Motor Controller Help

[jchalo99]

Hello and thank you,

Im looking to build a laser cutter in the future, but right now i have a pile of junk... i have assembled the base for any 3 axis device, but i have no way to get it moving. I have 2 motors mounted, with mounts for 2 encoders. its all set up to have a fairly good accuracy, it was an axial insert-er machine for PCB production.

What i am looking for is a cheep motor controller that can handle my motors. They are Kollmorgan U12M4 ServoDisc Motors:
42.4 v Terminal Voltage
8.8 A Continous Current
85 A Peak Current
8.1 A Stall Current

Does anyone know of where i can get a good motor controller for them? it should accept either 5v PWM or 5v Step+DIR.

thank you again,

edit: sorry forgot to subscribe to thread

[bdring]

It might depend on the encoder type in the servos.

I use Gecko Servo Drivers on my Large router. You might ask them.

http://www.geckodrive.com/g320x-p-28.html

[jchalo99]

i was looking at there drives before, but when i contacted them they said i needed a choke of some sort to change the inductance rating. i don't understand inductance. but i would love to work with there drives, and they have extremely fast customer service, and a large customer base.

thank you for the suggestion. if i do go that route could you help me select the right choke?

[frob]

i was looking at there drives before, but when i contacted them they said i needed a choke of some sort to change the inductance rating. i don't understand inductance. but i would love to work with there drives, and they have extremely fast customer service, and a large customer base.
thank you for the suggestion. if i do go that route could you help me select the right choke?

Hi, i can help you with your inductor if you like -
I had a thought / question for you:
When you said you can use a driver with PWM input, i assume you mean a high-frequency pwm from a control board that is doing closed-loop control using external encoders - (if it were R/C servo style PWM, it wouldn't work)

If this is indeed the case then a servo amplifier (basically a high-power H-bridge) should be a lot cheaper and easier to find - or make. Do you intend to drive the motors to their maximum ratings or are you satisfied with a bit less? 42V @ 85A is 3500W, that's a lot of power for moving around a laser head!

[jchalo99]

thank you for the offer to help.
The PWM i was thinking is the PWM From the ARDUINO, at least to start.

I would be fine running the motors at down to 50% of there power. these motors are beastly and i dont plan on doing anything that would require there full speed (my table would be moving 4+fps if i did the calculations right.

As of right now i how no goal set in stone, it will all be figured out once i get at least 2 of the axis moving under control. i learned its a bad idea to just hook the motors to a switch and even at 24v, it threw my table and luckily i was smart enough to wire in the limit switches to my test rig. but this machine might become a milling machine, a 3d printer or a laser cutter/engraver.

i will start a buildlog once we get better weather in North West Connecticut. (the machine is about 5'tall, sits on a large steel frame, weighs about 1.5 tons. has a circular bed with about 3' diameter, (thinking to make that my forth axis), it currently only has a z axis height of 3 inches, will be changed to about 3' once i figure out how.) table can support up to 1000lbs on it, and still move by the motors easaly.

[frob]

...The PWM i was thinking is the PWM From the ARDUINO, at least to start.
I would be fine running the motors at down to 50% of there power....

Thats going to be a really impressive machine ! i hope you post some videos when you get it running

I haven't played with the arduino yet so i don't know how reliable or fast its built-in PWM system can be, It might be too risky to directly connect that to an H-bridge. I would want to run the PWM at 50-100KHz or higher because of the very low impedance of these unusual motors.
If you can live with feeding the motors at 24V, that would be safer and allow you to use some of the cheap/common ~30V H-bridge DC motor drivers available everywhere. That's probably where i would start since you're already planning to use an Arduino to control it.
Either way you will need an inductor in series as these motors have hardly any internal inductance.

If you're not in too much of a hurry, i am intending to make some servo driver boards in the next 2-3 months.
Your platform / motors would be about the most challenging from a driver standpoint, so i'll gladly send you a couple of samples then if you agree to test them - and don't hold me responsible for any ensuing carnage

[jchalo99]

what would you recomend for a control board, and driver. im up for anything, i dont got much money but willing to try anything.

what would i be looking for in an inductor, i dont have any knowlage with them.

[frob]

what would you recomend for a control board, and driver. im up for anything, i dont got much money but willing to try anything.
what would i be looking for in an inductor, i dont have any knowlage with them.

Well to calculate the inductor we need to know the frequency of the driver's PWM (chopper frequency), and its maximum current and the current capacity of your power supply, and of course the voltage - the inductor is chosen to keep the current ripple/ peaks down to manageable levels that wont overheat the drive, the motors, or overload the supply. typically though it resolves to a minimum value, its always safe to go bigger, and its not a very critical number, anything "close" is good enough. Many motors have inductance in the range of 100mH or more, so thats typically what motor drivers are designed to expect - if i had to guess, the induct you will need will likely be around that. Which will make it pretty big. The higher the frequency, the smaller the inductor needs to be.

I'm not sure i would recommend anything in particular, i don't have much hands-on experience with commercial motor drivers.
Others on the forum here would know more about that.
I design electronics for a living, and have done a lot of "power" electronics, so the theory part is easy for me
I have seen lots of cheap DC motor driver "breakout boards" that might work on Ebay and sites like Sparkfun and others like it.

[Cre8ivdsgn]

This sounds like it was at one point a Universal Instruments or Dynapert VCD (Variable Center Distance axial component) inserter. The brush DC Kollmorgen motors are great, but ideally what you want is a drive that takes the encoder inputs and outputs to the Kollmorgens. In a perfect world the drive would take step and direction.

In the original system there was a servo amplifier card, DAC feedback card, and a DEC PDP 11/08 or similar beast. I have some info on them, and found the inductor on the power supply, but the info I have only lists the word "inductor" and a Universal Instruments part number, which is pretty much meaningless.

It might be easier to drop the Kollmorgen motors and replace them with steppers. The positioning system was excellent, with cast X and Y axis frames, ground leadscrews, and very low friction round rail Thomson bearings. Attach a stepper to the leadscrew and you should still get reasonable performance out of things. Everything was cast aluminum and so the X carriage frame was surprisingly light (10lbs?) and the Y carriage (which carries the X) might have rung up at another 37 lbs.

VCDs are fun to watch. I had one customer that used to chant "nickel, nickel, etc" because he basically charged 5 cents an insertion. The 6287s could hammer in up to 14,000 axial components an hour.

[jchalo99]

that's actually exactly what i have. i have the universal instruments one.

i was thinking to replace the motors with steppers, because that would just make everything easier. but i don't know what size i would need, whats nice about the servos is they bolt right in and i know they have the power.

you said you had info on these machines, i do in fact still have the PDP 11, it is too much of a marvel to just get rid of, so i keept it, i couldn't make head or tails of it, but i haven't really tried. I also still have the entire set of Universal Instruments daughter cards. i have i believe all of them. if i could get this thing running off the PDP 11 that would just be amazing.

if i could not figure out how to get the PDP 11 up and running, do you have any information on what signals the cards take?

thank you in advance.

EDIT: i dont think it is a PDP11, after doing a little more digging, i think its a 8221 Machine Controller. http://www.unidec.com/documents/8221%20slide%20show.pdf