Engineering Fair project

hongher2005 · 01-31-2008

Im in the 7th grade doing an engineering fair project! Im making a rubber band powered car.. I have sort of an idea of how I want to make it. I think I'm going to make it out of legos for less weight then put 2 straws for the wheels to spin to reduce friction. Then large wheels with a lot of grip for max acceleration.. But the thing I can't get is how to get 1 rubber band to turn it all and move it.. please help! Thanks! if you want more info, the accual rules and regulations are at --- http://www.ospe.org/associations/750...le%20Rules.pdf ---

freeztar · 01-31-2008

Quote:

Originally Posted by hongher2005

Im in the 7th grade doing an engineering fair project! Im making a rubber band powered car.. I have sort of an idea of how I want to make it. I think I'm going to make it out of legos for less weight then put 2 straws for the wheels to spin to reduce friction. Then large wheels with a lot of grip for max acceleration.. But the thing I can't get is how to get 1 rubber band to turn it all and move it.. please help! Thanks! if you want more info, the accual rules and regulations are at --- http://www.ospe.org/associations/750...le%20Rules.pdf ---

Good for you, it sounds fun!

I would maybe try to think of something other than straws as the axles as they are not very slippery. Although, the rules don't mention anything about using lubrication, so it might work with the right lubrication, though weight could easily become an issue as the car must support a 1 pound load (ie box of baking soda). Make sure you consider the box size when designing your chassis.

Something else to consider:

Quote:

Objective
To design a wheel-driven vehicle, powered only by one rubber band (size specified above), which will transport a one-pound "load" (specified above) the farthest distance (on a level, industrial type, carpeted floor) while remaining within the boundaries of a 3 ft. wide parallel track (marked off with masking tape). Speed is not a criteria.

The quicker the vehicle accelerates, the more drag it will incur. For this reason, I would suggest working on a design that slowly transfers the energy of the stretched rubber band to the axles/wheels. This way you will get maximum distance.

What ideas have you come up with so far?

CraigD · 01-31-2008

Quote:

Originally Posted by hongher2005

But the thing I can't get is how to get 1 rubber band to turn it all and move it.

On of the simplest ways to turn a wheel with a rubber band is to attach a spool wheel to the rolling wheels axle, wrap a strong thread around it, attach the other end of the thread to the rubber band (with a dowel or padding to assure that the thread doesn’t cut the band), stretch the band as far as possible, and attach it to a peg or hook on the car’s chassis.

The contest rules state “Transferring the energy of the rubber band to wheels via gears, fly wheels, etc., is encouraged.”. This is a strong hint. While a spool-on-axle transmission is very simple, it isn’t the most efficient possible scheme, especially for a fairly heavy car on a carpeted floor with an inconstant power supply (a rubber band). A more effective transmission could use an eccentric spool.

hongher2005 · 02-01-2008

Quote:

Originally Posted by CraigD

On of the simplest ways to turn a wheel with a rubber band is to attach a spool wheel to the rolling wheels axle, wrap a strong thread around it, attach the other end of the thread to the rubber band (with a dowel or padding to assure that the thread doesn’t cut the band), stretch the band as far as possible, and attach it to a peg or hook on the car’s chassis.

The contest rules state “Transferring the energy of the rubber band to wheels via gears, fly wheels, etc., is encouraged.”. This is a strong hint. While a spool-on-axle transmission is very simple, it isn’t the most efficient possible scheme, especially for a fairly heavy car on a carpeted floor with an inconstant power supply (a rubber band). A more effective transmission could use an eccentric spool.

I really appreciate doing this for me, but could you please tell me with more detail about what a spool wheel, or eccentric spool is and how to use the thread.. I've tried googling it but i had little out come. Thanks!

What I think you're saying is put a circly thing with little hooks on the axle (the metal thing that goes across), then put a hook on the chassi, hook then stretch the rubberband and wind it up.. am I correct?

Also, could you tell me the MOST effective way to get the energy of the rubberband to go to the car?

freeztar · 02-01-2008

Quote:

Originally Posted by hongher2005

I really appreciate doing this for me, but could you please tell me with more detail about what a spool wheel, or eccentric spool is and how to use the thread.. I've tried googling it but i had little out come. Thanks!

I think Craig was referring to this:
Eccentric (mechanism) - Wikipedia, the free encyclopedia

Quote:

What I think you're saying is put a circly thing with little hooks on the axle (the metal thing that goes across), then put a hook on the chassi, hook then stretch the rubberband and wind it up.. am I correct?

That would work.

Have you tried googling "rubber band car". I got 429,000 hits. Looking at other designs can give you some ideas about how to build your car.
This one looks pretty neat. I wonder what makes it go so fast.

Rubber Band Powered Racers - The Sling Shot

I recommend you don't simply copy a design though. It's not as fun that way and takes away from the spirit of the competition.

hongher2005 · 02-01-2008

That would work.

Have you tried googling "rubber band car". I got 429,000 hits. Looking at other designs can give you some ideas about how to build your car.
This one looks pretty neat. I wonder what makes it go so fast.

I recommend you don't simply copy a design though. It's not as fun that way and takes away from the spirit of the competition.[/quote]

Alright, thanks.. also, i saw the spool, but i dont get how it works...

hongher2005 · 02-01-2008

Alright, thanks.. also, i saw the spool, but i dont get how it works...

Turtle · 02-01-2008

Quote:

Originally Posted by hongher2005

Im in the 7th grade doing an engineering fair project! Im making a rubber band powered car.. I have sort of an idea of how I want to make it. I think I'm going to make it out of legos for less weight then put 2 straws for the wheels to spin to reduce friction. Then large wheels with a lot of grip for max acceleration.. But the thing I can't get is how to get 1 rubber band to turn it all and move it.. please help! Thanks! if you want more info, the accual rules and regulations are at --- http://www.ospe.org/associations/750...le%20Rules.pdf ---

How about using a ducted fan, rather than driving the wheels?

Ducted fan - Wikipedia, the free encyclopedia

If you make the ducting removeable, you can run the car with and without to show what effect the ducting has.

freeztar · 02-01-2008

Quote:

Originally Posted by Turtle

How about using a ducted fan, rather than driving the wheels?

Ducted fan - Wikipedia, the free encyclopedia

If you make the ducting removeable, you can run the car with and without to show what effect the ducting has.

Rule #5 states:
Propulsion of the vehicle must be through the wheels (i.e., no propellers, no launching mechanism).