I purchased the 1:32 Carrera Mercedes 300 SLR before I read the review at www.slotcargarage.com (http://www.slotcargarage.com/scw1000.htm), where Ken states:
"The Mercedes has good speed down the straights but it likes to fishtail (oversteer) any opportunity it has. You will need to also take care when punching the throttle even going down the straights because it will tend to whip the backend around. . . I was not all that happy with the handling. So you might think the car is a little hard to control but the main problem comes when you try to push this 300 SLR a bit. The car loves to flip over. If this was a car made specifically to do stunts, it would get a dazzling review."
I couldn't agree with Ken more. I had great difficulties keeping the car on my Carrera track. It excelled at spectacular, spiraling deslots at even the lowest speeds around corners, and I couldn't find another car in my stable that was slow enough to keep it company. It was frustrating just to keep it on the track. After reviewing the tuneup tips at slotcargarage.com, I determined the car needed three things: 1) rounded edges on the tires, so the square tire edges wouldn't bite into the track on corners; 2) a lower center of gravity, and 3) adjustable magnets toward the rear wheels for increased rear-end traction (it comes with one adjustable bar magnet behind the front axle that does an inadequate job of keeping the car on the track).
First, I significantly rounded both edges of the front tires with a file held against the spinning tires and afterward applied clear nail polish. I also rounded the outside edges of the rear tires slightly. After reassembly, the car slowed down less in the turns, but still flipped at the slightest speed in a corner.
Second, I cut away the complicated system for the adjustable forward magnet (and the switchology) and simply epoxied the forward magnet into its most useful position, as far back and as low as it could go (near the motor). I then cut a piece of brass to fit in the remaining hole, allowing me to weight the front of the car a bit while adding this additional weight as low as possible. I also invited the passenger to leave, as he was extra weight up top. My car now has a single plastic occupant, the driver. It's his job to keep the Mercedes from body damage on deslots by keeping his head strategically located between the track and the car when it's sliding along upside down.
Finally, I determined to install magnets behind the motor and ahead of the rear tires. In addition, I wanted these magnets to be adjustable, so I could speed or slow the car as needed to performance match the Mercedes 300 SLR with other cars. However, there's precious little room between the motor and the rear tires.
To solve this problem, I created a two-piston adjustable magnet system which you can see installed behind the motor and to either side of the crown gear above. The system relies on friction-fitting brass tubing (available at most hardware stores), allowing me to adjust the height of the magnets that are located in the inner tube or 'piston.' The tightness of fit of the inner tube carrying the magnet within the outer tube which is soldered onto a carrier assembly can be adjusted by slightly and carefully "ovalizing" the outer tube with a pair of pliers. The first photo below is of the carrier assembly, the second is of one of the 'pistons' pictured with three magnets previous to assembly, and the third shows one 'piston' installed into the carrier assembly.
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I used tiny 1/8" neo magnets in the inner piston tubes, available at Radio Shack for about $1 each. Though small, they are the perfect size for this project small enough to fit in the space allotted, and since I could precisely set a small amount of distance between the magnets and the track, less magnet power was needed compared to more powerful magnets mounted higher on the car's chassis. I discovered that a small pipe cutter pinched the ends of the inner brass tube just enough to keep the magnet from escaping through the bottom of the inner tube.
I epoxied the magnet at the bottom end of the inner tube (and thus nearest to the track) permanently into place, and capped the end of the 'magnet piston,' with a hemisphere of epoxy in the event of contact with the track. After trial and error, I finalized on placing 4 of these tiny magnets into each 'piston'--you could stack in more of them if you wanted to, allowing you to raise the 'pistons' further from the track. However, I wanted the overall weight as low as possible, and wanted few enough magnets in each 'piston' that I could still enjoy some of the fishtailing the car wanted to do only in a more controllable fashion, and at a much higher speed! An additional benefit of this system is that it allows me to get a bit of additional weight just in front of and under the rear axle.
The result is a very fun car to drive lots of flashy, predictable fishtail when you want it, but much more controllable and able to negotiate turns at much higher speeds than before. The Mercedes 300 SLR is now able to compete with some of my slower classic Fly cars, and yet it still feels less "magnety" than many of my other stock 1:32 cars. Lowering the center of gravity of the car means that it now flips only about a third of the time it deslots instead of nearly every time as before. However, some deslots are still rather sudden and dramatic, as is the case on high CG cars that utilize magnets. The spiraling deslots that still occur tell me the CG isn't low enough yet, and I may need to add a bit more weight on the underside of the chassis toward the front tires.
The aesthetics of the modifications are pleasing to me only two discreet 'pistons' tucked in under the rear wheels, the brass inset under and toward the front, a total weight of 2.8 oz, and a missing passenger indicate the car has been modified. If I want to slow it down and increase the amount of fishtailing, all I need to do is to push the two magnet pistons up a fraction of an inch into the body, and the car again demands all the concentration you can give it. -- Kelton Rhoads, Adjunct Professor, University of Southern California
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