[mtlmouth]

I need to design a mouse trap car for a competition. I have never built one before, and was hoping I could get some suggestions from the brilliant minds of CGR!

Here are my requirements:
- The car has to pull a bin, clipped on with a carabiner. For the first round, the bin is empty, and the cars that go the furthest will advance to the second round. For the second round, a weight will be added to the bin (don't know the amount yet, but it will be less than one pound). So I'm looking for a combination of distance and towing power, but speed doesn't matter.

- The track surface is dirt, so I'm guessing that Google's suggestion of using CDs as wheels won't be the greatest option.

- We can use up to four mousetraps. These can fire simultaneously or in phases. I have no idea how I would get them to fire in phases, though.

- The car cannot use any batteries, electronic devices, chemicals, or live animals.

- The vehicle must be smaller than 12x12x12 inches.

Has anyone done these before? Any strategies I should keep in mind?

[Sean.thomson]

Originally Posted by mtlmouth

- The car cannot use any batteries, electronic devices, chemicals, or live animals.

Can they use dead.... wait, THIS ISN'T CPF!

[mtlmouth]

Originally Posted by Sean.thomson

Can they use dead.... wait, THIS ISN'T CPF!

Sadly, that's... exactly what I asked my teammates when we read over the rules.

[walkwjc]

Figuring out how to make them fire in phases will get the best results. You will want two of the traps to fire simultaneously to get the car moving, especially for the towing part, and then the next trap to fire at the mid to end of the expense of the first two, and the last trap to fire at the mid to end of the third trap.

Initially you want torque to get rolling, and then space the other two traps out for a long roll.

I attached a quick idea for a two phase car. Be sure to test your design out in the dirt before hand. If the wheels spin, you will want to add some weight to the vehicle. If it is hard to get rolling use bigger dowels for the axles on the first phase. Be sure everything is lubed up good too. If you are using wood parts you can get some powdered graphite (usually where they make keys in the hardware store) to reduce friction.

After I drew this out, I think maybe a better design would be to use a popsicle stick and use it as a bar across the two mouse traps on each end and just use one string on each axle, tied to the bar instead of two strings to each trap. This way you would get a more even pull and less chance of tangle. Do the same with the popsicle sticks and fulcrum set up to set off the second phase. Just use one stick with a cross beam at each end.

And you could get real fancy and mount the traps on the bottom of the chassis. This may be a more powerful model because you would eliminate the friction of the string going through the holes in the chassis.

Yes. I have nothing to do.

[Art]

Lego wheels. They are awesome for dirt.

[MtlMom]

Originally Posted by The Phantom Mohawk

Figuring out how to make them fire in phases will get the best results. You will want two of the traps to fire simultaneously to get the car moving, especially for the towing part, and then the next trap to fire at the mid to end of the expense of the first two, and the last trap to fire at the mid to end of the third trap.

Initially you want torque to get rolling, and then space the other two traps out for a long roll.

I attached a quick idea for a two phase car. Be sure to test your design out in the dirt before hand. If the wheels spin, you will want to add some weight to the vehicle. If it is hard to get rolling use bigger dowels for the axles on the first phase. Be sure everything is lubed up good too. If you are using wood parts you can get some powdered graphite (usually where they make keys in the hardware store) to reduce friction.

After I drew this out, I think maybe a better design would be to use a popsicle stick and use it as a bar across the two mouse traps on each end and just use one string on each axle, tied to the bar instead of two strings to each trap. This way you would get a more even pull and less chance of tangle. Do the same with the popsicle sticks and fulcrum set up to set off the second phase. Just use one stick with a cross beam at each end.

And you could get real fancy and mount the traps on the bottom of the chassis. This may be a more powerful model because you would eliminate the friction of the string going through the holes in the chassis.

Yes. I have nothing to do.

Wow. This is a side of Donnie that we don't usually see - the Toy Engineer. Now that I think about it, it doesn't really surprise me at all.

