393 Motor Problem

Has anyone experienced a motor not spinning very well. Our front left drive motor is VERY stiff to move. I took it off the robot and tried to spin it free handed, but it was very stiff/hard to turn.

What is wrong with the motor?

Either the brushes inside the motor are starting to break or the gears have gotten jammed some how. More than likely it is the brushes inside the motor. Can you check the internal gears and see if any of them are broke?

Where are the brushes? I took off the bottom part and the gears appeared to be fine.

Have you greased the gears lately?

No. Are we supposed to? I don’t think I have ever greased any of our motors.

Brushes are the electrical connection between the coil in the motor and the wires that connect to the cortex. It allows the shaft to spin while maintaining electrical contact. Here is a diagram:

The brushed are inside the actual motor inside of the housing, what we all call a motor is really a motor plus gearbox. There is no access to the brushes, they are not serviceable. Take both sides off the motor and check all the gears.

Alright, I took the green cover off the motor, and then proceeded to take the gears out. They all look fine.

Then I put one gear in at a time and turned it. Everything was fine until I put the top gear in. Why would it do this?

Edit: Hmmm… I then just attempted to free spin the top gears without spinning it with an axle spinning it. It spun fine. Maybe it’s the gears in between the 2 sets?

try running the motor with out the gears being in place. we have had similar issues and found that the brushes were the problem. also check the metal bearing in the black cap end, this may require some grease.

I did and it ran fine.

If the brushes are the problem, do I need to purchase another motor? If so, does this problem occur a lot? Will I need to buy more motors “just in case”?

we have had four motors having issues with the brushes this year. i believe it is how we are using them that is the main issue. usually the motors will operate in one direction fine and not in the other direction.

if yo have found that all is good without the gears inplace, repleace these with new if you have and apply a small amount of grease to all moving parts. use a high speed bearing grease as other types will be thrown out.

Does it turn ok when you apply power?
Lots of people believe there is something wrong with a motor if they cannot turn it manually. As far as I am aware this is not true as.the high gear ratio in the motor can prevent manual movement. You should really avoid manually turning the motors anyway if you can.

It does not turn at all when I apply power. I know it is harder to turn manually, but it is REALLY hard.

Just wondering, but when you took the motor off of the robot did you remove it from any motor controller it was connected to? Last year I had a similar problem with a drive motor. It turned out not to be anything mechanical with the motor, but rather a fried motor controller. If it is, try removing it from the MC and then turning it by hand.

Hope this helps!

I checked the motor controller, and it was fine. I think it is the motor. I went ahead and ordered 4 more motors to replace the broken motor, and to have 3 back ups “just in case”.

Thanks for your help guys!

I had two motors die on me in a similar manner over the past few days. They failed to move at all when driven electrically, but felt fine when turned by hand. I suppose we all just have to remember that the motor modules have a limited life span, so we should make sure to have spares on hand before attending competitions.

I am SO glad it happened before our competition. It would have been a sad first competition.

100% sure its the brushes
we have a couple of “brushed” motors last year (HS and normal 2-wire) we just took the entire gearbox apart and dumped them in the “spare” bin
cuz usually some other motors will have other parts breaking and we can just easily swap them out