View Full Version : soapbox derby in hinckley.
right, you good people, and also the blue fonters...
i am considering in putting an entry in for the hinckley soapbox derby.
the course is 180m long, with a chicane, and on a gradient of 1 in 15. and straight down the shopping street...
there are adult & kid classes, so me & my eldest daughter can both run.
the rules are simple, 2300mm x 1118mm max dimension, fixed seat, no sharp edges, 4 wheels, and a workable brake.
i need the techy engineer/maths type to tell me what is the best way of doing this.. i'm thinking large vs small wheels, heavy vs. light, obviously it needs to be well built to pass scrutineering.. would aero even need bothering with??
i have been thinking of borrowing a wheelie bin for comedy reasons, but a chance of a win would also be great..
Won't your wheelie bin be too loud? lol
Soapbox Derby sounds fun, but also like Hinkley is the land that time forgot! lol
MattBrown
27-05-11, 11:05 PM
Get onto bentley.
I'm being serious, we looked into and designed a kart for the "greenpower" championships, aero plays a massive factor.
Also, there's an optimum ratio of "angle x weight x drag = speed" sorta thing.
I'd imagine being a 1/15 it won't get up that much speed, so I'd be looking into bmx wheels. With racing tyres at 80psi for less drag.
Castor, camber, tow, and especially Ackerman angles play a huge part in drag, and I'd be going for a tubular aluminium chassis.
i need the techy engineer/maths type to tell me what is the best way of doing this..
what a shame he's banned haha lol
Childrens bicycle wheels are your friend.
what a shame he's banned haha lol
who?
Get two old mtb's and chop/weld frames.
hers a clue john....
http://t2.gstatic.com/images?q=tbn:ANd9GcSDFtPP2hFAipju-98QfSLUZkfDw5q6CinpH4VoKdyst1oXaeR9zA
http://t1.gstatic.com/images?q=tbn:ANd9GcSBJTF9Mj_jsNaaRrjsG2_XrbjKWtO2_ WN-bPQzc-ikRGt7_nrLOw
lol
lol mk9999999 banned? wooot?
Jacked a for sale thread when Pudley was on the rag. lol
and bimmer156?
rule 18 at nats iirc
and bimmer156?
Long sideways story involving some gravel & a broom....
rule 18 at nats iirc
oh dear! :tard:
Mark only got two days, calm down lol
Mike, get a pallet, bolt on four pram wheels and screw on a milk crate, tie a bit of string to a brick which you can chuck out as an anchor, and bobs your uncle.
If you start looking at camber and castor I will punch you in the face at Billing lol
brownbear
28-05-11, 01:31 AM
Don't you need to get off it before you race it?
Mark only got two days, calm down lol
Mike, get a pallet, bolt on four pram wheels and screw on a milk crate, tie a bit of string to a brick which you can chuck out as an anchor, and bobs your uncle.
If you start looking at camber and castor I will punch you in the face at Billing lol
there is one chicane...
i'm just interested in should it be heavy or light..etc...
the last one i made was in 1979 and used a fence stake as a chassis, a cupboard door as a seat & pram wheels..
Light, with big skinny wheels and aero.
I'd link you but I'm on the iPad, and it's a pain. But search "lotus soapbox". Admittedly, it cost them 50k iirc, but it's probably the worlds best racer. Take a look you might get a few ideas.
Light, with big skinny wheels and aero.
I'd link you but I'm on the iPad, and it's a pain. But search "lotus soapbox". Admittedly, it cost them 50k iirc, but it's probably the worlds best racer. Take a look you might get a few ideas.
There you go!
http://www.deferredprocrastination.co.uk/blog/wp-content/uploads/2010/08/2006-Lotus-Type-119C-Soapbox-FA-1024x768.jpg
Gordon Murray did an article about him and his mates building soapbox racers for under £100 in Evo magazine. I'll try and dig the article out for you mate.
the goodwood hill is a tad longer.......
skateboard wheels are your best bet if its smooth...think of the speeds longboards get upto
and how will i have a working brake????
some sort of rubbery clamp on the axle? or possibly an air brake. :d
MK1_Ben
28-05-11, 08:17 PM
and how will i have a working brake????
Your palms are there for a reason? seems to stop Skateboarders well
Given its a short run with a low angle, you wont get much speed up and imho Aero is a waste of time to care about.
I was stood next to that lotus soapbox car the other day, very cool but I think the wheels were the key to it.... very very very narrow high pressure tyres (like road racer bikes, but smaller lol).
Your biggest enemy is going to be rolling drag.... so rock hard tyres, excellent bearings and a touch of weight to help with momentum.
i'm considering doing a spot of sneaky testing over the bank holiday. as in standing start against the clock in bike type things..
i am planning a cardboard nova shape shell, and i have a couple of dead kids mountain bikes about...
MK1_Ben
28-05-11, 09:49 PM
and i have a couple of dead kids mountain bikes about...
You're using bikes that used to belong to dead children?
pedant..... the kids are still alive, but the bikes are a bit dead...............
Eliminating any kind of losses should be your main target, rolling resistance in bearings will be your main one so I'd look at a large lightweight wheel, bike fits rather well here and a good quality bike hub oiled with a light oil rather than greased should work well (light oil will be lower resistance where grease is normally used for durability) a bike wheel reduces the resistance by having a lower rotational velocity for the same normal velocity, so less friction effectively.
Run it on bald/racing tyres at whatever PSI you can get them in before they burst to lower the tyre footprint and hence it's friction.
Aero might be less effective at 15mph for downforce but it's a huge % of the drag when your only being powered by gravity, the whole aero only 'works' above 90 thing is bull, you can feel it on your face at 15-20 on a bike, so it will be slowing you down at 15-20 on a wheelie bin down hinckley high street.
