Hi!
I'm new to using and controlling stepper motors but I have already some experiences with microcontrollers. I would like to know if my setup does work. I have to use 2 stepper motors strong enough to move a resting forearm (up-down, left-right) via exoskeleton. I think 110Ncm=11kg/cm should be enough, or isn't it?
I have no idea if those motors will be powerful enough - you really need to make some measurements to figure that out.
If the motors are OK the rest of the equipment seems OK.
The motor only needs 1.5amps so the A4988 with heatsiinks should be OK. If you really need 2 amps I would consider the Pololu DRV8825 driver.
Your power supply should probably be able to supply 5 amps (to give a comfortable margin) and probably at 20v or 30v. Higher voltage will give better motor performance at speed. If you already have a 12v supply you could try that before buying a higher voltage supply.
On steppermotors using a current controlled drive the supply current actually decreases if you increase the voltage. This because of the energy conversion in the motors windings. But it is crucial to have large enough capacitors to provide a large enough pulse current. Also unstabilzed supplies tend to work better since they are not affected by the high pulse currents.
I would have said either of those supplies would be fine.
But I suspect @nilton61 knows more about the subject than I do.
Unfortunately I have no idea how his comments relate (if at all) to either or both of the power suppies you have linked to. Hopefully he will enlighten us.
Also unstabilzed supplies tend to work better since they are not affected by the high pulse currents.
I believe the term "unstabilized " as it refers to power supplies is a term used to designate a power supply with NO regulation components whatsoever, such as a simple ac transformer or transformer with rectifier outputing unregulated DC.. This has to be a language translation error from Google Translate or someone who doesn't know power supply nomenclature.
It may be a US/UK terminology difference because I have never heard here in the US but I can find it's use in reference documents such as the following. Any way you cut the cake , it means unregulated.
My forearm exerts about 2kgf at 40cm from the elbow due to weight alone,
meaning 8Nm is needed just to overcome gravity, excluding any exoskeleton
mass. 8Nm = 800Ncm
This is the realm of geared motors, and quite rightly because you can trade speed for
torque and electric motors are much faster than is needed without gearing.
A stepper with a good gearbox (64:1) gives you a lot of power to lift or move things. The belt drive pulleys are very usefull to translate the rotatation to other shafts.
Thank you so far! For the movement of the forearm I think a stepper would be a good choice because of position control.
So my question now is if it is possible to add a gearbox to this stepper with 1.1Nm (http://www.emisgmbh.de/antriebs/sm/dl/103-H7123-0440.pdf) so it can lift my forearm? If I want a torque of 10Nm, does that mean that I need at least a 1:10 gearbox? The stepper is NEMA23 size, what kind/brand of gearbox can you recommend?