is deemed to be legal,
At our off season event, ROBO-CON, one of our eleavator motors sollowed a zip tie. I wrap itself so tightly in the motor that there is no hope of getting it out. 
RIP 775 #6
Even if the motor still spins after the brush flies out, it will run at a fraction of the performance it once had (and eventually fail). Discard the motor so you don’t accidentally put it on a future robot, and change it out for a new one.
I would assume that if you put the same brush back in (if the motor isn’t already killed and the brush is in good shape) that R34 would not be violated since the motor was not changed in any way. If a completely new brush is used, I would expect that to be in violation of the rule.
That being said, if you get it fixed (big if), I wouldn’t use it on a competition bot because the motor has to be at least partially killed if it ran any after losing the brush.
Edit: +1 to the post above, label this motor for no competition use.
Am I the only one who read the title and thought of someone in a 775pro costume getting sick and vomiting?
This is why I generally have a strict “No used motors on the competition bot” policy, you just never know what kind of shape they’re in.
We had a similar failure on our two motors running our elevator… twice. While our brushes didn’t forcibly eject themselves, you could view inside the motor and see that they were clearly not attached anymore. We opened one of them (with a dremel because it was late Friday afternoon at Heartland and we were curious) and the brush didn’t just come out, the metal that was acting as the spring for the brush had snapped. What’s funny, is it happened the same side to two motors running two sides of our elevator. Same failure happened at a demo event a few weeks after worlds.
775 pros are a bit fragile. If you run them at full voltage and under about %50 free speed for any significant length of time, they will over heat. Brushes coming loose is a symptom of that. Which means you want to stay to the right of peak power on the power/RPM curve.
While it is possible to repair this motor, the fact that the brush fell out is proof that the motor has been damaged. I pulled one apart a few years back and found that the actual failure occurred in the brush holder. It cracked and released the brush. I could have used parts from a different motor if that one had failed due to an armature short but the motor is not a huge an expense. Repair is one of those diminishing return kind of operations. Your time costs more that the motor is worth repairing.
Spitting out brushes was always the failure mode on 1 motor swerve modules. especially on the practice bot that got ran hard in a 90 degree room. you can take 2 motors that have done this and fix 1 but they will fail again so don’t use them in competition. you take the broken brush holder out and replace it with one that didn’t break from a different motor making 1 usable motor out of 2 junk ones. we had to do this in 2016 due to 775 being sold out everywhere.
Nick
Sam,
To open the motor requires some end nippers or strong wire cutters and some experience in bending back the crimps that hold the motor end plate in place. It is tricky to get everything back together without additional damage but note that the end plate has bearings and it must be set back in place so the motor armature is correctly centered in the magnet structure. I would use this motor as an educational tool to show the electrical team what the working parts of the motor are.
Team 4926 has never really done a “this is what is inside a motor” session, so yep looks like we have a sacrificial volunteer!
The other current thread about 775 testing is really interesting regarding how folks are “managing” 775s at low speed and stall. It seems that current/voltage limiting is a must along with good/better mechanical design to get those motors moving safely and run them in their sweet spot!