After I decided to start with a small rover variant, I need to find actuators for a little rover. Since I want my design to be affordable and parts to be accessible worldwide, the most obvious candidates are the micro servos bundled in endless Arduino & STEM kits and used in many other hobbyist robot projects. There are two major categories: The more affordable all-plastic version is commonly sold under the "SG90"(*) name, usually with a blue plastic enclosure. Four of these can be found performing steering duty on the smaller Bricolabs rover. The slightly more expensive variant have metal gears and sold under the "MG90S"(*) name, usually with a brown plastic enclosure. Examples were put to work on Ryan Kinnett's Micro Rover.

I'm sure "SG90" and "MG90S" started as model names from a specific servo company, but nowadays they have become generic names. I had thought they were all copies of a common original, but that was wrong. I bought a few batches from different Amazon vendors for research and took them apart. It is quite obvious there are multiple similar but not identical designs being manufactured and sold. In one instance, I bought same item number from the same Amazon vendor again (*) and received different units!

That experience taught me vendors treat these as fungible commodities and I need to account for that fact. Unfortunately, as they are similar but not identical, their variation puts an additional layer of complexity to my rover design challenge. It's one thing to know dimensional tolerances will vary from one manufacturer to another, but here I don't even know what range I can reasonably expect for those dimensions. Buying servos from different vendors resulted in a few data points, but I won't know where those sample points lie on the global spectrum of sizes. It's going to get a little murky!

But on the upside, it is great that we have such an ecosystem of micro servo suppliers, lowering cost and making them available to more people. Ultimately aligning with my goals for the small rover project. So what I need to do is buckle down and study what I will work with.

(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.