A Quadruped Robot That Takes to the Skies

Most robots are designed to get around in one particular way. Some walk, others roll around on wheels, and some fly. But why settle for just one? Maker Dorian Todd decided to combine two different forms of locomotion by turning his miniature quadruped robot, Sesame, into a flying machine. The result is a four-legged robot that can walk around on the ground, unfold its legs, and take off like a quadcopter.

Todd originally developed Sesame as an open source walking robot that could be built for under $60. After noticing just how lightweight it was, he started wondering whether it might be possible to strap on some drone motors and get it airborne. Of course, making a robot fly isn't quite as simple as attaching a few propellers.

The biggest challenge was weight. A drone needs to generate enough thrust to overcome its own weight, and the heavier it gets, the more powerful its motors need to be. Todd looked to the lightweight "toothpick" class of drones for inspiration, aiming to keep the entire machine around 250 grams.

That meant putting Sesame on a serious diet. The original robot used eight MG90S metal-gear servos to move its legs, but Todd replaced them with lighter SG90 plastic-gear models, saving approximately 35 grams. He also redesigned the body with weight-saving cutouts and used carbon fiber-reinforced nylon (PPA-CF) for the 3D-printed frame. Additional carbon fiber components, machined on a desktop CNC, helped keep everything rigid.

But there was another problem. Drone motors need to stay firmly in position during flight, while Sesame's legs are designed to move freely. Todd solved this by adding mechanical stops that lock the legs into a 90-degree position when extended. During flight, the propellers pull the legs against these stops, keeping the motors properly oriented without putting excessive strain on the servos.

The electronics are split between two independent systems. A LOLIN S2 Mini ESP32-based development board handles walking and facial expressions, just as it did in the original Sesame. Meanwhile, an all-in-one flight controller manages the drone motors, stabilization, and radio communications. This arrangement also means that a problem with the flight system doesn't necessarily prevent the robot from walking.

After several design revisions, incorrect motor mounts, and a few crashes in the garage, Todd finally had a working prototype. The completed robot weighed 264 grams, slightly above the original target but still light enough to fly. During outdoor testing, Sesame successfully demonstrated the entire sequence. It walked across the ground, extended its legs into flight position, took off, hovered, and landed before returning to walking mode.

Sesame may not be the most practical drone or walking robot, but being able to do both is still an impressive accomplishment. Todd managed to squeeze two very different forms of locomotion into a machine weighing just 264 grams, overcoming some tricky mechanical challenges along the way. Check out the video below for more details about how he pulled it off.