One of the take-a-ways from last year’s Maker Faire was that having multiple battery packs and no overall power switches were problematic and actually dangerous.
As we were setting up our booth my boy took to hooking the batteries up to the robot. Somehow there was a short, followed by sparks and smoke. The battery was toast and the boy ended up with a small burn on his finger. It was at that moment that I knew a formal power system would be built before any further “playing” with the robot.
My requirements were simple.
- I wanted one source. I didn’t want one battery to run the servos and a different battery (or 2 as was the case) to run the motors.
- It had to be regulated for running the computer and all peripherals.
- Each sub system could be switched off
- It needed one main power switch AND an emergency cut off
In researching for ideas I came across the idea of using step-down voltage regulators running in parallel off of a large battery bank. This makes it easy to add power capacity as needed. I would carve off 5v for BeagleBoard, 5-6v for the servos (and controller), and 7v to each motor.
I used these 3amp Buck Converters for the BeagleBoard
I used these 5amp Buck Converters for the each of the the remaining sub-systems (servos, left motor, right motor)
For power switches I couldn’t resist lighted rocker switches (just for the bling) and of course the emergency switch had to be a mushroom button.
I had envisioned the switches running horizontal across the shoulders of the back of the robot, but the boy over-ruled me with a vertical design (which looks great and works better). We used a corrugated plastic sign trimmed down to the proper dimensions and spray painted white. additionally it was re-inforced with white duck-tape (so the painting ended up not being all that necessary).
On paper this all seemed great and was easy to layout in a crisp design:
The reality of the wiring was pretty messy
Labels make for a polished look.
And it works!