PDA

View Full Version : Unsolved Using standard servo



shaky5292
09-11-2011, 07:45 PM
Can I use a standard servo as a position feedback with the educational board?

Mike G
09-11-2011, 07:49 PM
Welcome to the forum.

Standard servos do NOT expose position feedback to external devices without modification. There is a way to "sense" position but it's a little complex.

sylvie369
09-11-2011, 07:55 PM
This may be of use to you:

http://forums.parallax.com/showthread.php?84991-Propeller-Application-Proportional-feedback-from-a-Standard-Hobby-Servo-%28Upda&p=582447

I've always wanted to try it, but haven't gotten around to it yet.
====================
Wow - 2006. I guess I'm an old-timer, remembering stuff like that.

Edit (from the link):


Hobby Servo Position Tracking Application 04-18-2006
************************************************** *****************
Coded by Beau Schwabe (Parallax)
************************************************** *****************

Sensing the position of a standard Hobby Servo? It can be done.


Theory of Operation:

If you supply just enough current to a servo for the internal electronics
to function, but not quite enough to power the servo motor. You can detect
the servo position simply by sweaping a valid servo pulse to the servo and
monitoring the current or voltage drop where the servo electronics attempt
to energize the motor and making note of the swept pulse width.

Publison
09-11-2011, 07:55 PM
A standard servo has no positional feed back. It's pretty much a one way communication. You tell it where to go.

There are more expensive servos like the:

http://www.trossenrobotics.com/dynamixel-ax-12-robot-actuator.aspx

that incorporate a feedback mechanism.

erco
09-11-2011, 08:27 PM
Two choices: you can tap into the servo's existing pot and read that voltage using an A/D converter, or you can mechanically add a second pot to the servo's output shaft and read that with RCtime.

$WMc%
09-12-2011, 01:31 AM
Heres a simple way that I have used to add a feedback pot.
'
This is for use with the RCTIME statement.
'
See Experiment#26 in the StampWorks Manule.
http://www.parallax.com/Portals/0/Downloads/docs/books/sw/Web-SW-v2.1.pdf
'
Welcome to the forums.

erco
09-12-2011, 01:47 AM
Nice method, Walt!

shaky5292
09-13-2011, 03:33 PM
Heres a simple way that I have used to add a feedback pot.
'
This is for use with the RCTIME statement.
'
See Experiment#26 in the StampWorks Manule.
http://www.parallax.com/Portals/0/Downloads/docs/books/sw/Web-SW-v2.1.pdf
'
Welcome to the forums.

shaky5292
09-13-2011, 03:35 PM
Thank you, seems pretty good. I'll try it.