First PWD Car - Plans

[geauxturbo]

This will be our first derby car. And here is our plan so far.... if you see something that screems "I wouldn't do that" PLEASE let me know

Body/Weight - fairly flat with a few curves for cool factor. Hoping body weighs around 1 oz or so. Really have no clue there. That leaves 3.5 oz of weight to add (minus paint). 3 holes drilled in lower back for easy cut tungsten cylinder weights. Centered one to be used by adjustable tungsten weight. We're not that good so I like the idea of being able to adjust the COM by adjusting the weight. Also have tungsten puddy. Going to leave 0.50 oz for paint and then add puddy in the center hole as needed. Kind of battling the idea of hollowing out the underside and flattening the cylinder weight or something to add it lower.

Wheelbase - Extended with slots. Must have slots per the rules. Going to press in straight axles while the block is square. Don't have a drill press but have an axle press guide. Honestly my biggest fear. I'd hate to have the poor kid work for weeks on this and the axles fall off and we can't get it aligned.

COM - shooting for 3/4" Not too aggressive but not "unaggressive" either. See if we are close to 1 oz on the DFW.

Alignment - 3 wheel RR. Shave 1/16" from DFW side. Cant 1.5 in front and 2.5 in rear. Shooting for 1.5" per 4 feet. Will run with rears only on a glass 4' test ramp. Look for rears moving outward in both directions and test without front wheels.

Paint - Duplicolor sandable primer, base coat, and clear coat. Glazer after primer for an extra smooth look. Sweet flame stencils. Lots of sand paper and polish to make it perty. My boy will definitely know how to spray paint and sand when its all said and done.

Axles and wheels. Test for straightness, groove, and polish. Wheels trued but otherwise must be stock. Can polish bore. Have pipe cleaners and bore polish. Put best two axle/wheel combos in back. Max-V graphite.

Final testing on a treadmill since we don't have a test track. Check for any wild irregularities. Glue axles in with wood glue (unless y'all know of something better, read superglue was not a good idea)

Run on race day

[RRS73]

All looks fine, but I think leaving 0.5 oz for paint is way too much. Our paint job usually adds 0.2 oz. We do have to account for some weight when filling in epoxy in the weight pockets.

[geauxturbo]

How much paint do you use? Meaning coats... I expect we'll have 3 coats of each primer, base, and clear plus the glazing and flames. I guess even if we're heavy on paint .3 oz for paint should be plenty then?

And I noticed you are in BR. 3 Wheels are ok in Tunica District? I didn't see anything prohibitting it in the rules I got from another dad.

[RRS73]

How much paint do you use? Meaning coats... I expect we'll have 3 coats of each primer, base, and clear plus the glazing and flames. I guess even if we're heavy on paint .3 oz for paint should be plenty then?

And I noticed you are in BR. 3 Wheels are ok in Tunica District? I didn't see anything prohibitting it in the rules I got from another dad.

We use Testor's One Coat lacquer with pretty good luck. We don't go overboard with the paint, but it looks decent. We feel that returns diminish with lots of coats, and we would be better served to use the weight elsewhere.

This year, my cub has a 1/4" thick car with extended wheelbase and RR alignment. We only used 1 coat of primer, 1 coats of paint, and 1 clear coat. The car looks great, and the paint only added 0.1 oz. Last year, we had a thicker car and had 2 coats of primer, 2 coats of paint, and 2 clear coats, and added 0.2 oz.

I notice you have a lot of coats planned. I think you should be able to get by with around 0.3 oz allowed for paint, even then.

I'm not sure about the rules in Tunica District. I am in Sewell-Eagle District. I would imagine they are similar. The rules are not very strict. As long as you use your BSA kit, and do minimal sanding of the wheels, you should be okay. Everything else is pretty much fair game in Sewell-Eagle.

[geauxturbo]

Good deal and thanks for the help. Good luck in your races!

[FatSebastian]

3 holes drilled in lower back for easy cut tungsten cylinder weights.

May we presume these are drilled horizontally across the body?

Centered one to be used by adjustable tungsten weight. We're not that good so I like the idea of being able to adjust the COM by adjusting the weight.

The foremost holes are likely closest to the CoM. Adding / removing mass close to the CoM changes the mass without shifting the CoM appreciably, but you want the opposite, i.e., shift the CoM while keeping the mass close to 5.0 ounces.

