Here's the build-up of the chassis after initial testing. It will need modification again when I add the grab, but it'll do just fine like this for testing the light-sensor positioning algorithm so that I can check it's sufficiently accurate to be handle the ball-sorting.

First, assemble two chassis sides. Note that after my first piece of butchery they're not symmetrical end for end. The grey plate joins the three upper bars and holds the side guards in place.

Now join them with an 8x2 plate (it's a spacer and will probably disappear in the final design) and lock the RCX in place using short connectors into the RCX and long ones into the outer top bars. To avoid a potential confusion when the rest of the instruction don't seem to work, note the Ria is thin at each end and fatter in the middle.

"Front" and "rear" wheel assemblies are identical except for the axle length. Two small wheels, two bushes to hold them in place, and two short bars to mount them. The "rear" fits behind the spacer, the axle running in the centre hole of a short bar.

The "front" one mounts in the front hole of a longer bar, to make room for the idler axle which runs in the same bar. The long bush allows the large gearwheel to clear the RCX.

To mesh with the large gear, the drive motor 4x1 plates mount it one hole proud of the edge on a small raft made of two short bars and two 6x2 plates. And there we go, Ria is ready to run the basic forward and backward software. Now put all the surplus pieces back into the baggies and check it out.