Long time coming.......................

 It's my age really.

The body parts of the Trundle all got checked against each other yesterday so I took the opportunity to begin documenting the build. I will publish the photos and instructions here as a continuing saga but also put then into a pdf that will be downloadable and printable at a later stage. First then, the cast.

These are the main hardware parts. Main body, template and partially assembled hubs.

The template is for the end plates on the hubs. The continuous rotation servo has to be mounted off centre in order to place the drive shaft in the exact middle of the circular plate. This could have been very complicated if not for AutoCAD and an expert user being available. The template was cut from 6 mm MDF by the laser cutter and, at the same time, a square from around it was also cut to enable the plastic discs to be accurately placed when they were cut.

This is a partly assembled hub unit. The servo has been fitted to show how the offset of the mounting enables the drive shaft to be at the dead centre of the plastic disc. The rim sitting on top of the disc will eventually be chemically welded to the edge of the disc and then they will slip on to the end of the main body tube to form a closed tube with a drive unit at either end. In the picture, the servo has been mounted from the outside of the disc but I am going to try mounting from the inside in order to see how close that brings the wheels to the hub. If they still turn without catching, then that will be my preferred position.

This is how the hubs will fit on the main tube, once they have been chemically welded, they will fit snugly over the end and a small hole will be drilled through the bottom of the hub and tube and a small locking self tapping screw inserted. The wheels will be fitted to each hub and, with the addition of some electronics and a battery, the whole unit will be able to trundle around on the floor. More will be documented when I have the next set of components to hand (They are currently all in the post).

The whole of the body and hub assembly is made from acrylic cut to very precise sizes. The main body tubing is 90 mm outside diameter by 200 mm long, the hub tubes are 100 mm diameter by 20 mm long. Each tube section is 5 mm thick making the hub tube inner exactly the same size as the body outer. To make them fit, all that was needed was to gently sand the inside of the hub until it is a snug fit. The hub discs are 100 mm diameter and the template was cut to 101 mm diameter in order to allow the plastic to sit snugly inside the square outer in order that the laser cutter has a good reference point to start from. In this photo, it is possible to see just how thick the tube is.