Test Tracks

DIY tracks.
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Sparky
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Test Tracks

Post by Sparky »

Questions to the group -
Who has built home use test tracks, what did you learn through the activity about tracks, "scaleability" of results to the real thing and making faster cars?

so far I have I have learned:

test times vary by about ~2.5% (~20mS) over multiple runs for a given car
the car my son and built this year is only a touch faster than last year's despite much extra effort (law of diminishing returns?)
times in general are much quicker than I hoped ~ 1.440 seconds for ~17' of track. This makes run to run comparisons more difficult and variation harder to interpret.
test track inside garage = much more scraping car windows in the morning
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terryep
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Re: Test Tracks

Post by terryep »

I think if your test track has a center rail this will give you lots of "run to run" variability. You have to take the average of many runs to be sure if you have made an improvement or not.

I have a 12 foot laminate top work bench in my shop that we use to test our cars. I built a small ramp about 1.5" H x 16" L to launch the cars. A rail clamped along the edge of the bench prevents wayward cars from reaching the floor! After many hours of trials it became necessary to add padding on the far wall as our cars eventually started banging into it (silicone) the year before graphite would only get the cars a foot or two from the wall. Later we made a 4 inch long block to limit the car's starting position on the ramp, if the car just about got to the wall it was ready!

This "test track" has no guide rail so if the alignment is off you’ll know it right away. Friction on the straight away is where races are won or lost. Low speed testing is valid. Timers are not necessary. Distance is cheaper to measure. The investment in a smooth level working surface is handy for fixing things and your wife can use it for crafts as well. :)

Terry
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Re: Test Tracks

Post by Sparky »

One of the key reasons to build a center rail is to be true to form. A tried and true way to validate something is to test the car as close to possible to the final use. Since the car in the final race has to content with a center rail, I'd like the car's ability to contend with the center rail to be part of the evaluation.

I like the idea of using a launch ramp onto a flat surface for alignment check. I had been using only a flat surface and hand pushing the car to see if it deviated. Since I can't start the car straight by hand, I'll soon build a start ramp.

I guess I can't yet make the mental leap that the car that travels furthest on an unconstrained horizontal surface will be the fastest one down the race track with a center rail and a much higher ratio of fall distance to horizontal travel. That's perhaps because I don't have the right intuitive feel for the problem.

One reason to build a timer (in your case, distance is the figure of merit and it seems to be a clever one at that) is that there is a dearth of hard, quantitative data on the Internet what makes a fast car. One notable exception is the Pack 146 site. There is a wealth of good theory and conventional wisdom, but not much real test data, e.g. we varied this parameter and got this result.... etc. etc.
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terryep
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Re: Test Tracks

Post by terryep »

You make a good point about needing a rail. The goal is not to hit it but that's not an achievable goal. I know from experience that if my alignment is good and I don't use radical wheel or axel treatments the rail is pretty much a non issue. If I were to consider canted axels, or some other innovation, I'd want those tested on a real track (the track) I believe in basic principles. Terminal velocity, friction, alignment. There are lots of theories, some make a lot of sense, some less so.

Happy testing!

Terry
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MathGuy
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Re: Test Tracks

Post by MathGuy »

Terry thanks for ideas.

Ad-hoc we inclined 8 foot board last year, but it wasn't that enlightening for testing. Your ideas would seem to work better. A small scale, low speed, tuning track, using distance as a gage, seems like a practical way to do some testing with our boys.

Distance method does seem to be a affordable option to a personal timer, compared to a more elaborate test track.

I am going to try your 1.5" x 16" ramp idea.
Fun for one, Fun for all.
Rob D
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terryep
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Re: Test Tracks

Post by terryep »

Glad to help MathGuy, here is a pic of my ramp.

Terry

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MathGuy
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Re: Test Tracks

Post by MathGuy »

I have put together a easy track for table top testing. The difficult trick that I had was trying to get the transition from ramp to the flat table.

I solved the problem by pick up a pack of wood shims at the local Home Depot, sanded them a bit. Put up a few inch incline, and I was done with a easy to create table top test ramp for low speed testing.

Thanks for the idea Terry
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Rob D
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