Alex

Alex is a general-purpose humanoid developed in collaboration with Boardwalk Robotics. It uses similar arms to those developed for the Nadia robot.

Many robots use actuators with high (50:1 or higher) gear ratios. These enable the use of smaller motors, but require torque sensors which are expensive and difficult to make. Others use Quasi Direct-Drive with low (e.g. 6:1) gear ratios. These are backdriveable and responsive, but require large diameter, heavy motors.

The actuators in Alex use custom cycloidal transmissions which I designed. The gear ratio is selected to allow open-loop torque control without a dedicated sensor, while still achieving high torques without a large heavy motor. The low-ish gear ratio means the robot is fast and responsive.

The actuators are backdriveable. This means they can swing freely, enabling the robot to utilize the system’s natural dynamics to save energy, just like animals do. For example, motions like the swing phase of walking can be completely unpowered. This opens up previously untapped possibilities for increasing motion efficiency in humanoid robots.

Unlike traditional planetary or cycloidal gears, our custom transmission design means we can achieve very low backlash without excessive friction. They are also extremely efficient (around 96%) – great news for battery life on mobile robots.

I came up with the idea of making these arms, and was lucky enough to be given the freedom (and funding) by IHMC and Boardwalk to make them happen. I did the mechanical design of the entire arm including three sizes of actuator, each with its own custom transmission. Electrical design was done by Alexis at H4 Lab and the whole project was done alongside the world-class team at Boardwalk.