Welcome to my instructable on how to build a differential out of K'nex!
A differential allows power to be converted to two separate speeds. The most common application for this is used in cars to allow the wheels to turn at different speeds while turning. Another cool thing about differentials is that we can create an exact 1:2 gear ratio (normal k'nex gear ratios are not capable of this) by preventing one of the axles from turning.
This video explains how a differential works in a vehicle application.
The design of this k'nex differential was largely influenced by the Smallest K'nex Differential by GWorks. I built this differential because GWorks differential although much smaller than mine, was not able to deliver a high enough torque for my application.
This differential is featured in my Automatic Dual Differential Continuously Variable Transmission. There you can find a video of the transmission in action using the differentials to change gear ratios.
Step 1: Parts List
Here is the list of parts you will need to build this differential:
2 - rubber bands
1 - red gear (or yellow gear)
2 - snap gears
2 - blue gears
2 - blue spacers
2 - grey clips
28 - black clips
5 - orange connectors
4 - white connectors
7 - white rods
8 - yellow rods
Step 2: The Orbital Gears
Build the orbital gear structure as shown using the snap gears.
Step 3: Attaching the Ring Gear
Attach black clips to the four white connectors as shown in picture 1.
Then secure the red gear to a white connector with wire. Thread the wire as shown to prevent friction with the axle.
Step 4: The Axles
Build the two axles as shown.
Note: the axles used in these instructions are yellow rods. However you may use whichever sized rods suit your application.
Step 5: Assembly
Attach the axles to the orbital gear structure as shown in pictures 1-2. Make sure that the gears are aligned properly. If they are not aligned properly it will create a lot of friction making it harder to turn.
Clip yellow rods on to the remaining black clips.
Once this is done make sure to pull the internal white connectors outward as far as they will go. This ensures the optimal pressure on the gears for the least amount of friction.
Step 6: Adding Rubber Bands
Loop a rubber band around one end of a white rod as shown. Wrap the rubber band all the way around the differential and loop it over the other side of the white rod. Repeat this on the other side.
The rubber band serves two purposes:
1. At high speeds the yellow sticks tend to fly off the differential so the rubber band holds the yellow rods on the black clips.
2. Under high torque load, the gears create an outward force attempting to push the snap gears off. The rubber band pulls in the yellow rod over the snap gear to hold the gear in place.
Thanks for viewing my instructable! I hope you enjoyed it and find it useful in your own creations. Be sure to check out my other instructables!
If you post an instructable which uses something from one of my instructables, let me know, I'll post a link to your 'ible in my applicable 'ible