Get 'em while they're there - SG92R servos
March 7, 2013
I've just received 5 x SG92R servos from here : http://www.ebay.co.uk/itm/261131115638?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 and ordered 5 more. 6 days to the UK from Hong Kong and 14 quid (20 USD) for the five.
Although the name is partially blanked out on the photo, these are the real deal - TowerPro SG92R. Weigh 10g, carbon fibre gears throughout, screwed case with what appears to be thicker than normal plastic. Loads of torque and easy to modify for continuous rotation. All 5 were consistent with speed and have a good smooth action with a nice 'buzz' rather than the nasty plasticky noise most small nylon geared servos make.
To modify, disassemble case with tiny screwdriver and remove gears - Final gear is a tight friction fit.
Chop off end-stop on final gear and ream out centre hole with handheld 1mm drill bit until it slides smoothly on shaft.
Apply servo pulse of 1.5ms and rotate final shaft / feedback pot until motor is stationary. Use small drop of hot-glue to fix pot at this setting.
Reassemble with an extra bit of silicone grease where needed.
Testing the one I've done gives a dead solid mid point with no jitter, very good slow-speed control and about 10 speed steps each way to full speed. All in all, a bloody good little servo for either standard use or continuous rotation!
Downside is the splines are not that well defined and the arms don't seat as well as some, but fine once screwed down. Also the output shaft is on the short side and it would have been good to include a disc with the supplied arms.