So this year's car is finished and District results

General discussions for car and semi-truck racers.
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Pacfanweb
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So this year's car is finished and District results

Post by Pacfanweb »

We tested it last night against our last year's 2nd place (by. 003) Tiger Cub car. (At district, it won pack)

Did a few test runs and then relubed both cars. I have a 2 land wooden 32ft Piantedosi track, with a "who got there first" finish indicator, but no timer. (Sweet Craigslist find for 150)

Ran then 20 times, 10 in each lane, in series of 5.

New car won 16 of 20. Since I have no timer, I stood at the end to judge the margin, and had my daughter do the starting. The 4 times the new car lost, she didn't slam the gate down fast enough and the new car rode the starting peg a bit. Those were almost dead heats, but the old one won.

The 16 wins, the margin varied from about 1/3 of the car in front to over a car length.

So I guess we at least made up that. 003 from last year.

One thing I noticed: It occasionally wobbles just before the finish line. Runs pretty straight otherwise. Balance point is about 5/8" or so in front of the axle. Rears are slightly canted. Used the slots. 4 wheels down, but one just barely touching. Drifts about 2 inches left in 4 feet.

We'll see how it does at the pack race this Saturday. Not sure what else could without a timer to test with. That's for next year. ;)
Last edited by Pacfanweb on Sat Mar 02, 2013 7:32 pm, edited 2 times in total.
Shawn Stebleton
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Re: So this year's car is finished

Post by Shawn Stebleton »

Pacfanweb wrote:The 16 wins, the margin varied from about 1/3 of the car in front to over a car length.

So I guess we at least made up that. 003 from last year.
I would think so. On the district Best Track, it appeared that the margin of victory for my son's car ended up being 0.076s in one heat, and it was approximately 1 car length, maybe a bit more. That would mean approximately 0.01s per inch. So, 0.003s would be about 0.3". If the new one is winning by more than 0.3" then it would be faster than last year's winner. 1/3 of a car length would translate to approximately 0.023s improvement. A car length would be approximately 0.070s improvement.

YMMV. :mrgreen:
Shawn
chromegsx
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Re: So this year's car is finished

Post by chromegsx »

We did similar testing on test and tune night. and ended up a full car ahead of last year. New car won every time by half a car or more depending on staging. Once my son wanted to run the new one backwards... I cringed and said "go ahead." I didn't want to spoil his fun and discovery. The new car was about tie with the old one going forward.

Shawn, I was seeing similar numbers on video about .01 per inch of car. Of course this number would depend a bit on the finish line speed... but this got me thinking of another thread... You could estimate your finish line speed by factoring in the time difference between two cars and the distance one is leading. I threw together a quick little spreadsheet to do calculations and...if my math is correct..

As an example...
At a finish speed of 8'/s there would be a margin of .96" per .01 seconds
At a finish speed of 10'/s there would be a margin of 1.2" per .01 seconds
At a finish speed of 12'/s there would be a margin of 1.44" per .01 seconds

So plugging in .003 seconds and a margin of .3", you could estimate that finish line speed was 8.33'/s. What does that tell us? :idk: Probably nothing without having a baseline to compare it too. But it was interesting to know that it could be done. I might use this for some experimenting in some future project. Hmmmm... now this gives me another :idea: Gotta go do some searching.
Pacfanweb
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Re: So this year's car is finished

Post by Pacfanweb »

Pack race was today. He won the Wolf/Bear division, in spite of the Cubmaster accidentally knocking his car off the starting line and the front wheels getting screwy. We had one wheel barely touching, and we put our worst wheel/axle combo on that one.
After the drop, that wheel was the one on the track and the OTHER one was completely not touching.

His first two heats before the drop, he was winning by over 2 car lengths. After the drop, he was down to a car length. In the runoff for the Pack, he was neck-and-neck with a Webelo, and actually lost two dead heats and won two. No tie-break race was needed because the other car finished 3rd in one race.
I think that had the car not been dropped, the Pack race wouldn't have been close, either, but oh well.

So Pack champ again, and on to District in 2 weeks. And we'll fix those axles tomorrow. Thanks again to all the people who share build and prep info here, it really is invaluable.
Pacfanweb
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Re: So this year's car is finished and Pack results

Post by Pacfanweb »

Okay, so we worked on the car yesterday. Removed all the wheels. Tossed one axle. Re-prepped the bores.
Ran it head to head with last year's car again....and it wasn't as fast. Tweaked and tweaked until we got the new one to just catch the old car at the finish. It was winning by about 1/3-1/2 a car. Not quite as much as before the fall, but it is what it is. I suspect we have a damaged wheel, but we are rolling with what it has. It's still a fast car, so we'll see how it does at District in two weeks.

I would have my son do a new set of wheels, but he can't really install them, and I am having shoulder surgery this Wednesday (round 2 on the same shoulder) so I won't be able to help. We'll see how it goes.
Pacfanweb
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Re: So this year's car is finished and Pack results

Post by Pacfanweb »

District was today. Car was disappointing. Ran on what I believe is a 32 foot, 6 lane wood track. VERY nice track.
Winning car ran 2.75 on a regular basis. That was the fastest car of the day. A couple others ran 2.76.
Ours ran 2.78-2.80. One inexplicable run, it looked like it hit the brakes and slowed to a 2.87. Went right back to 2.80 the next run.

Last year's car ran consistent 2.77-2.78's on the same track. So I guess we didn't get the damage from the fall it took fixed after all. It was originally significantly faster than the old car. Disappointed for my son, who spent a lot of time on his axles and wheels. He wasn't upset, though. His car still was competitive in its heats, and he won something in the raffle. I guess he learned a lesson that accidents can happen, and it's not the end of the world.

At least we know that as originally built, it would have been very competitive, so I feel good about what we did and how we built the car.

Next up, my daughter's Girl Scout Powderpuff Derby in April. I do appreciate the wealth of knowledge available here.
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