Bought the VEX IQ Planetary Gear set because it looked interesting. Never found an example build, so it took a while to get something working to show my students. Never found a good way to connect to a moving ring gear, so I pinned the ring and only moved the sun and carrier. YouTube videos of Allison transmission teardowns pointed me to cascading stages with carrier driving the sun gear of the following stage. Here is a 64:1 transmission consisting of 3 stages of 4:1.
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This looks really impressive but can you explain how it works? 
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Understanding Planetary Gears is a good introduction .
Using the concept and part names from the video, we can see that the Planetary Gear & XL Turntable Pack contains:
- 12 tooth gears for the Sun gear
- 12 tooth gears for the Planetary gear
- A carrier with four arms
- 36 tooth Ring gear
The video introduced that a planetary gear set can generate three different ratios between two moving parts with one stationary part. Lets use a Planetary Gear Calculator, to determine the three ratios.
Set:
- Number of planets = 4
- Solve for = Ring Gear
- Sun Teeth = 12
- Planet Teeth = 12
It calculates the Ring gear to be 36 teeth.
Ratio 1: Sun stationary
Set Sun to 0 and Carrier to 1 and observe Ring moves at 1.33
Ratio 2: Carrier stationary
Set Carrier to 0 and Sun to 1 and observe Ring moves at -0.33
Ratio 3: Ring stationary
Solve for = Sun Gear
Set Ring to 0 and Carrier to 1 and observe Sun moves at 4.00
For my build, I selected the largest reduction ratio of 4:1. In the picture of the assembly, the small crank on the left is the input. Power is input on the sun gear while the ring gear is held stationary. Can see these two parts on the left in the picture of the disassembled mechanism. The carrier with the four planetary gears is installed between the sun and ring gears. The carrier is the output. The input crank and sun gear have to turn 4 times to turn the carrier once.
To cascade into a compound gear train, the output of the first stage (carrier) drives the input of the second stage (sun). The input crank for stage 1 sun gear has to turn 16 times to turn the stage 2 sun gear 4 times to achieve one revolution of the stage 2 carrier.
The output of the second stage (carrier) drives the input of the third stage (sun). The input crank for stage 1 sun gear has to turn 64 times to turn the stage 2 sun gear 16 times to turn the stage 3 sun gear 4 times to achieve one revolution of the stage 3 carrier which is driving the output crank (larger crank on right side of assembly).
This assembly reduces the input shaft speed by 64 and multiplies the torque by 64. Good for a really strong lift, but it will move slow.
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