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enter image description hereIt's my first project using arduino. Simply trying to rotate three identical stepper motors, using three 293d h-bridges.

Although it does work properly (meaning the motors do rotate as they should), after the second or third rotation, they start to make a whirring electrical noise -when not moving.

I have attached a schematic of my circuit. The power supply is 5v dc 16A (old computer psu).

You can see exactly what I am experiencing on this video I made (try to listen in closely).

Video with noise.

Update: I checked by touching the h-bridges at the same time the noise starts, and I can feel them getting really hot.

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    \$\begingroup\$ A circuit diagram would be better than a video and infinitely better than the cartoon diagram you have embedded into your question. \$\endgroup\$
    – Andy aka
    Commented Feb 2, 2016 at 15:19
  • \$\begingroup\$ Sorry I don't know how to draw the circuit diagram the best I could come up with is the above diagram. As for the video it is the only way for someone to listen to the noise I am talking about. Thanks anyway \$\endgroup\$
    – the_plds
    Commented Feb 2, 2016 at 15:45
  • \$\begingroup\$ Your link is broken. \$\endgroup\$
    – uint128_t
    Commented Feb 2, 2016 at 16:38
  • \$\begingroup\$ Seems to be ok now \$\endgroup\$
    – the_plds
    Commented Feb 2, 2016 at 16:40
  • \$\begingroup\$ What happens if you disconnect the arduino from the drivers after the noise starts? \$\endgroup\$
    – jms
    Commented Feb 2, 2016 at 16:43

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What you're hearing is the effect of actually stepping the current. A sharp change in current produces a sharp change in the forces acting on the motor structure, which produces a certain amount of acoustical output. It's not quite the same as hitting it with a hammer (it's a step, not a pulse) but the idea is the same.

If you listen closely, you'll realize that the pitch of the sound you hear is determined by the stepping rate of your driver. If you vary the step rate, the pitch will change as well. The effect is not "pure", since the excitation (a step) produces lots of harmonics.

If you replace your steppers with a pair of sine wave drivers, 90 degrees out of phase, you can get rotation which is essentially silent.

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  • \$\begingroup\$ Thank you, but wouldn't that be the case if the noise was heard when the motor was asked to rotate? Instead the sound is only audible in between the motor rotations \$\endgroup\$
    – the_plds
    Commented Feb 2, 2016 at 17:23
  • \$\begingroup\$ Sorry, but did you mean the very high-pitched stuff? If so, I have no idea. At first playback I couldn't hear it at all, so I figured it was the stepping noise you were talking about. \$\endgroup\$
    – WhatRoughBeast
    Commented Feb 2, 2016 at 17:32
  • \$\begingroup\$ if you turn up the volume you should be able to hear it in the second half of the video \$\endgroup\$
    – the_plds
    Commented Feb 2, 2016 at 17:40

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