Introduction: K'nex Flywheel Powered Machine Gun

Please read this whole intro before you ask questions in the comments (I know it's long but this gun deserves it).

Let me introduce to you the first ever flywheel powered k'nex gun. Instead of most guns where you pull back rubber bands that push a ram rod that shoots a rod, in this gun there are 2 motorized wheels that propel the ball forward much like a pitching machine or a battery powered Nerf gun. This mechanism makes it much easier to create a true semi-automatic or fully automatic gun.

I originally made this to practice my ping pong spikes (that is why it shoots ping pong balls) but I thought this "gun" was extremely innovative so I am posting it in hopes that someone will develop this mechanism into a better gun that actually shoots k'nex. If you do develop this, please give me some credit because I introduced this idea, (if someone else actually came up with this before me, please let me know). Also, if you develop this please use a stronger motor! This machine only shoots the balls about 5 feet (I know, it's a bummer) because the power all depends on the motor (there are no rubber bands required) and we all know how powerful k'nex motors are. Like I said, this isn't made for performance, it's mainly just to introduce the idea of a fly-wheel powered gun. This machine uses a standard green k'nex motor, just about the weakest out there, so I only got the wheels cranked up to about 900 RPM, or about 15 rotations per second, and with around 2 inch diameter wheels, the edges are traveling about 7.85 feet per second, which is only about 5.35 miles per hour. With a stronger motor, you could get this going much faster, and probably turn it into an actual gun that shoots real k'nex.

I do strongly recommend that you build this, even though it isn't really an actual gun, because it is insanely cool to watch the 2 wheels shoot the ping pong balls. I made 2 sets of directions, so if you don't want to build the whole gun you can just make the mechanism and save a lot of time and pieces. If you do only make the mechanism, though, you will have to hand load each individual ball into the wheels to get it to shoot. If you do have all the pieces, or you just want to make something cool, you can make the whole gun. This includes the shooting mechanism, the feeding mechanism, a stand, a magazine that holds about 22 balls, (this is easily extendable or optional) and an optional funnel to make it easier to load the balls. Overall, you can fit about 40 or so balls into the magazine and the funnel, but the funnel will not constantly feed the balls into the magazine, because they will get stuck. Because of this, only about 22 balls will get fed into the shooting mechanism at a time. This is why there is a huge magazine on top of this gun. I would have made the gun hopper fed instead of magazine fed if the balls didn't get stuck. The feeding mechanism controls the feeding to about 1 per second, so they all don't get shot out at once. You could easily modify this to make it into a faster firing machine gun or a semi-auto with a trigger. I just wanted to keep it at a relatively slow rate of fire.

For some reason this gun is very picky about the size of the ping pong balls used. The smaller the better, I tried some slightly bigger balls and they didn't fit. The orange ones in the pictures are Kevenz 50 pack training balls. You can get the whole pack for around 3-4 dollars.

Lastly, this is my first instructable, so please comment and tell me what was good in this ible and what I should change for my next. I know the k'nex instructables days are pretty much over, but I would like to keep them going. Although I only joined instructables recently, I have surfed around this website and built pretty much every ball machine, gun, roller coaster, or cool contraption on the site. So I am not new to instructables, I just only decided to join recently.

Sorry for the terribly long explanation. Congrats if you made it this far. I just thought this gun deserved to be explained so I won't have to answer thousands of questions in the comment section. Alright, let's get building!

Note: Be sure to either read the image notes, or the numbered directions at the bottom of each step. (Or you can read both, but they say mostly the same things).

Step 1: Piece Count

This gun uses a lot of pieces, but you can substitute many of them. There are 2 piece counts, one for just the mechanism, and the other for the whole gun.

Important Note: In this gun, there are an absurd number of y-clips, metallic blue clips, one slot grey clips, etc. This is only because this gun needs a lot of spacers to function and I ran out of spacers about half way through designing this so I substituted them with small clips, which I happen to have a lot of. You can substitute many of the clips in this piece count with more spacers, or other clips. I will specify where in each step.

