Want to take it to the next level

Secrets, tips, tools, design considerations, materials, the "science" behind it all, and other topics related to building the cars and semi-trucks.
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Vitamin K
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Re: Rail Rider question - wheel base..help?

Post by Vitamin K » Sat Dec 24, 2016 11:19 am

Jojo wrote:I've done extended wheel base but found out it is better to have the wheels in the back(or further up the track) make sense to me....anyway this year doing RR again, but just want some confirmation on wheel base. I was going to extend the back wheels only and leave the front. but now I'm wondering what the best location for the front is? best wheel base dimension for rail riding??? Thank you!!!
In my builds, I've found that it is hard to keep an aggressively weighted car stable with a wheelbase of less than 4.75". Right now, I prefer a 5" wheelbase, but I'm certain there's plenty of room for experimentation.



Speedster
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Re: Want to take it to the next level

Post by Speedster » Sat Dec 24, 2016 11:54 am

I have a 5 1/2" wheelbase on our Mid America cars. I did that because someone, or many, on Derbytalk told me too. That's the only experience I have with an extended wheelbase car. The thing I remember being told is not to put the front wheels as far forward as they will go. Too much chance of the wheels being damaged especially if there is a hard stop.



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BullFrog
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Re: Want to take it to the next level

Post by BullFrog » Sun Jan 01, 2017 4:04 pm

Happy New Year!!We just got our cars. So we started some work. Drilled the holes on a drill press. 5 1/2 wheel base. I don't know if that's a little long. He doesn't know if he wants to cut out the center of the car or not. I'll let him decide. Definitely doing a lot more then last year so it's fun. And my older scout can do more of the work. I also have a tiger his attention span is about 10mins. Good thing we are starting earlier.
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Piece of tungsten. 3/8 thick and 1inch dia
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Stan Pope
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Re: Want to take it to the next level

Post by Stan Pope » Sun Jan 01, 2017 5:40 pm

Speedster wrote:I have a 5 1/2" wheelbase on our Mid America cars. I did that because someone, or many, on Derbytalk told me too. That's the only experience I have with an extended wheelbase car. The thing I remember being told is not to put the front wheels as far forward as they will go. Too much chance of the wheels being damaged especially if there is a hard stop.
Good advice!

Be aware that on a Freedom track (Piantedosi, gradual curve), a shorter wheelbase causes a slightly "deeper" curve for the car's center of mass. That means that early in the race, the car gets a small bit of extra acceleration. This is offset by slightly less control and slightly more DFW friction. Extensive testing needed to prove an optimum location.

Yes, if allowed, locate the rear's flush with the rear of the car and the front's a safe distance from the front of the car.

Lastly, assure that your rear's are aligned "dead on" so that they say off the rail AND don't fight with each other.


Stan
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Speedster
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Re: Want to take it to the next level

Post by Speedster » Sun Jan 01, 2017 8:31 pm

BullFrog, I think a very popular set up for an extended wheelbase car is 2 ounces behind the rear axle slot. Most racers get this with 2 rows of six, 1/4" tungsten cubes. I'm not sure you will be able to accomplish this with the single cylinder. Where do you plan on placing this cylinder?



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Re: Want to take it to the next level

Post by BullFrog » Sun Jan 01, 2017 8:46 pm

Speedster wrote:BullFrog, I think a very popular set up for an extended wheelbase car is 2 ounces behind the rear axle slot. Most racers get this with 2 rows of six, 1/4" tungsten cubes. I'm not sure you will be able to accomplish this with the single cylinder. Where do you plan on placing this cylinder?

Right in the front of the back Axle. I know its not what the elite racers do. But we are building 3 cars this year and I got the tungsten cylinders for free :bigups: Rather then buying 45 bucks worth of tungsten cubes. Still need to buy Axle lube and wheel polish. We are derbying on a budget :mrgreen:
Last year my son was able to place 1st in the pack and 4th at districts using fishing weights, graphite, straight axles and standard wheelbase. So we are definitely taking it to our next level.



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Re: Want to take it to the next level

Post by Speedster » Mon Jan 02, 2017 5:45 am

I like the sound of FREE. You can't beat that. I'm curious where the Center of Mass will be after the car is built. Would you let us know where the car balances when it is completely finished? Thank you.



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Re: Want to take it to the next level

Post by Mike Doyle » Wed Jan 04, 2017 6:28 pm

I may be able to offer some tips; I haven't posted here in years and thought I'd check in to see how everything is going. Looks like it's going well!

We won Districts 3 or 4 years in a row, and out District represented a few thousand cars, so it was always competitive. Here's a couple of things that gave us an edge: before doing any work on the basic block, we would do a "carbon fiber inlay" by machining a groove down the center of the bottom, and a slot behind each axle. Then carbon fiber tube was laid in the center, and interlocking carbon fiber flat stock behind each axle. The carbon fiber came from the local hobby shop back then, I'm sure it's online everywhere these days.

The fit was close, and they were set into epoxy. Then the block was cut to whatever car shape we desired once the epoxy set, and the wood remained perfectly in the plane of alignment. It also added great strength for thin profile cars, and strengthened the axles which prevented breakage. I did a write up with photos years ago on here, they're still up. I think the rigid frame helped with the conservation of energy in some part, and keeping breakage and alignment set were a nice trio of bonuses.

Weight placement included an offset cylinder to aid in rail riding, and while that has been covered well on this forum, we also used golf club lead tape to fine tune our weight. Scales will read 4.9 to 5.1 with a great deal of variance, our goal was always to be slightly overweight, and just pick off a square of lead tape so the scale would almost flicker between 5.1 and 5.0. Then we knew were had achieved maximum weight for that event based on the event's scale.

