Hobby City HXT900 Servos
#27


I have over 50 GWS Pico/Naro, and a number of HS55 servos. NEVER a failure. I consider both GWS and Hitec sub-micro servos to be top of the line. As for HXTs, I recently bought 3 HXT500 servos. With careful testing, I noticed that one of them would randomly hit dead spots, where a slight nudge of the arm would get it going again. The fact that the location is random basically rules out a bad spot in the pot. I assume the motor has a certain spot, where if it stops there, it will not run. The next assumtion is that this is due to using cheap motors. There has to be a reason why they cost less, and it's not the 3 cents worth of plastic parts.
The overwhelming bottom line is that they have an initial defect rate of 1 in 3 with me, and other good brands have had 0 in 100 defects. About the only reassurance is that the servo was noisy, which I believe is coming from the defective motor and not the geartrain. At least you can possibly weed out these bad HXTs, by simply not using the ones that sound like miniature rock crushers.
For those as insane as myself, I actually took apart the little coreless servo motor and reassembled it, and it still works. It actually has not hung up since reassembly, but I'm not sure why.
These little buggers are unbelievably tiny. The brush contacts are a bit larger than human hairs!

When I reassembled the motor, I realized that the brush plate/enbell assembly is actually keyed to the motor to work in only 1 positon. You can't just slam in on however you want, like most brushed DC motors. I had to try all 4 possible alignment postions of the endbell with the stamp marks on the case, to get it right. Getting the motor shaft/commutator in the brushes without bending or crushing them in unbelievably tough too. Fortunatley I have not lost my close vision, so I can still perform these worthless insane experiments. The servo seems to run now and not hang up, but I don't see using it in anything.