Semi-autonomous 4×4 rover Mark I

In January 2017 (the spring before I started at Missouri S&T), I decided that I wanted to take a stab at designing and building a simple semi-autonomous rover. It didn’t have to be anything fancy, I just wanted to try it to see if I could do it. Since I didn’t really have a mission for the rover, or specific task that I wanted it to perform, I spent some time and thought up a core set of functionality constraints and made an “operational wishlist” of other stuff that would be cool to have but not truly necessary.

When I started, I made a list of all the stuff I wanted the rover to do.

As a starting point, I chose to design the body of the rover first. The frame would be the thing that everything else would attach to, so it made sense to me to design it first. Once I had a serviceable rover body, I would worry about fitting everything that I needed into that volume.

To simplify the process a bit, I more fully defined the requirements and constraints for the frame. By doing this, I aimed to gain a clearer picture of the solution space. To make it manageable, I also broke the frame down into several sub-sections that I would consider individually: The main section, The access hatch(es), and the leg struts.

To join the sheets of acrylic, I wanted something that would be durable enough for structural purposes but easily waterproofed later. I chose to bolt my acrylic sheets to aluminum corner brackets because I couldn’t make a clean enough cut in the acrylic using a hacksaw to make a waterproof/structural glue joint.

The access hatches worked well enough, but the wingnuts turned out to be a major pain to use. Each hatch had at least two wingnuts, and I didn’t cut down the bolts they were threaded to. That meant that each time I wanted to get into the rover when it was sealed, I had to unscrew at least two wingnuts with about 3/4″ of 1/4″-20 bolt each.

Retrospectively, I find it very interesting how I approached this type of problem without previously learning concepts of Statics and/or Mechanics of Materials.

The main reason I wanted to avoid rounded tubing was that I knew round things were stronger than other geometric shapes (aside from triangles), and I was worried that I wouldn’t be able to bend a round tube to the correct shape.

A lot of the math I do here is motivated by my minuscule budget. I could have chosen to make the legs an arbitrary length, but I wanted to make sure they’d work before I spent money on (relatively) expensive aluminum extrusions.

For the wheels, I’d already chosen to use some 6″-diameter wheels that I’d found on a hobbyist robotics website. They looked similar to the ones that my team (Area 42 Robotics) had used in our regional competition (2015? 2016?) where we won 6th place.

Since the rover was supposed to be rain-resistant, I first tried very hard to find true “waterproof” brushed DC motors. When I realized that I’d have a lot of difficulty finding motors like that, I decided to use normal gearmotors and put some waterproofing casement over them after-the-fact.

After this, I continued to work on the design but forgot to document it. I did build the rover, but I never implemented much control after the first few tests. I had elected to use tank-type steering for turning (opposite wheels turn in opposite directions), and the rover turned out to be too long for this to work effectively. As a result, it would follow a circle about ten feet in diameter when turning. This was simply too constraining, and it wasn’t an easy fix, so I abandoned version one and began considering a mark II version.