[redbaron]

even if you can't use as many (due to size) if the rules don't ban it, rat traps are much stronger (spring wise). Alternatively you may be able to put the springs from rat-traps onto mouse traps but it will make them VERY hard to set.

remember, the best solution is to run as close to the edge of the rules as you can

I think donnie's design is a very good point to start from

[crazymoose]

I did this in grade 8. I remember trying to build it out of styrofoam and CD's and what not. Turned out the best option was just to build it out of lego. I even got pretty close to getting a gearing system set up but I was rushed and didn't have time to get it working right.

Some tips:
IIRC, a tight elastic band worked better than string.
For more distance, but less power, you can extend the arm of the mousetrap by tying a rod to it. This means you can pull more string, it just takes longer. In fact, using the chain idea from the phantom mohawk, you could leave the first to short to give you that initial power off the line, and then lengthen the other two to keep the car going once your momentum is built. Kind of like a two stage gearing system.
I seem to remember tightening the spring of the mousetrap to give it more power.

[Cam42]

If you're gonna go with rubber bands, I'd recommend using more than one, to prevent snapping.

This is kinda out there, but maybe tennis balls for wheels? I think they'd go pretty far on dirt.

[walkwjc]

I was thinking some more on this. My design with the two stage will not work unless you figure out how to make the front axle freewheel until the second traps kick in. Otherwise, you are unwinding your string while the first two are running.

Extending the bales on the traps is an excellent idea to get more distance. And the lego idea is great. Lego has so many parts that would work for this with no modification.

[walkwjc]

Another idea that might work better.

The idea of extending the bales gives you the ability to run one axle as the drive axle and still have three phases. I would use rubber bands instead of strings, as suggested above to give flexibility. The only problem with this design is you can't attach the rubber bands to the axles permanently or the first phase will back wind and stop the car. Anyway, you get the point, I think.

[mtlmouth]

Thanks so much, everybody. Donnie, I printed out the designs you came up with, so we'll look over those in class and see if we can make those work.

Originally Posted by redbaron

even if you can't use as many (due to size) if the rules don't ban it, rat traps are much stronger (spring wise). Alternatively you may be able to put the springs from rat-traps onto mouse traps but it will make them VERY hard to set.

remember, the best solution is to run as close to the edge of the rules as you can

I think donnie's design is a very good point to start from

Haha, rat traps are a good idea, but sadly, they'll be providing the mousetraps for us so everyone's using the same ones.

Originally Posted by crazymoose

I did this in grade 8. I remember trying to build it out of styrofoam and CD's and what not. Turned out the best option was just to build it out of lego. I even got pretty close to getting a gearing system set up but I was rushed and didn't have time to get it working right.

Some tips:
IIRC, a tight elastic band worked better than string.
For more distance, but less power, you can extend the arm of the mousetrap by tying a rod to it. This means you can pull more string, it just takes longer. In fact, using the chain idea from the phantom mohawk, you could leave the first to short to give you that initial power off the line, and then lengthen the other two to keep the car going once your momentum is built. Kind of like a two stage gearing system.
I seem to remember tightening the spring of the mousetrap to give it more power.

Hmm. Yeah, it looked like some of the cars on YouTube had added rods, which helped a lot with the distance. But if I'm decreasing the power, that would limit it's towing capacity for the second round, wouldn't it?

Originally Posted by Cam42

If you're gonna go with rubber bands, I'd recommend using more than one, to prevent snapping.

This is kinda out there, but maybe tennis balls for wheels? I think they'd go pretty far on dirt.

Huh. Interesting idea.

[redbaron]

You should be able to wind the strings/bands/etc so that they essentially pull themselves free when they reach the end and are not really attached. essentially you wrap the band over itself to give it a friction "knot" and when it unwinds far enough the tension will be too low and it will simply let go.

[Nate]

If you've got plenty of Legos available (especially technics), how about going with a rack-and-pinion approach instead of a string connected immediately to the drive axle?

Instead of connecting the spring arm of the trap to a string, attach it to the side of the rack. But, you don't want the rack to go up and down and all around, so attach it in such a way that the point of contact between the arm and the rack isn't fixed; the simplest way would just be to put a horizontal hole beside the rack and put the vertical arm of the spring arm through that hole.

I'll draw you a picture later. It just seems like this would be a more reliable mechanism. Plus, it's easily reset. At the very least, you'd impress them with a less common idea.

[walkwjc]

So...how did this go?