Ant-Weight Robots

"Robot Of No Name Yet"

Finally got round to designing a new chassis from the ground up. This will be based on the Sanyo-type gear motors and lithium polymer batteries that have become essential components of top-flight antweights during 2006/7.

Everything was modelled in 3D-CAD using the free version of Alibre. When I figured out how to make each part the correct weight, the software made it very clear that the design was grossly overweight. Many holes were added but weight was still a problem. This and other calls on my time meant that the re-design was shelved for a while, proceeeding very slowly and sporadically.

At long last RONNY Mk6 began to take shape. Using HDPE for the chassis instead of polycarbonate made quite a difference to the weight. The planned Kevlar shell was replaced by 1mm HDPE.

I discovered that HDPE could be welded using a soldering iron (and plenty of ventilation!). This gave me the idea of making RONNY's shell out of a single piece of HDPE, folded and welded to give a tough shell with no exposed joints. Welding also solved the problem of how to join the chassis pieces. The original idea had been to use polycarbonate, drilled and tapped and held together with M2 screws. HDPE does not tap very well, but in the event welding provides a much stronger joint.

All of the parts were hand cut; the chassis turned out very well, looking just like the 3D model! Over 350 3mm holes were drilled to save weight. The shell was worked out by hand and some prototypes made from paper to check the fit before cutting HDPE. One limitation of the free version of Alibre is that it doesn't support sheet metal design :( The 1mm HDPE was quite easy to cut and fold, following the paper template.

After some experimenting with welding techniques, strong, reliable welds were produced by welding large overlapping panels on the inside of the shell. The exposed edges on the outside were also welded, which gave a stronger result and a slightly more business-like look :)

The aluminium flipper is wider than on RONNY Mk4 and Mk5, and has a better RONNY logo, using a bigger grid of smaller (1mm) holes. The rest of the flipper features nearly 150 3mm holes for weight saving. The flipper is driven by the same HS81MG servo as used in RONNY Mk4 and Mk5.