CoG Calculator

[davet]

Its hard for me to become one with the car by tuning it on our kitchen table with the extra leaf added but I'll give it a try.

 

[Kinser Racing]

Its hard for me to become one with the car by tuning it on our kitchen table with the extra leaf added but I'll give it a try.

You have to stare at it for long periods of time and communicate with it telepathically. When you're ready it will speak to you, but you have to be ready.

 

[IAE Racing]

Its hard for me to become one with the car by tuning it on our kitchen table with the extra leaf added but I'll give it a try.

You have to stare at it for long periods of time and communicate with it telepathically. When you're ready it will speak to you, but you have to be ready.

I have also done "hmmmmm na na na na "

While the kitchen table will work, might be time for a tuning board. It doesn't have to be fancy. Every time you set it up to tune a set of cars, you will learn something new.

 

[davet]

You have to stare at it for long periods of time and communicate with it telepathically. When you're ready it will speak to you, but you have to be ready.

You guys crack me up. I'm ashamed to admit it but I will from the anonymity of my computer: I've held that darn car in my hand, turned it this way and that, held it from the front then from the back and took note of the weight difference all while trying to recall every single post I've read. While doing this, usually when my wife isn't around and the kids are in bed, I think of the different ways to weight and steer the car. I know that for this specific car there is an optimum weight placement and steer combo that would give the most speed available for this design. The problem I have is the weights and axles don't adjust themselves to that optimum position while I stare it.

And to think I'll do the same with next year's car which will have an entirely different personality is causing me just a little anxiety.

 

[GravityX]

You guys crack me up. I'm ashamed to admit it but I will from the anonymity of my computer: I've held that darn car in my hand, turned it this way and that, held it from the front then from the back and took note of the weight difference all while trying to recall every single post I've read. While doing this, usually when my wife isn't around and the kids are in bed, I think of the different ways to weight and steer the car. I know that for this specific car there is an optimum weight placement and steer combo that would give the most speed available for this design. The problem I have is the weights and axles don't adjust themselves to that optimum position while I stare it.

And to think I'll do the same with next year's car which will have an entirely different personality is causing me just a little anxiety.

I'm afraid we have all been there at one time or another my friend.

 

[davet]

Let me run these numbers by you guys and tell me what they're "saying" to you all.
--Pack race: 5.04 oz car, COM of 3/4" with DFW at .67 oz and steer at 3 1/2" over 4'. Took second overall.
--District race: Longer track (46'), 5.04 oz car, COM of 11/16" with DFW of .65 oz and steer of 4" over 4'. Took 1st in Bears and had faster times than the car that beat us in the Pack race.
--Council race coming up June 7th: Longer track yet (56', extra length added to bottom section). Still at 5.04 for the car, COM of 11/16" with DFW of .65 oz. This time we've covered the open center section top and bottom. For the longer track do we increase the weight on the DFW and go less steer for long flat section?

Prior to the first race (Pack race) we got a practice run on the track. We had 3 1/2" of steer in 4' and hadn't added our tuning weight yet. The practice run was with .64 oz on DFW and she was quiet and no wobble. We added our tuning weight just ahead of rear axle and raced it.

Stare at these numbers in the presence of silence, try to become one with our car and listen for what it's telling you. Pic included to help with the visualization. Please, no VOODOO curses if we happen to be racing against you June 7th. Remember!!!!, its for the kids!

 

[quadad]

davet - what is your car's wheelbase ? I am guessing std Scout WB, but IMHO any discussion of COM needs to list WB also.

And are you running graphite or oil ? Are the Council rules different from your Pack/District rules ? Is the track changing ? Are you reprepping wheels between these races or not ?

As the track gets longer, COM becomes less important and bore prep/friction losses become more important because the car is spending more time coasting down the track. No one person can give you the magic formula for your car as a function of any car specs though. The only way to "know" is to run it on the intended track. What have you learned form the races you have run already ?

 

[ngyoung]

CoM shouldn't really be a factor if the ramp and transition are still the same. The point where your car is in the most danger is in the curve from the ramp to the flat. If yours has been performing without any issues, a longer flat section isn't going to be a factor. Like quadad said, alignment and wheel/axle prep are what will be the biggest factor. You've seen the car run, if it ran smooth like you said you probably do not want to try to tinker with CoM and steer. At this point you won't have a way to tell if you're shaving off a thousandth of a second or adding. From what I have read here the guys that have a track and have posted test results it is a very small sweet spot for the fastest times when adjusting the steer.

Having a longer track just gives the cars that are stable a longer chance to catch up to a car that came out of the slope ahead but is wobbling down the flat. Watching a lot of the pro races and Mid America there were plenty of cars that won their heat but were wiggling the worst and would have lost if there was 1 more track section added.

 

[davet]

davet - what is your car's wheelbase ? I am guessing std Scout WB, but IMHO any discussion of COM needs to list WB also.

And are you running graphite or oil ? Are the Council rules different from your Pack/District rules ? Is the track changing ? Are you reprepping wheels between these races or not ?

As the track gets longer, COM becomes less important and bore prep/friction losses become more important because the car is spending more time coasting down the track. No one person can give you the magic formula for your car as a function of any car specs though. The only way to "know" is to run it on the intended track. What have you learned form the races you have run already ?

We're at 5 9/16" WB (5/8" in from both ends) and we're running oil. Same rules apply to all races and we're reprepping axles an wheels before each race.

 

[davet]

I'm thinking COM is a big factor after the ramp only in the fact that a less aggressive COM will allow less steer which means less friction down the flat.

 

[quadad]

I'm thinking COM is a big factor after the ramp only in the fact that a less aggressive COM will allow less steer which means less friction down the flat.

I think this is valid, but don't know how big of a factor.

Just wondering though if your car might get faster with more heats. Usually you don't get too many in those races. My fastest oil cars speed up for a while.