Wednesday, 13 February 2019

Refining My Rocker Bogie Design

Using my newly learned skills in CAD and laser cutting I started to build the rocker arms for my robot. I was pleased with the way my servos fitted into the arm, but concerned that using the servo itself as the only mounting point for the steering leg was not going to be strong enough. That tiny screw attaching the horn to the servo just did not feel like it would handle all the strain put on the robot leg.

My first prototype steering leg assembly

I had only attached one leg to the first part of an arm and already I was needing to redesign. Some browsing of possible bolt styles I might use online led me to shoulder bolts. These have a solid cylindrical section (the shoulder) with a short threaded section on the end. I redesigned my leg and arm ends to attach the leg using a long shoulder bolt as the axis. A nylon spacer provided the required separation of the leg from the arm. Moving the servo along enabled me to attach the servo horn to the leg via a hinged link. The shoulder bolts were also perfect for the other pivots in the rocker bogie arms. So with the entire arm remodelled in my CAD software I was ready to assemble a complete version.

My first attempt to put it all together in laser cut 3mm plywood proved that the design would work, but I could not fit the nuts onto the small bolts which held the servo mounting plates in place. I had not left enough room for the nuts to fit alongside the spacers on the pivot bolts. It was at this point that I discovered the collision detection feature of the CAD software and sure enough it highlighted the problem in my CAD model. Lesson learned I made some more adjustments and was finally able to build and assemble a complete pair of rocker bogie arms.

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