Contrary to what Stu is saying I would go for lighter weight also, your base acceleration is going to be the same no matter the weight (as it's due to gravity alone) then minus any losses, although momentum will reduce your losses effects on your speed, it will also add to your losses, so unless there's a gale in the wrong direction I'd go with lighter.
Also, I was expecting to be Lee if anyone that banned for me that one, for about 12 years, with the reason "for being a pisstaking barsteward" I thought it'd be genuinely quite hilarious if Lee got a PM saying "Hi, I'm here to sell you an N97, MK999 sent me!" tbh lol
blue_peg_16v
28-05-11, 11:06 PM
YouTube gadgetshow soapbox they race an Elise with there awsome
Welsh Dan
28-05-11, 11:18 PM
I'd probably use the wheels/hubs/bearings from a few road/racing pushbikes, depending on what you find at the scrappers. I think I've got a go-kart seat/chassis that you'd be welcome to - if you're near Wrexham any time soon let me know and I'll root them out if you want them? It might be worth taking the steering mechanism off the kart too...
just remember, smaller wheels means faster acceleration...
just remember, smaller wheels means faster acceleration...
and higher friction which means lower acceleration, it's not being powered so the gearing from lower wheels does not come into effect, check out the size of the wheels on the lotus one...
and higher friction which means lower acceleration, it's not being powered so the gearing from lower wheels does not come into effect, check out the size of the wheels on the lotus one...
The lotus one has 'only' 12-14" rims ;)
and higher friction which means lower acceleration, it's not being powered so the gearing from lower wheels does not come into effect, check out the size of the wheels on the lotus one...
last soapbox race thing i watched...the ones with skateboard wheels were annihilating everything...turns out the team was on scrapheap challenge previously lol
last soapbox race thing i watched...the ones with skateboard wheels were annihilating everything...turns out the team was on scrapheap challenge previously lol
That's because a lot of technology goes into skateboard bearings, as Stu said the lotus machine has 12-14" wheels, which are fairly large in comparison to the actual erm, kart-thing.
look folks, unless someone can actually tell me how to make a workable brake on a skate wheel, its out of the question to run them.
old bike brake pad with a lever type system to jam them onto the face of the wheels. Doesn't have to be complicated, just 'workable'
old bike brake pad with a lever type system to jam them onto the face of the wheels. Doesn't have to be complicated, just 'workable'
yep like a pedal go kart,wouldnt be hard to graft that.
sounds like i need to test it. i have a few spare skate boards too.. now i assume weight distribution is also important, as it needs to be a proper seat... i have an idea about leaning into corners too, but it might be too much to make properly..
look folks, unless someone can actually tell me how to make a workable brake on a skate wheel, its out of the question to run them.
http://img.groundspeak.com/waymarking/df9c252f-7392-4f92-8e8c-cb844b2210c9.jpg
Do you have to have brakes?
yes. its one of the rules, working & testable brakes.
http://www.freepatentsonline.com/6820881-0-display.jpg
mk1nova_rich
29-05-11, 08:11 PM
Note that cheapo skateboard bearings are truly ****e. Buy some Abec 7s and you will go like fook
MK1_Ben
29-05-11, 08:27 PM
Note that cheapo skateboard bearings are truly ****e. Buy some Abec 7s and you will go like fook
Brings up the cost alot though buying good spec bearings. A decent set of abec 7/9s for 4 wheels will easily cost you 30 squids... You can get cheapy ones for less than that, but may aswell run standard ones...
I had one of those long narrow boards with the orange 'big' wheels with crappy bearings that were washed in white spirit and it was deadly fast lol
considering the total mileage will be less than 1, i think i can manage with decent grease & not over tightening them.. i'm more interested in how to make it steer.. i will also try some proper testing before the event to see if big wheels is better than little wheels, and then ballast it.
considering the total mileage will be less than 1, i think i can manage with decent grease & not over tightening them.. i'm more interested in how to make it steer.. i will also try some proper testing before the event to see if big wheels is better than little wheels, and then ballast it.
Considering the total mileage is less than 1, I would use thin oil and reap the benefits over a more durable grease. RC cars use an oil thats thinner than water, and get stripped and rebuilt after each event, and it does make a hell of a difference.
MK1_Ben
29-05-11, 09:10 PM
considering the total mileage will be less than 1, i think i can manage with decent grease & not over tightening them.. i'm more interested in how to make it steer.. i will also try some proper testing before the event to see if big wheels is better than little wheels, and then ballast it.
Depending on how tight the chicane is, you could lean to turn like a skateboard, making a front axle that functions the same as the trucks on a skateboard will be easy enough. Remember, with the trucks loose skateboards are highly maneuverable.
ok, but place me on 4 skateboard wheels on block paving & see where light oil ends up.... as in the contact area & brake surface...
i'm still thinking of using 20" bike wheels in preference to skate ones.
ok, but place me on 4 skateboard wheels on block paving & see where light oil ends up.... as in the contact area & brake surface...
i'm still thinking of using 20" bike wheels in preference to skate ones.
Fantastic, even less rolling friction and the brakes only need to be workable not effective. Win win.
workable & testable... if they don't stop me, i'll end up both disqualified & in kfc.
Well it's also quite easy to use light oil as a light oil, rather than pumping a few 100ml in like it's grease, to be quite honest lol
with my surname & the fact that i worked in a kfc when i was 17, & it was still called kentucky fried chicken, the irony would outweigh the phail
trackdaynova
30-05-11, 11:55 AM
i'll see you on the cobbles then ;)
i'm hoping the finish line is before them.......
trackdaynova
31-05-11, 07:41 PM
lol
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