Gravity Vehicle C

andrewwski
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Re: Gravity Vehicle C

Postby andrewwski » March 5th, 2013, 11:41 pm

The annoying part about the ramp is the release mechanism... Our first two ES's had different interpretations of the rules... Just out of curiosity, what's everyone else been doing for a release mechanism? We just mounted an exacto knife to the ramp and tie the vehicle up with a string :D
Isn't it against national rules to ask for advice from other Sci-Oly Groups.
This site wouldn't exist if it was.

Stingray355
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Re: Gravity Vehicle C

Postby Stingray355 » March 10th, 2013, 7:10 am

Maybe there is some confusion about two things that are not allowed or discouraged. Science Olympiad does not allow you to post copies of the actual rules for the various events. I am sure there are a number of reasons for this but I have always assumed that one reason was that they sell that info as one of the ways to generate money to support the organization. If people could post the rules it would almost certainly reduce that income stream. It might also increase the chances for errors.
The second thing is that this site is not the place to go for official rules clarifications. When anyone seems to be soliciting or offering an interpretation of the rules they are often warned to only use the official National SO site for such information. We have adopted a practice of not only checking the official site for rules clarifications but we print them out and add them to our clipboard that we take to every tournament. If you happen to encounter a situation where the event supervisor is not aware of rules clarifications you can have your coach discuss it with them and/or offer a copy for their review. These events are run by volunteers and it can be a challenge to be fully up to speed on every detail of the rules and often they had a few days or even hours to prepare. Most will appreciate any help if it is offered respectfully and through the proper channels.
That leaves all sorts of topics that can be openly discussed on this board and it is a good tool to gain a better understanding of the technical challenges and a place to exchange and discuss ideas.

_HenryHscioly_
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Re: Gravity Vehicle C

Postby _HenryHscioly_ » March 10th, 2013, 5:19 pm

how do you set up the vehicle+ramp to go straight+consistent.?

I have lines on my ramp, and I've lined up my wheels onto the lines. I'm using rollerblade wheels, and its hard to match something that wide accurately+consistently.
Its a little better now that I'm using spacers between the side of ramp and the vehicle, but I am still getting significant left-right innaccuracy..like, .1degrees off,(2cm sway if I try to line it up exactly..)

I believe that one team at my regionals got 11mm off and had some type of pbc tube for the wheels to track on(but I didnt see it in person). The pipes were cut in half so it was like a trough.
Sounds like it would cause friction if wheel was too wide, and if wheel too thin, the track wouldn't do much...but 11mm!!


I have these bearings: 1/4" ID; 1/2" OD
http://shop.incomsupply.com/shop/produc ... sku=328906
It says its good for high rpm; is this the quality/type for gv?

joeyjoejoe
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Re: Gravity Vehicle C

Postby joeyjoejoe » March 10th, 2013, 6:08 pm

If you are consistently getting 1cm off (left-right), even at 5m, then I'd say you are doing great! Our car runs very straight but misaligning the car or ramp by the smallest distance is magnified greatly at the end of the run, especially at the farther distances. I'm sure this other team you mention worked hard for that 11mm distance but I'll bet there was at least a little luck involved. I have data right in front of me showing where my team launched their car 10 times in a row for a distance of 8.5m and got as close as 2mm and as far as 63mm from the target. Obviously there will be some inaccuracies in hand-built cars and ramps. Not to mention errors induced by variations in the level/texture of the floor, uneven wear of the wheels (we are using used rollerblade wheels too) etcetera

Balsa Man
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Re: Gravity Vehicle C

Postby Balsa Man » March 11th, 2013, 6:50 am

I described last year a (low friction) "guide rail" we're using. The "wheel troughs" described above would accomplish pretty much the same thing- a way to put the vehicle on the same run line, consistently, every time. Once you do that, then the residual variability is cut down to wheel interactions with floor imperfections (which there's not much you can do about).

With the guide rail, we're seeing left/right presicion consistently within +/- 2 to3 millimeters, at 10m. To get this sort of precision, not only do you have to have some form of run line guidance, the chassis has to be.....precise; no flex, axles really parallel, all 4 wheels equally loaded/in the same plane.
Len Joeris
Fort Collins, CO

joeyjoejoe
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Re: Gravity Vehicle C

Postby joeyjoejoe » March 11th, 2013, 2:30 pm

I think our choice of wheels is hurting us and it's really too late to make any major modifications to the car since the state tournament is this Saturday. Our wheels are outdoor rollerblade wheels and are therefore rather hard and have a slightly rounded bottom (ie small footprint). All of this, we thought initially, would limit the losses due to friction (which they did) but at the cost of accuracy. If one of the wheels even gets dirtier than the other, it will slowly track in that direction. We tossed the rail idea about but thought we'd lose too much potential energy to friction.

lmatkovic3
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Re: Gravity Vehicle C

Postby lmatkovic3 » March 11th, 2013, 5:53 pm

Hey Joey. You should try using cd's (possibly covered in balloons) for the front wheels.

ahoback
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Re: Gravity Vehicle C

Postby ahoback » March 13th, 2013, 9:06 pm

I hate to ask but what is the lowest score you guys have seen this year so far? Also any predictions for national's top scores, and before a monkey jumps on my back lets just say the target distance of 10 meters is our unit of comparison. Thanks guys!

lmatkovic3
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Re: Gravity Vehicle C

Postby lmatkovic3 » March 14th, 2013, 10:07 am

Our car can get ~240 at 10m, accounting for a reasonable distance from the target and a tenth of a second off on our prediction. However, we haven't optimized our car and ramp yet, so perhaps we could get it down to about 220 or so.

ahoback
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Re: Gravity Vehicle C

Postby ahoback » March 14th, 2013, 4:29 pm

Thank you, I was thinking that 220-225 would be the bar to meet by state. I have read through the forums but would like to know what you guys and girls think the best way to aim the ramp itself; scope, large t-square, ect.


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