Mesuring Distance

samsn4

My project involves a slow moving, variable speed turntable, that is able to start and stop it at points that i set. what i want is it to 'watch' my movement of turning the table and mimic it. My idea is to use a slotted disc on the motor shaft that turns between an lR and Receiver, The program will count the number of pulses passed and then rotate that many when the RUN button is pressed. Any other ideas, suggestions ?

StefanL38

Hi Sams,

what accuracy do you need?
there are all kinds of rotary encoders. The propeler-chip is fast enough do count thousands of pulses per second. I guess your turntable has a gear.
If you mount the encoder on the motor-axle you will gain a lot of precision.

best regards

Stefan

evanh

If you want repeatable position then go for a full quadrature encoder.

If you want to know the position on power up without having to search for a reference then an absolute encoder is needed.

kwinn

You need a quadrature encoder if the turntable needs to go in both directions. If the motor is geared down to drive the turntable putting the encoder on the motor shaft will give you greater precision, but backlash in the gears will will affect that. Having the encoder driven by an idler wheel in contact with the turntable periphery will reduce or eliminate the backlash.

max72

I asked a similar question here:
http://forums.parallax.com/showthread.php?131517-Absolute-angular-sensor-question
The Melexis works rather well for me. If you only need the "final" position it is an easy and robust solution.

Massimo

idbruce

In my opinion, to accurately mimic the table, you will have to acquire initial starting position of both the table and the mimicking device, which means an encoder device or setup for both. On the other hand, if your intention is to have the table mimic a control device, well I believe that could be a different issue. Will you be using two microcontrollers?

Bruce