Gearing up, Gearing down, and Gear Ratios

Gears are helpful for many things, such as changing direction, transferring power to other parts of the robot, increasing speed, or increasing torque. This post is about the last two, and is also about how gear ratios are calculated.                                                       



Gearing up
(Gear ratio = 5:3)



How do you make a gear spin faster?

If you want to make it spin faster, you gear up. When you gear up, you transfer the energy from a larger gear to a smaller gear (see picture on right). This may sound funny to you at first. Shouldn't it be called gearing down if you move the energy to a smaller gear? Well, they named it gearing up and gearing down based on the speed at which the gear is spinning, not how the sizes of gears are changing. Gearing up is great when you're trying to make something on the NXT spin really fast and you've already reached the 100 power limit, but BEWARE! Increasing speed also decreases torque.

What is torque?

Torque is the amount of circular force applied to an object. It equals the amount of force being applied perpendicular to the object times the distance from the object that force is being applied. If that doesn't make much sense to you, don't worry! You don't have to know the scientific definition of torque in order to use it. Simply remember that the more torque you have, the better chance you'll be able to move a heavy object.



How do you increase torque (strength)?

Gearing down
(Gear ratio = 3:5)

You can increase torque by gearing down. When you gear down, you transfer energy from a smaller gear to a larger gear (see picture on right). Once again, it's called gearing down because it decreases speed. An example of a good time to gear down is when you're trying to lift something heavy, not when you're trying to make something spin really fast.

What are gear ratios?

Gear ratios simply compare the gears you are using. If you're using two 8 teeth gears, the ratio would be 8:8, which reduces to 1:1. If you're using a 8 tooth gear and a 24 tooth gear, the ratio would be 8:24 or 24:8 depending on which one is attached to the motor. Remember this simple rule: when you gear up, say the larger number first. When you're gearing down, say the smaller number first. Gearing up would make it 24:8 (reducing to 3:1), and gearing down would make it 8:24 (reducing to 1:3). Always remember to reduce the number. 

I hope you found this post helpful. Please ask if you have any questions!