Spot Style 7dof Robot Arm

I’ve wanted to build a slender, flexible, dynamic robot arm ever since I first saw Spot’s and I finally had the time and inspiration to finish one of my own.

It’s a 6dof arm with a gripper on the end (so 7dof total). The build construction was something new I was trying. With companies like Fabworks, bent sheet metal is super affordable, fast, and quite accurate so I designed something where the complicated geometry is 3d printed, with a thin bent sheet metal skin for rigidity and to help with creep issues. Some bandsawed aluminum tubes make up the long links. Belts run inside the tube (total of 3 belts).

The arm is on one CAN bus and I’m able to comfortably do 500hz control of the 7 dofs.

As for actuators, earlier this year I built up a small batch of these custom actuators with a roughly 5010 stator size outrunner, a custom 10:1 planetary, a crossed roller bearing, and a controller, good for about 20N*m peak. These power the first 3 dofs of the arm.

The last 4 dofs are powerd by GIM4305s with custom small controllers I designed for them.

The wrist uses a differential made of some cheap sintered RC car bevel gears. This keeps the actuators far back and allows for more individual joint torque. In the future, I might skip the differential, but it was worth doing at least once. Decoupling is done on the SPIne side, so the control computer just commands J5 and J6 independently.

Not pictured is a bearing support between the two coaxial bevel gears

Lastly the gripper is a very simple 3 finger one (one dof), vaguely inspired by the shape of HD Atlas’s grippers (although much simpler). It uses bevel gears for packaging compactness.

Videos to follow soon!