First attempt....

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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Gtdhw
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First attempt....

Post by Gtdhw »

...at a "fast" car.

I had already completed the body/weighting of "Dads car" this year, but after learning so much more this pre-season, I decided to go ahead and try my hand at building another, instead of waiting until next year. Not sure that I did everything 100% "right", but so far, I'm pretty happy with the results, and have achieved my lowest COM yet @ 17/32", and DFW @ 13g. Any/all critique welcomed....

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Not sure what exactly everyone uses to hold the cubes in (other than sheets of balsa and/or some sort of epoxy), but I used pwd super glue, then applied a thin coat of JB weld to the bottom.

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Re: First attempt....

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I'm glad I'm not racing you.
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Stan Pope
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Re: First attempt....

Post by Stan Pope »

Looks good! Next try, I'd pull the front axles back a bit ... maybe by 1" ... to increase the weight on the front wheels so that less toe-in is needed to keep the car "glued to the rail." That also reduces the CMx location a bit, maybe to 16/32". :) My reason is that it protects the front wheels from impact with the stop mechanism. (Your car looks like it will outrun the length of the track's stop section.)
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Scrollsawer
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Re: First attempt....

Post by Scrollsawer »

That's a nice looking spoon-style design. Very thin, and the weight pockets and drill holes are very well done. How do you cut your weight pockets that precise? The wood looks like something other than pine, but that could just be my old eyes.

Your maxed out extended wheelbase is very similar to what I've done in the past. With time, you may elect to pull those front wheels a little further back by drilling your front axle holes 1/2" - 1" further back. It all depends on your results and experience. For example, our cars wheelbase is influenced by the build principles founds on the '5kidsracing' website. Noskills builds his cars with his front wheels a little further back than mine, and he built cars that go faster than ours. Just depends on what works for you. We never lost a race at the Pack level with our design if we were going for speed. It really comes down to dialing in the alignment and rail riding, when working with weight configurations like you are.

We like to use very thin basswood veneers to cover our weight pockets (top and bottom). If you use veneers on the bottom, be sure to factor for the veneer thickness when drilling your rear wheels as the additional bottom veneer will reduce the clearance between the bottom of the car and the center rail. Not enough to cause a problem during the race, but sometimes at weigh-in the night before, the Pack's car clearance gauges used to check ground clearance can be more aggressive than the actual ground clearance on the track. We've run into this problem in the past, so we usually just sand the veneer down to the point where you can almost see the tungsten weights through the the veneer (in other words, really really really thin).

Now, after the painting...onto the 'build and tune phase', good luck!

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Gtdhw
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Re: First attempt....

Post by Gtdhw »

Thanks fellas. Will for sure look into the front wheels further back, for all reasons mentioned.

The block does have a weird/different grain pattern to it, but it is straight from a BSA kit.

As for the cutting of the weight pockets, I was pretty crude/basic, as I have no scroll saw. I laid them out with a freshly sharpened pencil, then cut the rear pocket out on the band-saw. The front pocket, I drilled a couple 1/4" holes to get started, then used a dremel with an 1/8" cutting bit to carve out the hole. Once done with the demel, I went through and finished the corners and outer ears with a file to get them crisp.

Interesting that you mention bottom clearance. I noticed that our pro axle guide was getting worn, so while I was at the Scout store, I picked up a new one. Once the first axle hole was drilled with the new tool, I had to step back. There is big difference in the height of the hole location! The guides are/look the same in every other aspect, but the holes are just higher (including the raised wheel hole), therefor lowering the bottom of the car, lower than the other cars that we've built. I have some pics that I will post later, of a side-by-side comparison, I just found it odd that they are that much different.
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Gtdhw
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Re: First attempt....

Post by Gtdhw »

Old tool on left, new on right.

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New on left, old on right. A big enough difference, that I had to adjust the front layout of the block to compensate.

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Scrollsawer
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Re: First attempt....

Post by Scrollsawer »

I do not like the raised drill hole on the new tool. That location would definitely cause us problems in ensuring adequate clearance when the Pack whips out their homemade clearance tool.

We just bought a new one of those at our local Scout shop last month, and the hole locations are down low, just like on all the other tools we've ever seen/used.

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Gtdhw
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Re: First attempt....

Post by Gtdhw »

Well, what I did, was buy the body jig (two tools & the bar to connect them). I don't have any plans to use it as a body tool, but they didn't have any single tools in stock, and I thought "Well, we'll get two this way, so we'll have a new one when this one gets worn". I had no idea that they would be different than the singe, and still really don't understand why. I went ahead and went with it, since the other cars were already drilled, and this car will never see a pass down any track but our pack track, which is flat/has no center rail. Would an 1/8" lower body (exactly 1/8" difference between height of hole locations), lower the weight line enough to make the car faster on rail-less track (than same car with 1/8" high body)?

Edit to add: Pulled out an instruction sheet from one of the BSA boxes. It states that the "bottom clearance between car and track is 3/8"". With the old tool, we sit at 1/2", and with the new tool, we are at 7/16". That means that it "should" clear any center rail. Just curious as to how your pack can tell you (have a rule) that your car has to be higher than the BSA instructions state? I've seen packs with many, many rules, but none that are more strict than the BSA kit rules when it comes to height/weight/distance between wheels side-to-side, etc. (Not saying that 1/16" is "a lot" of clearance, especially on old beat track)
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