After seeing the popularity of K'nex ball machines, I thought it would be fun to build my own railed K'nex contraption. Unfortunately, I don't have enough K'nex on hand to build a crazy ball machine, but I do have motors, so I decided to make this instead. It's a simple, one-motor cart which rides on K'nex rails.

If you like Arduino, you might want to consider augmenting this project with an Arduino + K'nex Motor, something I've written another Instructable on. It gives instructions for modifying an ordinary K'nex motor into an Arduino-powered programmable motor.

Step 1: Materials Needed

To build this cart, you will need the following K'nex pieces.

3x yellow rods
2x red rods
6x white rods (9 for aesthetics)
13x green rods (17 for aesthetics)

2x red connectors (optional, for aesthetics)
2x light gray connectors (optional, for aesthetics)
2x white connectors
8x yellow connectors
3x purple end cap connectors (older ones can be found in gray)
11x tan gear connectors (12 for aesthetics)
4x gray corner connectors (older ones can be found in light purple)
4x black end caps

8x silver spacers
14x blue spacers

4x blue small gears
3x medium yellow gears
1x gray small friction-fit gear (optional, for aesthetic)
1x motor (can be any color/speed, I thought green was the best speed)

To build rails for the cart, you will need the following K'nex pieces per track segment.

2x thin blue rods
2x thin purple rods
1x thin black rod (for a curved track)

2x thin red connectors
1x thin purple connector (for a curved track)

Step 2: Build the Right Side

When building with K'nex, looking at pictures is infinitely better than text instructions. See the pictures above.

Step 3: Build the Axles

Though they may not look like much yet, these axles will be the drive for our little robot rail cart.

Step 4: Attach the Axles

Remember, whenever you use K'nex axles, make sure that there are no gaps between spacers and connectors, to ensure proper function.

Step 5: Build the Left Side

Almost done with the cart! This step will solidify the cart and finish it off.

Step 6: Aesthetic Extras

I added some wing-like struts on either side of the motor, to make the cart look more interesting. These are not necessary, so you can skip this step if you'd like.

Step 7: Build the Rail Segments

Now that you have a cart, you'll need some rails for it to ride on. Follow the above images to build track sections, then connect the sections together to form a track for your cart.

Keep in mind that, because of their design, the curved track sections will cause your K'nex rods to flex slightly. This is normal. However, if you're not comfortable with this, you can always stick with a straight track, or design a better curved track! If you come up with a better curve, please send me a message so I can see your creation!

For the most reliable curved track, alternate curved and straight track sections, to keep the turn from becoming too sharp.

Step 8: Run the Rail Cart

And you're done! Now you can build amazing K'nex tracks and send your motorized cart to take over the world!

If you want to take this cart a step further, you may be interested in my Arduino + K'nex Motor project, which gives instructions on how to take an ordinary K'nex motor and hack it into a programmable Arduino-controlled motor. Maybe you could even make a remote-controlled K'nex train... the possibilities are endless!

I'd love to hear any comments/suggestions you may have, and if you happen to have a question, just leave a comment or send me a message and I'll see what I can do.