krwlz

I have to build a mousetrap car for My engineering class.

Im considering powering a flywheel with the mouse trap, that in turn drives the axle. More, continuous power I think. Any ideas about it?

And this is legit, haha, she told us to research, how better then to ask professionals?

shakran

does it have to be continuous power, or can you give it one big burst and let it coast? You'll lose power if you run it through the flywheel first due to frictional losses. You'll also lose acceleration due to the extra weight of the flywheel. Are there limitations on the design parameters? I'd build a nice, low, wide-stance car with rubber-surfaced rear wheels driven direct drive by the mouse trap. Build it long enough to overcome the rotational torque (might need a little weight on the nose) and let it fly. But that's just me

krwlz

We can use up to 2 mousetraps. All materials must be obtained by us. Must be powered (directly or indirectly) by the mouse traps. The moustraps must remain 80% intact.

Must carry a payload with the dimensions of 2.5"x2.5"x2.5".

Run em on the 25 foot track, looking for the the lowest time.

Graded by the value determined by: Wt. of payload / time of run.

It was just an idea, but I didnt know how it was going to pan out.

I got thinking that 25 feet isnt all that far. If distance was what we were looking to achieve, I think the flywheel would take it. As it is, Im not sure.

And I have some good rubber wheels. Also, wouldnt driving from the front increase lateral stability? If it hits the wall its disqualified.

MSD

A flywheel will not be a good thing for a 25 foot drag race. What you want is maximum launch power, least weight possible, and the most weight possible over the drive wheels. If you go with rear drive, you may want to consider a wheelie bar, which can be as simple as a few traingles of matchsticks.

You want as much initial power as possible, but you want to provide power for as much of the race as possible. Being the mad scinetist that I am, I made a primitive two-speed transmission for my mousetrap car out of some gears and springs from the local hobby shop.

Rear-drive will be the most effective, as long as you test it enough that you can correct any curve in its path.

I'll post more when I have time.

krwlz

It would be appreciated MSD. I was thinking less and less of the flywheel the more I thought about it.

onetime2

Does the mouse trap have to be incorporated into the car or can it be the launch pad?

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shakran

wait a minute. You can use 2 mouse traps? Time for all wheel drive! No matter how the weight shifts you'll always have weight over drive wheels. You could even rig it more sophisticated:

rear wheel mousetrap fires, turning the rear wheels and launching the car. The mousetrap triggers a cable which releases the second mousetrap's trigger, driving the front wheels and giving you a second burst of speed. You'll have to build in a ratchet function into the wheels so that the mousetraps don't stop the car when they finish springing, but that shouldn't be too hard to do.






The flywheel will easily get it 25 feet, but it'll do it slower than a brute force application.

krwlz

It just has to be powered by the mouse trap. I thought of the racheting idea, but I have no idea how to make it a reality.

All wheel drive seems like the thing to do to me, but simply two wheel drive, wud be easier. Perhaps belt type thing to drive the fronts, off the backs? It would make tripping them both at the same time easier.

Otherwise, without a rachet, its going to uncoil the string wrapped around the axle.

krwlz

The standard way, btw, is to have a small pin on the axle, that a loop on the string hooks on, wind it, and then let it go. When it reaches the end of the string, it simply lets go.

shakran

for the ratchet, you could disassemble the rear sprocket of a 10-speed. Those are very low friction ratchets and would work nicely.

I know about the standard way, but I hate doing things normally

When we had to build those CO2 powered cars in industrial tech, everyone built something that looked like an older Indy car. I whittled mine into a sharp point, with the forward 2.5 inches being about as big around as a pencil. Weighed almost nothing and had great aerodynamics. Beat the HELL out of any car it challenged until one race, when it went a little too fast and smacked the barrier at the end of the track. Snapped in half. I think I hold the record as the only guy to ever crack the frame on a wooden CO2 car

saltfish

krwlz,

For Science Olympiad, I had to build a mousetrap car that went 25 ft, and it went 25 feet +/- 6" each time. If you're interested in my method, send me PM. I'd type it out, but its gonna take a while.

Fool Proof Plan..

-SF

MSD

Here comes the insane idea.



The two brown lines are the bases of the mousetraps. They will both start in the loaded position, with whatever release mechanism you are supposed to use for the first. The second is positioned so that when the first is done, it will strike the edge of the second mousetrap and set it off.

