Need Help!- Stepper motors stalling

[hub]

I'm new with this stuff so..
I connected everything and started testing with Mach3..
The steppers run fine at about max 500rpm, but stall if I try to go any faster (no load attached to the steppers).
I *think* I have the steppers wired correctly, but I'm not 100% sure. (Bipolar parallel, steppers has 8 wires).
The drivers are set to 3A, 48V. The steppers are rated 3A/phase.

Strange to me is, if I lower the amps to 0.7A I can run the steppers at approx 1000rpm..

Is this normal? Or do I have a problem somewhere? I thought more than 500rpm should be possible..

Thanks!

[hignog]

Have you got the details of the motor and stepper driver you are using?

[hub]

Originally Posted by hignog Have you got the details of the motor and stepper driver you are using?

Motor (Brand & model i don't know)
Bip. Parallel:
0.65Ohm
3,2mH
3,54Nm

Driver Leadshine ME742:
http://www.leadshine.com/UploadFile/...ves/ME742m.pdf

[hignog]

If the motor is an 8 wire motor the 3A maybe the current in series so you may need to set the curernt to 6A?
Also i hear that some manufactures have the name plate on an 8 wire motor as the unipolar current, so if this is right, it could be 4.2A in parallel.
I would check into the specifications of the motor further.

[hub]

Thank you for your help

The current is 2.12A in serial (bipolar) according to the motor data sheet.

[Dorsal]

??? How can you have a motor data sheet, and still not know the brand or model of the motor ???
Is this some kind of joke?

[hignog]

Ok, so the current in parallel is 4.2A.

Originally Posted by hub Thank you for your help The current is 2.12A in serial (bipolar) according to the motor data sheet.

[tivoidethuong]

may it is mid point resonance prolem

[hub]

Originally Posted by Dorsal ??? How can you have a motor data sheet, and still not know the brand or model of the motor ??? Is this some kind of joke?

Sorry there is no brand or model on the data sheet... And the steppers don't have any labels either.

[hub]

Thanks, I found this information, I'll try putting some load and see if it's any better..

"Unloaded, the motor exhibits a fair amount of ringing. This ringing translates into motor vibration. The motor will often stall if it is unloaded or under-loaded, because the vibration is high enough to cause the motor to lose synchronism. Loading the motor properly will dampen these vibrations. The load should require somewhere between 30% to 70% of the torque that the motor can produce, and the ratio of load inertia to rotor inertia should be between 1:1 and 10:1. For shorter, quicker moves, the ratio should be closer to 1:1 to 3:1."

[James Newton]

The faster speed at lower current is a classic symptom of resonance problems. With the higher driver current, the motor is shaking more because it is starting and stopping faster with each step. That vibration reaches a resonance point and you can't move past it. With less power, the steppers vibrate less and so will spin faster... of course, they won't hold or pull in as much load.

If your driver will microstep, you will find it moves faster in microstepping modes than it will in full step... again, less vibration.

The other way to verify this, you have already found, is to load them down and see if that changes the top speed.

Mechanical vibration dampers, or a smoother microstepping driver are the real solution. If your motors were smaller, I would recommend our driver (the Linistepper) but 3Amps/phase is the outside edge of our envelope, and if you hadn't purchased a driver already, I would point you at Gekko, but since you have already paid for a driver (which one?), mechanical vibration dampers are probably the way to go. I believe I remember seeing a design made from a hockey puck that looked pretty good; you will have to search for it, I didn't keep the link.

Good Luck! And please let us know how it works out.

[hub]

Thank you very much James for your reply

Yes, my drivers (leadshine ME742) has microstepping, I tried many different values from 400 to 25000 ppr, but I didn't notice much difference regarding stalling. Yes a little bit, but not much.

I haven't got a chance yet to test with load because the rest of the machine is still under construction.

I'll let you know how it turns out.