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Servo feedback

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Guru ( offline )
Posts: 2251
Posted: 2007-12-19 20:04 
 Post subject: Servo feedback
I'm sticking in the previously posted info below for anyone that might be interested in getting position feedback from a standard servo.

viewtopic.php?f=2&t=2748


Last edited by zoomkat on 2010-03-19 20:14, edited 1 time in total.

Guru ( offline )
Posts: 2251
Posted: 2008-01-19 22:46 
 Post subject: Re: Servo feedback
I've started doing some servo position feedback testing using a servo on which I've tapped the pot output. I have the pot output connected to an ssc-32 analog input. The voltage output from the pot is esentially 0-2.0v, so the measured range is limited due to the ssc-32 reference voltage of 5.0v. Below are pix of the test setup, and bottom is the pot output as seen by the ssc-32. "#0 P2200" is sent to the servo for initial position, then "#0P500T3000" is sent (~180deg. rotation is from ~500 to ~2200). The pot output voltage is measured every 200ms, with a 50ms delay to wait for the return value. The voltage is sampled 20 times after the move is started. Bottom are the values obtained. Next is to see if the servo can be stopped when a certin analog or digital is received, and its position determined.



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Last edited by zoomkat on 2009-10-28 04:03, edited 1 time in total.

Guru ( offline )
Posts: 2251
Posted: 2008-01-30 01:59 
 Post subject: Re: Servo feedback
I removed the chip from the ssc-32 and bent the AREF pin (#21) out to the side some and then put the chip back in its socket (disconnecing AREF from the board 5v). I then connected the hot side of the servo pot (~2.0v) to AREF and stroked the servo. The analog input range for ~full rotation from P2200 to P500 was ~248 to ~50 for this particular servo. I stalled the servo on the 250 side and didn't see any change in the analog voltage reading, which is good. This being the case, one could use the analog voltage input from the servo pot to find the actual approximate position of the servo even if something has physically stopped its movement to its commanded position. So if somebody needs actual servo position, it can be had from a $10 servo with just some wire, solder, and minor hacking.


Guru ( offline )
Posts: 2251
Posted: 2008-02-15 23:15 
 Post subject: Re: Servo feedback
Below is a quick shot how I've modified my ssc-32 for checking analog voltage input for other than 5v. I removed the chip, bent the analog voltage reference pin out the side a little, and the put the chip back in. then I carefully soldered a wire to the pin and jumpered it back to the board 5v power. Now when I want to use an analog reference voltage value less than 5v, I just unjumper from the board 5v supply, and connect to the desired reference voltage.

Edit: If one decides to solder a wire to the voltage reference pin, it would be easier and probably safer to do it while the chip is still out of the board socket.



 

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