Hello,
i want to accelerate a 12V unipolar stepper motor up to 300 rpm. Therefor I'm using the arduino motor shield r3 and the accelstepper.h library. The motor I'm using is the STH-39D236-02, it does 1.8 deg/step.
With the standart "stepper.h library" I'm able to run the motor up to 150 rpm but I already need a bit more. Therefor I wanted to use the "accelstepper.h library" but I haven't succeded anyway...
I very appreciate if anybody have a good advice for me.
Thanks
Have you measured the winding resistance? I found another site that claims 32 ohms,
in which case good luck - high impedance motors don't go fast driven from an H-bridge.
I couldn't find a datasheet so no idea what the motor is supposed to be able to do.
Its a fundamental limit of driving a high impedance motor from a fixed voltage, there
is a speed limit for two reasons.
Firstly when the motor turns the windings generate an EMF. At some speed this EMF
will be 12V, so there is no way to go faster than this speed if powered from 12V.
Secondly the faster the motor turns the more rapidly current has to change in the
windings to keep up with the motor poles moving from tooth-to-tooth - however the
inductance of the windings limits how fast current can change - at a fixed supply
voltage there is a fixed limit on speed of current change, which means the AC amplitude
of current to the windings will drop as speed increases - less torque will be available
until there isn't enough to overcome the load.
If you need a stepper motor to go fast you get a low-impedance motor (0.2 to 3 ohms
range typically) and you drive it from a constant-current chopper driver from 24V or
higher (big stepper drivers go up to 160V supply -> chopper -> 0.2 ohm motor with
current limited to 5A or so - the high voltage makes for extremely rapid current change
and can overcome loads of back EMF, 4000rpm possible).
Smaller steppers can be driven from one-chip driver boards like the A4988, but we are
talking 1A or so upto 1.5A, upto 36V supply. Should get to 300 rpm OK.
You need to state your mechanical requirements (speed, torque) and start again perhaps?
Hello MarkT,
thanks for your reply. I had a consultation with someone who works often with stepper motors and he also said that the voltage for my stepper is way to low. he often uses a "pololu a4988" to control the motors with the arduino.
the big advantage with this motor driver is the external power supply.
now my big problem is I don't have a clue whether it is possible to connect an external power supply directly to the motor shield.
I guess it could be kill my arduino because there's no separation between the external power supply (e.g. 24V) and the 5V power supply of the arduino....
Does anybody have an idea about the right application of the arduino motor shield r3 and an external power supply?
I can't access the motor shield page right now but I think they are designed to take a separate motor power supply.
HOWEVER ... you can't use a high voltage for a stepper motor with a motor shield because the motor shield is not designed to limit the current in the motor coils
AND ... you can't use a A4988 stepper driver board (which can limit the current) with a unipolar motor - only with bipolar motors.
Some unipolar motors can be converted to bipolar - but ONLY if the 5th connection is actually a pair of wires joined together. By separating those wires you have a 6-wire stepper and if you ignore the centre wires (the ones that were previously joined) it will work as a 4-wire bipolar stepper.
...R
Robin2:
AND ... you can't use a A4988 stepper driver board (which can limit the current) with a unipolar motor - only with bipolar motors.
If you google the part number you'll see it seems to be a 6-wire motor so can be bipolar or unipolar.
However get a decent low-impedance motor if you are going to drive if from a chopper-drive,
you may only need 12V then. Well, perhaps.
BTW:
4-wire bipolar only
5-wire unipolar only
6 or 8 wire - bipolar or unipolar. 8-wire motors can be wired two ways for bipolar
with different impedances.
These wire-counts do not include any grounding wire to the motor's casing.