COG location in relationship to track length

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kokoruz
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COG location in relationship to track length

Post by kokoruz »

On Tuesday my son had his trial run to see how his car was doing. Our Pack has a 32 foot wood track. It's old but the Pack has done a good job of maintaining it.

As I looked at the straight away on this 32' track it made me wonder if the COG would vary depending on track length. We've always built his car with a 1" COG. This year we built 2 cars, one that was 3/4" and one that was 7/8". We raced last years car (1" COG) and depending on the lane they all were to close to call without a timer.

One boy and his father raced a sliver car with a tapered underside to take advantage of the gate drop and this car was greased lighting. When that gate opened that car took off like I've never seen and it made me wonder what the COG on that car was and if the tapered underside really does help.

His son is a Webelos II and when I asked the Dad what the COG was he said he did not know, but know ones builds a car like that without knowing. I almost wonder if it was greater than an inch the way that thing dropped like a lead balloon.

Does anyone have any thoughts on where the best COG is for a 32' track vs the longer 40' and 48' tracks.

Looking forward to everyone's thoughts.
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Re: COG location in relationship to track length

Post by rpcarpe »

Couple of questions:
- Gate drop is manual, spring or solenoid?
- How steep is the slope of this wooden track?
- What are your rules?

I might be wrong, but I though COG was more important for track type, not length. The slant on the slope, the tightness of the transition, the height of drop...

Length of track would be more important in deciding wheel weight and rail-riding.

If the 'silver car' starts faster, then the wheels are lighter or it's better lubricated.
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kokoruz
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Re: COG location in relationship to track length

Post by kokoruz »

The Gate Drop is Manual

This picture looks identical to our track
http://www.oocities.org/~pack215/pwd-piantedosi.html" target="_blank

Slots are not mandatory (we typically drill holes to extend the wheel base)
All 4 wheels must touch and be flat
minimal wheel clean up. No lathe work
nails can be debured and polished. No lathe work. No notches.

Interested to hear your feedback.
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FatSebastian
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Re: COG location in relationship to track length

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kokoruz wrote:When that gate opened that car took off like I've never seen and it made me wonder what the COG on that car was and if the tapered underside really does help.
A tapered underside can help on a manually opened gate (but the outcome is usually not jaw-dropping).

CoM placement tends to have little noticeable effect on performance right out of the gate. CoM placement foremost affects speed coming out of the transition and onto the flat.

If the Webelos II car is coming out of the gate like greased lightning, it is more likely due to improved staging, alignment, and lubrication. Also, lightened wheels will exhibit the same behavior - do your rules allow wheel modifications?
kokoruz
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Re: COG location in relationship to track length

Post by kokoruz »

What could I do to help with lubrication? Is there a trick to applying graphite? Is there a certain amount of break in time? Someone once told me they put their car on a treadmill? Has anyone ever heard of this? If so how long do you leave it on and how fast or slow should you make the belt speed? How often do you reapply graphite if you do leave it on the belt?

Any advise would help. My sons race is on Saturday.

Thanks everyone.
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FatSebastian
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Re: COG location in relationship to track length

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kokoruz wrote:Someone once told me they put their car on a treadmill? Has anyone ever heard of this?
Yes, and it is not recommended.
kokoruz wrote:What could I do to help with lubrication? Is there a trick to applying graphite? Is there a certain amount of break in time?
Lubrication is a completely different topic than "COG location in relationship to track length," so it may be inappropriate to venture far into that here. However, graphite application is only one small part of a much larger lubrication process that also involves axle polishing and wheel-bore and wheel-hub treatments. Here's one of the more informative topics on graphite lubrication and break-in IMO, but don't forget about the search feature.
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Re: COG location in relationship to track length

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And keep the car OFF the treadmill.
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kokoruz
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Re: COG location in relationship to track length

Post by kokoruz »

He took first place in his rank! We were pretty impressed because his Den has about 16 boys, so he had some real competition. I found out he had the second fasted car in the entire Pack (about 60 boys) and just missed out first by a couple hundreds of a second. He now gets to race at the council level in April. They take the boys cars and box them up and we won't see them again till race day. Wish us luck! I'll post times when I get them.

Thanks for everyone's feed back!
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Stan Pope
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Re: COG location in relationship to track length

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kokoruz wrote:...
They take the boys cars and box them up and we won't see them again till race day.
...
Bummer! No chance to learn from the experience!
Stan
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geauxturbo
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COG location in relationship to track length

Post by geauxturbo »

Locking up the cars also lends an advantage to folks with a test track or access to one. Some boys are racing for the first time on a track at Pack with no tweak and tune prior. Learning is trial and error. How can you learn and tweak if the car is locked up?
kokoruz
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Re: COG location in relationship to track length

Post by kokoruz »

Per the rules of our Council, every Pack that participates in the Council race is suppose to follow these rules. Assuming all the Packs are following this rule it makes for an even playing field. As for test tracks, I have no idea where I would even be able to take me son to tweak his car. The morning of the Pinewood is when we find out if our ideas pay off.

I did find out his race results. On our 32 foot wooden track his car came out at 2.4577. They race the cars on all three lanes over the course of the afternoon and take his average. His best run was 2.4497.

He was 2nd in the Pack. The boy that had the fastest car in the Pack had a speed of 2.4425.

I consider it a success because we beat our own time from the year before 2.4798

I'm assuming these are pretty fast numbers. Wish us luck at the Council level.

K.
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Re: COG location in relationship to track length

Post by rpcarpe »

Congrats!
Also, too bad you have to run your prototype for the first time at the race.
Assuming your 32 foot track is actually 32' from start pin to finish line... those are good times.
Even taking off 2' for start ramp and finish/stopping area you're doing all right.
I did the feet divided by the time = feet per second to miles per hour.
This helped: http://onlineconversion.com/speed_common.htm" target="_blank
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drathbun
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Re: COG location in relationship to track length

Post by drathbun »

kokoruz wrote:On our 32 foot wooden track his car came out at 2.4577. They race the cars on all three lanes over the course of the afternoon and take his average. His best run was 2.4497.
rpcarpe wrote:Assuming your 32 foot track is actually 32' from start pin to finish line... those are good times.
Even taking off 2' for start ramp and finish/stopping area you're doing all right.
We have a 32' wooden track (total length = four 8' sections, so subtract some for starting gate and ending timer position) and our averages are in the 2.3 range. Winning times are consistently in the 2.2 range. We've seen this before; last year some of our pack went to another pack that held an open race. Our cars that ran low 2.3's or even 2.2's on our track were running much slower on the other track.

My oldest boy ran consistently 2.28 in all four lanes. His car was super smooth running down the track, I don't think I saw it wiggle ever. It was not intentionally set up as a rail rider.

Where is all this rambling going? I'm wondering, is there such a thing as a "fast track" when compared to others? I would think a 32' wooden track would run about the same times from one location to another. But 2.4 times on our track aren't going to come near the top times for our pack cars. Or maybe it's just that the floor of the cafeteria at our school where we run our races runs slightly downhill...
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FatSebastian
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Re: COG location in relationship to track length

Post by FatSebastian »

drathbun wrote:I'm wondering, is there such a thing as a "fast track" when compared to others?
You may want to glance at this topic.
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