First a correction. I misspoke when I started this topic. This is not the first chassis I've built for an LMP body. The first one was a hybrid chassis for my 2000 Cadillac Northstar LMP. This is the first chassis I've built using CK4 which has a top loading battery located on the side of the chassis. This was largely an experiment in an attempt to minimize the height (thickness) of the front half of the chassis. Both chassis are shown below.
Yesterday I mounted an LMP body to this new chassis. The rear axle, crown gear, wheels, tires, and body are from an SCX PRO 2003 Audi R8 slot car. The body weighs 18 grams. Today I spent some time testing it out against some other cars. I am extremely pleased with how this car performs, chassis and body combined. I don’t have an automatic lap counter and timer built into my layout, so I can’t be precise about lap times. My wife clocked several laps of mine at 10 seconds using her kitchen timer.
It measures in full seconds only. The fastest time ever recorded is 9.5 seconds 1 ½ years ago with a different timer. That was a stock magracer with enhanced tires on a newer and smoother outdoor track. I suspect this car is just as fast on my track, probably faster.
This car has a 26 tooth crown gear on the rear axle, compared to a 30 tooth gear on a stock magracer. The Audi has .779” diameter rear wheels compared to .839” on a stock magracer. I estimate that the top speed of the Audi R8 should be 7% faster than a stock magracer. That appears to be the case going up a 23 ft long straight with 5% grade. I compared the Audi speed against 2 other cars with stock gearing by running them on the same lane, one right behind the other, using the same controller.
The car handles very well, especially around tight right-hand corners. When running clockwise, my track has 3 tight right-hand corners. It has only one tight left-hand corner which can be avoided by taking a different lane. Only 2 of my cars can negotiate that left-hand corner consistently without some steering input. This car is not one of those two. (That corner is the later part of an S curve where the bank changes from right to left. I'm trying to modify the S curve slightly to make it easier to negotiate.) The car handles most left had corners with ease. I have not been able to test the lane changing ability of this car because something is wrong with the steering. It’s not the controller. It’s probably the coil or the control module on the PCB or related wiring. The car does not react at all when the steering wheel on the controller is turned. This does not concern me. I’m certain that the lane changing will work properly with a working coil and receiver board.
On a smooth flat level surface, this car tends to drift to the right. I’m not sure if it’s because of the greater weight on the right side of the chassis or if it’s due to slightly more negative camber on the right front wheel. (This was not deliberate. A hole for a kingpin in the upper suspension beam, located a few thousandths of an inch inboard or outboard, can affect the amount of camber. The geometry of the wheel and tire can also affect camber.) The “wear” on the front tires clearly indicates negative camber on both tires. On the right tire, the wear pattern is a consistently narrow band along the inside edge of the tire. On the left tire, the “wear” shows up as a variably wide band on the inside edge. The wear pattern on the rear tires extends all across the face of the tread which indicates that the entire tread is making contact with the track surface.
The good handling is probably due in part to the high quality aluminum wheels and good rubber tires. I sanded all 4 tires just a little before mounting them on the axles. They were almost perfect to start.
Concerning the spring metal strip for electrical connector, thanks to Wes, I found a vendor called Greenweld in the UK:
http://www.greenweld.co.uk/cgi-bin/sh00 ... 1#aCDT0091
It’s called bronze spring strip, 5mm wide by 0.2mm thick by 4 metre long. That should be enough to build at least 75 cars, a lifetime for me. The cost is about 5 British Pounds, which is less than $6.25 USD today. I hope to find a vendor in the U.S. also, so that folks living on this side of the pond can buy it closer to home.
I intend to make a few minor modifications to Chassis Kit CK4 and to design it to use the bronze spring strip mentioned above. Then I will offer it for sale on Shapeways. Hope to finish this within a few days since I’m leaving town next week for a couple of weeks. Eventually I will probably design 2 versions of most chassis and make them available on Shapeways. I suspect that most guys will prefer the chassis with the top loading battery and bronze spring strip connectors. With my collection of chassis kits on Shapeways, you will be able to convert almost any 1/32 slot car to a magracer.
