Siege Engine.com: Cardan Trebuchet (Cardan Gear Linear Motion Trebuchet)

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Cardan Trebuchet (Cardan Gear Linear Motion Trebuchet)
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The Cardan Gear Linear Motion Trebuchet is an adaptation of the motion found in a Cardan Gear adapted to a straight track-drop trebuchet. The straight track drop is an idea used in a FAT (Floating Arm Trebuchet), or in our Baby ASOK (Arm Slides Over Cam). The Cardan gear was invented to accept linear motion from a steam piston to create circular motion. For this trebuchet the geometry (without the gears) was used to fling.

You can read more about Cardano at the Flying Pig which also has an animated graphic of the gear. If you watch the graphic, you will see the point of linear motion traveling slowly near the edge, and quickly through the center. This is ideal for a weight drop, because a majority of the fall has little resistance against the projectile, and the last drop takes the brunt of the work. This after the weight has gained the most momentum.

The experimental structure to this trebuchet is 2 feet tall. 6 metal disks form a little more than 2lbs of counterweight. The articulation is slightly above center of the total drop. The trigger seen in the lower right is more of a safety mechanism, and is useless for launching. To launch, you need to hold onto the projectile/sling while removing the trigger/safety. Once everything is out of the way, let go. Something tells me this wouldn't scale well.


Here the weight is partially propped up to show the articulation. The distance between the track, the articulation pivot on the arm, and the articulation pivot to the frame match up so the weight can slide down the tracks without jamming. Ideally, the frame to arm/articulation pivot distance, and weight to arm/articulation pivot would be the same. Unfortunately, that wasn't feasible while also using external counterweight.


When the weight reaches the bottom, the arm is fully upright, and eventually hits the top-plate of the weight track. In this image the articulation is completely hidden.


On Baby ASOK, I had built wooden weight boxes. On this machine, I didn't have quite so much room, so had cut these metal disks to act as counterweight so that the weight would fit at the bottom of the drop with the arm fully swung.


Here again, you can see the trigger/safety mechanism. This holds things up while the pay load is set up. This is a Koosh ball with a few rubber band extensions on it. This machine so far has proven unreliable. When it works, the koosh flys 25 feet in a straight line. When it doesn't, the projectile goes backward.

Sometimes the articulation on this machine binds at the mid-point slowing things down just a tiny bit, but enough for the projectile to fly off backward. When the projectile is not lost at the mid-point, however, the final quarter drop of the weight gives the arm a big boost which really flings the projectile.

It may need a longer sling. It requires more experimentation.


Video Clip

I made this video in early October 2003. Getting a video of the thing working properly was quite the challenge. When it worked, however, it was in fine form, flinging the koosh on a low trajectory just under 30ft. This is just a few feet shy of Baby Asok.

I made this video extra large so you can see what is happening. The first firing in this video fails to work. The second one succeeds going 29ft. If you are able to step through the launch frame by frame, you can see the koosh-line wobbling half way through the throw. This is also the first time I've seen this, so perhaps some more analysis will let me tune the machine. If I can get the trajectory up, this machine has some potential.


Google Video Service
Siege-engine.com: Carden Trebuchet Model


Information:
Attempted two launches with a Carden gear Trebuchet model. The first one fails, the second one works. More about this machine at: http://www.siege-engine.com/CardanTreb.shtml
10 sec - Jan 19, 2007


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