Stepper max speed

max72

I have a friend looking for a solution in order to generate an optical signal at constant rate.
In his mind a motor with a reflective pattern should offer the reference signal he's requiring.
We where talking about that and I wondered what would be the max speed a stepper motor could provide. Providing only a signal it would be free running.
The stepper would guarantee a constant revolution speed, which is required, how can I assess if it will offer enough speed?
With the propeller step driving will be a piece of cake....
Thanks in advance,
Massimo

kwinn

Look at the speed/torque curves on the stepper motor specifications. What sort of rpm are you looking for?

JasonDorie

As a ballpark, 2500 to 3000 rpm is a normal usable upper range.

Stepper speeds are a function of voltage, amperage, and coil impedance. Basically, higher voltages but lower amps allow you to build the magnetic field faster, but also convert to heat faster, so you have to control the current being used, and watch the temperature doesn't get too high. Steppers produce poor torque at high speeds.

This page has a motor calculator that may help: http://www.daycounter.com/Calculators/Stepper-Motor-Calculator.phtml

Enter the driving amperage, impedance, voltage, and steps per revolution, and it'll tell you the maximum speed you can reach. It'll be different for each motor.

Phil Pilgrim (PhiPi)

You also need to consider ramping slope, which is a function of, among other things, the armature's moment of inertia and any additional inertial loading downstream of the output shaft.

-Phil

max72

Thanks.
My friend was talking about 5000 rpm. He said that could be less placing more marks on a disk.
Supposing to place 4 marks that would bring to a 1250 that looks achievable.
The scope is to create a reference, so it can be slowly ramped.

Thanks for the suggestions.

Massimo

kwinn

More marks also reduces the risk and amplitude of vibration.

Beau Schwabe

Ramping as well as current drive is important, but perhaps what's most important is only providing drive to the coils about 1/3 of the duty cycle of each step to provide a smoother response. Often refereed to as a "trapezoid" wave form. Otherwise if the coil is left energized too long in the cycle, it will cause the stepper to run rough and severely impact your top speed. Not to mention it will contribute unnecessary heat to the stepper motor. Ideally you want to drive a stepper motor with a sine wave. That would just solve many issues.

Doing the math ... most steppers provide 1.8 Deg per step, that's 200 steps per revolution.

If you are looking for 5000 rpm, that's 83.3333 rps (revolutions per second) so you will need to clock the stepper at 16.666kHz (83.33 x 200 = 16666Hz) <-- Make sure you can turn ON and OFF your transistors this fast without capacitive effects causing slow slew rates for rise AND fall times. This needs to be a clean and quick transition.

max72

Thanks!
Massimo