Hi,
I want to use an odrive micro (for form factor reasons) in a musical instrument application. Consequently I need the drive to be as close to silent as possible. I’ve tested an odrive 3.6 and there’s a quite audible whistle, which I believe this is the control loop frequency. On the website it’s suggested there’s a update for the firmware planned for the Micro which will take the control loop frequency from 8 to 24kHz. My question therefore is when can we expect this? If it’s imminent or there’s a beta firmware available with this now, I’ll buy one.
Thanks,
Luke
Hi! The 24kHz control loops won’t affect the sound levels, that’s mostly for raising the maximum possible electrical frequency of the motor. For instance at the current 8kHz loop rates, you can’t go much above 1200Hz electrical frequency, with electrical frequency == motor speed (RPM)/60 * pole_pairs. So e.g. a 7 pole pair motor spinning at 1000 RPM is 1000/60 * 7 = 116.7Hz.
The noise you’re hearing is the current sense noise coupling into the motor’s torque output, which then causes audible noise due to magnetostriction and other effects. The v3.6 especially has very high noise (+/- 250-500mA RMS), compared to the ~10mA RMS of the Micro. So I would generally expect that the noise will be at least an order of magnitude lower on the Micro. Note the noise is also heavily influenced by the motor geometry and construction itself, if you can use an inrunner motor then the noise will be heavily dampened by the fact all the sound-producing components are contained inside the motor body.
Additionally, if you don’t need really tight transient response, you can use “gimbal” mode (where the current controller is turned off), or reduce the current controller bandwidth, to filter out much of the noise. The former will result in essentially zero noise from sources other than the encoder (which you can also reduce the bandwidth of), but have a big speed penalty, the latter will affect position/velocity control fidelity, but continue to allow for operation across the speed range.
Note also we accept returns of used units with a 20% restocking fee, so if the Micro doesn’t work out for your application, you can always return it and get an 80% refund.
If you can let me know what motor you’re considering, and/or what your torque+velocity requirements are, I’d be more than happy to give you my thoughts / recommend a motor!