Transmission
From FIRSTwiki
A transmission provides different gear ratios to get the full potential out of the motors provided in the kit of parts.
Contents |
Synopsis
For many teams, the drill motor and it's built-in planetary gearbox (plus an additional chain & sprocket reduction) was plenty enough to power the drivetrain of their robot. In 2005, the drill motors were phased out and were replaced with 2 more CIM motors, giving a total of 4 CIM motors in the kit of parts. Additionally, a custom kit transmission was packed into the 2005 kit of parts, giving teams a 1 or 2 motor, single speed transmission.
Building a FIRST robot transmission
There are many options to consider when making a transmission. Here are a few:
- Multiple-Speed
- Multiple-Motor
- Continously Variable
Shifting
In recent years, shifting transmissions have started to make a larger appearance. The advantages to having a shifting transmission are being able to select a specific reduction ratio for a specific circumstance. If you are in a pushing match or need to accurately position your robot, you could select a high reduction to increase the robot's output torque and lower its speed, giving it more pushing power and controllability. If you are on the offense, then you could select a lower reduction and increase the robot's speed.
Most teams that build a shifting transmission choose to have only two speeds: one low gear for more pushing power, and one high gear for a higher top speed.
A handful of teams choose to construct 3 speed, 4 speed, or more, transmission.
The most common way to shift is with gears; there are two common ways to do it: via dog-shifting or via mesh-shifting. Some teams break away from the conventional methods and use different methods to shift gears. Team 222 uses a ball-shifter, which allows their transmissions to be much smaller. Some teams shift by changing the size of their wheels (they would switch between different pairs of wheels, a smaller wheel for more torque, a bigger one for more speed).
Some teams take it to the next level and incorperate a Continously Variable Transmission (CVT), allowing an infinite amount of reduction ratios.
Motors
Teams generally use the most powerful motors in the kit to drive their robot; these motors (2005) would be the 4 CIMs and the 2 Fisher Price motors. Since 4 CIM motors were included in the kit, constructing a 2 motor transmission was not very difficult, since no reduction was needed. Some teams chose to also add in the fisher price motor, either to replace one set of CIM motors, or simply to add to the drivetrain's power. Some teams chose to achieve the proper reduction through gears, some chose to use the AM-planetaries sold by AndyMark.
Types
- CVT - Experimental, at best
- Four speed transmission - Simple, powerful, light.
