Originally Posted by fredygump

I just had 2 rotors grenade on me, and I'm trying to figure out why.

I'm running a 4038 1350kv on 6S on a MBX7TR. On the first (original) rotor, the fiberglass wrapped around the magnets broke straight across, like it was cut along the edge of one of the magnets. The magnets came out completely intact, not broken. All 4 magnets separated from the rotor core, which came out by itself, leaving the magnets stuck to the inside of the can.

I wanted to keep running my truggy, so I pulled the rotor out of my 4038 2000kv motor in and put it in the 1350kv.

Now it's the next weekend, and half way through the third pack since the rotor swap, that rotor grenaded. This second rotor had a different failure. One of the magnets cracked toward the back of the motor. It looks like there was some rubbing, but I don't know if that caused the failure, or if it happened because of the failure. It looked fine when I installed it.

I don't see anything obviously wrong with the second rotor when I installed it. And the bearings look fine.

I'm running an RX8 ESC, with torque set to 1. I was using a 15T pinion at the time, but had run a 16T on the previous run. Motor temps ended at 180F, so I went back down 1 tooth. I ran the 15T last year.

So yeah, what's the most likely issue? Is something wrong with my motor, or is it somehow set-up related? Should I be geared higher, despite the motor temps?

I ordered 2 new rotors last week, thinking I'd have a spare (out of stock... ), but at this point I'm hesitant to install a new rotor in the motor. I don't want to ruin another rotor if this is going to happen again.