# Gear motor with encoder: minimum drivable step

I am fancying this motor http://www.pololu.com/catalog/product/2271/specs to motorize an X-Y stage. (Alternative High rpm motors with high reduction ratio and high encoder counts/rev are welcome ;)

If possible I want to not use stepper motors, as they are harder to control, and also it might be difficult to achieve speeds about 1k rpm?

What bothers me is the minimum angle/ amount of steps that motor can reliably be driven from rest.

Can anyone provide a good estimate what minimum number of steps I can expect?

Edit: I have a laser to measure a surface's depth, now I need to translate the surface in a zig-zag pattern. This requires one motor to do one very small step at the end of each line. In this case: <= 1/50 * 360° = 7°, which translates to <70° of the motor shaft, due to the gearbox.

Edit2: angle corrected.

• Assuming a quadrature encoder, 1/4 of the encoder slot increment, adjusted for any gearing between that and the output shaft. If the sensing technology is analog, possibly a bit better by comparing the actual strength of the two sensor phases. But in a gear motor, you also need to consider the concept of backlash if the direction of loading changes. Even if the encoder is at the output and not subject to backlash, driving it through the backlash of the gearchain may cause issues with the motor oscillating across the backlash distance. – Chris Stratton Oct 31 '13 at 15:10
• Are you sure you can immediately stop the motor after 1 encoder increment (intertia..)? – user765269 Oct 31 '13 at 15:12
• A proper control system compensates for modeled load properties. However, backlash in the gearchain may make that impractical. – Chris Stratton Oct 31 '13 at 15:13
• Which part of "... 465 counts per revolution of the gearbox’s output shaft." is confusing? There are other gearbox options that will give you higher resolution if you need it. – Dave Tweed Oct 31 '13 at 15:29
• @user765269 Even without going into the control mechanisms, there must be some reason that all the RepRap and other desktop 3D printer designs, various CNC machines, both DIY and commercial, and myriad other systems have designers opting for a stepper motor for precision movement, despite gear motors being "simpler". Food for thought. – Anindo Ghosh Oct 31 '13 at 16:07