A4983 and Quarter Step Mode

[silex]

Hello,

I read the datasheet of A4983 to be able to understand how exactly i can achieve quarter step mode. But i did not understand some facts.
I want to use a step motor Pololu sell and i need to run it at Quarter Step mode. What should the voltage rating of step motor be? And for quarter step mode, how much voltage should i send to Vmot of A4983?
Thanks.

[ryantm]

Hello, Silex.

The step mode and your motor voltage are mostly independent. In full step modes, the motor windings are given various combinations of full power; in the microstep modes, the motor driver gives them intermediate powers. Either way, the A4983 is limiting the current in the coils, so you don’t have to worry about the details changing because of the step mode you’re in.

Any of the stepper motors we carry should work with the A4983, and your supply just needs to be higher than 8V or the motor voltage, so you should choose your motor based on things like the torque you need, the size you can fit, and the power supply you have. For instance, if you have 12V available, that’s what you should probably use, rather than trying to find some other power source.

The A4983 can handle VMOT up to 35 V (be careful of LC spikes, if you choose a high voltage, though). With the A4983, you can choose a VMOT that is higher than the voltage rating of the stepper motor as long as you limit the current to the current rating of the stepper motor. The higher you choose VMOT the faster your motor will be able to transition from one position to another.

- Ryan

[silex]

Thanks for your reply Ryan.

In the product page of A4983, there is a statement like this:

To achieve high step rates, the motor supply is typically much higher than would be permissible without active current limiting. For instance, a typical stepper motor might have a maximum current rating of 1 A with a 5Ω coil resistance, which would indicate a maximum motor supply of 5 V. Using such a motor with 12 V would allow higher step rates, but the current must actively be limited to under 1 A to prevent damage to the motor.

As i understand from this, i cannot achieve a microstep mode with 5 volts of Vmot and 1A 5Ω ( 5V) step motor.
So what does change by using higher motor supply voltage for higher step rates?
I am planning on using 11.1V motor supply for 3.9V 600mA step motor Pololu sells. So, as long as i limit the current for motor, will there be any change about microstepping if i use a step motor with higher voltage rating like 10V 500mA?

[jan]

Hello.

I don’t see the connection between the quote and your understanding. If you have the max current set to 1A, the driver will limit the motor to fractions of that as necessary to achieve the intermediate steps. For a given inductance, a higher supply voltage allows the current in the winding to get to the limit more quickly. For a given supply voltage, the lower-voltage motor will probably go faster, though there will probably be other reasons for different performances in the two. There will likely also be different performances at different speeds. Don’t forget that the driver requires a minimum of 8V or so.

You could just try both, in which case we would be interested in hearing your results.

- Jan