Chunkiest motor the 1HCL can drive

deckingman

@Anon1337 According to this https://www.duet3d.com/duet-3-expansion-1hcl, the maximum stepper motor current is " 6.3A peak per phase (4.45A RMS)". It isn't clear to me if the motor specification you linked to is Peak or RMS. If it's 6.0 A peak, then your OK. If it's 6.0A RMS, then you might have a problem. AFAIK, manufacturers usually use peak current (because higher numbers look better so you'll likely be OK. Whether that's the most suitable motor is another matter as things like inductance play a part.

dc42

@Anon1337 that's the longer version (120mm instead of 85mm) of the motor that I use to test 1HCL firmware.

Anon1337

@dc42 You mean this one? I see they are both rated at 6A, do you drive them at the full current the 1HCL can make (4.45A RMS)? Does the 1HCL gets hot during the testing?

dc42

@Anon1337 I have tested it at 6A peak but for firmware testing I normally use between 2A and 3A.

Stepper motor rated current and torque is usually specified when doing full stepping, with both phases energised at the rated current. When microstepping, only one phase ever sees the full current at a time. If you set the EXP1HCL to 6A peak current, the torque you will get will be about 0.71 times the torque specified on the datasheet.

Anon1337

@dc42 if I understand it correctly the 1HCL uses load position control instead of the simple step-loss compensation. Does this mean the torque when micro-stepping is essentially higher (meaning instead of loosing the micro-steps the driver can compensate)? Or do the usual downsides micro-stepping brings still apply?

dc42

@Anon1337 no, the EXP1HCL implements servo control.

Anon1337

@dc42 so what's the torque of the stepper when "microstepping"? Since the stepper is let's say 200 steps/rev (1.8°) and the encoder is 1000PPR/4000CPR that would imply "microstepping" of 20 (as the wiki states). What's the available torque then? I mean when setting the microstepping to 16 you only have like 10% of the torque, 5% when setting it to 32.

dc42

@Anon1337 said in Chunkiest motor the 1HCL can drive:

I mean when setting the microstepping to 16 you only have like 10% of the torque, 5% when setting it to 32.

This is a common misconception. The torque does not depend on the microstepping, except that anything less than full stepping reduces the torque to 1/sqrt(2) times the full step torque.

What does change is the incremental torque per microstep. IOW, if the motor is at equilibrium and providing no torque, and you clamp the spindle and command it to advance a single 1/32 microstep, it will produce about half as much torque as it would if you had commanded it to move by a single 1/16 microstep. If you then command it to move by another 1/32 microstep, it will produce the same torque as if you had commanded it to move by a single 1/16 microstep in the first place.

Anon1337

@dc42 so let's say I connect a stepper motor that can do 10 Nm between each step. So each 1 of the 200 steps it can apply the full 10 Nm. I then set the microstepping to 1/2 and command it to go half a step. The force it can exert is approximately 7 Nm. If I set the microstepping to 1/4 and command it to go 1/4 of a step it's approximately 4 Nm and so on.
Since the 1HCL operates the stepper as if it was a servo this means that as soon as I start applying torque on the shaft that goes against the stepper and the stepper is let's say half a step between the 1.8° it can apply the full 10Nm instead of the normal 7 Nm?
Is that correct?

Sorry I'm a bit slow when it comes to these things

dc42

@Anon1337 said in Chunkiest motor the 1HCL can drive:

Since the 1HCL operates the stepper as if it was a servo this means that as soon as I start applying torque on the shaft that goes against the stepper and the stepper is let's say half a step between the 1.8° it can apply the full 10Nm instead of the normal 7 Nm?
Is that correct?

No, the maximum torque will be 7Nm. 10Nm can only be achieved at full-step positions, and only if the driver is programmed to drive both phases at full current simultaneously.

In principle you could get up to 10Nm by increasing the peak coil current to sqrt(2) times the rated value, but that should only be done when the motor is moving at a reasonable speed. Perhaps we will implement that on the 1HCL in future, but for now we don't.