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May 2013

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RC Car Action - May 2013

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Tech Center sponsored by How do I modernize my trucks? I have been in the RC scene for nearly 25 years, although I have had a couple of Q long breaks. I am just coming out of one now and upgrading my equipment to race my stadium truck and SCT in the modern era. With all of the changes in brushless motors and LiPo batteries, where do I begin to gear my trucks properly? No matter what changes with electronics and batteries, the principles of gear A selection still apply. If you want better acceleration and pull out of corners, change to a smaller pinion or a bigger spur gear. If you want more top speed, then use a bigger pinion or smaller spur. Of course, the smaller your gear ratio (spur divided by pinion), the more amps your motor will draw and the more heat that will be generated by the motor and ESC. Each brushless system will have its own maximum temperature specification for both the motor and the ESC, so consult your user manual. It is a good idea to keep a small temperature gun with you so that you can check your motor after practices and heat races to make sure that you are not in danger of damaging your equipment. If you find that the temperatures are getting close to the limit with the gear ratio and timing that you need to run to be competitive, then it is always an option to add heat sinks or a cooling fan. Your fellow racers are another great resource, and do not be afraid to ask what other people are running so that you have an idea of the gearing window for your particular track. Weight, CST, or CPS? I want to change Q the fluid in the diff to alter the handling of my e-buggy. I see setup sheets posted for my vehicle and the diff fluid is quoted as 5-7-3—or something similar. I realize this means 5,000 front, 7,000 center, and 3,000 rear, but is this weight, CST, or CPS? Are they the same and what do CST and CPS mean? The abbreviation CST is short for centistokes and CPS A is short for centipoise, which are both measurements of fluid viscosity. No matter how the weight is defined, it's all just a way to quote the viscosity. Weight numbers are a general grade rating of the fluid and are based on the CST rating of the fluid, but it cannot always be directly compared to weight. A centipoise is equal to CST multiplied by the density of the fluid. So diff fluids quoted in CPS and CST are not the same weight at first look. The easiest way to get the right diff setup is to always use diff fluid from the same manufacturer. Now you can be sure that changing to heavier or lighter fluid is going to be the correct direction of change from what you are currently running. If you are matching a specific setup from a driver, it'll be impossible to duplicate unless the manufacturer of the fluid is known. 26 MORE FROM THIS ISSUE AT rccaraction.com

HOW HOT IS TOO HOT? Q What is too hot for a .21 engine in a nitro buggy? I broke in my engine according to the manufacturer’s instructions and have made a few practice runs with it. With the factory-recommended needle settings, it seems to be running a little too hot. Is this OK? Each nitro engine is a little bit different and has a unique A temperature range where the engine seems to run the best. Some engines will run just fine at 200 degrees, and others might not come alive until they run 250 degrees. If it runs less than 250 with good power and you see plenty of blue smoke while running, it may be just fine. However, there are some things to check to make sure that you are not inadvertently running it too lean. The fuel delivery system is notorious for causing temperature issues. If there are any leaks in the fuel lines or a loose hose fitting, excess air will be introduced into the engine, making it run leaner. Inspect the fuel tank and the tubing for leaks. If you see any air bubbles in the line during bench running, there's a leak in the fuel tube and it should be replaced. Excess air can also be leaked in the through the engine. Make sure that the carb is installed correctly and it has the correct O-ring. Also check the backing plate for loose screws, as air can leak in there too. It's common to put some high temp gasket sealant in these areas to seal them up. WHY DOESN’T MY TRUCK STEER? I am having trouble with my 1/18-scale SCT. I just upgraded a bunch of parts including the servo, but now my truck does not steer. When I turn the wheel on the Q transmitter, all I get is a clicking sound. What could be the problem? You either have an installation problem or a bad servo. Since the servo is new, it is a A good idea to go back through the installation. Start by taking the servo back out of the truck. With the servo still plugged into the receiver, try to steer with the transmitter. If the trim is centered and you still hear a clicking noise, then there is a problem inside the servo and you may want to look into replacing it. If it travels smoothly from one side to the other, then the problem is in the installation. Start the installation process again, making sure that all of the mounts are properly installed. It is easy to put a servo arm on that has the wrong spline, especially if it is a different brand than the original servo. Make sure when installing the servo arm that it slides smoothly on the shaft and engages the spline. If either the male or female spline is stripped, it could make the servo slip, which could cause a clicking noise. Before connecting the steering linkage to the steering arm, make sure that the wheels are able to steer smoothly in both directions. Then connect the steering linkage back onto the servo. If there is still a clicking noise when you try to steer, the servo saver mechanism could be loose. If it is too loose, it will slip and not allow any steering torque to be transferred to the wheels. If this is the case, tighten it back down to the recommendations in your manual and you should be ready to drive. 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. MAY 2013 27

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