Balancing bot with ultrasonic sensor - no gyros

Here's my slightly unusual balancing bot.

Normally balancing bots use motors and gyros,but my minimal bot uses just servos and an untrasonic distance sensor.

Used an old boe-bot platform:

2x continuous rotation servos

Aluminium base

The boe-bot came with a a basic stamp MCU, so I replaced that with an Arduino Uno

Boe-bot's are normally rover type bots, but I moved the servo/wheel mountings to the edge

and stood it up on its end to make a balancing robot.

You need accelerometers and gyros for a balancing bot, right ?

Not here - I just used a HC-SR04 ultrasonic distance sensor pointed at the floor:

shorter distance = falling forward,

longer distance = falling backward.

Feeding that into a PID loop got some balancing, at least for several seconds,

and longer with some tuning (0:14 onwards in the video)

Connected the ultrasonic like this:

The two servos on top are just for weight

- balancing works better with the centre of gravity  higher up

I've put the full arduino source code on github here:

https://github.com/mikerr/SonicBalancer