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A Gear Ratio change is one of the easiest ways to change Mechanical Advantage in a mechanism or system to achieve desired speed and/or torque. Using different-sized gears meshed together in a gear train can change the speed or torque provided by the motor.
The speed/torque relationship is inverse, meaning they are opposite. When you increase speed, you decrease torque. When you increase torque, you decrease speed. Torque is the amount of power provided as a twisting force on the drive shaft.
Gear ratios can be mathematically calculated by counting the number of teeth on the gear. Here is a wikiHow website to help you do this.
The speed increases when a larger gear is connected to a motor and the smaller gear is driven. This works because the smaller gear rotates faster than the larger gear since it has fewer teeth.
When you increase the speed using this type of gear ratio, you sacrifice torque. When two gears are meshed together, they rotate in opposite directions.
The speed decreases when a smaller gear is connected to a motor and the larger gear is driven. This works because the larger gear rotates slower than, the smaller gear since it has more teeth.
You will often want to slow down the mechanisms to increase the torque in the gear system.
When two gears that are the same size are meshed together, there is no change in speed or torque.
The driven gear has the same torque or speed as the driving gear provided by the motor.
You may want to do this to transfer the motion of the gear to another area of the robot.
Sometimes a gear is used between two gears. This gear is called an idler gear.
You would want to add an idler gear to change the direction of the driven gear. When one idler gear is used between two gears, the driving and driven gears rotate in the same direction.
It does not matter the size of the idler gear, just the sizes of the driving and driven gear when looking at gear ratios for speed and torque.
Sometimes several idler gears are used to transfer motion to another part of the robot.
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