Homebrew encoder?

[anoel]

I've been thinking about servos encoders. Has anyone built an encoder using the guts from a mouse? If so did you reuse the wheel? I was thinking of laser printing new wheels on transparancy.

What's the target number of increments on the wheel. 100 units should be no problem on a 1" dia wheel. is that enough resolution? Assume that the motors would be direct driving the leadscrew.

[balsaman]

I think you need two channels from each encoder so the drive knows about motor direction. One pulse leads or lags the other.

Eric

[ToyMaker]

Anoel,
Yes, I've used a mouse to build a wheel encoder. Hacked mouse encoders are pretty common in hobby robotics. Reusing the mouse wheel is good if you have an easy way to mount it - chopping up the mouse board and coupling to the motor can be a problem.
Laser-print-on-transparency is often the best course.
Eric is correct, you do need two bits if you want direction input. If you are confident that your motor is turning the right direction you can get away with just one bit.
One hundred pulses per revolution should be adequate. With 20 tpi screws that's 0.0005 inch resolution (I think). Remember, a 100 count per revolution disk only needs 50 black wedges because you get a pulse off each edge.

robotic regards,

Tom

[anoel]

OK, the single wheel on a mouse is able to discern the direction that the wheel is rotating. So I don't see where that would be a problem. I'm assuming that I'd feed +5v to the circuit and use 2 of the other 4 wires off the PS/2 connector for the encoder signal back to the controller, Right? (Which ones depends on the encoder used)

100 "Black wedges fit nicely in a 1 " dia wheel. so that'd actually be 200 Pulses per rev. so we're back to a very nice resolution.

I'm going to have to dig into this a little further.... I'm keeping my options open incase I run across a killer deal on servos(DC motors) that I can make use of without spending a ton and make them useable if they don't have encoders already.

(Are ready made encoders expensive? I've never seen a thread regarding them. Only about servos)

[balsaman]

I have seen encoders for as little as $39.00 USD

www.usdigital.com

Eric

[ToyMaker]

Supplying +5 to the mouse is good, but looking for the two lines to read is going to be a lost cause. The chip in the mouse encodes the signals from the wheels and switches into a serial data stream.
You can find the data format on the web. Google "ps2 mouse data" or similar.
Eric's suggestion of a $40 solution is good.

robotic regards,

Tom

[HomeCNC]

The E2 encoder from USdigital I use on my servos are $36 each and work great with the Gecko drives. The 250 CPR for the G320 and the 500 CPR for the G340.

[balsaman]

Jeff,

if you could see this thread and shed some light on it for me:

http://www.cnczone.com/showthread.php?threadid=802

[bunalmis]

Hello,

I am doing own line encoder (254 dpi).

Laser printer resolution may be low.
I use linotronic 630 and autocad.

I use linotronics DPI parameters for the calculation of encoderline width. You can not use simple drawing programs.(paint brush,corel draw...)

(if you use this programs you can see same problem at line space and width)