position control of continuous rotation servo?

myk1323

Hi, as I understand it a continuous ratation servo has the pot. disabled, basicly making it act just like a geared motor. Is it possible to still have position control with a continous rotation servo ...like say for instance i want exactly 2 and 1/2 rotations? Can it be accomplished simply through on/off timing ...say a signal for exactly 25 seconds, would that produce the same result every time? how much of an error would there be? thanks very much if you can aswer any of this!!!

Phil Pilgrim (PhiPi)

No. What you're describing is known as "open loop" control and will not produce accurate results. For accurate positioning/turns count, you need a feedback mechanism, such as an encoder.

-Phil

W9GFO

If you only need two or three rotations you might be able to use a sail winch servo. They can make a couple rotations in each direction before hitting the stops.

Or you could use a simple feedback mechanism like a snap switch which engages notches around a disk - like this;



Rich H

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The Simple Servo Tester, a kit from Gadget Gangster.

Beau Schwabe

Similar to what W9GFO illustrated, A Geneva mechanism could also be applicable here if you always wanted to move at a specific division of the full amount of rotation.

en.wikipedia.org/wiki/Geneva_drive

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

erco

Or as someone suggested in a different·thread, use·a standard·servo to drive a step-up geartrain. You can overdrive the servo with Stamp-produced pulse widths to get nearly 180 degrees of travel. So if you drove a 6:1 step up geartrain, you could get approximately 2.5 full rotations, but you would have hardly any torque. You would have reasonable positioning accuracy anywhere in that range, at about 1/6 the resolution of the servo.

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·"If you build it, they will come."

myk1323

thank you for your help!