12T → 36T
Reduction0.00output turns
Gear Ratio Investigation
Same motor.
Different robot.
How can two gears make a robot faster—or make it strong enough to lift?
⚡ SPEEDMore output rotations
💪 TORQUEMore ideal turning force
Idea 1
First, follow the power.
Before thinking about size, identify which gear receives power from the motor.
Input
MOTORCreates rotation→
Driver
DRIVER GEARConnected to the motor→
Output
DRIVEN GEARReceives the motionKey rule: “Driver” does not mean “small gear.” The driver is whichever gear the motor turns.
Watch only the direction
One turns right. The other turns left.
Follow the gold marks. The gear centers and labels stay still.
Press play, or drag the slider to look closely.
Notice: Teeth pushing at the contact point make the two gears turn in opposite directions.
Watch only the tooth movement
12 teeth move 12 teeth.
One full turn of the small driver is only part of a turn for the large output.
Driver teeth passed 0 / 12Output turns 0.00
Press play, or drag the slider to look closely.
12 of 36 teeth = ⅓ of a turn. The output turns more slowly; no tooth is skipped.
Stop and think
12T driver → 36T driven
Compared with the driver, will the output be faster, the same speed, or slower?
Do not guess from appearance. Use the tooth movement you just observed.
Put numbers to what you saw
Count the turns.
Speed multiplier = driver teeth ÷ output teeth
1
12 ÷ 36 = ⅓ ≈ 0.33
2
One motor turn produces ⅓ output turn.
Now give three different gear pairs exactly the same motor movement.
Speed = turns in the same time
Same motor. Watch the outputs.
All three blue drivers turn once together. Which teal output turns the most?
36T → 36T
Direct0.00output turns
36T → 12T
Speed-up0.00output turns
Press play, or drag the slider to look closely.
⅓ turn · 1 turn · 3 turns. Same input time, different output speeds. Each filled strip represents one output turn.
A different question
Can it turn against a load?
Torque is turning effort. A spinning mechanism can still be too weak to lift.
Ready to test
Keep the same motor.
Change only the load.
Load needs 0.20 N·m
Motor can supply 1.00 N·m
Try each load. A stalled shaft does not rotate.
Press play, or drag the slider to look closely.
See the turning leverage
Same tooth force. A longer lever.
The larger gear receives the tooth force farther from its axle.
Torque = force × distance from the axle. Three times the radius gives three times the ideal torque. The price is one-third the output speed.
Torque = ability to turn against resistance
Which gearing can lift it?
Same motors. Same lifting drums. Change the load for all three together.
Each load needs 0.20 N·m
12T → 36T
ReductionReady to test
Available turning effort 3.00 N·m
36T → 36T
DirectReady to test
Available turning effort 1.00 N·m
36T → 12T
Speed-upReady to test
Available turning effort 0.33 N·m
Press play, or drag the slider to look closely.
Teaching model: what stays the same?
Input torque budget: 1 N·m. For a setup that can lift, input speed is held constant; all drums have the same radius. Available output torque = input torque × output teeth ÷ driver teeth. A load that needs more torque holds the shaft still. Gears do not slip. Animation is slowed, with no friction, acceleration, or motor speed–torque curve modeled. Real lifting limits require testing.
Everything together
More speed. Less turning effort.
Same input speed and torque. Blue = driver. Teal = output.
12T → 60T
Speed≈ 0.20×
Ideal torque5.00×
0.00 output turns
12T → 36T
Speed≈ 0.33×
Ideal torque3.00×
0.00 output turns
36T → 36T
Speed1.00×
Ideal torque1.00×
0.00 output turns
36T → 12T
Speed3.00×
Ideal torque≈ 0.33×
0.00 output turns
60T → 12T
Speed5.00×
Ideal torque≈ 0.20×
0.00 output turns
Press play, or drag the slider to look closely.
No free power: in this ideal model, speed multiplier × torque multiplier = 1. Gears trade speed for torque.
Follow the same shaft
The gear turns the wheel.
The output gear and wheel are fixed to one axle. They turn together.
Press play, or drag the slider to look closely.
One output-gear turn makes one wheel turn. With the same wheel size, more turns carry the robot farther.
Design decision 1
If speed is the goal...
⚡
The intake rollers are too slow.
The rollers already have enough force. Which change makes the output rotate faster?
Reasoning: To gain output speed, use a driver that is larger than the driven gear. Expect less ideal output torque.
Design decision 2
If turning force is the goal...
💪
The lift moves, but stalls under load.
It does not need to move as quickly. Which change increases ideal output torque?
Reasoning: To gain ideal output torque, use a driver that is smaller than the driven gear. Expect a slower output.
Speed you can see as distance
Same wheels. Same motor time.
These robots are lightly loaded. Watch the distance each gearing travels.
Press play, or drag the slider to look closely.
Distance follows wheel turns. The speed-up robot goes farthest here. The heavy-load test showed why that gearing cannot always do the job.
Apply the tradeoff
The arm is fast—but it stalls.
A robot arm currently uses a 60T driver → 12T driven. It moves very quickly but cannot lift the game object.
Which redesign best addresses the actual problem?
Finish like an engineer
Record the reason and the evidence.
Problem observedExact gear changeWhy it should helpTest evidenceNext step
Design decision: We changed from a 60T driver / 12T driven gear to a 12T driver / 60T driven gear to increase ideal output torque.
Evidence: Illustrative example, not collected data: the old design completed 0 of 3 lifts. The new 5:1 reduction completed 3 of 3 lifts, but moved more slowly. Next, we will test 12T → 36T to see whether it still lifts while improving speed.
Evidence: Illustrative example, not collected data: the old design completed 0 of 3 lifts. The new 5:1 reduction completed 3 of 3 lifts, but moved more slowly. Next, we will test 12T → 36T to see whether it still lifts while improving speed.
Exit ticket: For 12T → 60T, find the output-speed multiplier, ideal-torque multiplier, and one useful robot application.