Soapbox Racer
#1
Soapbox Racer
Some of us in my work are building a soapbox (gravity) racer over the next two weeks, does anyone here have any experience or insider information?
I have designed a basic chassis using some 0.9mm stainless steel folded up, with some light weight 20mm tubing for reinforcement. I was aiming for it to be as light as possible - although some in the team say it should be heavy as possible. Anyone want to back up or counter my argument? It is working out at estimated 40kg currently which I would like to improve on, but there is a maximum weight restriction of 120kg.
I am thinking increasing weight will slow acceleration, as there is more mass to move - acceleration is constant so a heavier object will not fall any quicker, but accelerate slower in the case of rolling down a hill. Also friction will rise, as F = uR hence more rolling friction. Only benefit I can see making it heavier would be to overcome drag at higher speeds?
What about aerodynamics though? Do they really make any difference at 30mph? I had thought about leaving the car bare without any aero, as the projected frontal area is less than what it would be if you gave it some nice aero panelling. Or would a nice slippery shape pay off?
Some pics so far below. Suggestions criticism and general mocking all welcome.
I have designed a basic chassis using some 0.9mm stainless steel folded up, with some light weight 20mm tubing for reinforcement. I was aiming for it to be as light as possible - although some in the team say it should be heavy as possible. Anyone want to back up or counter my argument? It is working out at estimated 40kg currently which I would like to improve on, but there is a maximum weight restriction of 120kg.
I am thinking increasing weight will slow acceleration, as there is more mass to move - acceleration is constant so a heavier object will not fall any quicker, but accelerate slower in the case of rolling down a hill. Also friction will rise, as F = uR hence more rolling friction. Only benefit I can see making it heavier would be to overcome drag at higher speeds?
What about aerodynamics though? Do they really make any difference at 30mph? I had thought about leaving the car bare without any aero, as the projected frontal area is less than what it would be if you gave it some nice aero panelling. Or would a nice slippery shape pay off?
Some pics so far below. Suggestions criticism and general mocking all welcome.
#6
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also maybe round off the end where the opening is otherwise the air will go up the inside and slow you down with the drag on the body etc.
It seems logical anyway
It seems logical anyway
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What are the rules pertaining to the karts? Can you have say go-kart wheels and tyres and some form of proper suspension? Or does it have to be a bone shaker steered by string?
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#9
Rules are - max 300mm ground clearance, max wheelbase 2.5m, max width 1.5m, must have mechanical steering (no string) and max weight 120kg.
We have some aluminium but not much in the larger size. we have hundreds of sheets of stainless, MD has said we can use whatever is out in the factory (no ordering in special parts or material)
We can do whatever we want with the wheels, max diameter is 550mm. looking to get some bike wheels.
We are going to round off the nose cone similar to the main body, haven't drawn it in though. I am still unsure if it makes a significant difference to be honest.
We have some aluminium but not much in the larger size. we have hundreds of sheets of stainless, MD has said we can use whatever is out in the factory (no ordering in special parts or material)
We can do whatever we want with the wheels, max diameter is 550mm. looking to get some bike wheels.
We are going to round off the nose cone similar to the main body, haven't drawn it in though. I am still unsure if it makes a significant difference to be honest.
#11
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on a more serious note, having the front covered must make a difference surely with aerodynamics? and if weight makes no difference why is there a limit? saving weight in a powered vehicle makes obvious sense but going down a hill having more mass gives more acceleration does it not? im no expert mind you lol.
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Firstly if you want to know how important aerodynamics are at 30mph there is a simple test, put your hand out of the car window at 30 and you can feel the affects. With regards to the weight, it has a lot to do with the track, weight may be great in a straight line but in the twisty bits light is your friend.
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AdrianFRST
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10 July 2001 08:56 PM