Over the years, Lego released various kinds and sizes of gears. The primary purpose of gear is to transfer/change the properties of an input. This input can be provided by a motor or a manual operation, like turning a lever.
Gears are used a lot in Lego Technic vehicles. They are mainly used for converting between torque and speed. For some vehicles, you want more torque, such as an off-road vehicle. For some cars, you want more speed, for instance, an F1 car. In addition to this, gears are used to change direction, for example changing the direction of rotation by 90 degrees.
Different types and sizes of gears are needed to meet the need for different gear ratios, space, and efficiency requirements. If you search bricklink for “technic gear” you will see there are more than 100 variations. But, most used gears fall into one of the following categories:
- Spur gear
- Bevel gear
- Worm gear
- Knob Cog
- Clutch gear
There are also support parts like differential housing, gear racks, turntables, axels, clutches, chains, and enclosing frames.
Gear Ratio
A gear ratio is the number of teeth on the driven gear, divided by the number of teeth on the driver gear. For example, if you are driving a 24 tooth gear (the output) with an 8 tooth gear (the input, where the motor is connected), the gear ratio is 24:8 and that is 3:1. That shows we lost 3 times from the speed but the torque is increased 3 times. When using the worm gear, it is also very easy to calculate, it is the number of teeth on the meshed gear divided by 1. For example, if a 24-teeth gear is meshed with a worm gear, the gear ratio is 24:1.
Gearing up: Gearing for speed, that is driving a small gear using a larger driver gear
Gearing down: Gearing for torque, that is driving a larger gear using a smaller driver gear
Cons of Gears
Let’s start with the bad news first. All these conversions between torque and speed and changing the direction of force are not free. There are two unwanted properties of any gearbox.
- Friction: Due to the friction you always loose some power. Friction adds up, the longer the gear chain is the bigger the lost. The bigger the gear is, the bigger the friction.
- Backlash: Also Lego gears don’t fit tightly to each other, there is always some gap between the teeth of connected gears. This air gap between the teeth generates a backlash. Backlash cause gears to move freely a little in an unwanted way and also cause delay during the operation of a gear chain. Small gears with less teeth generates more backlash.
Spur Gears
These gears are one of the simplest and most common gears. have full teeth and can only be connected to each other from end to end. They can’t be connected at a 90-degree angle. They have more backlash than bevel gears but they are more unlikely to slip. Compared to bevel gears, they are more unlikely to slip and can handle more loads.
Bevel Gears
Bevel gears have angled teeth and can be connected to each other at a 90-degree angle. There are two-sided bevel gears and these two-sided bevel gears can be connected with an angle and end to end like spur gears.
Worm Gears
They provide significant torque increase and speed reduction and they also change direction of the force 90-degree. They have minimal backlash but too much friction. Gear ration calculation is very simple, you can simply use the teeth count of connected gear as gear ratio. For example, if you connect it to 16 tooth spur gear then the gear ratio is 16:1. The worm gear can be inherintly self locked. The worm can drive the gear, but due to the inherent friction the gear cannot turn (back-drive) the worm gear.
Knob Cog
It may be considered a gear with a very low number of teeth. It can be connected end to end or at a 90-degree angle. They have a very high backlash. The advantage to them is that they are very rigid and stand very high loads.
Clutch Gear
Clutch gears are designed to work like normal gears until the designed force and after that, they start to slip around their axle. In this way, they protect the motor or connected axle damage.
