Motors weaken

Major Issue. This happens to both our drive and now lift motors, and whenever any sort of stress is applied to the wheels/lift (lifting a cone or driving over 10 pt pipe), the motors then respond thereafter with a minute fraction of their original power. This wears off after about 2 minutes so my first assumption was perhaps it was a burnout. However, my theories were shattered when an affected motor didn’t feel hot to the touch. We changed one of the motors on the drive and the problem persisted. Any ideas on what could be causing this and/or how to fix it?

I don’t think the motors have to be hot for them to overload. We built a flywheel for a classroom project, and when we started and stopped it quickly the motors would brown out/overload. But they weren’t really hot, they were sometimes warm and sometimes you couldn’t really feel a difference.

Is there a potential fix?

How heavy is your robot, are you using bands on your lift, and is your drive turbo?

Lifts banded and is 2 motor 1:5 on 13" arms. Our bot weighs about 10 lbs or so and is 4 mtr high speed on 4" wheels.

Might be too late for this, but going to 1:7 OR adding more motors to the lift would be a pretty safe bet. But have you checked the MC’s? A 10 lb robot should not be tripping PTC’s, especially w 4M HS. The only other thing is friction but I assume you already got rid of lots of that

WAYYYY too late for that. A change like that would only lead to multiple other things on their robot that would have to change for that large gear size.

We are running all of our motors on full 127, which makes me wonder whether or not we burnt them out by giving them too much current we don’t need. We’re going to try adding slew control into the program. Also, you mean motor controllers by MC’s, right?

Should we bother to replace our motors? We looked it up and it sounds like if you trip the PTC once, you’re more likely to do it again.

What this means is that if you trip it once during a match, and it cools down during the match, your more likely to trip them again, as not all the heat has dissipated. This doesn’t mean you should replace your motors, just drive more gently during the match afterward.

Would running my motors at 100 as opposed to 127 potentially decrease the chance of tripping the ptc?


do you have your motor controllers zip tied to metal? that might help

after around 90 motor power, you gain fractionally more speed, but gain a lot more heat to trip the ptc. I recommend run the motors at around 90.

I would recommend that you look at your motor distribution on your cortex as it looks like you may be tripping PTC’s. Make sure that your load is split evenly over the 2 shared breakers on ports 2-5 and 6-9. If that doesn’t work, make sure that all of your motors are working properly individually and no Motor Controller or Cortex port is damaged. Because you have a 10 pound bot, the load should not be significant and motors should not be slowing down like you say.

No. After around 90 motor power, you gain no more speed and it has no effect on the PTC either. From the motor’s point of view, there is no way to observe whether the command was 90 or 127, according the the research published on this forum, the output of the MC29 is the same for both 90 and 127.
Obviously, that applies to ports 2-9 through the MC29. Port 1 and 10 behave differently, but for those, both the power and speed still get gain on values over 90.

Some great info gents!

I am just starting to understand motor fade and this really helps!

Do you know of any good write-ups on VEX motors? I notice DC resistance varies a lot (2 - 50 ohms) and wonder if this is an indicator of motor health. I chose low-resistance motors and am plagued with stalls.

Are higher-resistance motors less prone to tripping breakers? Do they have same power?

So much to know…