Piece count for just the mechanism (picture 2)


  • Dark Grey (1 slot): 10
  • Red: 6
  • Yellow: 11
  • Green: 10
  • Light Grey (2 slot): 2
  • White: 24


  • Grey: 4
  • Red: 5
  • White: 12
  • Blue: 32
  • Yellow: 22


  • Small Triangular panel: 4
  • Standard Grey Wheels (Picture 6): 4
  • Wide Thin Tires (Picture 7): 2
  • Micro Black Rods (Picture 3): 2
  • Orange 1-slot Tubing Connectors (Picture 5): 3
  • Y-clips: 36
  • Micro Chain Gear (Picture 4): 1
  • Large Yellow Gear: 4
  • Metallic Blue Clips: 5
  • Small Gear: 4
  • Motor: 1
  • Tan-Clip: 9
  • Blue Spacers: 36
  • Grey Spacers: 42

Grand Total for the Mechanism: 290

Piece count for the whole gun (including the mechanism)


  • Blue 3D: 8
  • Purple 3D: 40
  • Light Grey (2 slot): 20
  • Dark Grey (1 slot): 85
  • Red: 36
  • Orange: 42
  • Green: 48
  • White: 96
  • Yellow: 120


  • Grey: 33
  • Red: 59
  • Yellow: 65
  • Flexible Orange (Yellow Rod Length): 4
  • White: 130
  • Green: 204
  • Blue: 127


  • Micro Chain Links: 54
  • Micro Chain Gears (Picture 4): 2
  • Micro Black Rods (Picture 3): 2
  • Large Yellow Gear: 4
  • Medium Red Gear: 1
  • Small Gear: 5
  • Metallic Blue Clips: 16
  • Standard Grey Wheel (Picture 6): 4
  • Wide Thin Tires (Picture 7): 2
  • Orange Tubing Clips (Picture 5): 3
  • Tan-Clips: 15
  • Small Triangular Panel: 4
  • Motor: 1
  • Y-Clips: 47
  • Grey Spacers: 57
  • Blue Spacers: 69

Grand Total for the Entire Gun: 1,406

Step 2: Mechanism

This is the mechanism for this gun. If you want, you can build just this but you will have to hand feed the balls into the machine. Many Y-clips are used in this step, and you can interchange most of them for spacers. You will need two micro black rods to lock the wheels to the gears, and you will also need two of the wide thin tires that fit two standard grey wheels inside of each of them.

  1. What you will make this step
  2. Make this
  3. Make 3 more
  4. Make this
  5. Attach them like so
  6. Make this
  7. Attach it like so
  8. Another view
  9. Make this
  10. Another view
  11. Another view
  12. Attach it
  13. Another view
  14. Make this
  15. Another view
  16. Another view
  17. Attach it
  18. Another view
  19. Gather these
  20. Put the 2 wheels inside the tire
  21. Build this with the wheel you just made
  22. Another view. Be sure to put this micro black rod inside the hold in both the wheel and the gear
  23. Build this
  24. Attach it
  25. Make another
  26. Build this. You can use spacers for the Y-clips. The orange tubing clip is helpful if you have it as it is extra wide so it spreads the Y-clips out more
  27. Build this. You can use spacers for the Y-clips
  28. Build this. You can use spacers for the Y-clips
  29. Attach it
  30. Build this
  31. Attach it
  32. Attach this
  33. Attach this
  34. Build this
  35. Another view
  36. Another view
  37. Make this
  38. Another view
  39. Attach it
  40. Attach it
  41. Another view. Make sure you put the blue rod in place
  42. Attach the wheels
  43. Another view
  44. Another view
  45. Done!

Step 3: Feeding System

This is the system that feeds the balls one by one into the flywheels. It is a long step but important.

  1. What you will make this step
  2. Make this
  3. Make a second panel, but make it a mirror image of the first one
  4. Make this. You can use spacers instead of the 4 gray clips
  5. Another view
  6. Make this
  7. Make this. You can use spacers instead of the 6 gray clips
  8. Connect them together
  9. Another view
  10. Attach them to the second panel you made
  11. Another view
  12. Another view
  13. Another view
  14. Attach the other panel on (the first one you made)
  15. Build this
  16. Build 2 of these
  17. Make this
  18. Attach them together
  19. Another view
  20. Attach this to the track you just made
  21. Attach what you just connected to the frame section
  22. Another view
  23. Another view
  24. Build this
  25. Another view
  26. Another view
  27. Make these
  28. Connect them to the axle like so
  29. Connect 54 micro chain links together
  30. Attach the chain to the wheel. It doesn't connect to anything else yet
  31. Build these
  32. Build this
  33. Build these
  34. Connect them
  35. Connect them
  36. Build this
  37. Another view
  38. Another view
  39. Connect them
  40. Connect them
  41. Another view
  42. Another view
  43. Build this. The 3 dark grey clips in the middle can be spacers instead
  44. Connect them
  45. Gather these
  46. Clip these on the front
  47. Clip these on the back
  48. Another view
  49. Attach the axle to the track you just made
  50. Another view
  51. Attach the bottom part of the magazine you made to the feeding system you just made
  52. Another view
  53. Another view

You finished the feeding system! I promise it gets easier from here.

