First car sanity check

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adayzdone
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First car sanity check

Post by adayzdone » Sat Feb 04, 2017 10:55 am

Hi all. This is my son's first race and I have never built a car before. This forum has a wealth of information and have spent the last two days learning as much as I can. I have a few questions and would also appreciate if you would critique my plan.

The rules:
The overall length of the car shall not exceed 7 inches. The overall width of the car shall not exceed 2 ¾ inches. The car must have 1 ¾” clearance between the wheels. The car must have 3/8” clearance underneath the body so it does not rub on the track.

The car shall not exceed 5.0 ounces. The official race scale that is used at car check-in shall be considered final.

The official pine wood block must be used. The block may be shaped in any way that is desired. Official BSA wheels and axles must be used. The wheels may not be cut, drilled, beveled or rounded. You may remove the seams and imperfections from the wheels. The axles may be altered, polished and dry-lubricated only.
Plan:
  • Three-wheeled rail riding car
    Straight drilled canted axels
    Standard 7" long car
    5" wheelbase, rear axles 5/8" from back edge
    .75 " Center of mass
    Flat body, angled nose
Things I am not clear on:
  • I have read the silver bullet default pin gives a 3° negative cant for rear axels. Is the front axel drilled straight positive canted or horizontal with a bent axel?
    If straight drilled positive canted, should I use the same angle as the rear axel?
    If bent axel, how many degrees should axel be bent? Recommended tool or should I buy BSA pre-bent?
    If I am using straight drilled canted axels, is there any way to fine tune alignment after car is done or am I stuck with what I have?
    Is it a good idea to use pro body tool or pro body jig to mark the holes before I drill them with silver bullet or is there a better way?
Thanks for any thoughts. Sorry for unloading all of these questions on you at once.



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Vitamin K
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Re: First car sanity check

Post by Vitamin K » Sat Feb 04, 2017 10:57 pm

Hi adayzdone, welcome to DT!

Here's my take on your questions:

- Most people drill the DFW axle straight and use a bent axle to give both positive camber and toe-in. I personally like to drill a 7 degree positively cambered hole and use a slightly bent axles to achieve toe. I think it is primarily a preference thing.

- The current wisdom is to get as much positive camber as you can on the DFW axle without making the axle too bent to insert through the wheel bore. Aim for 7-9 degrees.

- I bend axles with a pair of pliers and a piece of wood to brace the axle on. I would use one of those axle bender tools if I had one, but I am cheap so I don't bother. I would not recommend the DW tool that uses the hammer tap to bend axles, though.

- Typically, with straight canted rears, you want to verify your alignment very early on in the build and re-drill or toss the block if the alignment is off. See Lightninboy's method with the speed triangle for checking rear alignment. That said, you can tune a straight-drilled rear alignment by putting a very small amount of bend in the axles. Might be more trouble than it is worth, though.

- I've heard lots of folks suggest using a jig to mark the axle locations before drilling with the Bullet/Block. The nice thing about doing this is that it guarantees that the holes will be directly across from each other, and at the same height.



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Re: First car sanity check

Post by LightninBoy » Sun Feb 05, 2017 8:45 pm

Good response VK. I just want to elaborate on a couple things ...

- I bend axles with a pair of pliers and a piece of wood to brace the axle on. I would use one of those axle bender tools if I had one, but I am cheap so I don't bother. I would not recommend the DW tool that uses the hammer tap to bend axles, though.

I use that DW tool exclusively to bend axles. If you squeeze it in a vice (instead of pounding with a hammer) it works great. Use the 2.5 side and put some card stock in between the tool and the axle to protect the axle finish.

- I've heard lots of folks suggest using a jig to mark the axle locations before drilling with the Bullet/Block. The nice thing about doing this is that it guarantees that the holes will be directly across from each other, and at the same height.


I agree. However, the Pro Body Jig I have puts the axles too high for the typical 1/4" thick pro style wedge car. So, again, consider using some card stock under the block to lift it and thus lower the axle holes.



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Re: First car sanity check

Post by Speedster » Mon Feb 06, 2017 5:17 am

Good Morning, adayzdone. Welcome to Derbytalk.

It appears you have some very lenient rules. I'm just curious. Why did you choose a 5" wheelbase? Can you tell us specifically how you are going to prep the wheelbores and what products are you going to use?
I like LightninBoy's system of checking the rear wheels. The scouts like it too.
Thank you.



adayzdone
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adayzdone

Post by adayzdone » Thu Feb 09, 2017 11:12 am

Speedster wrote:Why did you choose a 5" wheelbase? Can you tell us specifically how you are going to prep the wheelbores and what products are you going to use?
I like LightninBoy's system of checking the rear wheels. The scouts like it too.
Thank you.
Hi. I was planning on using 5" wheelbase starting 5/8" off the back with a 3/4" center of mass (off the rear axle, right?) because of a post I read from LightninBoy.

However, I also liked the template posted here:
http://www.waynesthisandthat.com/how%20 ... 20car.html

I made a quick sketchup to incorporate the 3.5 oz canopy I bought, rather than using the round as shown in the article. Considering the weight, do these dimensions look correct? Is there a ratio of wheel base to weight that works?

http://www.maximum-velocity.com/tungstencanopy.htm

Image
Last edited by adayzdone on Thu Feb 09, 2017 11:48 am, edited 2 times in total.



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Re: First car sanity check

Post by Vitamin K » Thu Feb 09, 2017 11:44 am

Wayne's got some interesting work, but I think it's a little bit out of date. I would favor the flat bodies with tungsten cubes for weight. 5" is my go-to wheelbase, currently.



adayzdone
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Re: First car sanity check

Post by adayzdone » Thu Feb 09, 2017 11:49 am

Vitamin K wrote:I would favor the flat bodies with tungsten cubes for weight. 5" is my go-to wheelbase, currently.
Do you have a link to a template I can use? Or some good pictures?

