Boston Dynamics is a robotics company that is heavily funded by DARPA, and they often release videos of their experimental robots that have a tendency to go viral. That’s because their creations tend to perform in ways that almost doesn’t seem possible. In reality, it’s just modern technology and solid engineering. But Boston Dynamics has a whole team of talented engineers and huge project budgets. Not many of us makers have that, but YouTuber James Bruton is doing something very similar with his new Sonic the Hedgehog balancing robot.
This robot was actually originally intended to act as an R&D experimentation platform for Bruton’s other openDog quadruped robot that resembles Boston Dynamics’ Spot robot dog. While Bruton has made an incredible amount of progress on openDog, he has run into some challenges that are difficult to isolate among the complexity of openDog’s technology. This Sonic the Hedgehog robot is simpler than openDog, and allows him to test specific hardware components and engineering techniques. Specifically, he wanted to test a motorized active suspension system as well the communication between different areas of the robot that control that suspension.
Just because this robot is less complex than openDog, that doesn’t mean it’s simple. The meter-tall robot balances on two wheels, which are turned by brushless motors that are controlled by an ODrive motor driver. It’s made from a combination of aluminum extrusion and 3D-printed parts, which are appropriately blue, white, and red. The active suspension is what makes the design especially unique. It has two legs that bend at the hips and knees. Ballscrews turned by brushless motors are used to actuate those. Load cells in the shins detect deflection in the legs, and that data can be used to engage the active suspension. An MPU-6050 IMU is also employed for enhanced stability.
Communication between the load cells and the rest of the system is done through a CAN bus, just like a car. The difference is that this one is wireless. Teensy 3.2 boards are used to monitor the load cells, and the CAN bus helps to avoid interference caused by the massive induction of the large brushless motors. That all happens very quickly — a couple hundred times a second — so the leg motors will automatically bend to absorb bumps, which eliminates the need for a more conventional spring and shock absorber setup. Bruton’s tests with the Sonic the Hedgehog robot have proven to be mostly successful, which gives him the knowledge necessary to improve on his openDog robot.