Tungsten Cube Placement

[PushcartDerby]

On our scout car my son wanted to have a design that wasn't completely flat, but still have it as light as possible. With some work we have made the weight of the body, wheels, and axles at 1.15 oz allowing for 22 cubes or 3.74 oz making a total of 4.89 oz.

We have put two rows of 6 behind the axles and one row of 6 infront. Where would you place the other 4 cubes? Centered in the pocket, on the DFW side, or some other configuration?

 

[Eliminator Racing]

+1 on the DFW side.

 

[B_Regal Racing]

For me, it usually seems the the weight on the rear wheel on the DFW side is always lighter (my cars mostly flat, but always symmetrical). If you have a scale (or better yet, 2 scales), place the tungsten such that the weight on the back wheels are equal. It seems to help me. If you do not, I would place them towards the DFW side.

Then again, I'm still learning...

 

[PushcartDerby]

I am still learning as well, in fact this is my first build.

 

[Maglev]

Try replacing 3 of the last four 1/4" tungsten cubes with a 0.5 oz tungsten plate and stick it with double sided tape under the car centered between the rear axles, then cover the weight pocket with silver metal foil tape (3M, Lowes). Then the last cube can hang out in the DFW side corner - if you can tame this aggressive COM setup by tuning 3-4" over 4' and get rid of wiggles, you'll find the results are quite rewarding. Good luck and keep building, see ya on the NPWDRL track soon!

 

[B_Regal Racing]

Assuming you built your car with a stock wheelbase and you re-located your rear axle 5/8" from the rear of the car, with 12 cubes behind the rear axle, your car will have the following specs:

	Weight	Inches	8ths/In
Front Wheels	0.23	5.00	0.00
Rear Wheels	0.23	0.00	5.00
Weight 1	2.00	0.00	3.00
Weight 2	1.00	0.00	7.00
Weight 3	0.67	1.00	1.00
Weight 4	0.00	0.00	7.00
Weight 5	0.00	0.00	3.00
Car Body	0.70	3.00	4.00
Total	4.83

	COG	Inches	8ths/In	Weight
COG	1.24	1.00	2.00
COG (r/axle)	0.61	0.00	5.00	4.16
Wheel Base		4.00	3.00
FDW				0.67

It also assumes your car without weight and wood has a COG about in the center. The design will yield a 5/8" COM. I use the spreadsheet to calculate my front to back COG. I weight each rear wheel to get the COG in the middle from side to side (e.g. equal weight on each rear wheel). Most of the guys here probably do this in their sleep; I still need a bit of help from Mr. Gates.

 

[Obsessedderbydad]

Weight placement is one of those "secrets" that a lot of pro's won't talk about. I honestly haven't seen any tests that say one way or the other for weight on the DFW side or NDFW side. I have heard more leaning towards the DFW side though.

+1 on the aluminum tape. It's found by the glue, duct tape or flashing section of hardware stores.

Tip: weigh your car in grams if you can. It's more accurate then oz.

 

[Obsessedderbydad]

Calculating and knowing your COG is good, but when you have 12 behind and 6 in front, you COG doesn't really matter. People look more at the weight distribution per wheel.

 

[B_Regal Racing]

Seems to be that way, that there is standard basic weight placement. My cars seems to vary between .005 and .009 between runs without the tungsten, so its has been a bit hard for me to figure this enigma out. If I change the weight on the rear wheels (side to side), I can not determine if I am making progress or making headaches with the variation between runs.

 

[~JBD RACING~]

Thing is all cars are weighted almost the same... The only difference is 2-3 cubes moved around to get the sweet spot. Most all the speed is in the PREP. All my cars are weighted the same besides 2-3 pieces. I'm sure other PROS will agree with me... Those 2-3 cubes can determine more steer or less steer if places right.

 

[Mister B Racing]

Thing is all cars are weighted almost the same... The only difference is 2-3 cubes moved around to get the sweet spot. Most all the speed is in the PREP. All my cars are weighted the same besides 2-3 pieces. I'm sure other PROS will agree with me... Those 2-3 cubes can determine more steer or less steer if places right.

