[Dan911]

Hello all, I have a K2 slide for my Z axis with a leadscrew pitch of .1, 10 revolutions = 1 inch. I have the driver microsetting set to 1/4 and 8000 set in the motor tuning in Mach 3. It's Nema 34 Stepper Motor with 878OZ-In. I have a 48v power supply just for this motor and another same spec motor(Y).

I can't seem to get it past 35 ipm without stalling, is this what I should expect?

This is a new stepper motor and without going into details of why, I did remove the shaft from the motor(chair) and was later informed that I will lose holding torque. Is this the cause?

I'm trying to determine if it's a new 2 start leadscrew i need or a new stepper motor to bring up the IPM. Any help/info will be appreciated.

Thanks in advance,
Dan

P.S My kernel speed is set at 25000HZ, I have a dedicated Pentium 4 2.8cpu
computer running Mach 3, would raising the kernel speed help?

[acondit]

What drive are you using? It could be a problem with resonance. That stepper should be powerful enough even if you lost some of its holding torque by taking it apart (given its starting rating).

35ipm with a 10 tpi screw is only 350 rpm. 35 * 8000 = 280,000 pulses per minute.
280,000/60 = 4,667 pulse per second.

Alan

[acondit]

Maybe I am wrong about the loss of torque. The servo motor newsletter says:

First, any time a motor is disassembled, there is a high probability that the magnets will be discharged to a point where the torque will be diminished. The results vary and may or may not initially be noticeable. With some motors, the results will be immediate. In fact, disassembly of a stepper motor will typically demagnetize the magnets to a point that the motor is useless until it has been properly remagnetized. With a few motors, the reduced energy will have little effect until the motor is under full load. At that time the drive / controller will indicate an error.

[ger21]

I can get 55ipm with my 1/2-10 acme and a 250 oz motor.

It could be that the motor has lost most of it's torque.It also could be resonance. 1/8 or 1/10 microstepping might give you more speed, due to more smoothness and less resonance.


What is the inductance of your motor? Usually, as motors get larger, they have much higher inductance, which results in lower max rpm. It's not uncommon for a much smaller motor to have more torque than a larger motor at higher rpm's.

This could be the issue

[Dan911]

What drive are you using? It could be a problem with resonance.

I'm not sure what resonance means could you please explain.(Was working construction when I should of been in college)

Here's a link to the drive I'm using
Stepper Motor/Stepper Gearmotor/Stepper Motor Driver wholesaler and supplier

35ipm with a 10 tpi screw is only 350 rpm.

What would be the normal IPM with this set-up?

Would there be any advantages raising the Kernel speed? I thought I remembered in the Mach 3 tutorials recommending to keep it at 25000HZ, I could be wrong though.

I do appreciate you taking your time to help Allan.

Thanks again,
Dan

[Dan911]

I can get 55ipm with my 1/2-10 acme and a 250 oz motor.

It could be that the motor has lost most of it's torque.It also could be resonance. 1/8 or 1/10 microstepping might give you more speed, due to more smoothness and less resonance.


What is the inductance of your motor? Usually, as motors get larger, they have much higher inductance, which results in lower max rpm. It's not uncommon for a much smaller motor to have more torque than a larger motor at higher rpm's.

This could be the issue

Thanks Ger, you answered my question. (whats the normal IPM?) I was replying to Acondit when you posted. I would settle for 55ipm since the recommended max is 80.

The inductance is 15, the specs for motor below. I have it wired with the 2.8 amps, I think it's parallel bipolar.



I actually thought setting it to 1/8 microstepping would make it worse, I'll have to give that a try...Thanks. If that don't help I will try a different motor.

Once again thanks for your help,
Dan

[acondit]

I'm not sure what resonance means could you please explain.(Was working construction when I should of been in college)

I found this definition on the web:
All stepper motors suffer from a 'strange' phenomena, particularly al low speeds, that can cause a dramatic lost of torque or even a stall of the motor itself. This phenomenon regards the 'resonance' of the motor, a particular frequence where the motor starts a desyncronization because its natural oscillating frequency has been reached.

Here's a link to the drive I'm using
Stepper Motor/Stepper Gearmotor/Stepper Motor Driver wholesaler and supplier



What would be the normal IPM with this set-up?

My first router with a 3/4"x5tpi that would do 120ipm. If you cut that in half because of 10tpi instead of 5tpi that is 60ipm (pretty close to Ger's 55ipm). The z-axis on my lathe with a 5tpi ballscrew will do 210ipm. A lot depends on the torque of the motor, the weight and friction in the system, the drive and the power supply.

Would there be any advantages raising the Kernel speed? I thought I remembered in the Mach 3 tutorials recommending to keep it at 25000HZ, I could be wrong though.

I doubt it. My calcs were just to see if that could have been the problem. When I first ran my calcs I was off by a factor of ten and I thought that was the problem, but when I rechecked my work, I realized that you still had quite a safe margin. You are running less than 20 percent of 25khz.

I do appreciate you taking your time to help Allan.

Thanks again,
Dan

Alan

[doorknob]

As ger21 mentioned, using only 48 volts on that motor may be part of the problem. The motor should probably be driven with closer to 120 volts. Your driver has an upper voltage limit of 80 volts.

If you were able to get (for example) a 72-volt power supply, you would expect to be able to improve the speed that you get from the motor, but it will still not be getting all of the motor's potential speed.

[RomanLini]

6 RPS is slow even for a size 34 motor. It should do more than that even from a 48v PSU. It's about the revs where midband resonance is an issue.

Try changing to 8th microsteps, or 16th microsteps, as Ger21 said. Changing your acceleration profile may help, to get through that range of RPM quicker (ie try higher accel value).

Also if your motor has a second shaft you will probably see a big improvement around that RPM by adding some type of flywheel disc or resonance damper disc.

[Dan911]

Thanks for all the help and valuable info. I'm in the process of installing and wiring all electrical components in it's permanent case. I'm hoping to be done tonight because I'n anxious to try it with a 1/8 microstepping setting.

I should add I have the same type motor and driver set to a 1/8 setting for the Y axis, sharing the same 48V PW and I'm easily getting 1000ipm and cannot hold it back, but this is with the cncrouterparts R&P system.

I don't think it's friction on the Z that's causing the stall because I have pneumatic air cylinders balancing the weight, and when motor was disengaged I was easily able to turn leadscrew with index finger and thumb.

I'm hoping to see better results with a 1/8 or 1/16 setting, I never tried it because for some stupid reason I thought adding more steps would give me less torque. I tried it with 1/2 setting with same results.

Thank you all again,
Dan

[ger21]

If my math is right, 1000ipm with the rack and pinion is about 636rpm at the motor.

The 350 rpm you're seeing could easily be the result of taking the motor apart.

[Dan911]

Your 100% correct Ger. I didn't have the patience to wait to complete wiring my enclosure and temporarily hooked the Z back up. At 1/8 with 16000 setting in Mach there was no change. At 1/16 setting and 32000 setting in Mach I was able to get it at 40ipm with no stalling and seemed I couldn't hold it back to make it stall, but the motor just didn't sound right, set it back to 35ipm and sounded smooth like it did with a 1/4 setting.

I came back to post that these motors neither couldn't handle the higher rpm's or I screwed the motor up. After reading Ger's post with his calculations it's obvious which 1 it is.(chair)

I'm not going to bother and take apart and try another motor since I have no intention of replacing this motor with another 1 from China, or at least with the same specs.

Thanks all again been a great help,
Dan