Good luck! Nice to see this community still so active!



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Re: Want to take it to the next level

Post by Mike Doyle » Wed Jan 04, 2017 6:31 pm

Here's a link to the carbon fiber inlay write-up:

viewtopic.php?f=11&t=5180&p=48711&hilit ... 9ed#p48711



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Re: Want to take it to the next level

Post by BullFrog » Thu Jan 12, 2017 1:00 pm

Alright gang. I think we are going to try oil. I'm a little nervous. Been reading that oil is good if used correctly. The wheel prep is a lot more then what we are use to doing. Heck we have never even polished the bore before. Just got to order up the polish wax and Axel lube on amazon



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Re: Want to take it to the next level

Post by Vitamin K » Thu Jan 12, 2017 1:27 pm

BullFrog wrote:Alright gang. I think we are going to try oil. I'm a little nervous. Been reading that oil is good if used correctly. The wheel prep is a lot more then what we are use to doing. Heck we have never even polished the bore before. Just got to order up the polish wax and Axel lube on amazon
Best of luck! Report back if you hit any snags!



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Re: Want to take it to the next level

Post by BattleBorn » Fri Jan 13, 2017 2:47 pm

Hi guys, thanks for the awesome information, I've been reading a lot here and I'm not sure where the dust has settled on a few of these issues I'm still confused about:

1) In an extended wheelbase car, is it only important to extend the rear (giving more potential energy up the track) and leave the front standard? I thought you were supposed to extend the front as well for stability going down the track? Not sure where I read this or if I'm mis-remembering?

2) Is weight placement really critical if you focus on center of mass location? In that youtube video he just mentions that the center of mass should be 1" in front of the rear axle?

3) With respect to polishing the bores with the Walgreen's Q-tips stems, I'm confused how this works since the stem wont absorb any of the polishing compound right? I polished with the pipe cleaners last year and I gave it several passes with the Novus and I honestly had to convince myself I saw a big difference before/after.

4) I think I took too much material off polishing my axles to a mirror finish. Is this important? I'm thinking it may make the wheels/car wobbly when it goes down the track?

5) Once the wheels and axles are polished is it possible to get the graphite to really stay on there long? I soaked the axles in alcohol and then cleaned everything with soap and water but the graphite never really seems to stay on.

6) I've seen a lot of discussion about oil, this is not allowed in standard pinewood derby's right, or have the rules changed?

Many thanks!



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Re: Want to take it to the next level

Post by LightninBoy » Sat Jan 14, 2017 12:47 am

1) It is most important to extend the rear axle back as far back as you can (typically 5/8in from the back edge of the block). After that, opinions vary on where to place the front axles. If you want a more stable car opt for a longer wheelbase. If you want to maximize kinetic energy opt for a shorter wheelbase. I advise scout cars to use a 5" wheelbase, meaning the fronts axles are 5in from the rear axles (which are 5/8in from the back edge). That's a good compromise. I definitely would go no more than 5.25in and no less than 4.75in.

2) Weight placement affects center of mass and, yes, it is critical. 1" COM is a popular rule of thumb but that is on the conservative side. With a 5in wheelbase I'd shoot for .75in. Again, the trade off is that the longer COM is more stable but provides less energy.

3) It works. Just remember to run the drill SLOW. Too fast and you will ruin the wheelbores. If you don't have something already, get a magnifying glass to inspect the bores and see the before and after.

4) What makes you think you took off too much? Unless you used a file or really course grit sandpaper, I wouldn't worry about it.

5) No. BTW - I never use alcohol to clean the wheels and axles. Soap and water works fine.

6) There really isn't a "standard" pinewood derby. The rules are different everywhere. That said, its probably more common for oil to NOT be allowed. Which is a shame, because its so much cleaner. Our council rules (Northern Star Council) allows both, but strongly recommends oil over graphite.



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Re: Want to take it to the next level

Post by Vitamin K » Sat Jan 14, 2017 7:59 am

I'll add my piddly thoughts in addition to LB's. :)

4) If the wheel is wobbly, I'd suggest you check the bore. Some wheels are cast tighter than others. If a wheel wobbles excessively, try a different wheel on the axle. If that wheel spins true, I suggest you get some more wheels. BTW, if you're not /REALLY/ careful and really slow with polishing with Q-tips, it's easy to enlarge wheel bores. I know a lot of league racers have moved away from q-tip sticks for this reason.

5) Graphite likes to fly off. I add graphite as a two-step...first I try to burnish it into the hubs and bore (plenty of how-to on this) and then I'll actually add another coating of graphite in the wheel/axle interface. I actually use two different kinds of graphite...a fine, pure graphite (Max-V in my case) for burnishing, and a coarser, graphite/moly blend for the final lube (Hob-E-Lube, in my case). One more thing you might consider is giving the axles a pre-treatment spray of Pledge or Sailkote, if your rules permit this.



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Re: Want to take it to the next level

Post by BullFrog » Sat Jan 14, 2017 10:33 am

Picked up some goods yesterday. :bigups: Thanks to Vitamin K on the tip on where to pick up the heavy duty Silicone lube. Micro center had it for 6.99 other spots were charging 16 to 22 bucks for the stuff. :thumbup:
Derbying on a budget :mrgreen:
Picked up the studio 35 beauty swabs as recommended by speedster. Felt a little weird asking the kid at Walgreen's were I could find the studio 35 beauty swabs. :lol:
Another question. When using the silicone lube is it as critical to get the axels mirror finish if we will just be spraying them with silicone?
What's the best way to spray it on the axels? I worry about it clumping up.

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