I’m about to build a six-axis robot, like a mini industrial robot arm, and considering the Cytron geared motors with encoder like the model
Cytron 12V, 60rpm, 93oz-in Gear Motor w / Encoder
RB-Cyt-92
Deterministic movement and certain mechanical stiffness are must to have, so how would you describe the backlash of these Cytron gearboxes? Any data available from the planetary output shaft while the DC motor armature is locked in place? Also, do the Cytrons have a ball bearing at the final output shaft?
If you see the Cytron unsuitable for robot arm use due to backlash, how about the Devantech RB-Dev-38 then?
Ultimately I will be needing six of these of course, and certainly willing to pay extra for any stiffness and quality low-backlash action I can have in sub-200 $ per axis in the servo solution.
I guess high precision does not come cheap, once again. Low backlash is expensive. Industrial AC servos with gearhead can cost over 2000 $ a piece.
How is the backlash in RC servos? Ever heard of anyone fitting the motor inside with a makeshift encoder, ripping out the potentiometer, and using the motor in your own feedback loop? With low backlash and encoder, that could be a viable option. A brushless motor would be an added bonus, that is easy to keep in standstill.
I certainly can’t use the RC servos as-is. I would need speed and position control. Unless, of course, the internal position control is tracking the input command in a reasonably linear fashion so that I could just ramp the position reference. I have no idea how accurate the position tracking in these are.
There is very little data available about the backlash of the motor - they are intended to be used primarily for continuous rotation applications rather than in stall situations (keeping an arm at a desired location). Note that you can get even more torque from a less expensive servo motor - which are often used for smaller-sized robotic arms. RB-Cyt-92 can provide 93 oz-in whereas RB-Hit-29 can provide 133oz-in and is better suited for stall situations.
For hobby arms, RC servos are great, but there is backlash which is hard to quantify. If you want it to be industrial with minimum backlash and high precision, you’d need a geared DC brushless servo. There are servos which use magnetic encoders, so gutting a servo and replacing most of the components would not be very cost effective.
