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View Full Version : Renco open end encoders



ynneb
03-22-2004, 05:49 PM
I have bought these servos with renco encoders on them.

I dont know much about encoders, but i am told they are an open end type. I have been told that the longest control wiring that I can run to them is 1M and no more than 2M (yards).

Since my machine has a 3 M run, I think I am in trouble.

Does any one know a solution to my problem, or is it a matter of getting different encoders. If so, where?

The drivers I am using are Rutex.

I havnt yet tested the setup to see if what I have been told is correct.

Al_The_Man
03-22-2004, 06:11 PM
Benny, I think those figures you got are a bit conservative, I gather the encoders are open collector A & B only (not differential). If they are open collector you may need a pull-up resistor unless the Rutex have ( you need to know the Rutex encoder input details).
But either way, if you make sure you use shielded cable and ground the shield at the control end and run the cables separate to motor power, you will probabally get away with 3m or more. Often, open collector means you can run higher encoder voltage than 5v possibley 12v or 24v making them more immune to noise pick up, but that would be usually dictated by the controller.
Al

ynneb
03-23-2004, 12:39 AM
Thanks Al for answering the post, I was hoping you would, you seem to be the guru in this sort of area, judging by reading some of your other posts. I have now tested the encoders setup with 500mm leads and every thing seems fine. Now I think I will set up a 4M lead and test that. If that doesnt work I will cut it down until it does work.

So you think if I increase the encoder voltage I might be able to get a longer run?

Also, when I tested the setup the servos locked into position. This was done without a computer connected. I noticed if I swaped the A servo encoder with the B motor encoder plug that the servo would run away if I turned the other by hand. If I repositioned the servo the other would slow down and eventually stop when it was in the right psoition. I am thinking this is good ?

When all the servos were locked in position I noticed I could turn the servos by hand about 1 degree and it was spongey. Any more turning than that was impossible by hand. I am wondering if that spongyness was normal given that the encoders were 2000+ pulse per revolution? Even while they were spongy they seemed to return back to postion, but if there was a load on them I would guess they may not return quite back to postion. I guess If I am going to gear them down 10/1 then it would be very small error gap. Is this thinking correct?

Edit: Oh and yes you were right, The encoders are just simply A and B , not differential.

http://www.cnczone.com/gallery/data/500/2793tttt.jpg

Al_The_Man
03-23-2004, 10:52 AM
Benny, If the servos are a little spongy under control then your in-position band amount would be affected, but that error would decrease with reduction gearing. I am not that familiar with the servo's or amps you have, but generally if the amplifiers have a gain control, this can be increased untill the servo's start to oscillate, and then back off half to one turn, (or increase software feedback gain.)
If you have problems with noise pick-up, and it is electrically possible to use the high encoder voltage, this may solve the problem. But try them at 5v first.
Al