While investigating the weird hesitation and vibration, I destroyed the motor.
I've been having trouble with a strange hesitation, coupled with a vibration noise. The hesitation is concurrent with a sound like the motor spinning freely. The vibration sounds like a growl, and there's no acceleration at all while it happens. The hesitation is more noticeable at high acceleration, and the vibration occurs at high revs.
I planned on checking this out with Nathan today. We were going to put the car on jackstands and run up the revs, but I wasn't sure this would duplicate the problem. I wanted to have a dataset to duplicate, so I took the car out early this morning to observe and record the problem. I ran the car gently through the gears, recording the speed where the hesitation became noticeable in each gear. I also noted the speed and amp draw when the vibration ocurred. I used first through third gears.
On the way home, I decided to try SuperLow, too. I figured, with the car on jackstands, I don't want the wheels spinning at 30 mph. Gyroscopic forces might make things too dangerous. And since the motor wouldn't have anything to pull on the stands, I wanted to get the vibration at the lowest possible amp draw.
I know that my engine just blew itself apart. I'm so disappointed I don't even waste my time cursing. I just call Eri, get out and try to pick up the pieces.
Here you can see the little bits, as the car left them. The copper chunks that look crenellated like a castle wall are bits of the commutator. The springs are the brush clips, which held the brushes onto the commutator. The other bits are mostly insulation. Together, they are the remains of my dream. (Angst, angst.)
(bigger)
(bigger)
(bigger)
(bigger)
(bigger)
(bigger)
It doesn't look so bad, really. From the top. Then you start looking at it from other angles. Stuff just exploded out from all the brush windows. It went right through the metal and cloth mesh that's supposed to keep pebbles and dust out. Wires are hanging out everywhere, sometimes with pieces of brush attached. And when you look inside, it's nothing but an empty shell. Nothing remains but the shaft.
(bigger)
(bigger)
After we removed the motor, I took off the end cap to see the damage a little better. So now the challenge is to figure out why this happened, so I can prevent it from happening again. Did I just rev it too high, or was something wrong with our installation?
Lesson to all other hobbyists: install a tachometer! If you can figure out some way to limit your motor revs, do it! And wear safety gear when you troubleshoot. I almost couldn't sleep thinking of what would have happened if I had blown the motor up while Nathan was underneath, trying to inspect the moving brushes or something.