A Model of Sojourner the first Mars rover

Updated 2012-09-19

This project has been extracted from my old site dated 2004! – My apologies for not completing the write-up.
I will dismantle some of the model and take pictures for this new site when I have the time.

A Little Research

After much searching for a model of Sojourner, the Mars Pathfinder micro-rover, all I ever found was an Hot Wheels blister pack containing a 6mm x 4mm rover, a miniature Lander and the Mars Pathfinder space craft! Although the detail is good for its size, I decided on scratch building a ~1/4 scale detailed model.
I have in mind to add, if possible, front wheel motors and perhaps r/c steering (whilst not compromising detail). No schematics or engineering drawings are available to the public, it is in fact copyrighted! However, pictures and patent drawings (no dimensions just look and feel) are available.
Listed below are some of the Internet resources I have found useful:
Mars Pathfinder
The Mars Microrover

US patent D437,255 for the basic design of the Rover.

The Rocker-Bogie

A simple drawing was made, with all proportions taken from the JPL pictures, after assuming a wheel diameter for my model of 3cm.
The ‘rocker-bogie’ mechanism was challenging, but once thought out, was fairly easy to construct. I at first thought of using aluminium, however since this model would be rather small, aluminium might be overkill. So I decided (don’t laugh) that laminating wooden lollypop sticks together, with PVA glue, would be light yet robust enough and would be easier to work with.
Here are pictures of the rocker-bogie at various stages of construction. Notice I cut the arm at an angle, reverse one piece and glue to create ‘bends’.


The front arm has an extension for the middle wheel and a platform for the steering servo. I have used bearings here from two scrap 31/4 hard drives. They will either be free to move, in which case steering will be via the rear motors, or I may link the front wheels together and use a servo. The rear platforms should also have bearings; however, I may fix them and use stepper motors. The rear ‘C’ shaped wheel struts where cut from a plastic pipe and heat moulded slightly, they may change as I decide which motors to use.
The Body

The body is just a simple box shape with a bit sticking out (I think its a bit like the hull of an old wild west wagon!).
After sanding, I covered the body in gold holographic patterned, self adhesive, book covering (may change this to crumpled gold foil). The top is 10x14cm 1/8″ ply covered in blue patterned holographic, book covering. I need to draw the layout of the solar panels on this surface with the front right square having detail of the “dust abrasion experiment” carried on Sojourner.
The ‘A’ brackets are cut and filed aluminium, small holes where drilled in the brackets, cut dress makers pins where used, together with araldite, to fix to the body.
The shaped strut between the ‘A’ frames will carry detail of the black and white cameras used for ranging and picture taking.

The APX (Alpha Proton X-ray) Spectrometer

This device was used for spectroscopic analysis of rocks and moves in and out from the body of Sojourner.
I cut a plastic whiteboard marker pen and attached a suitable sized rubber grommet. The mounting lugs are moulded from milliput.
The three springs are taken from throw away cigarette lighters as is the aluminium caps. Dress maker pins are fixed in place with milliput. The sensor pack on the rear of the APX body is moulded from balsa wood and painted bronze.
The ‘Y’ frame is constructed of thin metal bar silver soldered and milliput.
The lever construction allows the model to deploy the APX just like the real thing, simply by rotating the left or right wheel assembly. I may servo this in and out from the body of sojourner.

The Motors

I think I have finally found the motors. They came from two old 120Mb floppy disc drives. The Motors are 3cm x 2.5cm, with gearing and a sensor pair. Now how do I feed the rear wheels? The model is too small to mount the motors in the wheel hubs, so they must go in the body, with some sort of flexible drive to the wheels (avoiding the APX as they exit the body).



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