Sojourner Construction 2005 and 2006

Click on a thumbnail sketch to see the full size picture.


The inspiration for Sojourner came from an innocent question at a get-together lunch for nerds. (We get together every Tuesday at some local restaurant.) Kurt asked if Kinetic Sculpture Racers have to have human power. Dave immediately answered "yes". And the conventional wisdom has always been that this is true. I didn't say anything, but it got me thinking.

I reviewed a copy of the KSR rules. (Unfortunately there are few rule sets online. But here is a similar set from Arcata. )

Now granted, the rules says "must be people-powered". But then they go on to make a bunch of exceptions. I figured these exceptions created a legal loophole I could drive a prank thru. In particular, the Corvallis and Arcata rules each specifically allowed solar assist.

JPL Sojourner Recently NASA's Sojourner craft had made a spectacular landing on Mars. I decided to model our craft after Sojourner. And of course name it Sojourner.
[Picture from JPL of NASA's Sojourner]

When I talked with Gary Oliver about this solar powered KSR he was enthusiastic. We agreed that since Sojourner would be designed to run without pilots, it had to be designed to operate without being touched. That meant there would be no transitions and no repairs during the race. The wheels would provide all of the flotation in the river. But those same wheels had to make it thru the mud and sand. A serious challenge.

From 2002 to 2005, he and I were the only ones working on Sojourner. We considered various designs for wheels, mostly working with bike and foam based designs.

From the start we planned to cover the top of Sojourner with solar panels. But we weren't sure how many. The initial vision of Sojourner was small, with a single 185W panel. But then we kept making it bigger. And then I experienced racing on sprint car wheels and decided these were what we wanted. That set the size of Sojourner and required three panels. Sojourner was no longer small. Fortunately Gary has quite a few solar panels, so we didn't have to buy any.


At the same time I struggled with how to make a suitable transmission. I demanded

Sojourner Transmission Prototype

shift mech shift mech shift mech
shift mech shift mech shift mech

It was a nasty set of constraints and I struggled with them for years. And then in 2005 an inspiration came to me while I was waking up. By reversing one rear bike cluster against the other and using two derailers I could get what I wanted.

At this point I brought in the rest of the Rex KSR team. Sojourner became our focus, well one of them anyway.

transmission mockup

Well, it wasn't quite that easy. But after building about 4 prototypes we finally had something that worked most of the time.

This was December 2005. For the first time the transmission is powered by an electric motor. We used the motor and gearbox from a cheap chordless drill.

Gary machining

I then prepared mechanical drawings. After building several more versions of the transmission, this time machined out of aluminum, we were getting close to a workable design.

Here Gary is machining part of the transmission.

transmission on quad

Since we didn't have a Sojourner frame yet, we tested the transmission by mounting it to a quadraped. That is Dave working on it.

We then tested it. It carried me around with some effort. It worked better without me sitting on the quad. I wasn't worried. The gear ratio wasn't right. I figured this was good enough to start building the rest of Sojourner.

This was January of 2006.

transmission on quad
transmission on quad transmission on quad transmission drawing

Once we had a workable transmission I designed the frame and we constructed it. At this point the frame weighed 70 lbs.

That's Edward, who is providing scale for the frame.

frame drawing
Drive mech

Sojourner will use tank style steering. The left three wheels will be ganged. And the right three wheels will be ganged.

The transmissions will combine their power, driving a system of differentials. In this way one transmission will control direction. Two other transmissions will power us forward/backward. Doing it this way should give us more directional control than driving each wheel gang with a transmission.

The drive mech, without transmissions attached, weighs 70 lbs.

drive mech drawing
Drive mech

Dave holds the drive mech with one of the transmissions installed.

Drive mech
Drive mech

Gary works on the electronics of Sojourner. It is June of 2006. We have three of the six wheels on.

Drive mech Gary and Dave are driving across my driveway on car batteries.

Three days before the Da Vinci Days race. It's not finished, but its good enough for a picture. Dave and I pose with it.

Icon I created an icon for Sojourner. It combines the Linux penguin, with the Da Vinci person in a circle, and Martian features.

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Copyright 2006 C. Allen Brown

Last modified 11 Dec 2006