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What size axle are you guys using? I'm using a 5/32" axle that connects to CD wheels

Is the axle too small for the wheels?

masterhat wrote:What size axle are you guys using? I'm using a 5/32" axle that connects to CD wheels

Is the axle too small for the wheels?

No way! Smaller axle = faster car and smaller axle = more distance per cm of string
All good things

Balsa Man wrote:It goes out on a 7cm arm - in about 4 sec. It stops, and heads back. In early testing, the prototype was coming all the way back - in about 5 sec on a 7cm arm. The issue we're working through is getting the come-back to engage quickly, like it once was. Speed is a function of both arm length, and wheel/axle size ratio.

If it's making it all the way, I assume your axle is really thin? Like <2 mm diameter?

winneratlife wrote:The fact that the two mousetraps can't be in exactly the same place does create a lot of weird stuff...not really much you can do about that...
The string not pulling off of one of the axles? Huh? If the mousetrap triggers, either the string pulls off or breaks... I think your analysis might be wrong and that won't be a problem, unless I'm misunderstanding

Overall, this design has so many variables that the only way to make it work is build it, test it, adjust it, test it, etc. A sheet of paper doesn't do much...

It's hard to explain, but what I said does happen the problem deals with tension on the trying yes the rod/ mousetrap when activated will pull of string but if there is nothing where the string has to pull against other than the axel sometimes as soon as the trap activates it does not pull that much string off. We needed to add a rod at one side of the vehicle so that when as soon as the mousetrap activates it immediately pulls and thus turning the axel. Without that extra rod at the front of the vehicle it will not be able to travel more than a few feet with power. So the angle where the string pulled from in combination the tension factor that I have tried to explain is the reason why I know the way I drew up my design will not function right, but I will show this to my coach to see if he thinks my idea to see if I missed something that will make this work.


Balsa Man that is a really easy fix from that I heard from you just get a few cm longer rod, Yes it will be a little slower but it will make it back. You probably only need to add 4 or 5cm at most to the rod so the speed will still be really fast.

bwy wrote:The manual doesn't cover these questions, so I'm hoping they're okay but I want to make sure:
The way my car's brakes work (which isn't actually very well, and I could use some tips), the mousetrap stops but then starts moving back again toward the 7m line. Is that okay?
Also, I was wondering if we had to actually use the mousetraps' built in release mechanism, or if we could just let go of the lever bar to start the car.
With all of that, how decent is a distance score of about 20 cm and a time of about 26 sec with the lane bonus for an overall of 26?

No. Check out rule 6 e ii. The timer stops once all motion ceases. If it re-reverses, that is a problem. It will hurt your time a little, and kill your distance. You do not need to use the built in triggering mechanism BUT you must trigger it with a pencil or dowel. Simply holding the lever bar down and letting it go won't cut it.

If people are using one mousetrap to get out and a different one to get back, how are you all getting the second one to activate?

packer-backer91 wrote:

winneratlife wrote:The fact that the two mousetraps can't be in exactly the same place does create a lot of weird stuff...not really much you can do about that...
The string not pulling off of one of the axles? Huh? If the mousetrap triggers, either the string pulls off or breaks... I think your analysis might be wrong and that won't be a problem, unless I'm misunderstanding

Overall, this design has so many variables that the only way to make it work is build it, test it, adjust it, test it, etc. A sheet of paper doesn't do much...

It's hard to explain, but what I said does happen the problem deals with tension on the trying yes the rod/ mousetrap when activated will pull of string but if there is nothing where the string has to pull against other than the axel sometimes as soon as the trap activates it does not pull that much string off. We needed to add a rod at one side of the vehicle so that when as soon as the mousetrap activates it immediately pulls and thus turning the axel. Without that extra rod at the front of the vehicle it will not be able to travel more than a few feet with power. So the angle where the string pulled from in combination the tension factor that I have tried to explain is the reason why I know the way I drew up my design will not function right, but I will show this to my coach to see if he thinks my idea to see if I missed something that will make this work.


Balsa Man that is a really easy fix from that I heard from you just get a few cm longer rod, Yes it will be a little slower but it will make it back. You probably only need to add 4 or 5cm at most to the rod so the speed will still be really fast.

So, how exactly does this work? Given your explanation, it seems that you're describing that the string doesn't get pulled off? So the mousetrap just hovers there like this?:

......../
......./
....../
...../
..../
.../
../
./
-----------------------------

And doesn't end up like this?:


-------------------------------
...............................-----------------------------------

Or:
The string does come off, it just doesn't turn the axle...
In which case friction tape will solve the problem

masterhat wrote:If people are using one mousetrap to get out and a different one to get back, how are you all getting the second one to activate?

Attach something to the extension that hits the "cheese" when the first mousetrap goes all the way out.

Great, I've been answering questions for a while, now I get to ask

When I use an equal number of winds on either side of the pin (on the pin axle design I've been pushing so hard), my car overshoots. When I use more on the way there and less for the way back, I'm okay. However, this is at my testing site, which I find suspect. At an invitational however, I used 16 winds on each axle (16=16) and I ended up okay. So, I suspect that the testing site has messed up elevation or something. However, I added tape to my CD wheels for traction, and got the same results. The extra traction should prevent slippage though, and prevent slope from affecting my car (to a point, of course). Regionals is Saturday. I've been used 16 out-16 back winds at invitationals and pulled it off. I've been using 16.5 out-15 back in testing and that does pretty well pretty consistently. What do I do at regionals???

EDIT: The periods in my drawing are just space holders, since apparently pure spaces are rejected...

sorry, what i meant was if people are using one mousetrap to go out and one to go back, does their car coast at all? If it does, how are they activating the second mousetrap?

Omfg! My car completely failed regionals! I had this problem in testing once, fixed it, and it came back to haunt me, for no apparent reason!

Basically:
I wind up my car, 16 rotations, around pin, 16 rotations
I put it down with the mousetrap locked. At this point, I am not touching the traps.
The car starts going forward?!?!?
It ruins my winding. I move it back to the starting point, my winding is ruined, it goes, I fail with a distance of like 30.

I am using a fairly thick fishing wire for string...
Somebody please help!

winneratlife wrote:

Omfg! My car completely failed regionals! I had this problem in testing once, fixed it, and it came back to haunt me, for no apparent reason!

Basically:
I wind up my car, 16 rotations, around pin, 16 rotations
I put it down with the mousetrap locked. At this point, I am not touching the traps.
The car starts going forward?!?!?
It ruins my winding. I move it back to the starting point, my winding is ruined, it goes, I fail with a distance of like 30.

I am using a fairly thick fishing wire for string...
Somebody please help!

If I remember correctly it would mean that your line has slack in it and the mousetrap when extended is always trying to return to equilibrium and therefore moves until the string holds it moving the car forward

two problems:
1)your string
2)your method

solution
1)use a different string, mono-filament(fishing line) tends to keep a certain shape, causing it to want to un-wind when you wind it it up, you need to use some sort of braided fiber(regular sting will work)

2)it is moving forward because there is still tension in the mousetrap/string. slowly let the wheels unwind. you need to find the point where the the wheels don't move by themselves and the string doesn't unwind itself


if those two things don't solve your problems, then you have a problem with the weight distribution/ center of mass of your wheels

let me know how it goes