Last edited   14 December 2004

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Previous Projects:
Scratch built K-9,  Robby the Robot (Polar lights Kit).
Neat little Azimo Card model  

Current: Cybot and Sojourner

Building Sojourner  the Mars Micro-Rover

After much searching for a model of the Mars Pathfinder microrover, Sojourner, all I ever found was an Hot Wheels blister pack containing; a 6mm x 4mm Sojourner, 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. Although, its the detail I'm after; 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 the Internet resources I have used.

Sojourners Family tree (with pictures) http://robotics.jpl.nasa.gov/infrastructure/genealogy/homepage.html
Pathfinder information, Images and Communications info http://mpfwww.jpl.nasa.gov/rovercom/rovcom.html
Description and pictures http://www.jsc.nasa.gov/er/seh/marsrove.html 
US patent D437,255 for ornamental design of the Rover. (need to download a tiff viewer)

The Build

A simple drawing was produced, with all proportions taken from 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 take that back the bogie eventually evolved, but was difficult). I at first thought of using aluminum, however since this model would be rather small, aluminum might be overkill, and anyway, after reading of another rover project 'Gross Hund' on the internet, I decided ( don't laugh) that laminating lollypop sticks together, with PVA glue, would give enough strength and would be easier to work with.
Here are pictures of the Bogie at various stages of construction. Notice I cut the arm at an angle, reverse one piece and glue to create 'bends'.

  
On the original, the centre arm is nearly straight, but to align the end servo platforms, I  placed a 'bend'. The 'rocker' linkage and 'ride height' struts on the centre arm were added later (as is most things on a scratch build). A Threaded bolt is used for the lower pivot, and an aluminum tube 'bush' at the top. I have drilling smaller holes in the arms, for authenticity, without weakening them to much, and filled the cracks, crevices and horrendous breaks with Milliput. 

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 have decided to fix them and use stepper  motors. The rear 'C' shaped wheel struts where cut from a plastic pipe and heat molded slightly, they will change slightly as I decide which stepper motors to use.  (Stepper motors because they are available from floppy drives, small, and will not need gearing (although I foresee a problem with the nature of the bearings within such small steppers!)). 

(Update - see Motors below)

The main pivot point goes right through the body and pivots the rear and middle arms (on Sojourner this is called the "Jeff tube"). I used 7/32" aluminum tubing from the local model shop. I also decided at this point to use a slightly larger tube as bush's for the arms. (The large size of these tubes proved to be a mistake as the holes in the arms proved difficult to drill without splitting the arms, so much so that at one point I had to mold the complete end from Milliput!), remember I want this to be a functional model.

The Body

The body is just a simple box shape with a bit sticking out (I think its a bit like the hull of a old wild west wagon!).
After sanding, I covered the body in gold holographic patterned, self adhesive, book covering:

 
The top is 10x14cm 1/8" ply covered in blue patterned  holographic, book covering. I need to draw the layout of the solar panels. The front right square will have detail of the "dust abrasion experiment" carried on Sojourner.
The 'A' brackets are cut and filed aluminum, 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 b/w 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.

The body is a whiteboard marker pen with a rubber grommet , suitably trimmed. The mounting lugs are molded 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 body is molded from balsa wood and painted 'bronze'. 
The 'Y' frame is constructed of thin metal bar silver soldered and milliput.
The lever construction allow the model to deploy the APX just like the real thing, simply by rotating the left or right wheel assembly. The white outer cases will be fixed to sojourner 

The Motors

I think I have finally found the motors. They came from two old 120Mb floppy disc drives.
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.