I might recommend filling the back holes to maximum capacity and using the foremost hole for weight adjustments if possible. If you are running a fully extended wheelbase then it is very unlikely you could get into trouble with the CoM using "tungsten lite".

Going to leave 0.50 oz for paint

Agree with others that this seems like too much. I would suggest half that. As you seem to be using "tungsten lite" that can be drilled, you could always drill some out from the bottom if your paint and body work went slightly "over budget". Our strategy might then be to aim for 4.8 unpainted (get a precise scale if you don't already have one!).

Honestly my biggest fear. I'd hate to have the poor kid work for weeks on this and the axles fall off and we can't get it aligned.

Agreed. Suggest getting the axles holes / slots the way you want them before doing any body work. Remove the axles, do the painting, etc., then reinstall.

Cant 1.5 in front and 2.5 in rear.

Presume you are using the Pro-Rail-Rider tool. If so, go ahead and use 2.5 in front with positive camber.

Shooting for 1.5" per 4 feet.

Presuming that your track is smooth (aluminum), this is probably okay given the fact that you do not plan for overly aggressive CoM.

Final testing on a treadmill since we don't have a test track.

[Stan Pope]

...
Final testing on a treadmill since we don't have a test track. Check for any wild irregularities.
...

Even a short (3') combo tuning board/alignment board tells you a lot more!

[RRS73]

Good deal and thanks for the help. Good luck in your races!

Good luck to you guys also!

I do recommend using the alignment board as shown by Stan. We have a makeshift one and use the yardstick. I made mine from the side of an old bookshelf that my wife wanted to get rid of. We don't use the treadmill, though I've seen others use it.

We are trying RR for the first time this year. We're a little nervous, but folks here have been very helpful.

[3 Cub Dad]

Hey Geauxturbo,

The plans sound fine, but one thing jumped out at me.

You said you're using an extended wheelbase with slots, because the rules require you use slots...

As a district co-chair and lead inspector, usually, when the rules say that slots must be used, it means that the wheelbase cannot be modified.

I'm not trying to re-start a discussion here about the pros / cons of allowing extended wheelbase, slots, drilled holes, etc. There's plenty of threads on that! What I'm saying, is that unless your rules are pretty explicit about allowing extended wheelbase as long as you re-cut slots, you really should check with the race organizer and get their response in writing that it is allowable to move the wheelbase as long as you use slots. I'd hate for you to show up for race day and have some inspector say, "the rules say you have to use the slots, that "means" you can't change the wheelbase"!

3 Cub Dad

[RRS73]

Hey Geauxturbo,

The plans sound fine, but one thing jumped out at me.

You said you're using an extended wheelbase with slots, because the rules require you use slots...

As a district co-chair and lead inspector, usually, when the rules say that slots must be used, it means that the wheelbase cannot be modified.

I'm not trying to re-start a discussion here about the pros / cons of allowing extended wheelbase, slots, drilled holes, etc. There's plenty of threads on that! What I'm saying, is that unless your rules are pretty explicit about allowing extended wheelbase as long as you re-cut slots, you really should check with the race organizer and get their response in writing that it is allowable to move the wheelbase as long as you use slots. I'd hate for you to show up for race day and have some inspector say, "the rules say you have to use the slots, that "means" you can't change the wheelbase"!

3 Cub Dad

I agree with checking into this. Geauxturbo and I are in the same area, but two different districts. Our district and pack rules allow extended wheelbases, though I had to make a polite argument over our pack rules last year (pack rules didn't specify that you had to use the slots, but pack leaders were trying to enforce slot use one week before the race).



Sewell-Eagle district allows extended wheelbases, but I'm not sure about Tunica district. Obviously your pack rules are most important, as you have to be successful there before going on to districts.

[geauxturbo]

May we presume these are drilled horizontally across the body?

No, we don't have a drill press so we were going to drill in from the back of the car. Figure he has more room for error that way

The foremost holes are likely closest to the CoM. Adding / removing mass close to the CoM changes the mass without shifting the CoM appreciably, but you want the opposite, i.e., shift the CoM while keeping the mass close to 5.0 ounces.

I might recommend filling the back holes to maximum capacity and using the foremost hole for weight adjustments if possible. If you are running a fully extended wheelbase then it is very unlikely you could get into trouble with the CoM using "tungsten lite".

