control the precise rotation of a Continuous Rotation Servo?

playinmyblues_nscc

After searching the forums for a while and not finding what I am looking for, does anybody know of a simple way to control the precise rotation of a Continuous Rotation Servo? I am using a BS2.

I have already tried the following:
1) Measured the time it took the cts servo to rotate 20 times. Determined the time for a single rotation. Divided the time by 3 to get the time for one motion through 120 degrees.
2) Calculated the total time for a pulse with the PAUSE 20 command; PULSOUT pin, 760 (same cts servo speed as measured for step·· 1).
3) Used a FOR NEXT loop to run the cts servo through approximately 120 degrees. FOR NEXT is counter = 1 to 75.

The problem is that it does not return to the same spot after 3 movements so the cts servo is not controlled precisely.

Post Edited By Moderator (Joshua Donelson (Parallax)) : 10/23/2009 4:10:44 AM GMT

Mike Green

There is no simple way to control the precise rotation of a continuous rotation servo. They're not precise devices and there's no feedback mechanism to improve that (since it's been removed or disabled to make a continuous rotation servo). Have a look at the position encoders used with the BoeBot (and the sample code): www.parallax.com/Store/Microcontrollers/BASICStampModules/tabid/134/List/1/ProductID/80/Default.aspx?txtSearch=position+encoder&SortField=ProductName%2cProductName. That's a reasonably accurate, inexpensive solution. There are other types of position encoders that you might be able to build or buy, either using an optical encoder or a potentiometer, but there's nothing simple and cheap.

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