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  • Darryl L

Exo Arm

Updated: Jun 30, 2023

A pneumatically-powered dual-cylinder exo arm. Controlled by a pneumatic valve system mounted across the chest. More of a proof-of-concept prototype than a fully-functioning finished product.

Holding down the red button on the valve block causes one output opening to release a continuous stream of air from the air compressor's tank, while essentially making the second output opening on the valve block "limp", allowing air to flow freely. Releasing the same button does the opposite, where the first output opening goes "limp" and the second output opening releases a stream of air.

In tandem, from one press of a button, these two actions can be manipulated to simultaneously control a dual-action set of two linear actuators operating in opposite directions--one acting as the bicep muscle and the other acting as the tricep muscle.

The mounting system is simply a few nylon belts that wrap the exo contraption onto the exterior of the arm. The bicep-tricep section of the exo arm consists of the pneumatic cylinders and the pneumatic attachments. The forearm section of the exo arm consists of a single steel bracket bar that attaches perpendicularly to the elbow section's three-point joint bar, which in turn attaches perpendicularly to the two pneumatic cylinders in the exo arm's bicep-tricep section.

As seen in the footage above, the exo arm works somewhat. It achieves some degree of induced elbow-movement, but it is clear that to achieve a greater range of motion, linear actuators with a greater displacement have to be utilized in the exo arm. With a greater linear displacement on both cylinders, the elbow will be pushed and retracted to greater angles, better accomplishing the job of the exo arm.

Through the testing of the exo arm, my right arm that wore the exo contraption suffered some bruising. This was likely due to the rough construction of the mounting system--the nylon belts. An improvement would be to build an entire softshell sleeve that better integrates the hardware with my skin.

From a bigger picture, another necessary change would be to reposition the cylinders to sit directly on the bicep and tricep surfaces, making for a more direct-drive solution--besides increasing the displacement of the linear actuators.


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