SkrapIron
Posts: 2093
Joined: 5/18/2004
From: Pittsburgh, PA, USA
Status: offline
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What is the best set-up for my truck? How fast will it go?
These are questions that have haunted me for nearly 10 years. I have been running 1/10 scale R/C trucks off and on, without a real good understanding of how to properly set it up. To me, it was FM ( friggin magic). What pinion should I use? What if I change the spur gear. It was all trial and error, that resulted in several melted motors, blown ESC’s and damaged batteries.
But I have found the answer! And it is good!
Question 1: What size spur gear should I run? Well……. When selecting the spur gear size, you need to keep in mind that the ratio between the tire circumference and the final drive ratio should be 1 to 1. 1 to 1? What? Here’s how it works. We’ll use my RC10t3 as the example vehicle. The first thing to consider is the diameter of your tire. It is used to calculate the circumference of the tire. Multiply the diameter of the tire by pi. ( Ex: 3.25”xpi=10.2101”) Now, you need to consider the final drive ratio of your drive train. Begin by dividing the number of teeth on the spur gear by the number of teeth on the pinion gear. This will give you your drive ratio. ( Ex: 87/19=4.5789). Now multiply your drive ratio with your transmission gear ratio ( Ex: 2.4x4.5789=10.9893 ). This is your final drive ratio.
Now the magic part. Subtract the final drive ratio from the running circumference of your tire . (Ex: 10.2101-10.9893= -0.77926) That is VERY close to a 0, but is geared a tad to the torque side of the motor ( anything below 0 is always geared towards more torque). Want more speed than torque? Redo your calculation adding another tooth on the pinion : ( Ex: 87/20= 4.35 ( drive ratio )x2.4 ( transmission gear ratio )= 10.44 ( final drive ratio ) Then subtract your final drive ratio ( 10.44 ) from your circumference ( 10.2101 ) ( Ex: 10.2101-10.44= -0.2299 ) This is your optimum gear ratio, since it is closest to a 0 margin. Any ratio that is greater than 1 will run faster, but will overheat your motor, battery and esc, eventually damaging them.
Question 2. How fast will it go? Well, we have half the equasion already. Using the circumference of the tire divide that by the final drive ratio. ( Ex: 10.2101/10.44=.977797) multiply that number by the maximum working rpm that your motor is capable of. I have a Trinity Jade 15 turn motor. It is rated for 23,500 rpm. ( Ex: .977797*23500= 22982.504 inches per minute )
Convert that sum to feet per minute by dividing by 12 ( 12 inches in a foot) ( Ex: 22982.504/12=1915.2087 feet per minute ). Now multiply your feet per minute by 60 minutes ( Ex: 1915.2087*60= 114912.5239 feet per hour ). Now divide your feet per hour by 5280 ( the number of feet in a mile ). ( Ex: 114912.5239/5280= 21.7637 miles per hour ). Keep in mind that this number is theoretical and is affected my the age of your motor, condition and charge of your battery, friction and or slip from your tires etc. Despite this, it is pretty close to accurate!
So, the key to speed and longevity is a high rpm motor coupled to a properly geared drive train. It will make for many a happy afternoon of backyard bashing with your truck!
Enjoy!
< Message edited by SkrapIron -- 1/27/2005 3:24:35 PM >
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All Forums >> RC Cars, Buggies, Trucks, Tanks and more >> RC Electric Off-Road Trucks, Buggies, Truggies and more >> Mystery Solved! How to select the proper gearing for your electric RC! 
Mystery Solved! How to select the proper gearing for yo... - 
