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Servomotor disaster

Servomotor disaster
March 29, 2021 03:07PM
I was forced to reduce the size of the sand table mechanism I've been powering with iHSV servomotors and was running tests after reassembling the mechanism. The machine homed OK, so i selected one of the old pattern files to run, forgetting that those patterns were for a slightly bigger table. The machine did what it was supposed to and when the carriage hit the end of one of the axes, there was a snap, a spark and the whole thing stopped dead. The death toll included the Duet 2 WiFi controller board (the source of the snap and spark), and the 200W power supply that was powering both the motor and controller board, about $180 worth of damage. Fortunately, the motors are OK.

I think that when the motor was physically forced to stop, the current spiked, probably causing the power supply to protect itself by shutting down, creating a back EMF voltage spike that was sufficient to destroy the controller and power supply.

Lesson to learn from this: don't share a power supply between a servomotor and an expensive controller board!

The new controller board is going to get its own power supply...

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Servomotor disaster
March 29, 2021 04:38PM
... ouch! eye popping smiley

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Call for the project "garbage-free seas" - [reprap.org]
Re: Servomotor disaster
April 01, 2021 11:33AM
The problem I ran into is apparently well known among those who work with servomotors on a regular basis. There is a pretty cheap and easy solution described in this document from the Gecko Drives website.
The document illustrates a snubber that shunts the current from the motor to ground as long as the voltage from the motor (the back EMF) is higher than the supply voltage. That will protect the power supply, the motor driver, and anything else connected to the same power bus.

I'll be installing that circuit and using a separate power supply for the controller board in future servomotor projects. I suggest you do the same.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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