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Red Bull soapbox race
dano - 9/5/15 at 01:43 PM

im part of a team that got accepted into the redbull soap box derby this year in london, my job is to build every thing that wont be seen: chassis, wheels, brakes, steering etc,
i dont have very long to build it and have decided to go with suspension, double wishbones on all corners,

heres where i need help from the vast knowledge of locostbuilders,
what spring rate should i go for?
i was thinking i would use shocks from a pit bike or quad, about 280mm eye to eye, maybe 200-250lb
the soapbox will weigh 80kg and have 2 people in it.
i will be using 12-14 inch pit bike wheels.
anybody have any ideas on this or any other advice, ive not built one before.

thanks Danny, (team turtle heads)
we have a twitter and facebook page to follow progress , or vote for us on the red bull website.

Sam_68 - 9/5/15 at 04:23 PM

quote:
Originally posted by dano...I've not built one before.


It shows. You're taking the whole thing far too seriously!





FWIIW, however (and thinking about it in a way that is completely contrary to the spirit of the event!), the problem you have is that Red Bull cleverly incorporate features into their courses that result in diametrically opposed design requirements.

For the most part, you don't want any suspension: dampers essentially take energy and convert it (ultimately; via a lot of squishing of fluids through small orifices) into heat. With a soap box, you don't want anything absorbing energy...

... but Red Bull usually put a severe ramp on their course, which is aimed at destroying or destabilizing cars. The optimum design here would be a soft, long-travel suspension such as you're expect on off-road buggies or Paris-Dakar contenders.

Maybe the, logical, if unsporting, solution would be a suspension that's locked solid for most of the run, but released as you hit the top of the ramp, to cushion your landing?

As an observation, the other issue that seems to bring a lot of cars to grief is oversensitive steering... over-correcting on the steering must increase rolling resistance too, and seems to be a prime source of crashes when competitors go into tank-slappers? Maybe do some testing with much lower-geared steering, to see if it still gives you sufficient control?

Have they given you any technical rules you have to adhere to?

Matt21 - 9/5/15 at 05:07 PM

suspension.... how about MTB rear shocks? a lot of which can be locked out when not needed as well, simply by flicking a little lever

Travel will depend on the pivot points, mtbs tend to have between 100-200mm suspension travel.
You can also dial them to the stiffness you want via air chambers and a high pressure pump.
Rebound can be adjusted, and preload.

http://www.ebay.co.uk/itm/W503-FOX-DHX-3-0-REAR-SHOCK-COIL-MTB-SUSPENSION-245-MM-X-70-MM-/161683162622?pt=LH_DefaultDomain_3&hash=item25a51145fe r />
one of them on each corner?

gremlin1234 - 11/7/15 at 06:35 PM

good luck to
http://www.redbullsoapboxrace.com/uk/en/team/turtle-heads/
for
tomorrow, SUNDAY 12th

coverage on 'dave' from 6pm...

MikeRJ - 11/7/15 at 09:16 PM

I've just been watching 2014 Red Bull soapbox racing on Dave this evening, looks like a lot of fun. There were a couple nasty looking accidents, though everyone seemed to walk away relatively unscathed.

Best of luck for the OP