for a university project, I want two Stepper Motors to turn 2 threaded rods so that a box which is mounted on top will move back and forward (a bit like in all these DIY CNC machines).
I have been looking a lot into Motors and Drivers the past two days and even though I feel like I learned a lot, I still very unsure and simply don't want to waste money of our already very limited budget.
Unfortunately I am really insecure with being able to tell if the Driver can provide the necessary current and what power supply to chose. I approached this like this:
The Motor has a rated current of 1.3A (I guess here per phase)
Driving the motor in full-step will result in 2.6 A per motor
The driver can output 1.3A (even up to 2A)
I just read that a motor at full-step will double his current and therefore need 2.6A, while I am not sure if the driver can give this out to him or if it just depends on the rated current, not minding full or half step.
Using the schematic from my last link I would bring both drivers/motors in parallel relative to the power supply. Therefore it would not kill the driver by providing 9V and around 5.5A, right?
I hope you understand my points and are able to bring a little light into my thinking here.
The A4988 chip on the BED is overrated and can't handle more than 1 ampere per phase without extra cooling. You would be better off with the DRV8825 stepper driver from Pololu.
The most important aspects in choosing a stepper motor are the application torque, speed and power requirements. Hopefully you have worked through those calculations.
thank you for your quick answer. I just checked and the DRV8825 is indeed available where I live.
I read on Pololu.com that this Driver is rated to provide 1.5A per coil. The question I asked in my first post stands nevertheless:
My understanding with Stepper Motors is still bad. I just read that by running these motors in full-step (for the biggest torque) you basically have to be able to provide twice the current, hence 3A. Therefore I am really not sure what values to look at. Or do this full-step / half-step values not matter as long as the 1.5A driver can provide the needed 1.3A?
Regarding the power supply, I am also still wondering what to go for. I learned that I have to provide a rather high voltage to the driver yet with the current I am not so sure. Taking the motor from above, do I need to provide 1.5A or 3A (and 3A and 6A with two drivers/motors in parallel)?
It is normal to state the per-coil current for a motor and for the stepper driver. So an A4988 should be able to operate that motor. A DRV8825 would have a little more capacity.
With switching step motor drivers, the higher the motor power supply voltage, the less current is required.
Nevertheless, for safe and reliable operation, the motor power supply should be rated to supply at least twice the per-coil steady state current, per motor.
Robin2:
It is normal to state the per-coil current for a motor and for the stepper driver. So an A4988 should be able to operate that motor. A DRV8825 would have a little more capacity.
I read through the both links you provided once again and since I understand now a little more from Stepper Motors, I can appreciate this even more. Thank you.
I also looked into the alternative you mentioned with the A4988.
I found a short tutorial on YouTube and also on the manufacturer's page, so this is already very good. In the video, the guy uses a 3.2V 1.3A motor which is very equal to mine (2V 1.3A) and uses a 12V 1.5A power supply while running at full-step.
I also read a comment on current limitation, so I will consider this as well.
So I believe I will just go into this direction.
2 x (17HD4005-22B) 2V 1.3A Stepper Motor
2 x A4988 Stepper Driver
12 V 3A power supply (for two motors running in parallel at the same time)
Arduino Uno
It would be just great if one of you could give me an "OK" for this set-up so I can be a little more relaxed and focus on ordering and building the setup.
If you have a 2v x 1.3 amp motor that is about 2.6 watts. Roughly double that for the two coils - say 5 watts. And double that for two motors gives you 10 watts. A 12v x 3A power supply represents 36 watts so I suspect it should be plenty even if my calculations are very approximate.
I also read a comment on current limitation, so I will consider this as well.
If you supply 12v to that motor without a current limit the smoke will escape.
36W for two NEMA17 steppers? Sounds OK to me, such steppers take 5 to 6W typically at standstill.
Remember the stepper drivers output higher currents than they take from the supply. My suggestion
would be go to 24V supply for faster operation.
MarkT:
36W for two NEMA17 steppers? Sounds OK to me, such steppers take 5 to 6W typically at standstill.
Remember the stepper drivers output higher currents than they take from the supply. My suggestion
would be go to 24V supply for faster operation.
Yes, I thought about this at one point too, but since all the tutorials always used 12V power supplies, I aimed for that as well, just to be sure (and maybe change it at a later point)
But let's say I would go from a 12V to a 24V power supply for the drivers, would I also have to change the input current to stay at the same power of 34W?
So would be
12V 3A power supply -> 2 x A4988 -> 2 x 2V 1.3A motor
24V 3A power supply -> 2 x A4988 -> 2 x 2V 1.3A motor
both okay?
I keep asking these questions, because I am still very unsure what voltage and current is actually given out by the driver to the motors.
From my current understanding I got that the input voltage for the driver should be quite high (for me 12-24V) while the current fed into the driver can be a little higher than what the motor uses (1.5A to 1.3A) since I am current limiting the driver to fit my motor. Is this so far correct?
Current is whatever you set in the driver, but the (average) voltage depends on the resistance and more importantly
rotation speed of the motor.
The driver actually arranges that the sum of the squares of the currents to each winding is constant,
because they are in quadrature. Set to 2A this means sometimes only one winding is energized at 2A,
other times both would be taking 1.4A.
With the motor stationary or slow typically the average voltage is a few volts (the actual voltage is
switched rapidly between 0 and the supply). As the motor speeds up the average voltage will increase,
overcoming the large back-EMF due to the rotor turning.
When you look at things with a 'scope the waveforms are really messy, BTW.
