Is that strange smell from the motor or the gearbox Grease

We have had two incidents of a bag motor in a VP gearbox overheating and making a strange smell. I have heard that the smell could be from the motor itself or from overheating of the white lithium grease in the gearbox. I am wondering which is true. Has anyone smelled this when an overheated 7 7 5 was in a VP gearbox or is this an exclusive problem with bag motors? Can’t describe the smell but it is distinctive.

does it smelly burny? fruity? rotten eggy?

is the motor warm or hot to the touch?

I’d have to smell it. The 775pro can burn quite easily, so if that was on the gearbox rather than the bag motor, it may be the 775pro. What gear reduction are you using, what is the load on the gearbox, and what % are you running your motor at?

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Honestly, this is probably the best way to tell quickly. If it smells fruity, that’s likely the motor windings*. If it’s burny/smoky, its probably wire insulation melting. If the smell makes you want to throw up, it’s probably grease inside the gearbox overheating.

We’ve had a number of smoking robots on the field here in Israel this year, and we could generally tell what was burning even before the robot left the field based on the smell.

* or more accurately, the varnish/resin covering the windings


Find an old motor that you will never use (like a 550 series motor). Clamp the shaft down in a vise, apply 12 volts, and wait until you see it let out some smoke. You will now have a sample for what a dead motor smells like, good for future reference.


I’m not good at this but I would say fruity. But a nasty fruity.

Motor was very hot

The motor was getting prolonged low current accidently due to code problems.

its most likely the motor windings burning up, take the motor in question and remove it from use. What was the application of this motor and what was the gear reduction?

It was an arm with a 100:1 VP and a 3:1 external. It either fine for 1 comp and hours of practice, until the code change.

has it/are you going to change it out?

It was the motor, in our applications you’ll never get the grease that hot.

All in all definitely sounds like the motor burnt up. It might still move when given voltage, but it almost certainly won’t have the same power as a non-burnt motor. If you’ve traced the cause of the motor burning to prolonged low-currents and can fix the code, you should be fine if you just replace the motor.

I have definitely seen grease burn before. It’s a lot more common with CIM motors because they can generate a lot more heat before self-destructing. Grease can also burn due to mechanical issues causing high friction.

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weve had grease burn in our drivetrain gearbox, usually burns after quick high speed cycles

Definitely will change it out

This seems on-topic enough:

We smoked a Neo last night and it smelled like paint. Anyone know what exactly we were burning in there?

Likely the varnish that the windings are coated with. It’s a plastic, so it may smell a bit like spray paints.

If the motor is still running and the smell had a fruity tinge then it would be the varnish on the windings. Idk what material the brush carriers are mounted on, but i’ve seen those burn up. Some companies will use a composite which could be near the burning point of the varnish.

does it smell like burnt pineapple and butter? this is my best explanation of a burnt 775 motor. I have lots of experience with the magic smoke.