I figure I would start small and work my up the progression of rovers. This little guy didn’t do a lot but was the first. The idea is to use stepper motors to allow the rover to crawl using remote control. The scale is based on the largest parts being able to be printed on a standard 220x220mm printer bed. The brains will be an Arduino Uno. This model is complete and out at Sojourner Mars Rover by bglasford1 | Download free STL model | Printables.com
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This little rover uses a rocker bogie suspension as do most other rovers. You can see I am using screws to hold many of the parts together instead of gluing. The bottom of the main box is screwed on and numerous small bearings are used.
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The box would just flop over if it wasn’t for a torsion bar mounted to the back of the box. I used threaded rod to adjust the length until the box was level. I also installed the heaviest electronic parts towards the back.
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Instead of driving all six wheels I chose to drive the four corner wheels using small motors that fit into the center hubs. The wheels are knurled. This is achieved by printing the tread flat and bending and gluing them to the wheels. One of the center wheels is encoded so they can visually see how far it has traveled. The steering was very simple for this rover. It either went straight forward/reverse or the four corner wheels were crabbed in and it would rotate in place. For the rotation I used very small stepper motors.
Printing the encoded wheel tread uses a trick I learned by printing someone else’s model. For very thin parts (2 layers thick) you can print different parts without removing the previous print. I had to turn off elephant foot compensation so the next color would fuse with the previous colors. I started by printing the black, then the white and finally the outer knurled tread parts.
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The real rover has all its wires lashed to the outside of the rover body. Some of these wires are real, driving the motors, and some are fake just to bulk up the bundle. I used a wax tape to hold the bundles together and zip ties to attach them to the body.
There are also quite a few non-functional parts such as the motor position sensors that add to the fidelity of the model. The black/gold posts use a trick where you insert a pause into the print allowing you to change the filament color before continuing.
The front is chocked full of cameras and laser position sensors. The connector where the wires go into the box is functional, the motor wires. This is the actual location on the real rover.
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The solar panel was an interesting part. To get it to look as realistic as possible it is a three color print; the base, a copper substrate and then the black solar panel parts. Here is a test print.
I’m very happy with the results.
The solar panel is large enough that it is printed as two pieces and connected together with a part that fits into the top of the body box. You can’t really see the seam from the top.
There are black and white side parts glued to the sides of the solar panel with along with front and rear bumpers, an antenna and colored strips.
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The business end of the rover consists of an Alpha Proton X-Ray Spectrometer that analyzes the composition of rocks. It contains many little parts. The actual spectrometer is held on with threaded rod.
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The electronics consist of an Arduino Uno (a Nano would also probably work), two motor controllers (controls two motors each), and four stepper motor controllers. This picture is of the work in progress. The stepper motor controllers will go on the proto board along with a 9v to 5v converter since I am using a 9v battery. The joystick contains an off the shelf joystick.
The unfortunate part is the stepper motors that rotate the wheels work fine on the bench but are not strong enough to rotate the wheels under load. Given that they are the correct size from a modeling standpoint I decided to leave them and not replace them with larger, non-scale motors. If you wanted to scale this up to 1/1 you could install large enough stepper motors.
