Introduction: K'nex Bending Rod Launcher

About: Hi! I'm Ruben, better known as RNB. I'm a student Mechanical Engineering and hence like to build contraptions related to that. I mostly make use of K'nex, which is convenient to use since it is easy to design …


The Bending Rod Launcher is a new type of K'nex ball launcher. The launcher does not use rubber bands, instead, as the name suggests, it utilizes a bending rod to launch balls. This eliminates the need for replacing worn out rubber bands.

Some key aspects to this design are:

  • Easy integration into a blue rod based tower.
  • Possible to launch the balls up approximately 2.5 red rods.
  • Launcher shoots six balls each minute.
  • No regular maintenance needed (no rubber bands).
  • It is very fun to watch!

Here is a video showing the launcher in action:

Note: This design does not permanently deform the black rod, as long as the black rod is not loaded when the launcher is shut down. Just make sure the black rod is not bend when the lift is shut down and you will be fine!

Have fun building!

Step 1: Motivation

Many K'nex ball launchers (example) rely on rubber bands. Whilst those designs are often simple and effective, maintenance proves to be problematic. Replacing worn out rubber bands can be very fiddly on big ball machines where the launcher is not easily accessible.

Because I did not want to deal with rubber bands, I started looking into different launching methods. Being an ice-hockey player, I decided to try to mimic the shooting techniques we use on the ice. To shoot, we bend our sticks, storing energy. On release, all the stored energy from bending the stick is put into the puck. This technique allows us to shoot a lot faster.

Translating that technique back to K'nex, I choose to utilize a long, black rod to 'replace' the stick. Because these rods are stiffer than the regular 190mm grey rods they can store more energy and therefore launch the ball faster. By preventing the balls from moving forwards this black rod is forced to bend. Once enough force is applied by the bend black rod, the ball squeezes through the blockers and the ball is launched.

Step 2: Parts List

Here is the list of all parts needed to build the bending rod launcher. I named the parts similar to how the K'nex User Group does. If you are missing parts I suggest looking there to buy them.

Please note that the colors of the pieces is irrelevant. I listed the colors I used in this instruction, feel free to deviate.

I used a grey battery motor with long lead that came with the Sawblade Thrill Ride, which is sadly discontinued. If you wish to use a different motor, you can use the green, blue or black battery motor. This requires the additional pieces shown in between brackets (). The modifications you need to make are shown in step 4.


  • 16mm Green: 56 (+1)
  • 32mm White: 44 (+4)
  • 54mm Mid Blue: 31 (+1)
  • 86mm Yellow: 9 (+1)
  • Rigid rod 190mm Black: 2


  • 2-way Light Grey: 4
  • 2-way Straight Orange: 2
  • 3-way Red: 15 (+1)
  • 4-way Green: 5 (+1)
  • 4-way 3D Purple: 28 (-3)
  • 5-way Yellow: 14
  • 5-way for Track Orange: 6
  • 7-way 3D Blue: 10 (+3)
  • 8-way White: 7 (+1)


  • Clip with Hole end Dark Grey: 17 (+1)
  • Clip Blue: 2
  • Snap cap Black: 1
  • Interlocking Clip Tan: 6 (+2)
  • Clip with rod end Black: 4
  • Gear Small Mid Blue: 2 (+1)
  • Gear Medium Red: 2 (+1)
  • Spacer Blue: 31 (+4)
  • Spacer Silver: 23
  • Knex Ball Red/Yellow/Grey: at least 1
  • Track (Tubing): 2 parts
  • Grey Battery Motor with long lead (Came with the Sawblade Thrill Ride): 1 (-1)
  • When using a different motor, one green, blue or black battery motor.

Total: 323 Pieces

Note: The old, thin, orange tubing does not work. This design is intended to be used by the classic balls, shown in the picture. To use the newer, 1-piece K'nex balls you need to modify the design. Although I did not try that, I am confident that it is possible.

One of the two rigid black rods (190mm) can be replaced by a normal grey rod, this is indicated in the guide. The blue clips can also be replaced by any clip you prefer.

Step 3: Base

Let's start construction! In this part you'll make the bottom part of the tower and install the motorized parts.


