Shaping wheels

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chobo
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Shaping wheels

Post by chobo » Mon Mar 11, 2013 6:24 pm

My kids and I have our cars at our church pinewood derby and we are allowed to modify our wheels. This is more of a question for the future as we have already had our cars race and there isn't much we can do to them before district this Sunday. My youngest took first in his age group and my oldest took third in his age group (my oldest kids car was .007 seconds faster). I don't have access to a lathe, but I had shaped the wheels to a V point slightly offset towards the inside of the car to try and center it over the hub (approximately 3mm from inside edge). Is there a better shape I should be aiming for being as we are allowed to do this? We did cone the inside hub and removed plastic from the face of the wheel so it is flat (it gave us about .2oz we could put towards the back in weight).

I had to use a drill (in a mounted drill clamp), wheel mandrel, razor blade, and a micrometer to get them as close to each other in size as I could given the circumstance. We also have to use the straight rods that come with the kit in the slots provided in the block - I'm under the impression it's a PineCar kit.

Right now they are built as straight runners, but we are going to give rail running a try next year. Not sure how that will go - our church is a wood track with no flat and a nasty bump on lane two and then we move on to an aluminum track for district.

Anywho, just kind of looking for suggestions as this only our second outing as a family; thanks in advance!
Last edited by chobo on Mon Mar 11, 2013 8:35 pm, edited 1 time in total.


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sporty
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Re: Shaping wheels

Post by sporty » Mon Mar 11, 2013 6:34 pm

Is the cars bsa or awana ?

It sounds like you have some good thinking into what you already did and a good start.

Many people do not have or use a micrometer and its a very needed tool, in my view, when doing wheel work.

Did you do canting ? canting to me is more valuable then then the V groove you made on the wheels.

So, If you did not do canting, this is something to look at and read about and learn.

Even if you have a ruff track, 99% of the time, rail riding provides a better advantage over not. More control of the wiggles.

It's just the way to go.

So, spending time, reading about that is a plus.

Then axle prep and wheel bore prep are all things to focus in on in the future.

Good / great axle whole drilling is the way to start a good foundation.


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Re: Shaping wheels

Post by whodathunkit » Mon Mar 11, 2013 7:09 pm

:welcome: chobo,
chobo wrote: We also have to use the straight rods that come with the kit in the slots provided in the block - I'm under the impression it's a PineCar kit.
Are the straight rods made out of wood or metal..
And do they run all the way across the bottom of the kit block?

PineCar brand kits use metal rods with plastic caps to hold the wheels on
but can also use the nail type axels also.. with this type of kit.
Where the Royal Ranger kit's use wooden dowl rods with screws for axles and use a thin wheel type.
Alot of church groups use this type of kit also..
But from the sounds of the wheels and stright rods for the kit type in question.
I'd say it was PineCar also.

But then again.. Awana kits use a wheel that kinda looks like pinecar brand wheel also.




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chobo
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Re: Shaping wheels

Post by chobo » Mon Mar 11, 2013 7:42 pm

We use the metal rods with the plastic cap. I can't say for sure that it is Awana or BSA, unfortunately. It is within our kids Wisconsin Evangelical Lutheran Synod (WELS). They have a rule book that states we can only use the wood from our original block, original slots for axles have to be used, axle rods have to be used (no cutting them), have to meet size dimensions, and we must use the original wheels (we can modify them to our liking). I kind of get the impression they are customized rules for that derby?

I haven't tried canting yet either; would it be beneficial to do that combined with shaving/shaping the wheels or just do the canting alone?


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sporty
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Re: Shaping wheels

Post by sporty » Mon Mar 11, 2013 7:56 pm

The one piece metal rods. Hmm. Someone else will have to chime in here. if it has been done before and how.

I have Zero exp with trying to cant with 1 piece metal rod, I imagine this to be very difficult to do. if near impossible.

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Re: Shaping wheels

Post by whodathunkit » Mon Mar 11, 2013 8:01 pm

chobo,
Sporty might be on to something about rail rideing and canting the wheels.

Heres a topic that W_I dad posted some time back.. he is from around your area.
And maybe from the same Church group.

Hope this topic is helpful to you for the wheels mods.
http://www.derbytalk.com/viewtopic.php?f=11&t=6634" target="_blank


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Re: Shaping wheels

Post by chobo » Mon Mar 11, 2013 8:10 pm

whodathunkit,
I would have to assume he is from the same WELS group we are in as the rules he posted and the lingo he uses (boys pioneers and being in a train), but from a different congregation. The first and second place car in my oldest kids group (train) look different than that (they reuse the same car from previous year) and I am not familiar with his face (but he does look happy with his results lol). I'm reading that thread as we speak; thanks for pointing it out!

Sporty,
I think if I clamped a piece of wood over the axle and found a small bit of metal tubing (deburring it also), I could probably manage to tweak the axles (would have to find a way to ensure I'm going straight up I assume also). I am just not sure how to measure how much I did to it and how much I should do? Or would doing it in that manner ruin the axle?
Last edited by chobo on Mon Mar 11, 2013 10:39 pm, edited 1 time in total.


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Re: Shaping wheels

Post by FatSebastian » Mon Mar 11, 2013 9:56 pm

chobo wrote:Is there a better shape I should be aiming for being as we are allowed to do this?
The alternative shape is an "H" groove (a channel where the wheel touches on the outsides of the treads). If we were modifying the treads and no canting was possible, we would first experiment with homemade razor wheels. Short of that, we'd probably go with the H tread just because that would seem less tricky to implement than a V.



