Prototype for next year?

[rlb1961]

So I am already working on my prototypes for next year's cars. Here is my first attempt. Remember that I am racing in Royal Rangers, and must use the dowel and screws. I will be plugging the dowels with wood putty and re-drilling the axle holes.

I am using a basswood body, and the body is 7-1/2" long and is a full 2" in width. By having the body wider, I can fit more of the weight further back, allowing a more aggressive COM.







Our last RR race for the season is on March 3rd. After that is done, I am going to build a car to race in league, just to get more experience before next year (and because I got bitten by the bug). Any suggestions as to what class I should start with?

 

[Obsession Racing]

By making the car wider, I believe that you will be opening up a whole set of other issues that are counter productive. The first of these is getting the car tuned for rail running. With the extra width, your car may end up tracking sideways, unless you cut in the front considerably.

If you are trying to stay thin, and want to move your weight further back, then I suggest that you change to tungsten cubes. By adding the extra .25" to the width, you can only add about another .15oz of lead weight behind the rear axle. However, by keeping the standard width, and using tungsten cubes, you can add as much as 1oz(total of 2oz) behind the rear axle, if you want. Also, with the cubes, you will be able to precisely manage your COM. Tungsten is considerably more expensive, but much more flexible for your design. Also, if you do it correctly, you could even recycle the tungsten for the next year.

O.R.

 

[Crash Enburn]

I really like it! Great bit of woodworking, there.

 

[Quicktimederby]

It is a great looking car. I agree with O.R. I think that you can narrow the frt and still get away with it. My theory on the width of the cars is the less of a car the less air it has to move, and I believe that affects speed more than COM. As long as you can still keep it fairly aggressive.

 

[Chief]

[font="times new roman, times, serif"]Cool Concept! And just a thought...after reading what Obsession said, you could modify it to take the cubes without starting all over...and keep the cool design.[/font]

 

[rlb1961]

By making the car wider, I believe that you will be opening up a whole set of other issues that are counter productive. The first of these is getting the car tuned for rail running. With the extra width, your car may end up tracking sideways, unless you cut in the front considerably.

If you are trying to stay thin, and want to move your weight further back, then I suggest that you change to tungsten cubes. By adding the extra .25" to the width, you can only add about another .15oz of lead weight behind the rear axle. However, by keeping the standard width, and using tungsten cubes, you can add as much as 1oz(total of 2oz) behind the rear axle, if you want. Also, with the cubes, you will be able to precisely manage your COM. Tungsten is considerably more expensive, but much more flexible for your design. Also, if you do it correctly, you could even recycle the tungsten for the next year.

O.R.

Well, I was going to use the tungsten cylinders on this car because, a) the dowel is 3/8" in diameter, so I can't go any thinner on the body (unless the dowel protrudes below the body, which results in the same frontal profile); b) the tungsten cylinders are more dense than the cubes; and c) I already have some of the cylinders left over!

As far as the width, even if the body is narrower, the dowels are still 2" long, so the distance between the DFW and the rail would not change. I will need to check the rules to see if I can narrow the dowels - if I can, then perhaps narrowing the front would be a good step to take as well. I hadn't thought about that...

 

[OPARENNEN]

For next year league racing:
The easiest classes to become competitive is Eliminator and Unlimited.
Although the unlimited has a significant expense in bearing wheels, this class requires much less preparation.
The eliminator requires more time and effort on the wheel and axles prep, but is still easier than SS SP.
Setting the drift in these two classes is much less time and effort.
Even with these 2 classes, you have got to go the Tungsten route for weight.

The Street Stock and Street Pro take the longest to learn the various tricks, and require significant testing and lots of careful preparation to become competitive. It took me six races and six months to finally break the 3.0 barrier, and even then I never did better then 12 place in SS. In my case, I am still trying to get an SP car even close to becoming competitive.

Creating and making a Street Rod competitive is the most challenging and time consuming of all the classes. I have spent an unbelievable amount of time creating 3 cars for this class, and my times on my own track are still terrible. I sent one to the Feb race, And if I end up even in the middle of the pack, I will be surprised. JAC, who isn't racing this year was one of the best in this class.

 

[Obsession Racing]

By making the car wider, I believe that you will be opening up a whole set of other issues that are counter productive. The first of these is getting the car tuned for rail running. With the extra width, your car may end up tracking sideways, unless you cut in the front considerably.

If you are trying to stay thin, and want to move your weight further back, then I suggest that you change to tungsten cubes. By adding the extra .25" to the width, you can only add about another .15oz of lead weight behind the rear axle. However, by keeping the standard width, and using tungsten cubes, you can add as much as 1oz(total of 2oz) behind the rear axle, if you want. Also, with the cubes, you will be able to precisely manage your COM. Tungsten is considerably more expensive, but much more flexible for your design. Also, if you do it correctly, you could even recycle the tungsten for the next year.

O.R.

Well, I was going to use the tungsten cylinders on this car because, a) the dowel is 3/8" in diameter, so I can't go any thinner on the body (unless the dowel protrudes below the body, which results in the same frontal profile); b) the tungsten cylinders are more dense than the cubes; and c) I already have some of the cylinders left over!

As far as the width, even if the body is narrower, the dowels are still 2" long, so the distance between the DFW and the rail would not change. I will need to check the rules to see if I can narrow the dowels - if I can, then perhaps narrowing the front would be a good step to take as well. I hadn't thought about that...

