Engineering Fair project

[hongher2005]

hmm ill work on it..

 

so the flywheel.. is there any specific way it works? or do i just add it to the car instead of wheels.. or is the flywheel inside the wheels?

[hongher2005]

Pardon the crappy mouse-sketch, but hopefully even a badly drawn picture can communicate the idea better than words.

 

 

So in the drawing, the blue is the thread correct? and the rubber band is pulling the thread, spinning the wheels right?

 

also, would putting something above and below the rubberband, slightly holding it, reduce the energy it gives? it would definately reduce speed..

[CraigD]

So in the drawing, the blue is the thread correct? and the rubber band is pulling the thread, spinning the wheels right?

Yes.

 

You can try this basic scheme on any toy car you can find that has wheels solidly attached to an axle. Duct tape can be used to attach a thread or string to the axle, and can be layered to make spools of different sizes. You can skip the thread/string and attach a rubber band (especially one bigger than you’re allowed to use in the contest) directly to the spool/axle, though this is inefficient, since the part wound around the spool wastes energy slipping as it unwinds, and doesn’t contribute much of its force to moving the car.

[hongher2005]

hmmm... I can think of a basic way to make this thing, but could you tell me how to assemble a flywheel?

 

also, one more.. could you tell me please which materials for parts would work best? like wheels.. large, but where could i find them? and what would be a good thing to use for my chassis? if you could help me with that, with the info i have, i could make a pretty good model for my car. thx!

[Turtle]

hmm ill work on it..

 

so the flywheel.. is there any specific way it works? or do i just add it to the car instead of wheels.. or is the flywheel inside the wheels?

 

:doh: OK I searched the house high and low for a wind-up toy. I found one, but it does not have a flywheel much to my chagrin. :eek: Chalk that up to me bein' an old fogey and when I was a kid taking apart wind-up toys, they all had flywheels. :eek_big:

 

So, here's a photo montage of the drive unit. Rather than a flywheel to even out the spring tension release, it uses an escapement like a clock. Very clever.

 

Keep in mind this is supposed to be a learning process for you. The mistakes you are about to make actually working with the materials is where the real learning gets done. ;) :hyper:

[hongher2005]

i see.. hmm alright. but the materials.. can i just buy them? like ask for a wheel and they give em to me? and also, the drive thingy.. i have no idea how to use it :eek_big:

[Turtle]

i see.. hmm alright. but the materials.. can i just buy them? like ask for a wheel and they give em to me?

 

The last time I went to a hobby shop to buy gears, they looked at me like I was mad, and kept looking until they were sure I had left. :eek_big: I have in the past -long past- seen catalogs selling bags of parts but I don't know of any in specific nowadays. :hyper:

 

Go to Goodwill or your thrift store of choice and get some old mechanical toys with gears and then cannibalize them. Keep in mind scale, as you have to carry the 1 pound load as well as the vehicle weight. Gears as small and light as in the toy I gutted seem too delicate to me.

 

You could make your own gears by either attaching pins to the edge of a disk or cutting notches in the edge of a disk. Do you have much experience with tools? Is everyone doing their own vehicle? What are the other students doing? Do you have a wind-up toy to take apart? That's all I got. :doh: ;)

 

PS I just reread the thread and realized this is a 7th grade project. I'll try & keep it simpler. :eek: :cup:

[Turtle]

OK Building on Craig's spool arrangement. I used an appropriately sized rubber band and found I could wind it tight on the spool ~4 times. To compensate for no gearing, I suggest very big wheels.

 

Here is a rough design that uses only corrugated paperboard, pencils, and the spool. The rubber band should detach from the spool when it unwinds all the way I think, so you take advantage of any coasting. Hope this is more helpful. :eek_big:

[hongher2005]

hmmm.. looks similar to the design i had.. alright.. ill try that, but I dont have any gears or anything to take apart.. well, BACK TO THE DRAWING BOARD!

[freeztar]

I dont have any gears or anything to take apart.. well, BACK TO THE DRAWING BOARD!

 

Plastic Gears - bag of 20, assorted sizes | Edmund Scientific

 

That site has a gear "toolbox". But it might be even better to build your own. :eek_big:

 

What lightwight material might work as a gear? How would you construct it to work with the rubber band?

[hongher2005]

thx a lot for ur help! I think im just guna make my car simple because no one at my school has any idea how to make theirs.. haha. so large wheels, spool, thread, wood chassis, and something to slow the movement of my car.. sound good?

[freeztar]

and something to slow the movement of my car.. sound good?

 

Everything you mentioned sounds great, except for the part I quoted above.

 

You don't want to slow the movement of your car. You want it to go far. :doh:

[hongher2005]

Everything you mentioned sounds great, except for the part I quoted above.

 

You don't want to slow the movement of your car. You want it to go far.

 

ah, but i just want it to slow down but have as just as much strength.. but the thing is.. i was wanting to know if it could happen without making it lose power

[Turtle]

ah, but i just want it to slow down but have as just as much strength.. but the thing is.. i was wanting to know if it could happen without making it lose power

 

The power of the rubber band wound on the spool does not change, only how fast it is delivered I believe. Here is my thinking with the big wheels.

 

Remember, or if you don't know, that you can measure the diameter of a circle (distance across the round end of the spool) and multiply that by 3.14 (pi), to find the circumference (the distance around the spool).

 

So I have a spool 1" diameter and 1" * 3.14 = 3.14" around. Now let's use my test of 4 wraps of the rubber band around the spool. If the wheels were also 1" around, the car would move 3.14" * 4 turns = 12.56" before the rubber band was all unwound, and anymore forward movement would have to be coasting.

 

Now imagine you make the wheels 8" across. This means they are 8" * 3.14 =25.12" around the circumference. So now after the four turns of rubber band on the spool run out, you have traveled 25.12"*4 turns = 100.4". Because the rubber band power doesn't change, the large wheels make the car slow down, but go farther before the power runs out.

 

Hope this helps, and by all means if I have misstated the case, don't anyone hesitate to correct me. :thumbs_up

[hongher2005]

alright, well, im going to the store today to buy the stuff for my project..

 

hmm.. so let me get this straight. if I have 5'' radius wheels, and say i wrap it.. 5 times.. the equation for circumference is Pie, R, Squared. So, i get 25*3.14 and it would be 78.5'' of distance? and Im thinking logically here.. If i had TOO big wheels, the rubber band wouldnt be able to pull the wheels resulting in the car stalling.. correct?

[Turtle]

alright, well, im going to the store today to buy the stuff for my project..

 

hmm.. so let me get this straight. if I have 5'' radius wheels, and say i wrap it.. 5 times.. the equation for circumference is Pie, R, Squared. So, i get 25*3.14 and it would be 78.5'' of distance? and Im thinking logically here.. If i had TOO big wheels, the rubber band wouldnt be able to pull the wheels resulting in the car stalling.. correct?

 

No; circumference is 2 * r * Pi, not r squared. The diameter is twice the radius, so you can substitute diameter for the 2 * r. For your 5" radius wheels, they would be 10" in diameter and 10" * 3.14 = 31.4" in circumference.

 

Yes; if the wheels are too big, the car will stall. Good luck, and keep us posted. :)

[hongher2005]

Lol its going ok. I was going to post wut i looked like, but ill do it later.. i have thing to do xP