Soapbox or gravity racer

This was one of my quicker projects – I found out about the race, due to start at 1000 on 1st Jan, with only a month to go. And to complicate matters, that month included xmas.

The chassis was fully modelled in CAD (Fusion360) to check that the intended 25mm square, 2mm thick wall, box section aluminium was going to be sufficiently strong and stiff. Aluminium may seem a strange choice for a sport where extra weight is usually an advantage but there were two conflicting briefs – when not being used for the race, it was to be used by kids and so needed to be light enough for them to push about. I took the view that we could always add weight for the race.

The main chassis coming together (1745 on 23 Dec):

Part of the double wishbone front suspension, showing the steel rod holding everything (reasonably) square while I tacked it together (1400 on 28 Dec):

Getting creative – I didn’t have any suitable channel, so I made some

Coming together (1715 on 28 Dec):

Then I ran out of gas… thankfully a good friend bailed me out and I continued, here are the axles and part of the steering (0945 on 31 Dec, feeling the pressure now!):

And, at last, it’s beginning to look like a runner but still no steering and, more importantly, no brakes! Taken at 2315 on 31 Dec, in a brief escape from a New Year party:

Made it! The first run on New Year’s Day, with 3 adults on board:

It’s a dangerous sport, you know!

Aerodynamics proved lacking, so we improvised with cardboard. The smile on the little girl’s face says it all, it got up to about 28mph and handled remarkable well. Stopping 200kg from 28mph, however, is a different matter all together!