Input Voltage issue for OpenRB-150 and DXLs needing 12 V to operate


So far, the OpenRB-150 had been working well for me - see this post:

I was using XL-320s (7.5V) or XL-330s (5 V) mostly and I powered everything via the Terminal Block with the Jumper set on the VIN(DXL) side. And everything worked fine.

Recently, I switched to using AX-12/18 and XL-430, i.e., DXLs that need 12 V, then I found a peculiar problem when I used the typical 12 V Power Supply that comes with the typical ROBOTIS Kit:

  1. When this 12 V PS is plugged into an EMPTY OpenRB-150, the Power LED on the OpenRB-150 turns on first, and then 1-2 second later, the DXL LED on the OpenRB-150 turns on next, and Windows sounds out with a ding telling me that the USB C Com Port is connected OK. And ARDUINO can connect to this COM Port OK also.

  2. However, if I have some DXLs (AX-12 or XL-430) connected to the OpenRB-150 before I turn on the 12 V PS like in the previous paragraph, then the sequence of events is like this: OpenRB-150’s Power LED comes on, but DXL LED does not come on, and Windows does not connect to the USB C Com Port and consequently Arduino also does not see this COM Port and of course Arduino then does not work for me.

  3. I have a Variable PS 3V-12V that I can use instead of the ROBOTIS fixed-12V PS, so I did some more experiments, and this is what I found:

  • If an XL-430 is used, then I cannot go higher than 11 V for the power on sequence to work out like in Paragraph 1) - And everything works fine again, from Windows to Arduino.

  • If an AX-12 is used, then I cannot go higher than 10 V for the power on sequence to work out like in Paragraph 1) - And everything works fine again, from Windows to Arduino.

  1. I also found a work-around solution:
  • I can use the ROBOTIS fixed 12 V PS to power the DXLs separately from the OpenRB-150 which I can power with a separate PS at 5 V for example. Of course, the X3P cable , that connects the DXL bus on the OpenRB-150 to the actual network of DXLs (AX-12s or XL-430s), needs to have its VDD wire severed as the OpenRB-150 only needs the GND and DATA wires to control the DXLs in this configuration.

I have two OpenRB-150s that act like described above, so maybe I am just unlucky or maybe ROBOTIS needs to look into this issue further - some kind of interaction between the USB C and the VIN(DXL) option, as the OpenRB-150 specs say that it can function between 3.7 V and 12.6 V, but it really does not (at least from my experiences). :grinning:

Hi @roboteer,

I’m sorry about the delayed response.
I’ve look into this matter and I was able to reproduce the issue with the beta test units that were distributed before the OpenRB-150 is officially released.

The work around for this 12V issue is to short the jumper in the back of the OpenRB-150 and bypass the FET switch.
By doing this, DYNAMIXEL will be powered whenever the power is supplied regardless of status of the power enable pin.

Fortunately, the same issue has not been observed in the final OpenRB-150 product that are currently sold as there were design updates right before the product release.

Thank you very much.

Thanks for the update. Can you be more specific about the nodes to bypass the Power FET?