I’m trying to run a stepper motor at 300 RPM ( 1000 pulses per second if my calculations are correct).
It stalls out before reaching the required speed (no load).
I am using the following pololu components:
Stepper Motor: Unipolar/Bipolar, 200 Steps/Rev, 57×41mm, 5.7V, 1 A/Phase
DRV8834 Low-Voltage Stepper Motor Driver Carrier
(with a 47uf 16V cap I believe)
Wall Power Adapter: 5VDC, 5A, 5.5×2.1mm Barrel Jack, Center-Positive
And a 3.3v step down regulator to power the microcontroller:
Pololu Step-Down Voltage Regulator D15V35F5S3
One thing I note, the amperage delivered to one coil reads: 0.4 A, regardless of how I adjust the current limiting trimmer.
When I swap out the power supply with a 12V/8A PC power supply, the amps to a coil gets to 0.8A max (though the trimmer does seem to effect it now).
Ive considered driving it a 2khz and half-stepping, but short of that, am I way off base here?
Thanks very much.
You may or may not be able to achieve that speed, especially if the motor has a load, but there are a couple of things you can try.
First, ramp up the speed slowly until the motor starts slipping. You cannot start a stepping motor at a high step rate and expect to achieve maximum speed.
Second, the voltage and current matters a lot, especially the voltage. If the motor is rated for 1 ampere/winding, use a power supply that is capable of more than that and with some safety margin, a voltage close to the maximum allowed by the driver. A 24 V, 1.5 amp power supply should work well, but you will need a different driver. The DRV8834 you have is rated for 10.8 V maximum, so you are already taking a chance. I recommend one of the others, and make sure that the current adjust is set to 1 amp/winding.
More than you ever wanted to learn about stepping motors is on this site: homepage.cs.uiowa.edu/~jones/step/
Sorry, wasn’t clear, I am ramping up the motor speed. First automatically, then finally with a pot to manually control the speed. I can just about achieve 280 rpm this way (tried quarter and full stepping, not sure if I saw much difference).
Thanks for the catch on the 12V on the 10.V driver! totally missed that.
My power supplies were both 5V@5A then 12V@8A.
I’ll try 24V with a different driver.
But as long as I keep it to 1A, is there no damage driving it at 24V ??
It says 'rated at 5.7V’
Thats the part I find confusing.
Thanks very much!
PS. Thanks for the link.
The voltage rating and the current rating of a stepper motor are redundant. The determining factors are the coil resistance and the average power that the motor can dissipate without overheating. That can be either expressed as the maximum steady state current per winding or the maximum steady state DC voltage across the winding, which will result in the maximum rated current.
For a chopper style stepper driver the voltage can be much higher - in fact in industrial applications the motor power supply often provides 10 times the rated steady state voltage of the motor. This gives the most rapid response as described in “Jones on steppers”. You rely on the switching characteristics of the driver to keep the average winding current down to a safe level.
Hi Jim. Thats excellent information.
I think I’ll make the most of the components I just purchased and reduce the speed to 180rpm, but use your information for the 2nd prototype at 300rpm, when I’ll need to buy a new power supply (24V @ 1.5Amp) and matching stepper driver.
Looks like I spoke to soon.
Im unable to achieve 180rpm at 5.2 volts.
I am able to achieve 180rpm at 11.7 volts (though that exceeds the stepper driver spec).
It seems to start stalling out (unloaded) around 280rpm at that voltage.
I think I’ll go to 24vdc as you suggest.
Just a follup up:
Found a surplus power supply: 24VDC @ 2Amp
and switched to Pololu Stepper motor driver: A4988 (8-35V, 2A)
Seems to run fine with my quick tests.
Lets see what it does under load