Mali06

When do you need to replace the rotor of a brushless motor?

mrreet2001

iTrader: (9)

When it is no longer performing as it should. A lot of variables go into it. Age, brand, heat.

Mali06

I have a 13.5t motor for years and I've got a new rotor for it. Just don't know when's the time to replace it.

The motor seems to run fine now....Maybe I should give the new rotor a try and see how much of a difference it makes.

Mali06

Is there a good way to check the straightness of a rotor shaft?

BaconRaygun

If you thermal a motor a few times, that's gonna do it, lol.

Another example would be if you had a bearing start to slip between the inner race and the rotor shaft. That would quickly diminish the tolerances and start to cause radial play, which would cause even more wear, which would cause more play, and so forth... In that case, don't forget to swap the bearings too.

I guess if you manage to break a shaft, but I imagine that's kind of hard to do with a car.

BaconRaygun

The easy way would be to remove the pinion and spin the motor. If the shaft wobbles, then it's bent. You can also remove a shaft and roll it on a glass table.

The most accurate way is to remove the rotor and roll it on two flat edges. Place the edges on the shaft ends so the magnet portion is in the middle. You need to use a non-magnetic medium for this like acrylic, glass or polished stone slabs. The motor will wobble as it rolls and settle on the low side.

Ok, the MOST accurate way is to use an external bearing block and a dial indicator. But I'm guessing you don't want to spend $100 on a dial indicator.

Mali06

I think I will check the shaft between a pair of droop blocks. Droop blocks should be fine since they are aluminum and flat.

Thanks!!

Mali06

the shaft looks fine at where the bearings touched. Can't believe it's a few years old.

Roelof

You can get or make a gauss meter to show the strength of the magnetic field and follow it over the life you are using it.

BaconRaygun

That's great! That means you did not have any weird bearing problems (sometimes very difficult to pin down, especially in cars because you wont always hear it like you would with a different kind of model).

Based on that and your other post, I would say keep using that rotor for now. You can always try the other one to see if you feel a difference, and if not, then just stick with this one till it wears out.

AMachines

iTrader: (3)

so do the windings go bad as well

Timmahh

iTrader: (16)

Info on making a gauss meter?

Timmahh

iTrader: (16)

The windings are generally made of high-quality copper. They wont go bad persay, but if the motor gets too hot, it may cause some insulation issues.
Takes quite a bit to melt copper. Otherwise, there is not much that one can do to the windings unless overheating has causes shorts from loss of the wire insulation.

Roelof

purplegrape

What does it mean when the motor is “crunchy“?

when you turn the arm and there are definite hard clunks?

I have a motor from Surpass racing that had very few packs on it and was never run hot, no major impacts

can I fix it just by putting a new rotor in it?