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There have been many questions about the chassis 2 design. Lots of people have built them, and there have been some common errors.
One young man named Randy Davis asked for permission to build them, and he calls it the "FLEX."
Grandpa calls it simply "Chassis II." Since then, people have built some nice looking and some very innovative ones.
This page is to give a little more information, so you can actually have the advantage of the design, and not just the look.
One complaint I've seen is that it's hard to get good wheel alignment, drilling such thin components.
Solution: Drill the axle holes first, while the block is whole. Then do all the other cutting. (-;
Another observation someone made: "This flexible design may be useful only if your track is not smooth."
Response: The lower frequency motions that a rougher track would cause are more visible to us, but more energy is wasted on much higher frequency vibrations - those that let us "hear" the rolling. No matter how smooth the track is, energy will be saved by this flexible design. Silence is the goal. You don't have to "see" what's happening, if you can "hear" it.
Chassis 2 Graphic by Jeremy Miller
Jeremy Miller sent this graphic to me. It's a fine graphic. It shows very clearly how the wood is cut. He sent this with a 3-D software that could turn it and look from all angles, but this picture is clear enough to give you all you need. Incidentally, Jeremy won a highly competitive race at division level with a chassis 1 design. Next year, he plans to use a chassis 2 design. He also won "Best of Show."
Grandpa loves the beautiful cars. He just doesn't build them. "If it don't go, chrome it," he has remembered since high school. He had a very fast very ugly car he bought for fifty bucks. "Old Buck," he called that car; it was a 1937 Buick Straight Eight. Grandpa didn't have the money to paint it, but he had the time and the inclination to make it fast. The rich kid with the new Corvette (they were straight sixes then) was not happy at losing three times in a row to this old beat up Buick. At the end of the third race, Old Buck boiled over, there was water everywhere, and that just made it better. Actually, those old Corvettes and the larger-engine version of Old Buck, the Century, were in the same drag-racing class - D-Stock. When the Corvette was built and entered that class (it's based on horsepower to weight ratio), the Buick continued to hold the record - 87 in the quarter mile. Old Buck had a horsepower rating of 101 and was a heavy car. Even today, a car with that horsepower and that weight would have trouble beating this record. The transmissions from these Buicks were favorites for hotrods, because they were very strong.
There are five places for this piece of wood that will be weak. These places usually need some strengthening. On this graphic, you see three parallel lines that come to an end. This area is weak, because breakage can occur with the grain. Wood is weak along the grain. Breaking it across the grain is much harder. Glue a thin piece of wood over this area with the grain going the other way; then it won't break here. There are two lines that end going the other direction; these are weak also - do the same in these two spots. Now you have a strong chassis. You may also cut your shape to make it thicker in these areas. (The thickening is what Grandpa did, and the car is several years old and unbroken. It was raced quite a few times.)
The other important thing is to have the long sections quite thin, so that each wheel comes up rather easily when you put weight on it. The lighter the weight required to move the wheel up, the lower frequencies will be handled down the track. A stiff suspension helps for high frequencies only. Don't get it too thin, though - you don't want anything to touch the track while the car goes down. On mine, the wood was about a sixteenth inch thick. As long as the areas of weakness are strengthened, there should be plenty of strength in the rest of the chassis. Not all wood has the same stiffness, so I sanded and tested - sanded and tested. Just place one wheel on a scale, and see how much it takes to move the wheel up and down. If each wheel moves up about an eighth inch with five ounces, that's about right. Put one wheel on your scale - push down until the scale reads 5 ounces - you want that wheel to move up about an eighth of an inch. If it takes more than 5 ounces, thin down the long part going to that wheel.
Watch the location for your weight - if it's too far back, you will run unstably as you get going fast.
Still, you want it as far back as will remain stable. Centered about an inch and a half in front of the rear
axle is fine, and you may get away with an inch and a quarter. Grandpa tried one inch and had trouble.
Here is the original car again -
If the long springy parts are thin enough, the chassis will bottom out unless you do this reshaping.
It gets the wheels down further so they have room to move up without the main chassis touching the track guide.
With a thicker cut and thus stiffer car, it won't bottom out, but you won't have the suspension advantage anyway.
Shaping this chassis in hot water is important.
The reshaping is very easy to do. Here's a repeat of the instruction:
After the wood is cut, take two little sticks and put them in like in the picture below.
Then put this in boiling water for about a minute.
Then let it dry with the sticks left in. That's it.
This picture is just to show the method - it's not a real chassis - too thick, etc. Many have built these, and almost always, the arms to each wheel are too thick and stiff to give the real advantage. Make your car, and then sand the arms until pushing against a wheel with 5 ounces moves it about an eighth of an inch. Just put the wheel against your scale and push it until the scale reads 5 ounces.
Good luck - and win your race.
Some people have made very fancy versions of this design, and I'm including two of them here - with permission from the builders.
This one was built by Peter Kappertz
(Troop 740 Cascade Pacific Council)
Peter calls this the "LeapFrog," and it has to be among the most impressive PineWood cars Grandpa has ever seen. This, nonetheless, appears to have arms too thick for the independence needed. It could be sanded, as described above, and then would be faster.
If this is strong enough at the "knees," and if the long flexible parts are thin enough, this could be a fast chassis - perhaps very fast.
And the second one -
-- Stephen and Evan (age 10) Pyle sent in this Chassis II design - quite impressive:
Again - the arms appear a little thick. Some sanding - with the 5-ounce measurement above, will make this a faster car.
The "weight" on this car appears to have moving parts - for most competitions, your weight will have to be entirely static, perhaps getting away with just the foam mounting.
Note: Most who build these cars - end up with far more beautiful cars than Grandpa builds. He is impressed. Win the race, and you will have the beautiful car and the other trophy as well. (Kind of like having your cake and eating it too.)