Now that we have a rover wheel that can drive and steer, it’s time to figure out how all the individual wheels relate to each other. This is the most important part of making a motorized model of Curiosity Mars rover: copying its sophisticated rocker-bogie suspension system. It is critical for appearance because a huge part of Curiosity’s unique look comes from its suspension. It is equally critical for functionality, as the suspension grants Curiosity its ability to traverse rough terrain. It wouldn’t be a model of Curiosity at all without its suspension!
On the flip side, copying Curiosity’s suspension also means taking on some of the trade-offs that made sense for Mars but not for Earth. The first example is that Curiosity’s suspension had to fold up for its journey to Mars, which our rover model would not need to do.
The second example is that the rocker-bogie suspension system is most capable climbing using the bogie, which is why JPL’s Open Source Rover (and ROV-E that proceeded it) had their bogie in the front. Curiosity has its bogie in the back. I asked why Curiosity is more capable going backwards than forwards and the answer was that Curiosity must be able to back out of whatever situation it gets into. If a little rover got stuck here on Earth, we can walk over and pick it up. If Curiosity got stuck on Mars, the nearest tow truck is many millions of miles away.
There are more sacrifices of similar nature, but since the model is intended to be mechanically faithful, we’re going to accept all these downsides of copying the design. So, onward to the internet to find references! While there are many pictures of Curiosity rover, it was unexpectedly difficult to get an isometric three-view drawing. The best I could find was in a JPL presentation MSL Rover Actuator Thermal Design (08-0699.pdf) for Spacecraft Thermal Control Workshop 2008. Page 6 of this slide deck had a good side view of Curiosity with major dimensions labeled.
This diagram became my primary reference for Sawppy the Rover. I copied it into Onshape as an image overlay and drew Sawppy’s component layout on top. This gave us a very high fidelity in the side view, unfortunately no similar top view diagrams were found so I had to guess using less precise images as reference. After some fiddling, I got a reasonable facsimile of Curiosity rover. Compare the rough sketch in Onshape with a JPL official photograph of Curiosity.
Comparison: Curiosity rover at JPL Mars Yard