Servo Control with encoder

I would like to use this controller to create a positional servo setup and am trying to decide if i should use pots or encoders so i know which unit to buy. I like the idea of encoders because they seem like they will last longer, be more accurate, and will not require frequent calibration. However, I do not see how it is possible to reference the "zero" position. What is normally done to solve this problem? Another issue with using a pot is i need about 540 degrees of rotation. How well do the multi turn pots work?

Thanks.

We have implemented position feedback using encoders in the next version of the software (1.7). As you point out, however, there is a problem of reference every time the controller powers up or resets. If you are using a microcomputer to drive the controller, you could have the motors slowly move to a limit switch and use that position to reset the reference.

Pots have the benefit of reporting absolute position. They are typically sufficiently accurate. Over the long run, the concern would be wear since they would be moving a lot compared to any other use. You can find very high quality and expensive pots. One of the Grand Challenge participant of last year showed us one that he bought for a few hundred dollars. Multi turn pots should work fine as well but the question of wear remains, and the servo's min and max mechanical postiion should match the total number of pot turn.

You can find position sensors that will report an angular position with a voltage output, built with other technologies than pots. This device looks like it would work <A href="www.beiduncan.com/9900se/9900Series_ds.p...l%20angular%20sensor'" target=_blank>www.beiduncan.com/9900se/9900Series_ds.p...l%20angular%20sensor', although rotating range is only 90 degrees. You will find more doing a yahoo search for "hall angular sensor". Look for devices that take 5V power and report a voltage from 0 to 5V.

You can also find absolute encoders + D/A assemblies. However, getting a Digital value (from the encoder), converting it to Analog to send it to the controller, and converting it back to Digital inside the controller, is not the most elegant, or cheapest solution - but it should work.