Does the wheelbase length on a car make a difference when you weight the car? More or less aggressive to the DFW side with the 2-3 cubes depending on wheelbase length?

 

[Kinser Racing]

The difference is a few cubes. /images/boards/smilies/thumb.gif Wheelbase will add to the equation. Every car is a little different and you have to find what works best on that particular car. There is no secret being held back except by the car itself. /images/boards/smilies/biggrin.gif

 

[PushcartDerby]

All very interesting responses. Looks like I have some learning to do when it comes to racing NPWDRL. At this point I only have one scale, but it does do grams ODD and I do have foil tape. The wheelbase is 5/8 from back B_Regal. I will have to learn how to move a couple cubes around JBD. Thanks for all the great info guys.

 

[speed bump]

This is something I have not played with. Waiting on my car to get back and I have to play around with the weights. Maybe find something. Great info guys!!!

 

[OPARENNEN]

With 2 scales, equalize weight on two rear wheels.
I found out that the further back the COG is, the more drift the car needs. Even Elim and Unlm.
If you have a body that only takes 10 cubes behind the axle, glue two tungsten plates to the bottom. Same effect, plus during testing, you can move the plates back and forth to find the sweet spot.
I am still using one plate on the bottom even with 12 cubes behind the axle. Except, that plate is further forward, about even with the rear axle. You can do the same with a piece of sheet lead.

 

[HMH Racing]

With 2 scales, equalize weight on two rear wheels.
I found out that the further back the COG is, the more drift the car needs. Even Elim and Unlm.
If you have a body that only takes 10 cubes behind the axle, glue two tungsten plates to the bottom. Same effect, plus during testing, you can move the plates back and forth to find the sweet spot.
I am still using one plate on the bottom even with 12 cubes behind the axle. Except, that plate is further forward, about even with the rear axle. You can do the same with a piece of sheet lead.

Oparenen, I was wondering if anyone was using the flat plates with the tung. cubes. I weighted one of our 3 cars in graphite like this and it was the slowest. I do not have a test track, yet /images/boards/smilies/smile.gif Can you tell me how much steer you recommend in 4'?

 

[speed bump]

Thanks Oparennen. This something I have not done but looking at it very close. Going to change some of that weight in car that I raced last month.

 

[OPARENNEN]

Oparenen, I was wondering if anyone was using the flat plates with the tung. cubes. I weighted one of our 3 cars in graphite like this and it was the slowest. I do not have a test track, yet /images/boards/smilies/smile.gif Can you tell me how much steer you recommend in 4'?

[/QUOTE]

I have 2 UNL's and 2 ELIM's weighted like this. Snake from April Unl Event is done so. Check out the results.
Old Blu (Elim) also. Was 5th. Give or take, the steer on both cars was somewhere between 7" and 9" over 8'. Didn't check sit at 4'.
But COG was only 1/2". That's why it need more steer. On my own test track, I ran both cars at least 20 times, moving the steer up or down 2 inches at a time (on a glass tuning board). Obviously all used oil.

 

[davet]

With 2 scales, equalize weight on two rear wheels.

I have a question regarding this. I have 2 identical scales that calibrate the same. In order to weigh the rears together using the 2 scales on of the scales is facing one way while the other faces the other way. I can't get consistent readings. It does seem better if I remove the wheels and run the axles only in the rear. This way I can face both scales the same way since the contact point on the scale is now way out at the head of the axle. Can you show a pic of how you set your car on the 2 scales?

With 1/2" COM you mentioned a steer of 7"-9" in 8'. That's only 1.3"-2.0" steer in 4'. Are you getting .67 oz on your DFW with that COM and offset weight? I don't have a test track either but a darn smooth diningroom table and death wobble scares me. WE run extended wheelbase with wheels 5/8" from front and back so the numbers might be different I guess. Thanks.

 

[IAE Racing]

Generalization here but often time the SS's like a little more steer than UNs and ELs.