Comments on: Cheap XY table using hobby servos

By: Dai

Dai — Sun, 01 Mar 2009 22:05:46 +0000

thanks for the info on the scripts.

By: CarlS

CarlS — Mon, 06 Oct 2008 22:03:07 +0000

Yes, there is a resolution limit to this approach, but it works pretty well with the digital servos we use over the size of table we have (~30″). Smaller tables would have better precision, and there are better potentiometers out there.

Since it’s a closed loop system, the potentiometer never turns past the limits. We basically took out the single turn pot and used a 10-turn one in it’s place, so instead of the typical 90-180 turn, you get 900-1800 degrees. In practice, hobby servos don’t actually use the full range, so we are using ~6 turns.

By: Sparky

Sparky — Wed, 01 Oct 2008 08:59:54 +0000

The disadvantage is that you also get 10x the positioning error, and the resolution can get pretty bad.

Also, what’s stopping the servo from breaking the potentiometer? They must have removed the notch to get the servo to make 10 full turns, and there is nothing from stopping it making a 11th turn. Maybe a little window comparator to turn off the servo when it gets to close to the end of the potentiometer?

By: macegr

macegr — Tue, 30 Sep 2008 21:03:30 +0000

I like this idea a lot. With a good PWM generator, you could actually get decent resolution and speed for X-Y positioning tasks. Not so much for plotting and machining, but maybe pick and place operations like building mosaics out of different colored M&Ms or legos, automatic puzzle solver, etc.