Leg day

A project log for Tardygrade

3D printed quadruped with a tiny BOM

Dejan RisticDejan Ristic 07/12/2021 at 13:490 Comments

"A clever man climbs the stairs. A wise man rides the escalator. An enlightened man turns his feet into stairs."
Quote: some crazy biohacker

As far as I'm concerned the concept of a walking robot is just cool, and its existence needs not be justified beyond that. 

What would be even cooler though, is if that robot were actually useful in some way.

In that spirit, a goal I've had for Tardygrade was to make it able to negotiate rough and undeven terrain. After all, that's the main USP of having legs rather than wheels.

The articulation of the robots legs couldn't be simpler, with only 1 DOF. But since the legs lifts off the ground it does lend itself quite well to climbing.

That's only half the battle though. If the legs can't retain grip on obstacles the robot will just slide back to where it started.

I had to go through several iterations before I ended up with a foot design that was suitable for climbing.

Evolutionary steps in leg design.

Here's the solution I ended up with and why I found it to be effective:

  1. The sole of the foot has a stair-step profile with steps of increasingly large size toward the end.
  2. When the leg is retracted, the stairs are perpendicular to the ground, to give the foot good purchase on obstacles.
  3. As the leg extends, the stair shape turns steeper and more claw-like, which helps the foot retain its grip on the obstacle.
  4. The backward facing leg has a spur on its heel. When that leg is extended the spur maintains purchase on the obstacle while the forward facing foot retracts for its next step.