E-Stops and ODrive

1

Hello fellow ODrivers,

Long time reader, first time poster.

I am using a 4 ODrive S1 controllers along with two encoders - an incremental encoder and an RS485 absolute encoder - per motor. I also have a regen clamp to power all of my controllers.

My comms connection scheme looks something like this:

[RPi4] -->[USB ISO] → [USB-to-CAN adapter] → [ODrive 1] -->[ODrive 2] -->[ODrive 3] -->[ODrive 4]

I’d like to incorporate an E-Stop along with a safety relay for shutting off my motors in the case an emergency occurs.

I was thinking I could just remove power from the ODrive’s DC_IN terminal but I fear that this will also power down the 5V output pin that goes to the absolute encoder resulting in a loss of position. Is this a correct assumption?

Alternatively, I could use a contactor to remove power from the 3-phases of my motor. I would also then need to have some way reroute the energy in the motor’s windings some how. Any good ideas on how to do this?

Thank you in advance,

Emi

2

Hi! A few options here:

  1. Usually a contactor on the DC bus is how I’ve seen safety rated e-stop approached. The S1’s logic domain (including encoder) can be powered over the I/O header or CAN connector on the 12V IN line – note this is referenced to DC-, and has a pretty tight voltage tolerance range of 10-13V or so. Note to also be careful to have a precharge/antispark circuit with the contactor.
  2. Alternatively, if you configure a GPIO pin as an endstop, the ODrive will exit into idle once pressed, and refuse to re-enter closed loop until it’s no longer pressed. This isn’t a true STO method, and I wouldn’t rely on it for a safety critical application, but it’s a pretty straightforward method.

Generally I’d recommend against three-phase contactors for the reason you enumerated – it gets iffy with the inductive kick.

3

Hey solomondg,

Thanks for quick the response. Are there any COTS precharge/antispark circuits you recommend?