Rover Wheel Tricycle Tests Steering Mechanism

If you’re reading these Sawppy construction blog posts in sequence, you should have predicted what was coming. After the first test using a 180mm wheel on a stick, we had two 120mm wheels on a stick. And now…

Tricycle test rig

Three wheels on a stick.

The pair of wheels side-by-side have no motors driving them, and they share a 8mm steel shaft solid axle. They are not the focus here, the focus is on the third wheel here to verify our steering mechanism is going to work.

Unlike the previous servo wheel drive experiment, we’re fairly confident in this servo’s ability to steer. This serial bus servo is a close cousin of remote control hobby servos, which are used extensively for steering in remote control cars and boats as well as RC aircraft control surfaces. This is what it was designed for, it’s a very powerful servo for its size, it was able to steer without problems even with some weight placed on the aluminum extrusion beam to simulation rover mass. In fact this test rig worked better with some weight on the front as that is the only driven wheel.

The focus of this test was more about how the steering knuckle is mounted to the end of the aluminum extrusion beam, how it tolerates load from rover chassis, how the servo is coupled to the 8mm steel steering shaft, and other mechanical details of that nature. Like some earlier component tests, this test was mainly just to make sure nothing silly was overlooked in the digital design phase.

Functionally, this mechanism worked perfectly well.  The two- and three- wheel test rigs give us confidence a six-wheel rover with servo drive and steering will work.

The question this test rig raised was not about functionality, it was about design and construction. There’s room for improvement with common shared components, an idea to be explored in the next post. (Apologies if you are disappointed the next post is not about “four wheels on a stick.”)

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