Mousetrap Vehicle C

[DarthBuilder]

What rod are you guys using for the string?

[4Head]

so my build goes forward but it just stops and doesnt rotate back (i wrapped the string the opposite way as well..)

any ideas on what could be causing this? my string seems to be really long and doesnt cause any tension on the lever arm until i wind it a good amount which i think could be the cause? idk if thats due to too short a lever arm or just bad string. (try fishing wire instead?)

you diagnosed your own problem. If your string is too long then the problem isn't with the kind of string. Just cut it shorter

It's long but i have small wheels that need a lot of string to be able to cover the distance.

From my understanding of your post it seems like you have to wind the string a few times to get any tension on it? That part of the string without tension is useless. If that's what you mean, you have excess string that doesn't serve any function other than to pose a risk of tangling your axle or running under your wheels.

Aside from this, I'd recommend increasing the size of your drive wheels to around 3" if you can. Anything smaller than that will end up reversing slowly regardless of the type or length of string or lever arm length.

[4Head]

What rod are you guys using for the string?

anything lightweight and rigid. Carbon fiber is good, depending on the length that you need you might be able to get away with wood dowel

[rafaelnadal]

How much time does a wingnut braking system save? After adjusments and more testing, I can get my vehicle time to ~15 seconds with no braking system but by using the momentum of the vehicle to max out the cup distance (i leave just a little less string forward).

Also should i drill out my banebots to reduce weight? I haven't measured the weight of my build yet, but would that help speed?

Also im using wooden dowels for axles (.25 in), would CF rods (http://dragonplate.com/ecart/product.asp?pID=736&cID=18) be better? I cant find a hollow CF rod thats the right size, so im wondering how a solid rod would be

Thanks

[dcambrid]

How much time does a wingnut braking system save? After adjusments and more testing, I can get my vehicle time to ~15 seconds with no braking system but by using the momentum of the vehicle to max out the cup distance (i leave just a little less string forward).

Also should i drill out my banebots to reduce weight? I haven't measured the weight of my build yet, but would that help speed?

Also im using wooden dowels for axles (.25 in), would CF rods (http://dragonplate.com/ecart/product.asp?pID=736&cID=18) be better? I cant find a hollow CF rod thats the right size, so im wondering how a solid rod would be

Thanks

I have worked a couple of Mousetrap Invitational Events, and have seen cars with wingnuts to stop and cars that just secure the string to the axle and wrap the correct number of winds for the distance. Without the wingnut at the end, the string will start to wrap around the axle the other way, then come back and forth a few times before coming to a complete stop, this rocking adds 2-3 seconds to your time. A Wingnut will stop abruptly. Also, the wing nut makes it easier to control distance.

[nnaya]

Also should i drill out my banebots to reduce weight? I haven't measured the weight of my build yet, but would that help speed?

We found that bulk of the weight comes from the rubber in BB wheels. Drilling holes in the BB wheels barely moved the scale for us. But every little bit counts if the vehicle is already light.

[JonB]

Also im using wooden dowels for axles (.25 in), would CF rods (http://dragonplate.com/ecart/product.asp?pID=736&cID=18) be better? I cant find a hollow CF rod thats the right size, so im wondering how a solid rod would be

Thanks

I would avoid solid- it will be really heavy. Are you restricted to only one size that can be used? If you can make hollow CF tubes work, that would be ideal (assuming they won't bend).

[rafaelnadal]

Also im using wooden dowels for axles (.25 in), would CF rods (http://dragonplate.com/ecart/product.asp?pID=736&cID=18) be better? I cant find a hollow CF rod thats the right size, so im wondering how a solid rod would be

Thanks

I would avoid solid- it will be really heavy. Are you restricted to only one size that can be used? If you can make hollow CF tubes work, that would be ideal (assuming they won't bend).

Yeah i'm kind of restricted to 1/4" atm.

[PM2017]

Also im using wooden dowels for axles (.25 in), would CF rods (http://dragonplate.com/ecart/product.asp?pID=736&cID=18) be better? I cant find a hollow CF rod thats the right size, so im wondering how a solid rod would be

Thanks

I would avoid solid- it will be really heavy. Are you restricted to only one size that can be used? If you can make hollow CF tubes work, that would be ideal (assuming they won't bend).

Yeah i'm kind of restricted to 1/4" atm.

Does 6mm work for you? (1/4 in = 6mm)
if so try this: https://hobbyking.com/en_us/carbon-fibe ... 0x6mm.html
That's what I'm currently using.

[PM2017]

Does anyone know of a lighter replacement for axle collars?

Vinyl tubing works great with a good square cut and either nylon or teflon washer of a close fit. You can stretch vinyl by dipping it into hot water and quickly put it on your axle.

Thanks. (What's a square cut? Is that just a 90 degree cut?)

If I have a 4mm drive axle, and a 5mm brake axle, should I get two separate sizes of vinyl tubing? Also, where is a good place to buy these inexpensively?