good match for these motors?

[holyjewsus]

I just came into two vexta pk-268 stepper motors, these are 8.6v 1amp motors.

I'm going to be running them on 1/4" 16 - 4 start screws, whats a good driver/ps combo to get these running.

I'm not too interested in speed, 40 - 70 ipm is good for me.

Thanks for any advice.

I've used these drivers before pretty well,

Pololu - A4983 Stepper Motor Driver Carrier with Voltage Regulators

but I'm not sure if running at 24 - 30 volts is going to cut it with these motors, please advise.

m

[dmiller47591]

I think this is the data sheet for your motor.
http://www.interinar.com/public_docs/PK268-02B.pdf

You are running bipolar, right?? I don't think you can do bipolar parallel with a six wire motor. Bipolar series has some pretty high coil inductance, so I don't know if the standard "square root of coil inductance (in mH) times 32 = optimum supply voltage" applies. That would come out to 121.43 VDC. That seems way too high.

I'd say a driver that can handle 35-50 VDC would be good. I don't know what kind of microstepping you want. Geckos would probably be ideal with a multi start lead screw. Keling's KL-4030 or KL-5042 would also work. It seems i remember Mariss from Gecko mentioning using similar sized Vexta motors. Send a PM. She knows her stuff.

[holyjewsus]

Unfortunately, thats not the data sheet for the specific ones I have. I've got the pk-268-01A, not 02, so the current is lower, and the rated voltage is higher, 8.6v... Whats the minimum voltage I can run these at?

[dmiller47591]

Have you read this post http://www.cnczone.com/forums/gecko_...xta_pk268.html ?

That pololu driver will run the motor. Probably not at a very high rpm. What's the minimum, you ask? Supplying the 12v [Bipolar (Series)] or 8.6v [Unipolar] and 1 A[Unipolar]
0.71 A [Bipolar (Series)] will spin the shaft.

What are you doing with the motor is the question. What kind of load are you wanting to move? Sounds like a good quality stepper, just some really high inductance, requiring higher voltages for maximum speeds.

[holyjewsus]

Originally Posted by dmiller47591 Have you read this post http://www.cnczone.com/forums/gecko_...xta_pk268.html ? That pololu driver will run the motor. Probably not at a very high rpm. What's the minimum, you ask? Supplying the 12v [Bipolar (Series)] or 8.6v [Unipolar] and 1 A[Unipolar] 0.71 A [Bipolar (Series)] will spin the shaft. What are you doing with the motor is the question. What kind of load are you wanting to move? Sounds like a good quality stepper, just some really high inductance, requiring higher voltages for maximum speeds.

Thanks for the link. I'm using the motors to drive 1/4" 16 4 start rod. I don't want to go more than 70ipm, so that should be around 200 - 300 RPM...

My router is going to be small, 11 x 11 x 3, my table will weigh very little, gantry 7 lbs plus cutting forces.

I'm curious if I can get away with running these at that low voltage and still achieve 300 rpm?

[dmiller47591]

This site has some calculators and charts for CNC building.
Calculators and Charts

I used this calculator Linear Force Calculator with a screw efficiency of Efficiency with Plastic Nut: 74% Efficiency with Bronze Nut: 69%. (screw efficiency estimator Lead Screw Efficiency)

That's the physical information you need to move your machine. There are some calculations out there to find if you have enough power (V*I) at a certain speed (in RPM) to move a load.

Roton also has some good info on screws, as well as efficiency charts for just about every size you can think of. Their formula .jpg is attached at the bottom. You want 30-70 imp. Lets meet in the middle and say 55 inches at 4 revolutions per inch = 220 RPM. Do you have a good torque speed curve chart for these motors? I'm using Oriental Motors website for the spec sheet and their's if for the PK268-01B. Here it is Image Popup.

At 200 RPM (bipolar) it looks like the torque drops down to 20 oz-in with the 24V power supply. According to the calculator your screws will still move 21 pounds at that low of torque. **And that's not counting the inertia/momemtum thats already accumulated from accelerating that mass to that speed initially**

Another good resource for steppers and drivers, info and formulas is GeckoDrive's Support. There are some calculations at the bottom of that page for motor torque size. Also some stuff about unipolar, which is a lower inductance option for your motors.

It "seems" like you can use those drivers to run these motors if you max out the voltage. I'd also try for a second opinion too, I'm just a newb tryin to help a newb!

[James Newton]

There is a calculator for translating torque required and top rpm into the wattage needed at techref.massmind.org/techref/io/steppers.htm#Estimating