Hello,
I'm setting up robot that uses hoverboard motors, controlled by Arduino-Mega and an oDrive 3.6/56v
Can I use a 56v battery-pack to power all the components? I have three buck-converters that step 56v down to 12v, 9v and 5v, can they be wired in series to the battery-pack, sending their dropped voltage to each 'board/component?
I'm not sure what you mean by this! You can wire the 12V to the battery, the 9V to the 12V output, and the 5V to the 9V output, or if the specifications allow it they can all be connected in parallel to the battery!
And, to add to what @missdrew said, the current ratings must be appropriate too.
The power drawn from the first regulator will be the power out from it not just to the 12V devices, but will also include power drawn by the 2nd and 3rd regulators. Similarly for the 2nd regulator
Aagh sausage-finger typing, I should have said 'parallel'. This page has relevant info Ground Loops — ODrive Pro Documentation 0.6.4 documentation