[cnczoner]

Hi all. Long time lurker here, but getting active now since I picked up a pre-converted mill now.

- The mill is a converted HF geared-head mill (model # 42827).
- IM805 drivers (5A RMS, 7A peak, up to 75V) currently setup for half-steps.
- A 24V, 6.5A switching PS
- 276 oz-in motors (1.8 deg) which are rated to 2.8A, but the drivers are setup for 3.0A...???
- Final gearing (belting actually) is 4:1 (4 motor revs = 1 lead-screw rev).

Currently I can run up to 18-20IPM max, but I keep it at 15IPM for now for problem-free operation.

But I'l like to kick it up a bit. 60IPM would be nice, and going to 8ustep would be nice, but I'll need some PC-side upgrades for that. On the controller side though, what performance gains can I expect from going up in voltage? Say 48V (using a switching PS from a telecom)? What about 72V (which would be a home-built linear PS)? Will this increase torque or speed? If torque, I guess I can change belt ratios, but I'd like to know what to expect rather than buying a bunch of gears to experiment.

Any thoughts?
-Neil.

[ger21]

Top speed is roughly proportional to voltage, so if you double the voltage, you should get approximately double the speed. However, the fact that your gearing your motors 4:1 may limit your top speed somewhat. You may need to decrease the gearing to fully utilize the higher voltages.

[cnczoner]

Sounds great then. I assume you mean that the 4:1 gearing would cause me to hit the the speed limit because of the top speed of the motor being reached much sooner, right? How do I determine the max speed of the motor? The datasheet does not say directly, but the graph of torque vs rpm stops at 1425rpm. Is this the top speed then? If so, 1425rpm ==> 35IPM on my machine, so I can at least double the current speed (assuming my PC can operate that fast).

Also what is the max voltage I can put thru the motor? I know the specified voltage on the motor is for continuous use, but with the stepper drivers' current limiting I can push a lot more -- but how much more? I have a 24V 10A transformer here, which will give me about 33V after rectified and filtered. If I use another identical transformer in series, I'll get 66V. Can I really put 66V thru them? All I can find is 1.1ohms, 2.8A on the back of the motor and not much more in the datasheet (http://web1.automationdirect.com/sta...stepmotors.pdf). I calculate 1.1 x 2.8 = 3.08V static. 66V would be 21.4x that. I've read guidelines that I can run 20x to 25x the static voltage to stepper motors, but not sure if this applies to all steppers. Would be very nice if I could as I'd get about 2.5x the existing voltage to them and it should at least double the motor speed.

Finally, is the existing configuration bad where 3.0A is going to the 2.8A motor? I know I can push more voltage thru because of the nature of inductance, but never heard about putting more current through these. I'm very uncomfortable with this.

Thanks,
-Neil.

[ger21]

Yes, with the 4:1 you might just run out of speed. There's no hard rule on what the top speed might be. Keep in mind that torque drops off as rpm's increase, although the higher voltage will flatten the falloff curve. And yes, you should be able to run at 66V, but you have to make sure the motors don't get too hot. If they do, you'll want to back off the voltage.

[cnczoner]

I was thinking I'd kick up the speed by getting 500 oz-in motors (vs. the existing 276 oz-in) that fit in the existing Nema 23 mounts, then change belt ratios to 2:1. But I don't have the clearance on the Y-axis for a longer motor. So I'm mostly stuck with 4:1 for that axis (and I don't want to make new brackets/mounts/etc for Nema 34). I have some width around the motors though, so perhaps I can heatsink the motors? What exactly is "too hot", btw? Too hot to touch?

[ger21]

What exactly is "too hot", btw? Too hot to touch?

Usually between 80°-100°C. Way past the touching point.

[cnczoner]

Thanks.