COM/Weighting for Long Track

[speedmerchant]

Hello everyone! I am new to the forum and really appreciate all of the great insight the forum has to offer.

My son and I are coming up on our 2nd PWD in late January. Last year he won his Pack race and went on to the districts where he finished 5th. We spent a lot of time together learning about the physics involved in making a PWD car as fast as possible (on an elementary level, of course). We did a ton of research and were meticulous in assembling the car. He won his Pack by a wide margin. There wasn’t a car within 2 car lengths all day. ;D

However, at the District race we couldn’t manage better than a 4th place finish. We lost to cars that “appeared” to have very little science involved. In fact, the winning car was a rather large, blocky design with the weight screwed onto the top and well forward of the rear axles. After the race, we checked the alignment and found all to be excellent. The COM on our car was at 1 inch in front of the rear axles.

The only difference between the Pack track and the District track was length and material. The Pack track was standard 32 foot wooden (great shape) but the District track was 46 foot aluminum. My question – were we too aggressive in our COM location for a long track? The car seemed to slow quicker than all the others. The dilemma – how to weight a car that needs to win on a standard track AND a long track since we can’t change it after the car is built? I have come up empty in my research in trying to find answers to this. I do not have a track to test theories on either, so I'm hoping the Pro's can help!

Thanks for any insight!
Mike

[RacerX]

Speedmerchant, Welcome!!!

Your COG is fine it is an alignment issue and these tend to come out the longer the track gets and it takes a little different set-up and some luck going from one track to the next.

On a 32' wooden track a "Dead On" alignment is usually the hot ticket if you can get it. In the past we have been able to get our best times like this and the car will tap the center rail 2 to 3 times lightly on the way down and produce a quick time. Now put this car on a 42" alu. track and it is slow because at around 30' it is glued to the rail and dragging the breaks. A rail hugger styl alignment is what you are looking for. Something that is lightly steered into the rail. of course the best way to set this up is with a track and timer and you adjust until it is as light on the rail as posiable, but I believe Wheeler or Warp Speed have a table top formult of around 1" of drift to 3' that will give you a starting point.

Race Fast

Racer X

[j2ce]

Speed,

Just my two cents. My son always cleans and relubes the wheels and axles between Pack and District races. This forces him to realign the car and has always done better at District than Pack. Because our area is small all kids are allowed to participate in both Pack and District. Good luck.


j2ce

[speedmerchant]

RacerX,

Thanks for the reply and info. I apologize if I'm a little ignorant here but in your mention of a railhugger design isn't it contact with the rail we are trying to avoid? I'm sorry this is probably a dumb question.

Thanks!

[wheeler]

Speedmerchant, very light contact equals control, equals speed.

[speedmerchant]

Well, given that the rail hugger design requires more expertise than I likely possess at this point (and given that I don't have a track to test on) I'm sure this mod is best left for the future. And, I suspect, based on what I've seen and heard in my neck of the woods, such extreme mods probably aren't necessary to create a winning design.

Which leads me to what I can control and what my son would understand, alignment. Can anyone point me to some tried and true alignment methods that are currently used? I've heard talk of wax shims or foil, etc. but have no idea how to actually do it.

Thanks guys, I really do appreciate your help. I only hope to be able to add some value to this forum someday instead of asking all the questions. Gotta start somewhere though I guess.

[dsracing]

I run a 64 foot track in aluminum. The fastest cars I have seen out of 5000 races in the last 5 years have the weight placement like yours. The biggest difference between a shorter track and a long track is the friction caused by wheels on axles and body shape. With a smooth sleek shape, wheels and axles are most important. Make sure the wheels are the same diameter, polished inside, light as your rules will allow and your axles polished and without blemish - nails usually aren't good enough. There are many sources for "machine pins" or speed axles. Notching the axles also helps to hold graphite inside the wheels during the racing.

Good luck - hope this helps

[dsracing]

One other thought and that is the lubrication. Read the threads on lube and make a decision about the type to use.

[maxx]

Hello speedmerchant,this i believe is my first post so here it goes.In the last few years I have found a few places with good info on alignment.probably the most detailed was at "Pope's Place''.Here is a link to the site,you will have to follow the link to the pinewood derby book.Hope this helps.If i come across some of the other links i have found in the past i will post them in this thread.

Maxx

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