I got a stepper motor translater/driver from allegro (SLA7051M). I hooked up the circuit as shown in the data sheet and interfaced it with a microcontroller to feed the control signals. At first my clock (step) signal frequency was too high, so i stepped it down A LOT. Then I was able to get the guy to step every 2 seconds or so, I was really excited! However when that frequency goes up, it goes backwards and forwards inconsistently... Any idea to why this is happening? The data sheet can be found here:
Let's whizz through half a dozen questions: What is the voltage 'rating' of the motor?. What is it's current rating?. What supply voltage are you using?. What is the current rating of the supply?. How have you got the current sense wired?. Are you half stepping, or full stepping?. What load is on the motor?. Are you _sure_ you have the wiring to the phases right?. Are you sure that the flyback voltage generated when a coil is released, and the energy is diverted by the internal diode, 'back' into the supply rail, will not cause spikes that will interfere with your processor.
The motor 'rated' voltage, is _not_ the voltage it should be run on, if you want to move it quickly. A '12v' motor rating, means that you can apply 12v to the coils when the motor is stationary, and it will not overheat. The coils are very inductive, and when you switch to a new coil, the inductance, implies that it takes a long time, for the current to build up. This massively limits the step speed, especially with heavy loads. You can make the current build faster, by increasing the applied voltage, and limiting the current to the 'safe' value, using the current control circuit in the controller, to prevent too much being applied, when the motor is stationary. Typically, overvoltages in the order of 4* to 6* are used. (obviously checking the voltage limits of the motor first). So a '4v' motor, may well be run on 24v. Especially when 'half stepping', where first two coils are engaged, then only one, there can be a significant amount of energy being fed 'back' into the supply rail, and care is needed in the connections between the processor and the controller.
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