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RC Car Gear Ratio Calculations
Calculating a gear ratio is not as difficult as many people think it is. In fact, it is one of the simplest, and most useful information an RC crawler should know. But before I teach you how to calculate gear ratio, let us look at the meaning of gear ratio calculation. Gear ratio calculation is simply calculating the rotational speed of two or more interlocking gears. Now, hold my hands as I walk you through this simple calculation.
As a universal rule, when dealing with two gears, if the drive gear (the one directly receiving rotational force from the engine) is bigger than the driven gear, the later will turn more quickly, and vice versa. This concept can be expressed with the formula Gear ratio = T2/T1, where T1 is the number of teeth on the first gear and T2 is the number of teeth on the second gear.
How to calculate gear ratio
We will first calculate the gear ratio involving two gears then we will calculate the one involving more than two gears.
Gear ratio involving two gears:
- You must have at least two gears engaged with each other if you are to determine a gear ratio. The first gear is called the “drive gear” it is attached to the engine of the car and the second gear is called the “driven gear”. To be able to find the gear ratio the teeth of these gears need to be mashed- in other words, these gears have to be interacting with each other whereby one gear (the drive gear) turns the other (the driven gear). For instance, let’s say you have one small drive gear (gear 1) turning a larger driven gear (gear 2).
- Compare the number of teeth on both gears. You can do this by counting manually or by checking for this information labeled on the gear itself. For instance, let’s say the smaller drive gear has 20 teeth, and the larger drive gear has 30 teeth.
- Divide one teeth count by the other. Now that the number of teethes are known, you can now find the gear ratio relatively simply. The driven gear teeth are to divide the drive gear teeth. Using our example, divide the 30 teeth of the driven gear by 20 teeth of the drive gear i.e. 30/20 = 1.5. We can also write this as 3/2 or 1.5 : 1. The meaning of this ratio is that the smaller driver gear turns one and a half times to get the larger driven gear to make one complete turn.
Gear ratio involving more than two gears:
- In this case, the first gear remains the drive gear, the last one remains the driven gear, while the ones in the middle become the idler gears. The idler gears are often used to change the direction of rotation or to connect two gears. For instance, let’s say the two gears described above is now driven by a small seven-toothed gear. in this case, the 30-toothed gear remains the driven gear and the 20-toothed gear (which was the drive gear before) is now the idler gear.
- Divide the teeth numbers of the drive and the driven gears. The important thing to remember when dealing with gears trains with more than one gears is that only the drive and driven gears (usually the first and the last ones) matter. The idler gear doesn’t affect the gear ratio. In this case, all you need to do is to identify your drive and driven gear and you can calculate it the same way we calculated the first one. Using our example, we would find the gear ratio by dividing the 30-toothed driven gear by the seven toothed drive gear i.e. 30/7 = about 4.3 (or 4.3 : 1). This means that the drive gear has to turn about 4.3 times to get the much larger driven gear to turn once.
Tips for setting gears for your RC cars
Everybody likes fast cars but not everybody knows the mechanism behind the speed of a car. Follow me closely and I will tell you how to set your gears to ensure maximum speed.
For rock crawling lovers, gearing is one of the most important things you should know. Getting the balance of your gears right gives you an edge over your competitors because you will be able to alter the performance of your car and maximize power even more efficiently.
Setting your gears simply involves changing your gear-box configuration- the pinion gear and the spur gear. like I said, follow me closely and you will be setting your gears yourself in no time.
The pinion gear is the small gear made from common metals like steel, while the spur gear is the larger gear that the pinion turns. To alter the gear ratio, change either the pinion gear or the spur gear by increasing or decreasing the teeth on one of the gears.
Increasing the number of teeth on the pinion gear, your car will have a higher top speed but less acceleration. That ultimately means that if you leave the pinion the same but decrease the number of teeth on the spur you will get the same result because in both cases, you have decreased the gear ratio. Also, reducing the number of teeth on the pinion gear or increase the teeth of spur gear will ultimately increase the gear ratio of your car.
Ok, let me make it quite simple for those of you that are a little bit confused or overwhelmed by the long gibberish.
Important tips on gear setting
A high gear ratio = lower top speed, more acceleration (to get a higher ratio, decrease the teeth on the pinion or increase the teeth of spur gear)
A lower gear ratio = slower acceleration with higher top speed (to get a lower ratio, increase the teeth on the pinion or decrease the teeth of spur gear).
Best Gearing for your RC car
Getting your gearing balance is a key feature in RC crawling competition.
Gear setting your Brushless motors
For a higher turn motor like (17.5t, 13.5t etc.) which has more torque but less top speed, needs a larger pinion/smaller spur combination.
Low turn motors like (5.5t, 8.5t) will generally need to use a small pinion large spur combination. You can as well check the manual of your gears to see the recommended pinion and spur sizes for your car.
If you are an RC racer, you should spend a lot of time trying to figure out the perfect balance of gears to give your car enough speed but still have enough torque for fast acceleration. In getting a perfect gear balance, take these factors into consideration: tire size, track conditions, traction of the track, duration of race, motor types, and battery specs.
Thank you for reading this post.
Written by Chrixtopher and edited by Carlos Santos, your webmaster
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