Hey Iggy - stepper motors ?

+2 on that. Decent low cost steppers af reasonable power are readily available at reasonable cost, and stepper drivers are likewize easily available. When you are done you have something that works properly and looks like it will.

To put a decent decoder on a wiper motor takes some hacking. Do you put the encoder on the motor shaft, or on the output gear? On the motor shaft gives much higher resolution, but requires a lot more hacking (physically) to get to the motor shaft. - and then it is all exposed unless you build a housing for it. Or are you talking about a circuit to determine the revolutions by reading the waveform from commutation? If so, even the big manufacturers can't seem to make THAT work reliably..

I've often made something and ended up replacing it with something purchased , even though what I made "worked". Generally I'd have been farther ahead buying the right parts in the first place. Buying "parts" does not preclude building the machine.

If you are using it for "full stroke" milling I guess a wiper motor is useable. Certainly not if you are going to try to set it up as CNC

- which is more what I was thinking of when you mentioned power driving the feed.

snipped-for-privacy@snyder.on.ca fired this volley in news: snipped-for-privacy@4ax.com:

The original post never smelled of CNC, or I'd not have suggested that a wiper motor could be "servo'd".

For the sort of app he seemed to be asking for, the "feedback" could be a simple as a limit switch. As I wrote earlier, "feedback" covers a lot of ground.

Lloyd

snipped-for-privacy@snyder.on.ca prodded the keyboard

I wouldn't say CNC. Certainly the wiper motor stops dead when the power is removed, well maybe not the armature, but the table does. I can cut a slot within a tenth of a given distance. A caveat is to take the backlash out before cutting or you end up cutting short.

snipped-for-privacy@snyder.on.ca prodded the keyboard

No just take the output from the DRO scale.

Cutting short isn't as bad as cutting long!! You know the old saw - "I cut it again and it's STILL too short"

I'd rather just punch in a number - from this point go 100,231 counts, knowing 10 counts is 1 thou, or whatever, and the control does the rest. And you can program the feed speed by adding a delay loop between steps on the stepper. Just using a PWM the motor slows dwn under load so you could get a variable speed feed, which could affect the look of the finish.

[ ... ]

Depends. If you make it a *real* servo, there should be some form of speed feedback, so the PWM is automatically adjusted to maintain the desired speed.

A *real* servo motor has a tach generator on the shaft as well, so this is easy to do.

If you've just got an encoder, you need to integrate the pulse rate from the encoder to derive a speed value, and tuning it is a bit trickier.

Enjoy, DoN.

Standard modern found that out, in spades, on their NC lathes. They attempted to use integrators to control the "servos" for the X and Y axis, and repeatability was terrible. After Standard Modern gave up on the lathe I spent hours on it getting it useable (sort of, anyway)- we changed grounds and sheilding, and put the PC on a dual conversion UPS (separately derived power source) and got the failure rate down from over 30% to less than

3% on production runs of 600 parts. It was the most useless damned piece of equipment I ever had the msfortune of running across, My buddy Steve lost his shirt on it - this was back at the time that Standard Modern failed and before LeBlond took it over.

Those cheaper ones are all nema 17's , I already have 2 of those . I have the power supply here now that I intended to power those with , I'll be looking at some reduction for torque increase . I can get either 9:1 or 16:1 in a fairly small package using 20dp gears . I never expected the responses this thread generated ... I just wanted a uniform speed for the X , and if I can work it out the Z .

With steppers on x and y you can program for angle cuts too.

I noticed that a minute after sending the URL. Vendors put "NEMA 17

23 34" in the titles and it screws up searches. I saw one listing for a boresnake which stated that it worked on bores from .17 to 12ga. ;)

Also, don't forget Burden Surplus

for all sorts of gearhead drives at different RPMs for cheap prices.

It's my impression that for the DIYer, stepper controls are easier and cheaper to source - but if good surplus servo controls are available at reasonable price, of coarse use them. I've got several rather large and clunky servos around, but no drive circuitry. Definitely too big to put on my Myford lathe - - - - . Then there are the servoed motors out of inkjet computers - too small for the job. Steppers out of old LaserJets are a dime a dozen and about the right size.....

I've got a couple Nema 23s I have considered putting on the Myford.

Coffee can (2 pound) sized servo's are used on CNC CAD/CAM plasma tables. Might find one for sell and have two X/Y nice ones with internal glass. Mine does - and has a third smaller one for Z. So I can cut wavy sheet metal following he metal up and down while cutting.

Martin