Sunday, December 1, 2019

Mojo3 - A Compliant Quadruped Robot Dog (#5) - First Servo Leg Tests

Mojo 3 - First Tests!

It is always exciting to start the testing in an iterative design/build phase.  I have made a few changes to the leg and SEA design. It was really important to allow for the servo to pull the actuator with as little friction as possible. two additional prints later, I have a working servo actuator.  However, the weak 9 gram servos will continue to be an issue, as well as how much 'hooke' to put into the spring. 

First:  the new movie!

first test - on the TNERA YouTube Channel

Design status - from the movie, you can see that the servo is functioning and pulling the actuator up.  This motion is critical to lifting/contracting the leg as the leg will be moving forward.  It must have enough clearance to avoid stumbling and the return swing. I would like to have 1cm or more of clearance.  However, from the video you can see that the design is only giving 5-6mm of contraction.  It it clear that the servo will need to have some more pull, or that the spring constant (see Hooke's Law) is weaker.

There will have to be a balance between two competing factors:

1) the servo must be strong enough to contract the SEA
2) the spring must be strong enough to absorb some of the weight of the robot

the competition in physics and mechanics:  a larger servo can pull the spring, but will create additional weight that will further contract the spring. To help/confuse this engineering issue is that the 'foot' spring will also be absorbing the weight of the robot. This may result in the SEA contracting - but not resulting in a lift due to the 'release' of the foot spring.

Tune in to see how we can resolve these design issues.  At this point in time, I am not beyond creating a completely new iteration on the SEA perhaps adding a new linkage.

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