Yes its true these things generate a *ton* of switching noise. Trying to increase the frequency can help but its complicated by the fact that they don't work at a fixed frequency at all; the frequency is a factor or several things, mainly motor inductance, input voltage, the timing resistor on the IC (sets the off time), and the instantaneous current setting. Going to low inductance motors will increase the frequency but also likely increase the noise intensity. The other approaches will be easier and work better:TeleFunKen wrote:I don't need too much hold torque, compared to some applications I guess. The motors I'm currently using are the Pololu 1208 bipolar stepper motors with the A4988 carrier board. I'm just now developing the first prototype, so I'm not sure if those motors are going to have sufficient torque anyway. So far they seem to, but with a lot of chopping going on. (at least from what I can hear)
I've wondered if there are better drivers out there that either chop at frequencies above 20khz, or at least have control of the switching frequency. I'll look into the geckos, I have a friend who has some on his Novakon Mill, driving significantly larger steppers.
Not exactly. if you lower the voltage to just that point you will get about the same torque. only if you keep lowering it further will torque start to decrease. This may be in fact the easiest thing to try. the downside is it will quickly limit the max speed you can attain with your motors, and torque will drop off very rapidly with increasing speed. this would work best if using only full steps or uncompensated 1/2-steps. if you have a variable supply you could adjust it dynamically to keep the voltage up high for active motion and then drop it down for "hold mode" when the motors are stopped....Am I correct to understand if I lower the voltage to a point where it doesn't chop that I will see a significant decrease in hold torque? I'll try some experimenting tonight to see if I can find a happy medium.
>>>WARNING: adding capacitance to the the output of a switching stepper driver, especially at the motor, will only make the problem much worse, overload the drivers, and likely destroy them. don't do it. this trick is good for DC brush motors *only*.A little capacitance on the motor? Across both windings? What kind of value would be a good starting point?
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