Thanks!



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Re: First car sanity check

Post by Vitamin K » Thu Feb 09, 2017 3:48 pm

adayzdone wrote:
Vitamin K wrote:I would favor the flat bodies with tungsten cubes for weight. 5" is my go-to wheelbase, currently.
Do you have a link to a template I can use? Or some good pictures?

Thanks!
Here's my template...though it wouldn't be hard to just put your own lines down with a ruler. I can make a printable PDF if that's of any use.

Image



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Re: First car sanity check

Post by adayzdone » Thu Feb 09, 2017 7:50 pm

Very cool. Do you have a profile shot? Or a finished picture? Thanks again.



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Re: First car sanity check

Post by Vitamin K » Thu Feb 09, 2017 11:38 pm

adayzdone wrote:Very cool. Do you have a profile shot? Or a finished picture? Thanks again.
Here's a shot of my current build (it'll be for the Box Stock class over at NPWDRL).

Image

I start with a 1.75" x 7" x .25" piece of basswood (I buy a 1.75" x 3" x 7" block at Michael's and cut them into .25" pieces on the bandsaw). I tape and print the template to the wood and cut out the open areas with a scrollsaw. Then I cut a piece of 1/64" birch plywood and glue it to the bottom of the piece with wood glue and clamp it firmly between two blocks to dry.

The front taper I cut on the bandsaw (after clamping the body to a block to keep it at a 90 degree angle.

Once I've added weight, wheels and fenders, I'll print a design on cardstock, spray it with matte clearcoat and glue it to the top.

Hope that's helpful!



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Re: First car sanity check

Post by LightninBoy » Fri Feb 10, 2017 12:38 am

Vitamin K wrote:
adayzdone wrote:
Do you have a link to a template I can use? Or some good pictures?

Thanks!
Here's my template...though it wouldn't be hard to just put your own lines down with a ruler. I can make a printable PDF if that's of any use.

Image
:bigups:



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Re: First car sanity check

Post by Speedster » Fri Feb 10, 2017 4:48 am

I'm presently using LightninBoy's shape. How much does the wood weigh that was cut out of the large section? How much does the wood weigh that it will take to cover it up. I'd like to keep the car as strong as possible and don't really want to cut that section out. Will I really gain anything by removing that piece of wood?



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Re: First car sanity check

Post by adayzdone » Fri Feb 10, 2017 6:48 am

Vitamin K wrote:Hope that's helpful!
Extremely! Thank you. I was wondering if the cut outs were indeed cut outs or just fancy routing! Can I assume that a car like this is not legal given the terms of the race I posted above? Also, can you use the block (silver bullet) to drill canted axles on a piece of wood .25" thick?



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Re: First car sanity check

Post by Vitamin K » Fri Feb 10, 2017 7:56 am

Speedster wrote:I'm presently using LightninBoy's shape. How much does the wood weigh that was cut out of the large section? How much does the wood weigh that it will take to cover it up. I'd like to keep the car as strong as possible and don't really want to cut that section out. Will I really gain anything by removing that piece of wood?
The chassis as shown in the picture weighs approximately 0.37 oz.

An uncut piece of basswood of the same dimensions is about 0.77 oz.

The 1/64" birch I used on the bottom weighs roughly 0.14 oz.

So, if we consider the cut wood before I glued the birch to the bottom, then we're looking at a removal of about .54 oz.

Honestly, if you're not running full-length fenders like I plan to, I don't know that it is worth doing the ultralight body thing.
adayzdone wrote:I was wondering if the cut outs were indeed cut outs or just fancy routing! Can I assume that a car like this is not legal given the terms of the race I posted above? Also, can you use the block (silver bullet) to drill canted axles on a piece of wood .25" thick?
Some people are capable of routing out beautiful bodies and leaving a thin layer of wood below. I am not one of those people. :)

You can indeed drill a thin body with the Bullet. Whether to do the weight pockets before or after the drill seems to be a topic of some debate. Do whatever Lightninboy recommends for that. ;) Also verify your alignment after the drill AND after the weight pockets are cut (If you drill before you cut out the weight pockets, that is.)

I don't see why this body would be illegal for any ruleset. I haven't seen anybody banning "thin" so far. If you can't use basswood, you can do the same with pine.



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Re: RE: Re: First car sanity check

Post by derbypain » Fri Feb 10, 2017 8:02 am

Vitamin K wrote:
adayzdone wrote:Very cool. Do you have a profile shot? Or a finished picture? Thanks again.
Here's a shot of my current build (it'll be for the Box Stock class over at NPWDRL).

Image

I start with a 1.75" x 7" x .25" piece of basswood (I buy a 1.75" x 3" x 7" block at Michael's and cut them into .25" pieces on the bandsaw). I tape and print the template to the wood and cut out the open areas with a scrollsaw. Then I cut a piece of 1/64" birch plywood and glue it to the bottom of the piece with wood glue and clamp it firmly between two blocks to dry.

The front taper I cut on the bandsaw (after clamping the body to a block to keep it at a 90 degree angle.

Once I've added weight, wheels and fenders, I'll print a design on cardstock, spray it with matte clearcoat and glue it to the top.

Hope that's helpful!
Great information VitaK. A few questions:

Where do you buy the 1/64" Birch plywood? Having some difficulty in the Dallas area finding it. Not at Hobby Lobby or any of the major hardware locations.

Since you are using basswood for the body and not pinewood do you not have a body twist concern? ... I noticed many will put in Balsa ribs or even blocks in the large hollowed area of the Pinewood so just curious.

Last question do you drill your axle holes prior to attaching the 1/64" birch plywood or after?

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