Gravity Vehicle C

[fishman100]

Well, the rules in two places refer to the competitors being called (by the Event Supervisor) to retrieve their vehicle. Also to adjusting clip between run. As discussed under various events, Event Supervisors do not always run events in accordance with the rules
At our regionals, when they finished measuring, vehicle was left in-place, competitors allowed to come get it-- do any measuring they wanted, told time, which seems to be in accordancee with the rules.

Yeah, I would think that after the (official) measurements are taken then the competitors would be allowed to retrieve their vehicle without it being moved by the Event Supervisors, and during that time they could take any measurements they wanted...

[bearasauras]

Yah, with my tournaments, I always tell the event supervisors that they're not to touch the students' devices. So after the measurements are done, the students are the ones to retrieve the vehicle, etc.

[NinjaChicken]

What would be the problem with putting the mass behind the rear axle? Not completely behind it, but something like 3/4 of the mass.

[chia]

What would be the problem with putting the mass behind the rear axle? Not completely behind it, but something like 3/4 of the mass.

...Would there be a problem? I would think having most of the mass towards the back of the car would be better, since it would increase the speed of the car - it will begin as high up on the ramp as possible --> more potential energy. (Then again, don't put so much on the back that your car tips over )

[Balsa Man]

It's a matter of tradeoffs & balance.
Yes, more mass to the back means higher at launch, means higher velocity off the ramp. Two issues if you push it too far, because the more of the weight on the rear wheels, the less you have on the fronts; 1) steering/linear stability- if the front is loaded too lightly, it will tend to wander off line; 2) more skidding (if braking is on the front axle)

[illusionist]

First at regionals!

Distance- 7.5m
Distance Score- 47mm
Run Time- 3.44 seconds
Predicted Time- 3.6 seconds

Edit: What are the reasons to use smaller wheels? After doing a search and reading the wikis, I know that it allows the vehicle to get higher up and lower down, and allows for finer adjustment for distances. Being higher up won't be of significant use in my case because my vehicle weighs very little, probably around 700-900 grams. We were using traditional CD wheels, but now I'm thinking about switching to the smaller pocket CDs.

[bookluvr-yoyo39]

Hey! Does anyone know if lasers are allowed to be used in the event? I think that there is a section of the rules that say no, but I wanted to check.

[blazer]

Hey! Does anyone know if lasers are allowed to be used in the event? I think that there is a section of the rules that say no, but I wanted to check.

Rule 3k: "Electrical components must not be used on the vehicle, the ramp, or any alignment devices."

[Balsa Man]

First at regionals!

Distance- 7.5m
Distance Score- 47mm
Run Time- 3.44 seconds
Predicted Time- 3.6 seconds

Edit: What are the reasons to use smaller wheels? After doing a search and reading the wikis, I know that it allows the vehicle to get higher up and lower down, and allows for finer adjustment for distances. Being higher up won't be of significant use in my case because my vehicle weighs very little, probably around 700-900 grams. We were using traditional CD wheels, but now I'm thinking about switching to the smaller pocket CDs.

Congrats- good numbers!
Pocket CDs vs regular ones, I suspect the difference would likely be small enough to fall within the .....uncontrolled variable of human/hand timing. The time number you get is almost certainly not the actual (to a hundredth of a second) run time; its the average between the timers. So, probably not enough difference to be meaningful. That's the wild card in this event, and there's not really a workable way to eliminate it. My sense, from our own multi-timer testing, and talking to event supervisors, is the range of times is on the order of 0.2 to 0.3 sec. The "real" time lies somewhere in between; the likelihood of it actually being the average is pretty small. So, if you do something that picks you up a tenth of a second, the likelihood of that performance increase being (consistently) "seen" in timing is pretty small.
Theoretically, it would get a faster time in 2 ways:
1) by allowing the vehicle to start higher up the ramp, more "h", which means higher "v" off the bottom of the ramp, and you also get a bit more "h" by the (center of mass of the) vehicle being closer to the floor at the bottom. The weight, as discussed before, all other things being equal, does not affect "v"- only "h." What the weight does affect is momentum. More momentum means that the rate at which you loose speed over distance is slower.
2) the rotational momentum/rotational intetia of the smaller wheels is smaller; in this case not a lot, but a bit. Rotational momentum/inertia is a function of both radius and mass. As the vehicle goes down the ramp, a small part of "g x h" goes into spinning up the wheels; more for bigger, heavier wheels, less for smaller, lighter; that reduces final velocity. Compared to #1, a significantly smaller factor, btw.

[illusionist]

First at regionals!

Distance- 7.5m
Distance Score- 47mm
Run Time- 3.44 seconds
Predicted Time- 3.6 seconds

Edit: What are the reasons to use smaller wheels? After doing a search and reading the wikis, I know that it allows the vehicle to get higher up and lower down, and allows for finer adjustment for distances. Being higher up won't be of significant use in my case because my vehicle weighs very little, probably around 700-900 grams. We were using traditional CD wheels, but now I'm thinking about switching to the smaller pocket CDs.

Congrats- good numbers!
Pocket CDs vs regular ones, I suspect the difference would likely be small enough to fall within the .....uncontrolled variable of human/hand timing. The time number you get is almost certainly not the actual (to a hundredth of a second) run time; its the average between the timers. So, probably not enough difference to be meaningful. That's the wild card in this event, and there's not really a workable way to eliminate it. My sense, from our own multi-timer testing, and talking to event supervisors, is the range of times is on the order of 0.2 to 0.3 sec. The "real" time lies somewhere in between; the likelihood of it actually being the average is pretty small. So, if you do something that picks you up a tenth of a second, the likelihood of that performance increase being (consistently) "seen" in timing is pretty small.
Theoretically, it would get a faster time in 2 ways:
1) by allowing the vehicle to start higher up the ramp, more "h", which means higher "v" off the bottom of the ramp, and you also get a bit more "h" by the (center of mass of the) vehicle being closer to the floor at the bottom. The weight, as discussed before, all other things being equal, does not affect "v"- only "h." What the weight does affect is momentum. More momentum means that the rate at which you loose speed over distance is slower.
2) the rotational momentum/rotational intetia of the smaller wheels is smaller; in this case not a lot, but a bit. Rotational momentum/inertia is a function of both radius and mass. As the vehicle goes down the ramp, a small part of "g x h" goes into spinning up the wheels; more for bigger, heavier wheels, less for smaller, lighter; that reduces final velocity. Compared to #1, a significantly smaller factor, btw.

I guess it might not be worth re-calibrating the braking system for such a small advantage then. Thanks again!