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4 months ago

June 2013

  • Text
  • Racing
  • Suspension
  • Tires
  • Chassis
  • Buggy
  • Drivers
  • Rear
  • Steering
  • Maifield
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RC Car Action - June 2013

Tech Center HOW DO I SET

Tech Center HOW DO I SET MY SLIPPER? SPONSORED BY QI 've heard that if the slipper is set correctly, the vehicle should pop a wheelie if both rear tires are held on the ground while grabbing a little bit of throttle. All I hear is a grinding noise, which I assume is the slipper. How do I get my slipper set correctly? If the slipper clutch isn’t tight enough, the friction pads will slip and the vehicle will A not accelerate very quickly. If it's locked down completely, there is a direct connection between the motor and the drive wheels and all of the torque from the motor will go to the tires. When a slipper clutch is slipping a lot, it makes a chirping noise as the friction material slides on the clutch disks. There should be no grinding noises. To check that the slipper is built correctly, tighten it all the way down and do the wheelie test. If it wheelies, then the slipper was just too loose. If it does not pull a wheelie and the slipper is chirping, then something is worn out or installed incorrectly. Rebuild the slipper and check for any broken parts. Inspect the friction pad (or pads, depending on your model) and make sure they are intact and not excessively glazed or worn. Either sand any glaze off the pads with dry sandpaper or replace them. If the slipper is good and there is still a grinding noise, then there is a problem somewhere else in the drivetrain. The most likely culprit is the differential. Rebuild the diff and replace any components that are excessively worn. While you are in the transmission case, check the input and the idler gears to make sure the teeth are not too worn out and pointy. Once the diff is freshened up, and the slipper clutch is properly adjusted, everything should operate properly. Glaze build-up on the slipper pad (A) or clutch disks (B) can prevent proper clutch action. A B WHAT’S AN ABEC NUMBER? QI’m working on upgrading my fleet of cars, and I want to install better bearings. I keep seeing an ABEC number on the bearings. What is this number and what should I get? Should I get the same ABEC number for my on-road and off-road vehicles? AThe ABEC scale is a measure of the tolerances that a bearing is held to, and is usually quoted as an odd number between 1 and 9. ABEC stands for the Annular Bearing Engineering Committee, which is a part of the American Bearing Manufacturer’s Association. The higher the ABEC number, the tighter the tolerances the bearings are held to and the smoother they'll run at high speeds. The majority of bearings are ABEC-1, which is the loosest tolerance. This is what comes with most kits, as they are also the cheapest. It's possible to upgrade to a higher rating. ABEC ratings as high as 7 are available from most aftermarket bearing suppliers. Typically, higher ABECrated bearings are reserved for on-road and carpet cars. The rotational speeds of these bearings are much higher than in off-road and the tighter tolerances make the tires and the drive components run more smoothly. In off-road, the speeds are usually lower and since they are exposed to dirt and moisture, it makes more sense to use a lower ABEC rating like 1 or 3 since they will be replaced more often. In off-road, there is more to be gained by keeping the bearings clean than by running higher ABEC bearings. 26 MORE FROM THIS ISSUE AT RCCARACTION.COM

540- OR 550-SIZED MOTOR? I keep hearing about 540- and 550-sized motors. What is Q the difference and what's the best to use? The difference between a 540 and 550 motor is the length of A the can (the motor's cylindrical case) and the rotor (the part within the motor that spins to power your truck). . Both motors are the same diameter, but a 550 motor is a little bit longer than a 540 motor and that changes its torque and speed characteristics. Since 550 motors are longer, they have wire in the stator (the wires wrapped within the can that energize to spin the rotor) and a longer rotor. This increases the resistance of the motor, but also increases the strength of the magnetic field. This gives 550 motors a lower top speed but more torque and more total power output potential as well. Usually, 540 motors are used in lightweight 1/10-scale vehicles like touring cars, 2WD buggies and stadium trucks, and 2WD SCTs. Heavier vehicles, like 4WD SCTs, use 550 motors because they need the extra torque to get them moving and to launch them over jumps. Since you’re racing a stock class, I would contact the track operator to make sure that there is not a rule that mandates one configuration or another before you make your purchase. If the rules are open, use a 540 if the vehicle is light or 2WD and a 550 if it is a heavier 4WD truck. HOW DO YOU CALCULATE DAMPING AND SPRING RATES? I have read in different Q setup guides that it is necessary to match the shock’s damping rate with the spring rate of the vehicle. It sounds like a great idea, but I have Properly matching spring rate and shock damping to driving conditions is essential to peak performance. never seen a resource that mentions how to calculate this in order to get them to match. Is there a way to figure this out? The phenomena you are talking about is called critical damping. In any system A that has a spring and a shock (or damper), there is an amount of damping that will allow the system to return to its original state as fast as possible without oscillation. Any more damping (stiffer shocks) will return the system to its original state slower, and less damping (softer shocks) will allow the system to return faster, but will result in oscillation of the spring. A critically damped vehicle is difficult to achieve and not always desirable. The critical damping rate depends on the mass of the vehicle and the spring rate. Even if you are able to calculate the critical damping rate, this needs to be translated to a piston and shock oil setup that matches it, which is nearly impossible. Critical damping is not always the best shock setup either. Off-road vehicles are typically under-damped, which means the shocks are too soft to prevent the spring from oscillating. Since there are so many bumps in off-road, under-damping allows the tires to follow imperfections without disturbing the chassis. In on-road applications, it may be advantageous to have over-damping. Slowing the damping rate on an on-road car can help to keep the body position more consistent to help the aerodynamics. NEED HELP? Send questions to techcenter@airage.com, or mail them to “Tech Center” c/o Air Age Media, 88 Danbury Road, Wilton, CT 06897 USA. JUNE 2013 27

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