Single-Wheel Robot

Overview

If I hadn’t decided to go into quantum photonics, there’s a good chance I’d have done robotics instead. There’s something immensely satisfying about building something from scratch and having complete ownership of it, and then watching it do something really cool!

The idea for this started a long time ago. Several years ago, I wanted to build a robot that looked like a single wheel but could drive around. It seemed like a challenging project, but the result would be worth it. This summer, I decided I was going to build it.

Design

I designed every part in Fusion 360 from scratch. I wanted an initial version that was a little simpler, so I designed a chassis that was modular and could serve as a roomba-style robot.

Fusion 360 model of a circular frame with cross-shaped spokes, a central hub and mounting feet — Another view of the design in preparation for the single-wheel operation mode, focusing on how a single half of the wheel would integrate onto the main chassis (later versions of the outer wheel had inner ridges to be driven by a gear).

Electronics

The electronics were the part I felt more confident about. Using a LiPo battery, a buck converter, and a couple of H-bridges, I created both the 12 V rail needed for the motors and the 5 V logic rail for the Raspberry Pi. The wiring wasn’t too difficult either, and when possible, I tried to solder things in place (as opposed to breadboard wiring) to reduce complexity.

Soldering iron held over the partly assembled robot on a lab bench, with its motors, driver boards and a LiPo battery nearby — Wiring the electronics into the printed chassis.

The robot's black 3D-printed chassis with a LiPo battery, two DC gear motors and their motor driver boards mounted inside — The final electronics, including DC motors, a buck converter, a LiPo battery, and two H-bridges. The Raspberry Pi is also mounted on the back side.

First version: roomba mode

The first version worked great! It could drive around using the two motors directly attached to wheels.

Final version: the wheel

Once the roomba-style mode worked, I started adapting the design. Instead of connecting the motor shafts directly to wheels, they attached to gears that drove inner ridges on larger wheels that fit around the entire chassis. Using the same two drive motors, that allowed for independent control of two halves of a large wheel. The central chassis would then rest inside, free to spin up and down along the interior of the wheel for acceleration.

Roomba mode: the first version, driving on carpet.

Wheel mode: the final product, a single wheel that can drive around and turn in place.

Lessons Learned

This was an awesome project! The only regret I have is that the semester started and some research deadlines came up, so I wasn’t able to work on the active control system that I wanted to make for this. I think integrating a gyroscope would have let me smooth out the acceleration and driving significantly. I still have the working robot, so that will likely be a future project when I have time again.