Sunday, October 27, 2019

Mojo3 - A Compliant Quadruped Robot Dog (#3) - Printing/Iterating Design

The first draft of the leg is starting to take shape. Each of the initial parts have been printed.  I have assembled them on paper, CAD (OpenSCAD), and now in 3D printed PLA.  It is interesting to see how well they align to the initial paper sketch.

Mojo3 - printed leg covering original sketch

Side by side, the first printed parts are next to the original conception. The upper right piece is the 'leg'.  The leg has a bearing in the top to transfer the weight of the robot. there is a 'control arm' that will connect to the servo. At the base are two connectors, that allow the 'arm' to move up and down. I call the connectors 'trap' - short for trapezoid, the shape created from the four fastened points. Finally, the 'arm' is made of the base, connected to the trap, and the fore-arm, which will touch the ground.  The fore-arm can slide on arm-base. There is a spring in the fore-arm that will absorb some of the motion of the leg and ensure good ground contact.

Mojo3 - Leg first draft print, next to original sketch.
What is missing?  the foot and claw.  Every Totally Not Evil Robot needs to have a claw, right?  ;)

Thinking about the next step of the development, there will need to be a 'Serial Elastic Actuator' (SEA).  This SEA is basically a spring, that provides a 'compliance' with the ground, but allow for the arm to be pulled up, allowing for the leg to lift and be moved forward.  (Here is a link to my previous designs SEA v5.) 

From the design of the fore-arm, above, it occurred to me that there may be a simpler design option for the SEA.  In essence, the fore-arm is a SEA.  The next phase of design will have a new SEA that is attached from the arm-base to the hip of the leg.  below you can see this new component in red on the CAD design. Let us see how this works.

Mojo3 - potential new style of SEA
Next steps are to print and test it out...

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