Tesla recently announced a walking humanoid robot called Optimus, and is implying that it will actually build and sell the thing for around $20,000. That is almost certainly just hype and Optimus will likely end up as vaporware, but it does raise a question: how easy is it to build a walking robot? Technology has come a long way over the years and what used to be state-of-the-art is now within reach of hobbyists. The inspired YouTube roboticist James Bruton to construct the cheapest and simplest walking robot he could devise.
Many walking robots attempt to recreate the human form and gait, but that is a difficult and expensive undertaking. Human bodies are very complex and walking requires the coordination of dozens of muscles and tendons. To even get close to mimicking a natural human walking gait, a robot needs an absurd number of motors and actuators. Boston Dynamics is famous for this kind of work, but they have had the benefit of substantial funding from the government (including DARPA and several branches of the military) and private sector (like Sony and then an almost $1 billion buyout from Hyundai). Bruton doesn’t have the kind of funding that Tesla and Boston Dynamics enjoy, so his robot looks a bit clunkier than examples from those companies.
Instead of replicating a human gait, this robot uses simple mechanisms and just a handful of motors to walk. The key to its locomotion is a large sliding mass on the top. When that mass (driven by a motor with a belt) moves to the robot’s left side, the robot tilts in that direction to take weight off of the right foot. That right foot can then lift slightly (with a motor and leadscrew) and then move forward (with another motor and belt) to take a step. This process repeats, switching from one side to the other, so the robot can walk forward or backward. Each leg also pivots with a servo motor, which lets the robot turn.
Bruton constructed this robot using 3D-printed parts and aluminum extrusion, which kept the cost low. A Teensy 4.1 microcontroller development board controls the various motors through drivers. The motors were likely the most expensive components in the entire build. Bruton can pilot the robot using his universal remote that we featured a while back.
As you can see, this robot isn’t very graceful and probably won’t be winning any ballet competitions. But it does demonstrate the feasibility of hobbyist-built walking robots. Bruton himself has built much more sophisticated walking robots and so this was more of an exercise in restraint than anything else.