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Stan Pope
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Re: Shaping wheels

Post by Stan Pope » Tue Mar 12, 2013 2:59 am

Several issues:

1. (Quite) a few years ago, Hugh (Hodges Hobby House) published a comparison of his V, H and "Legal" wheels, noting hgher speeds (smaller ET's) as he progressed from "Flat profile" (legal) tread, to "H" Tread profile to "V" Tread profile. This made sense to me because some friction is produced bhe a width of wheel rolling on the track and the wider the width, the greater the rolling friction. I think Hugh's V Tread profile benefited by more mass reduction across the tread that for the other two as well as less track contact. His "H" tread profile follows a similar pattern of effect. Hugh's "V" was positioned approximately half way across the tread and, so, was centered over the bore. I believe that Hugh's tests were run on level axles.

2. Cambered axles appear to me to provide the followng benefits (for the rear):
a. Riding on a narrow band (width) of wheel.
b. Riding with narrowed possible lateral movement (about 0" vs. about 1/32")
In spite of these advantages, a tilted axle (alone) is a net drag.


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Re: Shaping wheels

Post by sporty » Tue Mar 12, 2013 5:18 am

I think the trick, is being able to bend them both and not create a toe in or toe out issue. Tricky stuff. cuz once you do it, theres not much adjustment you can do, other then bending to get it right and its seems to me, the more you bend or try and rebend, it gets ugly.

To bad you could not cut that rod in two, I think that would make thing allot easier for you.


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Re: Shaping wheels

Post by chobo » Tue Mar 12, 2013 7:06 am

I'll have to pick up some wheel/axle packs from hobby lobby and see if I can't also make a jig of sorts using a couple of pinecar blanks. I have a really half-cocked idea, but not sure about the expectation meets reality part - lol.

Stan, thanks for the insight on the wheel shapes :)


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Re: Shaping wheels

Post by Stan Pope » Tue Mar 12, 2013 7:44 am

For the moment, focus on the front, rail guided wheel/axle. Since you can shape the rear wheels, there is only energy loss from cambering the rear axle. Only bend the rear axle if it is already bent and needs straightening! Better yet, replace it with new one which is truly straight.

1) Must the 2nd front wheel touch? If so, you must really control the bend, and must mount the axle almost exactly horizontally.

2) If the 2nd front wheel need not touch, you have more freedom in mounting the front axle, including lift to raise the lifted wheel.

In both cases, you may introduce an axle bend by the DFW and rotate the entire axle within its mounting trough to manage toe-in against the rail. DFW camber is not as critical, so getting enough camber to "roll against" rather than "rub against" while having a good toe-in value should be pretty easy to accomplish.


You mentioned some tracks that were rough and some tracks that had no slope-to-flat transition. Rail guiding / Rail riding apply to both cases with comparable weight distribution issues. While a straight running on a ramp might prefer a center weight distribution, Rail guiding calls for less weight on the DFW, just as you would do for a ramp-flat track.


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Re: Shaping wheels

Post by chobo » Tue Mar 12, 2013 12:45 pm

Thank you Stan,

The rules don't mention anything about having to have all four wheels touching. I am making a test car to run on the track after district is done this sunday (hopefully theyll let me). It has a coat of primer drying on it right now as I type this. Center of mass for the car is about 1 inch in front of the rear axle; I tried to keep the car similar to my boys so I can try an eliminate variables (as much as I can for the circumstances) and see roughly how much of a gain their cars will get from it next year :)

I will hit google and the search function on here and see if I can get a rough idea of how much to tweak the front axle. I'm gonna sound uninformed and stupid, but what does DFW mean?

Again, thanks to everyone for all the replies! I'll probably still have some questions and I'll try to keep active on here :)

Here is a link to the rules we use: http://lutheranpioneers.org/linked/inst ... 20size.pdf" target="_blank


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Re: Shaping wheels

Post by Speedster » Tue Mar 12, 2013 1:59 pm

Chobo, DFW = Dominant Front Wheel. Might I suggest you purchase Troy Thorne's new book, "Building the Fastest PINEWOOD DERBY CAR". It doesn't demonstrate a straight axle but has a wealth of info in it. It is available on Amazon and I have seen it at Loews.
I'm wondering if the rear axle couldn't be bent slightly in the middle of the axle. The slot could be filed to accommodate the bend. This should keep from any toe-in or toe-out as long as the axle was set properly. The rules warn about getting a bent axle but I think they're trying to help you, not realizing you want the bend. It looks like you can use oil. That might give you an advantage. I'm not knowledgeable in that department.
Best of Luck.



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Re: Shaping wheels

Post by Stan Pope » Tue Mar 12, 2013 2:37 pm

Speedster, since he is accomplishing the narrow tread contact by shaping the rear wheels, there is no need to try for reducing tread contact by twiddling bent axles!
His best bet for front is to slope the slot (or insertion trough) higher in teh body on the liftes wheel side. A 2 to 3 degree bend just where the DFW (Dominant Front Wheel) would almost touch the body should allow plenty of toe adjustment, starting with the axle head lower than the body entry. Then rotate to end of the axle forward to increase the steer toward the rail

We talked about all the critical issues a few days ago with AwanaMom, I think it was. There are some critical checks listed there that you should verify.


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