Timer Test Car

General timing system discussions.
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dna1990
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Timer Test Car

Post by dna1990 » Wed Feb 06, 2008 4:49 pm

I know folks have talked about using paper or other objects to pass by a timer's sensors, looking for lane bias, occlusion factors, etc.

I am wondering if there is value in making a car designed to test multiple lanes?

It would be a basic flat board, the width of the whole track. Wheels in the outermost lanes. Probably feasible up to 4 lanes, probably too difficult to keep perpendicular beyond that. One end could be straight across to help see how 'ties' may look to your timer.

You could run the car backwards and the other end could be cut in a stair step pattern. Equally spaced so that each lane finished say 1/2" apart from each other.

Now this doesn't do anything to test overall accuracy from the start pin. But what you would expect that whatever the difference in time between 1st and 2nd, is a constant thru 4th place. Assuming you run the test car thru the finish gate at a constant speed. Maybe some lag starting to show between 3rd and 4th as the car deaccelerates.

The stair step pattern could be a separate piece of masonite and be screwed to the main car deck. Thus allowing for a collection of the 'profiles' with different finish orders and spacing gaps.

I guess the question is, what would it prove or show? It would only be good at showing relative time differences. And what is the likelihood of those being off...


What if you could go further, and add an independent timer to the car. Something where it actually runs from the starting pin like normal. Perhaps with a push button engaged at the pin. The gate drops, the switch opens and starts a high resolution timer running from some PIC and 9V on the car. But how to detect finish line? Most folks go sensors in the track with lights above. This means trying to put sensors on the car and ignoring ambient light until passing under the IR or LEDs at the timer.

Now the two times would likely never match exactly. The difference in just the two starting switches could be a millisecond. But again over a few runs, the car's time should be the same relative difference from your timer each run.

Fun design candy, but would it really be practical or useful?



We have four 'ol cars we use to test the track with when we setup. After only a few runs, one can learn the expected finish order, as they each run pretty consistent. This got me thinking to making the car interval fixed and known, and not just helping verify that finish order was being recorded properly, but that indeed the times were 'in the right ballpark'.

If nothing else, it helps visually show your audience that you are making attempts to detect inaccuracies.



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joe
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Re: Timer Test Car

Post by joe » Wed Feb 06, 2008 8:29 pm

dna, what an original idea. That seems like a great test to me! Of course, if more than one pinehead makes one, we'll have to have a race-off!



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Re: Timer Test Car

Post by jeffd » Wed Feb 06, 2008 9:27 pm

since this car wont race... Why not build it so it spans the width of your track?

For instance - we have a four lane track. the left wheels would go on lane 4 (left side of track) - and the right wheels would go on the outer part of lane 1.have the front be a perpendicular piece that would span the whole track. I think balsa might be good for this.

You could even take 2 kits - set 'em on the track to get the width - and glue a sort of stringer across the span.

The test would be if the software (I assume you have a timer) reports a 4 way tie. Or if they at least are mostly tied.

just my random thoughts on this.



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Stan Pope
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Re: Timer Test Car

Post by Stan Pope » Wed Feb 06, 2008 9:47 pm

jeffd wrote:since this car wont race... Why not build it so it spans the width of your track?
Yes, you grasped what he said! :)

I think that the car will have to be quite a bit longer than 7 inches so that it will stay even across the lanes. Adding a "trailing pair of wheels" snugged on one lane and ollowing the front wheels by about twice the track width should keep the front end pretty even. Suppose 1/16" play in the rear and front ends should produce variance of 1/32" across the front of the megacar. Same tolerances with a trailing pair only 1/2 the width behind produces about 1/8" variance across the front. That is way too much to do meaningful test with.


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jeffd
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Re: Timer Test Car

Post by jeffd » Wed Feb 06, 2008 10:08 pm

Stan Pope wrote:
jeffd wrote:since this car wont race... Why not build it so it spans the width of your track?
Yes, you grasped what he said! :)

.
Ok - this is my sign to not mix sleeping meds and posting :)

Good night all!!



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Re: Timer Test Car

Post by doct1010 » Wed Feb 06, 2008 10:12 pm

Guys there may be an easier way! When setting up the packs new timer and software, fresh from the timed vs points ahemmm debate, I decided to test it's accuracy. I took a T square modified the tail to fit snug between guides, at least 18" sat squarely on track. Broke laser beam at start, I then pushed past sensors, recorded 3 way tie. I was satisfied and relieved.



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Re: Timer Test Car

Post by dna1990 » Thu Feb 07, 2008 8:28 am

Easier way doc, well sure I knew that. :D But where is the fun in that?

And yes, Mr. Pope, I think it would need more than the standard wheel base and some feeler guides. But if it will still wiggle up to an 1/8" across the front, then that is no good.

But I think that could be reduced by using just homemade razor-looking wheels from metal washers, etc. Again, tight fit to a solid axle, etc. I guess depends on how good the guide strips are on a given track.



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Re: Timer Test Car

Post by doct1010 » Thu Feb 07, 2008 8:51 am

dna1990 wrote:Easier way doc, well sure I knew that. :D But where is the fun in that?
OK, slap some wheels on the T square, just for fun! :D But if you are interested in accuracy....



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pack529holycross
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Re: Timer Test Car

Post by pack529holycross » Thu Feb 07, 2008 8:59 am

dna1990 wrote:Easier way doc, well sure I knew that. :D But where is the fun in that?

And yes, Mr. Pope, I think it would need more than the standard wheel base and some feeler guides. But if it will still wiggle up to an 1/8" across the front, then that is no good.

But I think that could be reduced by using just homemade razor-looking wheels from metal washers, etc. Again, tight fit to a solid axle, etc. I guess depends on how good the guide strips are on a given track.

My recipe for a track testing device:

get X number of derby car kits ( equal to your lanes )
install the wheels and axles, weight them to 5oz each
line them up on the starting gate
using the plastic strips that are used to bind packages, or any other flexible plastic strip, lay the strip across the top of the cars and screw the strip into each car at its center point. when you run the "group" down the track you can watch for cars that jump due to irregularities in the track.



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joe
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Re: Timer Test Car

Post by joe » Thu Feb 07, 2008 9:00 am

I took a T square modified the tail to fit snug between guides, at least 18" sat squarely on track. Broke laser beam at start, I then pushed past sensors, recorded 3 way tie.
Doc, is this the original "no-wheeler?" You've eliminated all the axle/bore friction!



doct1010
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Re: Timer Test Car

Post by doct1010 » Thu Feb 07, 2008 9:25 am

joe wrote:
I took a T square modified the tail to fit snug between guides, at least 18" sat squarely on track. Broke laser beam at start, I then pushed past sensors, recorded 3 way tie.
Doc, is this the original "no-wheeler?" You've eliminated all the axle/bore friction!
:lol: Now you got me thinking! Hmmmm no wheeler. Magnets are prohibited right? :lol:



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