Stepper motor speed - Driver or motor limitation? - Page 1
Forum section: electronics / projects

author: metRo_
author_rank: Regular Contributor
timestamp: September 15, 2013, 09:31:29 pm
content: Hi,I'm using aA4988driver and the motor start to stop when I try step values of 500 steps per second. Is this a motor or driver limitation?I tried with diferents motors and the result is +- the same, some motors start to flip at 350 steps per second and another goes to 550/600.The motors I tried are:http://www.pololu.com/catalog/product/1204PF35T-48L4vexta px245-03aa-c6 - 2-pahse 12v 0.4AThe power source is a 9v 2A. I measured the current consumption with a multimeter and it never go higher than 1A with A4988 the current limiting in the max.How can I estimate the max motor speed?Thanks

author: johansen
author_rank: Super Contributor
timestamp: September 15, 2013, 09:39:52 pm
content: read the datasheet torque versus voltage and pulses per second.most show that torque drops to zero somewhere between 500-1000 pps at 12 volts for that entire product line.also note that the actual voltage at the terminals will be less than 9 volts due to power loss in the chip.so figure at best you're driving those motors with 8 volts.

author: metRo_
author_rank: Regular Contributor
timestamp: September 15, 2013, 10:04:03 pm
content: http://www.pololu.com/file/0J635/SY20STH30-0604A.pdfthe motor datasheet doesn't show that :s I can measure 3v in each wire.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 15, 2013, 10:17:06 pm
content: Stepper motors are basically synchronous motors with a very large number of poles. As such, there's a speed limit (dependent on many factors) before they lose sync.One way to get a higher maximum speed is to increase the drive voltage, but then you have to add current limiting to prevent them from overheating at low speeds. You could also theoretically do sensorless FOC, though I have never actually tried that with a stepper.

author: sdim
author_rank: Contributor
timestamp: September 16, 2013, 12:31:58 am
content: Fast answer: The motor limits your max RPMThe pololu can supply up to 2A with a heatsink and air flow (1A without heatsink). Your stepper motor has rated current 0.6A.Take care not to burn the pololu or your stepper motor. When you set the output current treat the potentiometer gently. Trust me on that, I've got at least 5 stepsticks burned when I calibrated my reprap. One full rotation has a HUGE impact on the output current. Try 45° steps or smaller when you turn the potentiometer.The limits of a stepper motor that are usually declared on the motor specifications document.http://sine.ni.com/ds/app/doc/p/id/ds-311/lang/en, search for "Max Speed rpm"In your case, the max speed is not declared but you can calculate it.You can find some on-line calculators. I hope this onehttp://www.daycounter.com/Calculators/Stepper-Motor-Calculator.phtmlworks for you.The stepper does not rotate with constant speed. During each step, the motor shaft accelerates for a part of the step and it decelerates until it reaches the next step position where it's rotational speed goes back to zero (actually it fluctuates a bit near the ideal position because the controller continuously makes tiny corrections , especially when you use microstepping).The stepper motor has a maximum torque limit.The torque needed to overcome the inertia of the moving parts limits your maximum RPM.http://en.wikipedia.org/wiki/Angular_acceleration

author: jahonen
author_rank: Super Contributor
timestamp: September 16, 2013, 08:08:39 pm
content: Try increasing the supply voltage (in limits that the driver allows). Stepper motors are driven by current. Higher supply voltage will usually improve stepping rate considerably as then the driver will be able to compensate the back-EMF and inductance effects better.Regards,Janne

author: nessatse
author_rank: Regular Contributor
timestamp: September 17, 2013, 01:44:07 pm
content: Are you applying an acceleration profile? 500 steps per second is very low, but no motor will turn if you just hit with that rate without ramping up to it.Also as others have mentioned, 9v is rather low, to get performance you will need to up the voltage, but make sure your driver can handle it and you have current limiting set up.

author: JuKu
author_rank: Frequent Contributor
timestamp: September 17, 2013, 04:14:10 pm
content: The motor is indeeddriven by current. This current needs time to build up. In other words, the motor coil inductance matters also.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 17, 2013, 09:57:09 pm
content: Think of the motor as a rotary spring-mass system. With a stepper in the stopped state and a mass attached to the shaft, excite it with your finger and note the vibration frequency. When you get near resonance, bad things happen. If you can apply damping and decoupling, you can often extend the speed range. You'll sometimes see fluid dampers that fit the back of dual shaft motors to control the resonances.

author: nctnico
author_rank: Super Contributor
timestamp: September 18, 2013, 01:18:42 pm
content: If you want to make a stepper go really fast you need to start at a low stepping frequency and gradually increase speed. Vice versa for stopping. The best power source is a current source with a high open voltage. A long time ago I built a stepper driver capable of running a 1.8 degree stepper from a disk drive at 6000 steps/second (1800 rpm).

author: CalG
author_rank: Contributor
timestamp: September 19, 2013, 03:25:41 am
content: Much as Conrad mentioned on the fluid balancers,To reach the highest motor shaft speeds you need to hang the appropriate mass on the motor shaft. A stepper will try to stop between steps and gets all confused if there is nothing to remind it which way and how fast it is supposed to be going.Inertia...don't fight it!

author: metRo_
author_rank: Regular Contributor
timestamp: November 03, 2013, 04:33:58 pm
content: Thank you allIncrease the speed really help to make it faster