Wednesday, June 6, 2018

Mojo - A Compliant Quadruped Robot (#2) Springs!

For my first set of designs of this walking robot.  I need to design out the compliant leg.  The active part of this compliant robot leg is called a Series-Elastic Actuator.  In layman's terms, I am using springs!  The springs provide the elastic capability for some important functions.  Primarily, it can conserve the energy of actuation - meaning it can store and reuse this force.  It also provides some stabilization when the robot when it bounces.  The trick in the engineering of such a leg will be in determining the right size and strength of the springs.  For this project, my plan is to reuse springs that were harvested from old printers.

here is my first design:

Mojo Leg Mark2

The leg will use two springs, one provide compression (squeezing), the other tension (pulling).  The compression spring appears to be the primary elastic source for walking.  The tension spring seems to just provide stability.

The Tension spring is the simple construction at the back of the "Tarsus".  It is just a small spring and a paperclip in the this prototype.  This was quick to assemble!

The Compression spring has more thought to consider.  The linkage must allow for compression (squeezing), but still maintain the structure of the leg to hold it up.  In this iteration, I printed two "sheaths" that are hollow tubes with the screw holes on the ends. The sheaths are holding a wooden chopstick section and a compression spring.  The length of the chopstick, and the dimension of the leg holds the construction together.  This seems to be sufficent for this test, but will need to be more robust in the next iteration.  And, as yo might notice, the top sheath broke under pressure of the initial tests.

Sheath mk1

For the next iteration:
  • strengthen the compression linkage
  • shorten the leg for testing purposes
  • add mounting holes for servo horn
  • rework the tension spring, move to other side of leg
  • create a more useful paw
  • much much much better linkage connectors!

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