Eliminating wobble from the track's standpoint

Discussions on race planning, preparations and how to run a "fair" and fun race.
Speedster
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Re: Eliminating wobble from the track's standpoint

Post by Speedster » Fri Feb 08, 2013 4:49 am

Do you have the exact same set-up as your Pack track? Start mechanism? Timer? EXACT same distance the cars travel between the 2 tracks? Same curve on both tracks? Assuming your older cars are still in Perfect condition, have you raced the older cars against your new one? Are the older cars beating your new car?
It's cold here in Ohio. Is your track in your garage with no heat? My two test cars both recorded times .03 seconds slower between the run times from June 2012 and then December 2012.
Forgetting about the Pack track, the real test would be how the cars do against each other on your new track as long as the older cars have not been damaged.



rpcarpe
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Re: Eliminating wobble from the track's standpoint

Post by rpcarpe » Fri Feb 08, 2013 9:27 am

Here's an idea we use for track testing:
- Postion a set of eyes at each joint of the track
- Check for bumps, burrs and gaps.
- Run a car slowly over each joint
- Run the car normally the length of the track, check for wobbles, wiggles and swerves.

Checking against older 'test' cars is a good idea as well as all the hints Stan gave.
Good Luck!


My wife started a new support group... Widows of the Pinewood Derby.

Shawn Stebleton
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Re: Eliminating wobble from the track's standpoint

Post by Shawn Stebleton » Fri Feb 08, 2013 11:30 am

Would it make sense to make rail-rider test cars? I think so, but they would have to be built so as to have the greatest chance of getting affected by a bad joint.
  • Have two cars--one car with the DFW on the left, the other on the right. That means two cars, right? Or would a well-designed thin car with 4 on the floor be able to run right-side-up for one rail test and upside-down for the other?
  • Have the DFW be vertical--no camber. This will have the greatest contact area with the rail and will result in the wheel slamming into the rail if it is misaligned.
  • Have as little toe as is necessary to keep the DFW on the rail. Adjust as necessary. Too much toe is definitely better than too little toe, but the smallest toe necessary will keep more of the inside rim on the rail. How to adjust toe without changing camber? Without re-bending or changing axles?
  • Have the COM very rearward (1/2" or less?), making the front wheel carry little load. This will cause imperfections to deflect the front more easily.
The car doesn't have to be legal for a race, so don't worry about things like 5oz limit, minimum 3/8" clearance, minimum 1-5/8" between wheels, must use slots, etc. It just has to fit the track and tell us what we need to know. They can also be used to satisfy parents that the track is in very good shape and ready to go.

This is all about making a level playing field for the boys. After all, they can understand when another boy's car beats theirs, but it's much more difficult when their car is faster but gets beaten by a bad track joint.


Shawn

chromegsx
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Re: Eliminating wobble from the track's standpoint

Post by chromegsx » Fri Feb 08, 2013 11:00 pm

Shawn Stebleton wrote:Would it make sense to make rail-rider test cars? I think so, but they would have to be built so as to have the greatest chance of getting affected by a bad joint.
  • Have two cars--one car with the DFW on the left, the other on the right. That means two cars, right? Or would a well-designed thin car with 4 on the floor be able to run right-side-up for one rail test and upside-down for the other?
Makes sense to me. I would make 1 car with 2 sets of holes in the front for DFW left or right. Or just drill both front axle holes the same and just leave off the other wheel.



TimInOhio
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Re: Eliminating wobble from the track's standpoint

Post by TimInOhio » Mon Feb 11, 2013 3:52 pm

Stan Pope wrote:
TimInOhio wrote:This is the situation I am in: my Scout and I put a considerable amount of work into his car this year, and bought a test track. The car runs much slower (on our test track) than any other cars we've built run on the Pack track, so I am really crossing my fingers that my first attempt at setting up the test track yielded less than optimal results, and that once we get on the Pack track, things will fall into place. :nervous:
Well, I see that the test track and pack track should perform comparably.

And you can not see any reason on the test track why its times are slow. If you did, we would not be talking.

So, how did it perform on the alignment table? What did you do on the alignment table to prove that the car was ready for on-track testing?
== Did you prove rear end alignment?
== Did you prove rear wheels off the rail?
== Did you prove planned DFW toe?

If you didn't do all those things, take it back to the alignment table and prove 'em. Bet one of them shows a significant problem ... and not the third! :)
Thank you for the reply, Stan.

I suspect that I had a guide rail joint on the track that was not perfectly aligned. Unfortunately, I had to tear the track down and return the living room and hallway back to normal usage (wife returned from out-of-town trip). I had about 4" of steer over 4' according to the alignment board. This is for a 4-on-the-floor setup. We wheeled the car forward and back and the wheels migrated to the axle heads in both directions.

Side note: I fought for quite a while with a thumbtack under the front end that was steering hard in the wrong direction. I'm guessing that the mold mark (all I had was a plastic-headed thumbtack) was acting as a rudder, so be aware of this if anyone else tries this.

We very slowly rolled the car along the test track and never saw the rear wheels touch the rail. Body has been narrowed 1/16" at the DFW.

The alignment board will come back out this evening and we'll begin going over the points you mentioned. Thanks again.



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