Hey guys,
- The ratio is usually defined by choosing a top speed after choosing a motor and battery. Keep in mind that the higher the top speed, the lower the torque will be.
- The number of teeth will be restricted by the diameter of the gear (can't be too large). Apart from that, the more teeth on the gear, the less strain on the belt (since it's pulling on more teeth at the same time, dividing the strain), but you shouldn't worry about that, just pick a good diameter.
- You can calculate the torque you will have using the formula T = Ki * I where T is torque, I is current (max current will result in max torque) and Ki = 1/kv (that's the well known kv-rating of the motor). I didn't do this, since the top speed is more important to know in advance and the torque doesn't say that much since it's hard to estimate how much torque you will need (you have to estimate road friction, air drag, ...).
So
torqueboards wrote:... What would be the best gearing for medium speed?
When you have the motor and battery and you define for yourself what 'medium speed' is, you can go to the calculations.
torqueboards wrote:What would be better 10T/50T or 6T/30T?
For the belt, 10/50 would be better, but you should go for 6/30 since it's lighter and smaller. The belt can handle it
Actually they're both bad choices though! You want the 'smallest common multiple" of the teeth to be AS LARGE AS POSSIBLE (
http://www.mathsisfun.com/least-common- ... -tool.html). I can explain this in detail, but summarized it means that the wear will be equal on all parts of the belt and gears. This means 9/50 is better and 11/50 is even better!
Quoting myself from another topic, here's how to calculate the ratio:
"Usually you chose the gearing ratio last, as there aren't many restrictions. When you have the battery (V) and the motor (kv) chosen, you know the max RPM you will be able to get out of it (voltage [V] * kv [V/RPM] = speed [RPM]). The next step is to calculate the circumference of your wheel (let's say C = Pi * diameter). If you put your wheel directly on your motor it'll spin at for example 4000 RPM. With a C of let's say 0,5m you will travel 0,5m per round of the wheel, thus 2000 m/min or about 33,3m/s, or about 120 km/h --> WOW! Now you chose the max top speed you'll want (let's say 40km/h) and you just pick 120/40 = 3. Of course there are losses to be considered and the actual top speed will be lower so you pick a slightly lower ratio, or you agree on a lower top speed (perhaps 35km/h). Also, keep in mind that top speed = 1/torque meaning that if you want twice the top speed, you'll have half the torque!"