Understood. See how well the boy does on some test wood and go from there. Maybe I can help guide his hand.

Agree with others that this seems like too much. I would suggest half that. As you seem to be using "tungsten lite" that can be drilled, you could always drill some out from the bottom if your paint and body work went slightly "over budget". Our strategy might then be to aim for 4.8 unpainted (get a precise scale if you don't already have one!).

Got a scale to .01 oz. So, we can pull that off.

Agreed. Suggest getting the axles holes / slots the way you want them before doing any body work. Remove the axles, do the painting, etc., then reinstall.

I thought the same. Concur.

Presume you are using the Pro-Rail-Rider tool. If so, go ahead and use 2.5 in front with positive camber.

Yessir. Hope I don't get a broken finger when he swings the hammer. 2.5 it is.

Presuming that your track is smooth (aluminum), this is probably okay given the fact that you do not plan for overly aggressive CoM.

Yes, I was told it was an aluminum track.

Even a short (3') combo tuning board/alignment board tells you a lot more!

10-4. I can whip one up real quick. I figured the treadmill may actually be used for more than a coat hanger for a change... maybe not.

You said you're using an extended wheelbase with slots, because the rules require you use slots...

As a district co-chair and lead inspector, usually, when the rules say that slots must be used, it means that the wheelbase cannot be modified.

Yeah, seems strange to me as well but the rules specifically say "Axle grooves may be moved to accommodate different wheel bases" and "It must be obvious to the inspectors that the wheels and the nails from the kit are being used". Only way I can figure that is if they can see the nails from the moved axle grooves.

Pak rules are Probably the Tunica rules. Problem with starting early I guess. Oh well, if we learn differently we get to make another car

[pwrd by tungsten]

Body/Weight - fairly flat with a few curves for cool factor. Hoping body weighs around 1 oz or so. Really have no clue there. That leaves 3.5 oz of weight to add (minus paint). 3 holes drilled in lower back for easy cut tungsten cylinder weights. Centered one to be used by adjustable tungsten weight. We're not that good so I like the idea of being able to adjust the COM by adjusting the weight. Also have tungsten puddy. Going to leave 0.50 oz for paint and then add puddy in the center hole as needed. Kind of battling the idea of hollowing out the underside and flattening the cylinder weight or something to add it lower.

Try and add at least 3.6 ounces in tungsten. Uses cubes and not the cylinders. a 1" disc would be OK as well but you would need to cut axles and that is not always allowed.


Wheelbase - Extended with slots. Must have slots per the rules. Going to press in straight axles while the block is square. Don't have a drill press but have an axle press guide. Ordered the block with the slots cut since we don't have the tools to do that. Honestly my biggest fear. I'd hate to have the poor kid work for weeks on this and the axles fall off and we can't get it aligned.

Use elmers glue to secure axles. Or thick CA
(If you are very careful to not get it in the bores).

COM - shooting for 3/4" Not too aggressive but not "unaggressive" either. See if we are close to 1 oz on the DFW.

Great. Use a ruler to find the balance point and not a scale. Weight on the front wheel is dependent on COM and wheelbase.

Alignment - 3 wheel RR. Shave 1/16" from DFW side. Cant 1.5 in front and 2.5 in rear. Shooting for 1.5" per 4 feet. Will run with rears only on a glass 4' test ramp. Look for rears moving outward in both directions and test without front wheels.

Bend DFW 3.5 degrees would be my choice..

Paint - Duplicolor sandable primer, base coat, and clear coat. Glazer after primer for an extra smooth look. Sweet flame stencils. Lots of sand paper and polish to make it perty. My boy will definitely know how to spray paint and sand when its all said and done.

Glazer before primer. Use high build duplicor primer. Make sure base coat and clear coat match. I like the truck/auto/van paints.

Axles and wheels. Test for straightness, groove, and polish. Wheels trued but otherwise must be stock. Can polish bore. Have pipe cleaners and bore polish. Just ordered a set of trued wheels since I have no clue how to check the runout, etc. Put best two axle/wheel combos in back. Max-V graphite.

Final testing on a treadmill since we don't have a test track. Check for any wild irregularities. Glue axles in with wood glue (unless y'all know of something better, read superglue was not a good idea)

Dont use a treadmill. The speed can ruin the bores...

Bring spare wheels and axles for race day...