Well, my take on this is that your rules don't prohibit narrowing the body, so there's no reason why you shouldn't. The rule states that you need to use the original parts, it didn't say you had to use it in it's original size/shape...think outside the box here. You are using the original block too, but that's being re-shaped. Unless they specifically say that you CAN'T reduce the width, then you CAN. At least that's how I read it.

As for the cylinders, I apologize, as I didn't realize you were using tungsten cylinders. When I see 3/8" holes, my mind immediately goes to lead, since that's what I use in the workshops I do for our Pack. I still prefer the cubes, as they use the space more efficiently, but the density on cubes and cylinders are the same.

Finally, if they interpret the rules differently than written and you are required to keep the dowels at 2", you may want to consider offsetting the front dowel with the dominant wheel side pushed in so that you can achieve your fix for rail running(dominant wheel starting closer to the rail).

O.R.

 

[Quicktimederby]

RR cars sound like a pain!!!

 

[rlb1961]

Well, my take on this is that your rules don't prohibit narrowing the body, so there's no reason why you shouldn't. The rule states that you need to use the original parts, it didn't say you had to use it in it's original size/shape...think outside the box here. You are using the original block too, but that's being re-shaped. Unless they specifically say that you CAN'T reduce the width, then you CAN. At least that's how I read it.

As for the cylinders, I apologize, as I didn't realize you were using tungsten cylinders. When I see 3/8" holes, my mind immediately goes to lead, since that's what I use in the workshops I do for our Pack. I still prefer the cubes, as they use the space more efficiently, but the density on cubes and cylinders are the same.

Finally, if they interpret the rules differently than written and you are required to keep the dowels at 2", you may want to consider offsetting the front dowel with the dominant wheel side pushed in so that you can achieve your fix for rail running(dominant wheel starting closer to the rail).

O.R.

See, this is why I like coming here - I get ideas that I might not have otherwise considered! I am so used to using the dowels at full-length (because I always have, and I have never seen anyone else shorten them), that I didn't even consider the fact that I might be able to do so. We have our District race a week from tomorrow, so I will ask for a clarification of the rules at that time.

On the cubes vs. cylinders point, I had read in a couple of other places (I think on the Maximum Velocity website and on Derby Talk) that the cubes were less dense than the cylinders because the cylinders were cut from solid tungsten rods, while the cubes were "sintered" - basically, tungsten powder poured into a mold and formed into cubes using pressure and heat.. However, I am perfectly willing to admit that could be wrong. And I also agree that the cubes give you more flexibility. On at least one of my cars next year, I plan on using cubes and keeping the body down to 5/16" thick - the dowels will still protrude below the body, but I might be able to determine if completely enclosing the dowels in the body (as on this design) is better than a thinner body with part of the dowels exposed.

 

[rlb1961]

RR cars sound like a pain!!!

They are challenging. It it also hard to compare results vs. the BSA style cars. Since they can be longer and heavier, we are consistently getting sub-2.9 second times on a 42' Freedom track, and none of the builders have the level of skill seen here.

 

[Obsession Racing]

On the cubes vs. cylinders point, I had read in a couple of other places (I think on the Maximum Velocity website and on Derby Talk) that the cubes were less dense than the cylinders because the cylinders were cut from solid tungsten rods, while the cubes were "sintered" - basically, tungsten powder poured into a mold and formed into cubes using pressure and heat.. However, I am perfectly willing to admit that could be wrong. And I also agree that the cubes give you more flexibility.

Well, we are both right, in some sense.

The thing about "tungsten" is that it's not PURE Tungsten typically, it's an alloy of some sort. What is true about the cylinders is that they are usually cut from a more pure rod, if not 100%. Cubes are another story, as the alloy ranges can vary greatly. However, we are talking about a few percent difference that is usually made up by the fact that you can pack more cubes into the same relative space because you aren't wasting the areas around the arc of the circle. Some cubes are as low as 93%, so you do have to watch your sources. I know that DD4H cubes are high density alloy, so they will give a density comparable to rods.

By the way, if the dowel protrudes, then why not sand it down? Again, you are still using the parts, but slightly altering it's size/appearance.

O.R.

 

[rlb1961]

Well, we are both right, in some sense.

The thing about "tungsten" is that it's not PURE Tungsten typically, it's an alloy of some sort. What is true about the cylinders is that they are usually cut from a more pure rod, if not 100%. Cubes are another story, as the alloy ranges can vary greatly. However, we are talking about a few percent difference that is usually made up by the fact that you can pack more cubes into the same relative space because you aren't wasting the areas around the arc of the circle. Some cubes are as low as 93%, so you do have to watch your sources. I know that DD4H cubes are high density alloy, so they will give a density comparable to rods.

By the way, if the dowel protrudes, then why not sand it down? Again, you are still using the parts, but slightly altering it's size/appearance.

O.R.

So I decided to e-mail the district official in charge of the Pinewood Derby and get an official ruling. I was informed that it IS required to use the dowels, but they can be modified. So that opens up some more possibilities. Of course, to get down to a 5/16" profile, I will need to glue the dowels into the body and then either sand them down or use my table saw to get to the proper thickness. I can also narrow the dowels to reduce the width. So,what is the optimum spacing for the rear wheels? I know that 1-5/8" is the width of the rails, so 1-3/4" would seem to be the minimum. However, if the DFW need to be inset at least 1/16", then that would place the DFW right on the rail at the start (assuming the car is staged straight). So is 2" a good width for the rear wheels, or something closer?

(I always run my wheels shaved down to 1/16" wide or thinner, if that helps.)