- Build and test the assigned gear combinations.
- Record driver/driven gear information and calculate each ratio.
- Describe how each ratio changes speed, torque, and direction.
POE Unit 1 • Lesson 1.4
Gears and Drive Ratios
Focus question: How do gear ratios and gear trains change rotational speed, torque, and direction to meet a design need?
Start Here
What You Need to Do
Use this section as your checklist before moving through the lesson resources below.
- Completed gear-ratio investigation table
Your table contains the ratio, observed motion, and correct speed/torque tradeoff for each setup.
Lesson Targets
What You Will Be Able to Do
The simulation is the main learning tool for this lesson.
Analyze a gear pair
Identify driver and driven gears, calculate gear ratio, and predict output speed and torque.
Track direction
Use the number of external gear meshes to predict clockwise or counterclockwise output.
Explain idler gears
Show why an idler can change direction or spacing without changing the overall simple-train ratio.
Launch Prediction
Before You Touch the Controls
Make a prediction first. Then use the simulation to find evidence.
12T driver → 36T driven
Will the output be faster or slower? What happens to ideal torque? Will direction match the driver?
40T driver → 20T driven
Will the output be faster or slower? What happens to ideal torque? Will direction match the driver?
24T driver → 24T driven
What stays the same in a 1:1 pair? What still changes because the gears are externally meshed?
Interactive Lab
Gear Ratio & Gear Train Simulation
Work through the worksheet while you use the simulation. Record actual values rather than guessing from the animation alone.
If the embedded simulation feels cramped on a smaller screen, use Open Full Screen. Your worksheet remains the required lesson evidence.
Worksheet Roadmap
Complete the Investigation in Four Parts
The page and worksheet use the same sequence so you can move between them without hunting for the next step.
Part A
Predict
Predict speed, torque, and direction for three gear pairs, then check each prediction in the simulation.
Part B
Explore Gear Pairs
Run four trials: a reduction, a speed-up, a 1:1 pair, and one system of your choice.
Part C
Build a Gear Train
Change the idler size in a 20T → idler → 40T train and determine what does and does not change.
Part D
Make a Mission Decision
Compare three lunar sample-storage door options and defend the strongest choice with numerical evidence.
Core Math
Use the Simulation to Check the Equations
Gear Ratio
GR = driven teeth / driver teethOutput Speed
rpm_out = rpm_in × (driver / driven)Ideal Torque
T_out = T_in × (driven / driver)Direction Rule
Every external gear mesh reverses rotation direction. One mesh reverses once. Two meshes reverse twice. Track direction separately from the ratio.
Mission Challenge
Lunar Sample-Storage Door
Use the third simulation mode and the worksheet table to make an engineering recommendation.
Design Need
The motor operates efficiently near 1200 rpm. The storage door should rotate slowly and gain ideal torque so it is less likely to stall in lunar dust.
- Option A: 12T driver → 24T driven
- Option B: 12T driver → 48T driven
- Option C: 24T driver → 36T driven
Your recommendation must use at least two numerical pieces of evidence.
Exit Check
Close the Loop
What happens to output speed and ideal torque when a small driver turns a much larger driven gear?
What is the purpose of an idler gear in a simple external gear train?
How does each external gear mesh affect rotation direction?
Resources
Lesson Resources
Simulation Worksheet
Record predictions, four gear-pair trials, the idler investigation, and your lunar storage-door recommendation.
Gear Lab - Full Screen
Open the same simulation in its own browser tab for more workspace.
POE Unit 1
Return to the unit overview and continue to the next mechanisms lesson when finished.