Scat(\/)an
03-15-2001, 07:50 PM
First of all - WHY is gearing? WHY do we need gears on our motors anyway? Because ours is not a perfect world... In a perfect world, motors would produce infinite torque and infinite power at all rpms (with no rpm limit), and tires would have infinite amounts of traction and the cars wouldn't weigh anything (not to mention an end to world hunger, no taxes, etc). Instead, we have motors with a finite amount of torque and power for a specific rpm, tires have limited grip, and the cars we are trying to accelerate have mass - we live in the real world.
It's important to properly gear a car - be it full sized or 1:10 scale, both for performance and for longevity of the motor. If you gear too tall, you put an increased load on the motor which causes the motor draw more current (amps) and causes the motor, ESC, and battery to overheat. The extra load on the motor also increases comm and brush wear which means more frequent rebuilds and a premature death for the motor. The increased power demands also reduces run-times. Proper gearing means that you must reach a compromise between top end speed and bottom end acceleration.
So, how we do we gear our cars correctly? I’ll try to explain…
When trying to find the proper gearing on a new motor, use the stock gearing first. The 26/84 gearing is on the conservative side and gives you a nice, round ratio of 3:1. Run a pack through the car like you would normally. Try accelerating hard from a standing start, from mid throttle, out of turns, etc… Use the brakes too. While you’re driving, make a note of how the car behaves – does it bog down and accelerate slowly, or does it seem to reach maximum speed very quickly and stay at maximum rpm for a long time? Now, carefully touch the motor can, ESC heat sinks, and battery. They may be hot so be careful you don’t get burned. Ideally, you want to be able to hold your finger on there for a second or two before it gets too hot to touch. If they are extremely hot, you need to make some changes.
If you need to make some changes (and you will), the best way is to play with the pinion gear (that’s the small gear on the motor). A difference of one tooth here will make a bigger difference than one tooth on the spur gear. Robinson Racing sells a pinion gear assortment of 6-7 gears in one package for about $9. There are actually two sets – one even sizes (20, 22, 24 tooth, etc) and one in odd sizes. If you can afford both sets great – if not narrow it down between two gears and then buy the one in between.
If you need to gear taller, go one or two teeth larger on the pinion gear and run another pack through the car (after it cools down from the first pack of course). Check the motor temps again. Keep doing this until the car has good punch off the line, but doesn’t reach maximum rpm too soon. Playing with the pinion gear will get you in the ballpark for the correct gearing – any fine adjustments can be made with the spur gear.
Ok. If you race, you might need to gear a little different than our ideal above. If your track is very tight and technical, you’ll probably need to gear the car lower than ideal. Remember – gearing is a compromise. In this instance, we would be wise to trade off a bit of top end speed for more acceleration out of the slow speed corners. Gearing lower will also give us more torque for better throttle steer and better braking going into the turns. As a result, we can brake later and come out of the turns faster than the other guys (hopefully). If the track is more open with wider turns and longer straights, we would be wise to gear slightly higher because the car has the room to go faster.
HOW TO:
Some of you guys will have read my article on calculating speed, so you should know how to find your gear ratio from that. For those that haven’t read it, you simply divide the spur gear by the pinion gear.
Example. If your spur gear has 84 teeth, and your pinion gear has 26 teeth you divide 84 by 26, giving you a result of 3. Your gear ratio is 3:1.
All this talk of gearing taller or gearing lower may leave you wondering “What the heck is he talking about?”. The smaller the number you get (i.e. 2:1) the taller the gearing, the smaller the number you get (i.e. 4:1) the lower the gearing.
It's important to properly gear a car - be it full sized or 1:10 scale, both for performance and for longevity of the motor. If you gear too tall, you put an increased load on the motor which causes the motor draw more current (amps) and causes the motor, ESC, and battery to overheat. The extra load on the motor also increases comm and brush wear which means more frequent rebuilds and a premature death for the motor. The increased power demands also reduces run-times. Proper gearing means that you must reach a compromise between top end speed and bottom end acceleration.
So, how we do we gear our cars correctly? I’ll try to explain…
When trying to find the proper gearing on a new motor, use the stock gearing first. The 26/84 gearing is on the conservative side and gives you a nice, round ratio of 3:1. Run a pack through the car like you would normally. Try accelerating hard from a standing start, from mid throttle, out of turns, etc… Use the brakes too. While you’re driving, make a note of how the car behaves – does it bog down and accelerate slowly, or does it seem to reach maximum speed very quickly and stay at maximum rpm for a long time? Now, carefully touch the motor can, ESC heat sinks, and battery. They may be hot so be careful you don’t get burned. Ideally, you want to be able to hold your finger on there for a second or two before it gets too hot to touch. If they are extremely hot, you need to make some changes.
If you need to make some changes (and you will), the best way is to play with the pinion gear (that’s the small gear on the motor). A difference of one tooth here will make a bigger difference than one tooth on the spur gear. Robinson Racing sells a pinion gear assortment of 6-7 gears in one package for about $9. There are actually two sets – one even sizes (20, 22, 24 tooth, etc) and one in odd sizes. If you can afford both sets great – if not narrow it down between two gears and then buy the one in between.
If you need to gear taller, go one or two teeth larger on the pinion gear and run another pack through the car (after it cools down from the first pack of course). Check the motor temps again. Keep doing this until the car has good punch off the line, but doesn’t reach maximum rpm too soon. Playing with the pinion gear will get you in the ballpark for the correct gearing – any fine adjustments can be made with the spur gear.
Ok. If you race, you might need to gear a little different than our ideal above. If your track is very tight and technical, you’ll probably need to gear the car lower than ideal. Remember – gearing is a compromise. In this instance, we would be wise to trade off a bit of top end speed for more acceleration out of the slow speed corners. Gearing lower will also give us more torque for better throttle steer and better braking going into the turns. As a result, we can brake later and come out of the turns faster than the other guys (hopefully). If the track is more open with wider turns and longer straights, we would be wise to gear slightly higher because the car has the room to go faster.
HOW TO:
Some of you guys will have read my article on calculating speed, so you should know how to find your gear ratio from that. For those that haven’t read it, you simply divide the spur gear by the pinion gear.
Example. If your spur gear has 84 teeth, and your pinion gear has 26 teeth you divide 84 by 26, giving you a result of 3. Your gear ratio is 3:1.
All this talk of gearing taller or gearing lower may leave you wondering “What the heck is he talking about?”. The smaller the number you get (i.e. 2:1) the taller the gearing, the smaller the number you get (i.e. 4:1) the lower the gearing.