When using the K’Nex 12v Motor Pack to drive Large Ball Contraptions or High Resistance Builds, a single motor may not generate enough power (Torque.) These instructions explain how to use a differential to take two input motors turning at potentially different speeds and combine them into a single power source (rotating axle/gear) safely.

Possible Solutions

Gear Ratios: You can use gear ratios to increase the power however your speed will drop.

Grade: Good. unless too slow

Two Motors Same Shaft: If you connect two motors to the same shaft (Axle) and one motor is not rotating at the same speed or at all then you will create resistance for the faster motor. This will cause heat and possible damage from the extra resistance. You will also lose some or all of your torque and speed in this case.

Grade: Poor. It may work or it may break something

Two Motors With Differential: One of the best ways to solve this problem is to combine the power of two motors using a differential. Often differentials are used in cars to send one input power source to two output destinations (Wheels) at potentially different speeds (This is necessary when turning) however we are using this in reverse.

Grade: Great. This may even offer unexpected features. Example: Adjustable speed (1 Motor vs 2 turned on) or independent shut off when connecting small components to a single power source’s axle.

Supplies

Count - Name
2 - 12v Motors

2 - 12v AC Wall Adapters

9 - Silver Spacers (or 3 blue spacers = 1 silver spacer)

8 - Blue Spacers

8 - Tan Locking Clips

8 - Blue Non-Locking Clips (or Tan Locking Clips)

Gears

2 - Large Yellow Crown Gears

2 - Medium Yellow Crown Gears

2 - White 12v Motor Gears

2 - Small Blue Gears (locking)

Rods

8 - Green Rods

45 - White Rods

47 - Blue Rods

9 - Yellow Rods

2 - Red Rods

3 - Gray Rods

2 - Black Rods (or Gray Rods)

Connectors

7 - White Connectors (Snowflakes)

10 - Yellow Connectors

10 - Red Connectors

3 - Orange Connectors

22 - Gray or Purple 3D Connectors

26 - Blue 3D Connectors

Step 1: Create the Main Box

Build the Main Box which will house our Differential.

Step 2: Build One Side

Begin to build one side. This includes the axle to deliver power from the 1st Motor to the differential.

Step 3: Build the Differential

Time to build the differential.

Step 4: Build the Other Side

Time to build the other wall

Step 5: Build the Output Side(s)

This wall handles the output shaft or axle and can be built on any remaining open side. It can even be built on two opposing open sides at the same time(top and bottom OR front and back). Just add blue rods with yellow connectors (or gray 3d connectors if two connecting sides) in place of red rods where needed.

Step 6: Make the Motor Enclosures

We are almost ready for the motor. We will build smaller boxes (enclosures) to hold them in place.

Step 7: Connect the Motors

Time to connect the motors and review what we have built. After this you can test sending power to each motor independently and also test together. The output shaft (or Axle) should go twice as fast with both motors powered.

Connecting your Elements

Attach to the output shaft(s) for higher torque and continuous energy as long as one motor is powered. Half speed when only one motor is running.
Attach directly to the motor input shaft to have optional components that can be powered off while the main output shaft continues to receive energy from the other motor.

Note: I have seen some cases where the incorrect polarity is used for AC adapters where the positive and negative are backwards. This will cause the motor to spin in the wrong direction. If the motors are spinning in opposite directions then they will cancel each other out causing almost no rotation at all. Either get a new AC adapter or flip around one of the motors to have them rotate in the same effective direction.

Final Remarks

Enjoy your new higher torque motor assembly for your Big Ball Machines/Contraptions or other awesome builds. Please keep small children and pets away as this does increase the chance of fingers/paws getting stuck.

This design includes changes and improvements from "Knex Differential : 5 Steps - Instructables"