Servo Diode and Capacitor Protection Hookup Guide

ardenpm

The documentation on hooking up servos makes specific reference to using a Schottky diode and 220uF capacity as protection from voltage rise due to regenerative braking from the servo however I haven't seen any guide (or details from anyone that implemented it) on how to actually hook this up. Likely it's trivial for an EE however it would be helpful if there were more details.

For example, should the diode be between the Duet 5v+ and the capacitor or between the capacitor and the servo? The guide makes reference to crimping the capacity directly into the connector which makes me think the later but I'm still not sure.

It also doesn't specify which Schottky diode would be appropriate, I imagine because it would vary with the servo specifications but some guidance there would be useful as well.

For using a separate power supply, which seems to be the preferred method it would also be nice to see the preferred wiring so as to avoid ground loops etc. I understand there are quite a few different ways to hookup depending on whether using a single power supply, step-down etc but some examples for the common cases would really help.

dc42

@ardenpm said in Servo Diode and Capacitor Protection Hookup Guide:

For example, should the diode be between the Duet 5v+ and the capacitor or between the capacitor and the servo?

Between the Duet 5V rail the the capacitor. The capacitor is connected in parallel with the servo +5V and GND connections.

It also doesn't specify which Schottky diode would be appropriate, I imagine because it would vary with the servo specifications but some guidance there would be useful as well.

The servos likely to be powered from Duets rarely draw more than 1A, so a 1A Schottky diode such as 1N5817 would be suitable in almost all situations.

Small servos such as HS70MG do not need the diode and capacitor. Larger ones such as MG996R do need them.

ardenpm

@dc42 thanks for the quick reply. So just to confirm, this would be what I want then.

I was only able to find a 1N5819, hopefully the slightly higher voltage drop wouldn't be an issue. The servo I am using is the KST DS215MG which unfortunately doesn't provide details of stall current but it seems in between the small and large ones mentioned in the guide and your message with a torque of 3.7Kg.cm. Based on stall currents of the others it might be getting close to the 2A for the Duet2.

dc42

@ardenpm yes that diagram is correct.