  1. This is the bottom part.
  2. These are the driving axles.
  3. Build the crank with the bending rod. This bending rod needs to be a rigid black rod!
  4. Connect the crank with the driving axles.
  5. Put the crank with driving rods on the bottom part of the base.
  6. This is the motor with the blue gears. If you use a different motor, please see step 3! You can replace this black rod with a standard grey 190mm rod.
  7. Attach the parts.
  8. These two parts form the top of the base.
  9. Assemble the base.
  10. Another view.

Step 4: Modification for a Different Motor

You can skip this part if you use the gray, leaded motor I used throughout this instructable.

This step shows how to modify the base in order to use a different motor. I advise the green or blue motor. You can opt to use the black motor, which is a lot slower, decreasing capacity but enabling you to increase the launch speed (See step 8).


  1. Some flat parts.
  2. Install the first part.
  3. Attach the second. This can be fiddly to do if you have already build the next steps.
  4. Attach the motor and the red gear.
  5. Attach the yellow driving rod through the motor with blue gear.
  6. Overview.

Step 5: Tower

In this step you will build the main part of the tower. This part includes some systems to guide the bending rod.


    1. These are two frame parts.
    2. Now build the front and backside.
    3. This is the part that forces the bending rod to bend.
    4. Snap the two parts together.
    5. Put the parts together.
    6. Tower completed.
    7. Put the tower on top of the base. Check the orientation of the tower!
    8. Another view.
    9. Make sure the black rod goes through the white 8-way connector and in between the two blue rods.

    Step 6: Launchpad

    Now it is time for the last big part, the launchpad! First you will build the blockers and afterwards the surrounding structure. Last but not least, the track will be build.


    1. These are some small parts needed for this step.
    2. Two more parts. The direction of the 3D-connectors is extremely important here!
    3. These are the blockers. You will need the loose pieces as well.
    4. Add the shown parts to the blockers.
    5. Add more parts to the blockers.
    6. Both blockers are done!
    7. Build these track parts.
    8. Assemble the track.
    9. Put one side-part on the tower. Check the orientation!
    10. Slide the track in. Again, check orientation!
    11. Put the second side-part in. This part can be very tedious to do.
    12. Launchpad completed.
    13. Another view.
    14. Attach the tubing (rails).

    Step 7: Entrance Track

    Almost done! In this final step the entrance track is made. Just one of the many possibilities is shown here. Adapt this track to whatever fits in your ball machine.


    1. Make these pieces.
    2. Put the track together.
    3. Attach the connection points to the structure.
    4. Attach the track to the structure.

    Step 8: Improve the Design!

    If you are happy with the design and do not intend on improving it, you can skip this wall of text.

    This design is a compromise between power, capacity and compactness. If you don't mind your launcher being way bigger and just shooting 1 ball a minute, you can certainly increase the power a lot. Similar statements can be made about compactness and capacity.

    Despite having tried many different combinations, there are so many ways to build this launcher that there is a fair chance one can improve power, capacity or compactness - without negatively affecting the others.

    This design pushes its critical components to their respective limits. Therefore you will need to change them in order to improve the design.

    If you improved the design, make sure to send me pictures and/or a video showing it! If you want, I'll add the improved designs here. To get you started, I added information on how this system works and its critical components below.

    • The bending rod should never permanently deform. If you want more power you should have a longer rod, meaning you will need to connect multiple rods together. Note that this only helps when you increase the launching area!
    • The connection to the rod on the crank can easily be improved: it just takes more space. The first picture in this step shows how to improve that.
    • The crank itself cannot handle a lot more force than it receives in my design. If you want more power you need to make the crank sturdier.
    • The motor is not strong enough to handle much more torque (power). Using gears you can improve the torque at the cost of capacity. Halving the rotation speed of the crank (and with that capacity) doubles the torque. It also helps to select a slower motor: visit this link for more information on motor rotation speeds.
    • The ball is launched when the force needed to bend and twist the blockers in a position where the ball fits trough is equal to the force the bending rod exerts on the ball. To increase the force in the launch rod, you should make the blockers stiffer. Flipping the 3D connectors in picture 2 and 3 already helps a lot.
      • If you do not mind having a less power launcher (in favor of capacity or compactness), try weakening the blockers by removing the top panel, shown in picture 4.

    Step 9: Finished!


    I hope you enjoyed building this launcher. Load the balls in and have fun watching the balls as they shoot away! If you have build this launcher, post a picture and I'll add it to this step.

    If you need the balls to go just that tad faster, check out step 8. There are many ways to change the design and improve the launching speed. If you encounter problems with this design, feel free to ask.

    Thanks for building!