Sunday, November 21, 2021

Mojo3 - A Robotic Dog (#11) - Wrapping up the Design

Mojo 3 has been a good learning experience, but for now i will shortly be moving to a 5 bar design and more complete robot concepts.

Here is the latest video:


I really like the small compact design of Mojo3. The prototype fit nicely on my desk. It is easy to assemble and did not take long to print on the 3D Printer.  I intentionally made it smaller than Mojo2 in order to get it to work with small 9g servos.

Also in this design, the weight of the robot was carried from the legs directly to the chassis through a 8mm (skateboard) bearing. This is a significant improvement over Mojo2.

Finally, I took the 'compliance' part of the robot out of the design. These legs are driven strictly by the servos, and gears attached directly to the servos.  This approach has the advantage of providing the most direct torque to the leg components. 

Unfortunately the Knee arrangement with a gear and type of pinon/cam, does not work.  It was easy to calibrate. You could just lift the arching gear teeth and put them in the right locations.  However, once the robot was under load, it was prone to slip.  The video shows this very clearly.

Going Forward

I have started a 5 bar leg design.  This arrangement should be easier to get a full range of motion. The next design will incorporate Inverse Kinematics. I will try to write some meaningful blog entry on that.

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