One of the main objectives of SGVHAK rover build is to beta-test the instructions before it is opened to the world. Much of this involved feedback along the lines of “this part of the instruction is not clear” or “this part is the wrong part.” But we also occasionally send in feedback of “here’s a problem we see, and here’s the solution we came up with.” An example is the how the corner wheels bear their weight.
In JPL’s original build, the entire weight of the corner wheel comes through the shaft used to steer the corner wheel (highlighted in blue) pushing into the steering gear motor. Motors are typically designed to handle rotational stress and not force along the rotation axis pushing into the motor.
In the short-term, things will push against each other until the force makes its way to the gear motor outer casing, which will then push against the motor mount and eventually make its way back down to a structural member. But this long roundabout way will cause undue wear on the gearbox and certainly reduce its life.
So we offered a solution: Add a small piece of metal to take the weight off the steering shaft, transmitting it directly from the wheel assembly to the bearing block that looks like it should be strong enough to do the job. With this addition, the gear motor no longer has to worry about supporting the weight, it can focus on its job: steering the wheel.
We think this is a worthwhile addition to our rover. Unfortunately this spacer was cut on a lathe, which is not a piece of equipment most people have access to. If the authors agree this is a problem, and agree with the general idea of our solution, we’ll need to think up a variant of this fix that would be easier to make.