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I've been collecting ideas for building a Mars Rover. This can easily cost a few thousand dollars so I'm not quite sure I'm willing to fund such a venture, but it's fun to dream (and plan).

Apparently lots of people have been inspired by the NASA Mars rovers, as there's lots of projects out on the Web. NASA has even created an "open source" robot project, with downloadable plans.

Design Notes#

Open Source Rover Patch (click to enlarge)

So far I've been scanning the cool robot parts at ServoCity for ideas for the steering mechanism and rocker arms. The scale and weight of the overall robot help decide the size/power of the motors and servos. It's a bit of a balancing act. I also want to, unlike most of the "civilian" designs, somehow tuck my motors inside the wheels or otherwise not have them hanging down near the ground as many/most of the rovers I've seen seem to do.

There's a huge impact on ground clearance if your motors are down there banging into rocks and such. The difficulty seems to be locating some suitably deep wheels. I can't imagine simply 3D printing them, as plastic wheels wouldn't last very long on rocks or concrete. I want a robot that can actually roam outdoors. Also, unless the motors have durable ball bearings protecting the shafts, there needs to be some significant insulation between the motor shaft and the shocks that the wheels will create as they go over rough surfaces. Unless the robot is only going to run indoors, and then what's the point?!

Rocker-Bogie vs. Triple-Rocker Design#

The ExoMars (and ExoMy) robot uses a simpler "Triple-Rocker" design.

Someone-Else's Specifications#

I'm going to (initially) steal the specs from the JPL Open Source Rover Project, as a point of reference. Their robot is a bit larger than I'm planning and has an estimated cost of around US$2500, and that's certainly at the upper limit of my budget. But it's a start.

Initial Specifications#

The basic idea is this: six wheels, all ~25mm 180-200rpm motors with encoders. The two center wheels are driven but not steerable. The four corner wheels are mounted on ServoBlocks so they can be steered. Rather than a Rocker-Bogie, we opt for the simpler Triple-Rocker. This requires two identical and one almost-the-same rocker arms, with dual ball bearing mounts.

There will be three pairs of motors, three dual motor controllers, and three batteries. Basically three separate systems, with two I2C isolators communicating between. The front and back motor/controller pairs (with the steering) are effectively identical. The central system won't have the steering, so that's where we'll mount the controller (likely a Raspberry Pi) and the rest of the sensors.

Links#

• JPL Open Source Rover Project on github
• NASA Open Source Rover
• Raspberry Pi Zero or Microbit M.A.R.S. Rover robot £120, a brief review of 4Tronix M.A.R.S. Rover Robot for Microbit or Pi Zero (there are variants for the Raspberry Pi Zero or Micro:Bit)
• Yuri 3 rover (The MagPi #82), describes the Yuri 3 mini Mars rover, which was designed by Airbus engineer John Chinner
• Build your own NASA Curiosity rover from the Raspberry Pi Blog
• Students Can Now Build Their Own Rover Model (JPL)
• NASA, Raspberry Pi and a mini rover, built by NASA scientist Dr. Jamie Molaro with an estimated cost of US$5333
• Robot Garden’s Mars Rover. a 3D-printed robot (YouTube video also available)

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