The drive gears are set into slots in the frame, so that when tension is on a string, the drive gear attached to that string will engage the axle gear. The slots are the orange lines in the picture.

The wheel gear is the type with teeth around the outside, and another, smaller ring of teeth on its side. If you can't find one like that, glue a big and a small gear together on the axle. The first drive gear is set up for approximately 1/3 of the size of the larger axle gear. The ideal setup is for the gear to accelerate the axle at a slightly lower speed than what would cause the tires to spin. The second gear is approximately a 1:1 ratio to the smaller axle gear.


Here's how it should be set up, to clarify the picture. The first mousetrap should be set so that the string is initiall perpendicular to the mousetrap arm. The string should be short enough that the first drive gear is already meshed with the large axle gear. This will provide optimal torque to launch it off the line. The string should be tied around a pin on the axle, so that when the first mousetrap is almost finished pulling, it will be pulled clear of the axle, thereby preventing it from slowing the car or fouling up the geartrain. When tension on the string is released, the first gear should fall down the slot, clear of the axle. The release point should be when the string is at a 10 to 15 degree angle to the mousetrap arm. After the release, the arm should continue about another 3/4" to pull the string clear of the mechanism. At the end of this 3/4", it should strike and set off the second mouse trap.

The second gear should be weitghted so that it will not bounce and strike the axle gear before it is supposed to engage. It should have no more than 3/8" to move before meshing with the small axle gear, and some sort of blocking mechanism (such as a pin between the teeth on the side opposite the axle) should prevent it from spinning before it engages the axle gear. The gear transfer should probably occur at about the ten foot mark. Once again, the string should be attached to a pin on the axle so that it will disconnect and allow the gear to disengage when the string is 10 to 15 degrees from parallel to the mousetrap arm.

krwlz

MSD, thank you for providing us with your ingenuity. Provided you dont mind (and I take it you dont) I think that I will take this and run. Sounds like a solid plan.

The wheels im using are these rubber friction wheels my dad got me from work. Tad bit heavy, but talk about hooking up on the floor.

MSD

I wouldn't have posted it if I didn't want you to take the idea and run

For the wheels, heavy is good if it keeps them from losing traction. Now that I look at the design again, the upper (second) mousetrap should be tilted forward a bit so that the initial pull will transfer more power and accelerate it a bit more.

Just keep in mind that the first couple of feet are the most important. If you're going faster than the other guy after 3 feet, you're going to win, just like a 1/4 mile drag in which the first 60 feet are crucial. The big thing is that the continued power after the first trap will put your car way above the level of anyone with a 1-speed

JStrider

drill out the sidewalls of the wheels to help lighten them up.... and get some graphite to help reduce friction in all the gearing....

also you can attach a wooden dowel to the mousetrap to get some more length on em...

and i used erector set gears on mine... only had one gear.... but the erector set gears worked really good

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Tirian

Are you allowed to dissasemble toys ?

How about using one of those "zip tops" type of things where a long plastic thing (zip strip) with teeth on one side slide through a small whole and travels against a gear providing rotation. Or an actual SSP car if you can find one.

Or put rubber (rubber paint or a tight elastic band) around the top itself, and use it as the tire.

The top might be usefull as the flywheel.

Like these old cars (SSP mentioned earlier)

http://www.bigredtoybox.com/cgi-bin/toynfo.pl?sspindex


Just a thought.

Tirian

Another idea that crossed my mind would be to gain distance advantage by using LARGE wheels instead of momentum.

Like those old bicycles that had a huge wheel on the front.

If you built it so the wheels were so large that the mouse trap and string around the axle could just barely get it to move, you would go along way based on the large circumference of the wheels.

Try scratched CD's for possibly light large wheels. Drill large holes to further lighten. I would think that weight would want to be really low if you are going for mechanical advantage distance.

The larger the difference in diameter/circumference between the string coil and the wheel the further it will go as long as you have enough torque to make it move.

saltfish

From my past experience, old 33-1/3 speed records work really well.

By the way.. ..how far does your car have to travel?

-SF

krwlz

25 feet

Parker

I the key is get your momentum going and let the wheels do the rest of the work. I won the same race a couple of years ago and the key step was the fiberglass wheels that I cut. I tried four different sizes(10", 15", 25", 30") and I found that the 25" wheels worked best. The wood shop teacher at my High School let me cut these wheels. Good luck and get creative.

iamnormal

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http://www.machinistsfriend.com/links.htm
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Some sites that maybe helpfull