Don't know of anyone offering technical help beyond a website, or even a shop selling steppers that can be visited. Sign of the times I'm afraid! But there are several experienced stepper users on the forum who can probably advise.

My number one suspect would be the power supply. For convenience and cheapness I run my steppers from LED PSUs. They work OK but aren't ideal because they're voltage stabilised and designed to feed a constant load. Steppers are pulse driven and a stabilised supply trying hard to keep the output at a constant voltage may not deliver the wildly varying current needed to maintain torque. These supplies often have current limiting circuitry; that's great for LEDs but is likely to throttle a motor under heavy load. A basic transformer supply with plenty of amps and simple rectifier and capacitor might be a better option. Which motor are you using and how it is powered?

Dave

Edited By Emgee on 06/10/2019 12:28:42

It does, and the combination is pretty much what I would have bought. Not quite perfect maybe, but I would certainly expect it to work. A few points:

• The 8-wire motor should be wired bipolar rather than unipolar. (I expect it is.) As a fancy point of detail, if the torque is wanted most at low speed, the windings should be in series, parallel if more torque is wanted at high speed. May be worth trying parallel for more power.
• The motor should has a 70% duty cycle to avoid overheating. 2.8Nm happens to be 70% of 4.0Nm, perhaps a coincidence!
• The power supply is the stabilised type I said wasn't ideal but it has plenty of volts and amps, better than I pay for! I'd be surprised if it's the problem.
• The DM556 controller is a little underpowered for the motor. Although the motor pulls 4.24A and the DM556 peaks at 5.6A, the controller limits to 4.0A RMS. Even so I would still expect the motor to get close to full torque.

Is the problem holding or turning torque? 4Nm is the motor's maximum holding, and it's turning torque falls off with rpm. If the problem is turning torque at high rpm, the motor is on the small side. This graph shows the torque down by nearly 50% at 600rpm when the motor is at 36V. Again, this doesn't look obviously wrong to me.

Last suggestion: the booby trap that gets me every time is the current setting DIP switches on the DM556 controller. These should be set to maximum. Anything lower will restrict the motor.

Hope that helps. I can't see anything obviously wrong.

Dave