Step 4: Magazine

This is the top half of the magazine for this gun.

  1. What you will be making this step
  2. Build this. You can use spacers instead of the 6 gray clips snapped on to the white and blue rods
  3. Another view
  4. Another view
  5. Another view from the back
  6. Build a second one, but make it a mirror image of the first one
  7. Make this
  8. Make this
  9. Another view
  10. Connect like so
  11. Connect like so
  12. Build this
  13. Another view
  14. Build this
  15. Another view
  16. Connect like so
  17. Another view
  18. Build this
  19. Build this. You can use spacers instead of the 2 y-clips for this
  20. Another view
  21. Connect like so
  22. Another view
  23. Make 2 of these
  24. Make this
  25. Connect like so
  26. Make this
  27. Connect like so
  28. Another view
  29. Connect these pieces together
  30. Another view
  31. Another view
  32. Another view
  33. Put the other track piece on
  34. Another view
  35. Another view
  36. Another view
  37. Attach the cover to the magazine
  38. Done!

Step 5: Front Stand & Support

This is the front stand and support for this machine. The reason there are these pillars is to take the weight off the mechanism and put it on the stand at the bottom. This lets the mechanism run smoothly. If the pillars weren't there, the motor wouldn't be strong enough to power the machine because of the weight on it.

  1. What you will make this step
  2. Make 2 of these
  3. Make 2 of these
  4. Gather these
  5. Connect like so
  6. Connect the others like so
  7. Another view
  8. Make this
  9. Make this
  10. Make this
  11. Another view from top
  12. Connect the first 2 together
  13. Add the 3rd on. The 2 orange connectors on either end must be perpendicular to one another
  14. Make this
  15. Connect like so
  16. Another view
  17. Make a second one
  18. Gather these
  19. Connect like so
  20. Connect to the pillars
  21. Gather these
  22. Connect like so
  23. Connect like so
  24. Another view
  25. It should look like this. The pillars are supposed to bend
  26. Connect them to the base
  27. Another view
  28. Another view
  29. What it should look like now

Step 6: Rear Stand & Support

This is the rear stand and support for the machine, probably the easiest step. If you don't have an orange rod (red rod length) you can just use a red rod.

  1. What you will be making
  2. Make 2 of these
  3. Gather these. If you don't have the orange rod, you can use a red rod
  4. Connect them to one side panel as shown
  5. If you are using the orange rod, be sure to connect the yellow connector to the outer slot in the orange rod
  6. Put the other panel on. The panels should not be parallel to each other, they should instead veer apart from one another
  7. Make sure you connect the yellow pieces to the outer slots, so the panels get spread apart
  8. A view showing how the panels are supposed to spread apart

Step 7: Funnel

This step is optional, but it is useful and looks cool. I suggest you build it.

  1. What you will make in this step
  2. Make this
  3. Make another
  4. Make this
  5. Make this
  6. Make a second, be sure it is a mirror image of the first
  7. Connect them
  8. Build a second one
  9. Connect them
  10. Another view
  11. Build this
  12. Build a second
  13. Build this
  14. Another view
  15. Build this
  16. Another view
  17. Connect them to one panel
  18. Put the other panel on
  19. Another view
  20. Another view
  21. Get these
  22. Connect them. You only have to connect them in 6 places
  23. Another view
  24. Another view
  25. Another view

You finished all the building! Now it's time to put it all together!

Step 8: Assembly

Yay! you built everything. Now the fun begins.

  1. Gather all of the parts of the gun
  2. Put the mechanism and the front stand together
  3. Another view
  4. Attach the feeding system
  5. Another view
  6. Another view. Make sure to attach the chain to the other gear, and to put it around the protruding rod
  7. Another view
  8. Another view. Make sure you attach the three gray clips to the blue rod
  9. Another view
  10. Attach the rear stand
  11. Another view
  12. Another view. Add the two grey spacers onto the red rod
  13. Attach the magazine
  14. Another view
  15. Another view
  16. Attach the funnel
  17. Another view
  18. Another view

Step 9: Finished!!!

You're done! This is the part where I say that I am not responsible for any damage done by this gun, but let's be honest, this thing isn't going to cause damage any time soon. Go have fun with it. Practice your ping pong spikes, turn it into a semi-auto gun, or experiment with it and mod it. There is lot's of potential for this gun. (I would love to see someone turn this into a ball machine lift!) Note: This gun is very picky about the size of the ping pong balls used. The smaller the better, as slightly bigger balls might not fit down the magazine. I used Kevenz 50 pack training balls. You can get those for about 3-4 dollars per 50 balls. Lastly, please comment if you have any questions.

- Jessbuilt