These are footrests I designed for Herman Miller's Mirra version 1 chair legs.
The chair legs on the first version of the Mirra chair -- which is the one I've happily been using for about 10 years now -- have curved legs which aren't comfortable to rest your feet on.
NOTE: Herman Miller recently came out with version 2 of their Mirra chair. One of the changes they made was to flatten the tops of the chair legs. I don't have a v2 Mirra on which to test, but I'm going to guess that these footrests will not be stable on a v2 Mirra.
All the pieces print better with a zero-offset brim at the base. This is especially necessary for the straps, which print vertically.
I would also recommend that you print the straps with 100% infill because otherwise they are liable to break. The base/footrest itself can be printed at around 40% infill and still be rigid and stable.
Designed in Sketchup (but don't recommend)
To design these parts, I used Sketchup, though I would not use Sketchup again. While Sketchup is a great tool in a lot of ways, it has some really annoying drawbacks.
One big problem with Sketchup is that it's very difficult to create completely sealed/solid models suitable for 3D printing. Cura didn't complain about the models I was producing, though there were some weird artifacts. After upgrading to Simplify3D as my slicer, I saw lots of issues with my model meshes. I tried fixing them in Sketchup, but that was a nearly impossible task -- there's no easy way to fix or even find unclosed surfaces and missing egdes. Ultimately, I fixed the meshes by using Netfabb's online mesh repair tool (https://service.netfabb.com/login.php)
Also, when designing in millimeters in Sketchup, the smallest adjustment you can make is 1 millimeter. That's fine if you're designing a large object where 1mm is a reasonable resolution. That limitation is not so great when you need to design in sub-millimeter increments, as was the case with the footrests.
In order to get around this problem, I scaled up my models by 10 times -- meaning 1mm became 10mm in the new model. That allowed me to make changes on the large model that when scaled down again for output would result in fractional millimeter sizes. For example, to create a feature that was supposed to be 2.5mm I made that feature 25mm in the scaled up model.
Once I was done working on the scaled up version of the model, I would make a copy, and scale it down to 10% of its original size, resulting in a correctly-sized model that was ready for export to STL.