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Hello and welcome to this video.
Today I will be showing you how to make a pencil trebuchet.
If done well, table top trebuchets will throw very similarly to their larger cousins.
Constructing one will allow you to troubleshoot parameters and practice tuning before committing resources to a larger trebuchet.
This particular trebuchet is well tuned
and leaves little energy in the arm or counterweight,
which are very still after the throw.
This is easier to see in slow motion.
You can see the counterweight falling almost straight down
and the projectile being thrown.
We will be constructing our A frames using diagonal lashings.
Start by tying the string to a pencil.
I am using a clove hitch, but many other knots will work.
We then cross the two pencils and wrap them together diagonally.
Cross over and wrap diagonally on the other side.
Next, wrap the string around your lashings to tighten them. These are called frapping turns.
Finally, tie the end off on the pencil.
We repeat this process three times for our A frame.
Wrap, frap, and then tie off the string again..
This is more of an exercise in rope construction than anything else.
Please feel free to use epoxy or hot glue instead.
Once finished, our A frame is strong and rigid.
We will need two A frames.
We will use square lashings to connect the A frames.
Start as you would with diagonal lashings, but wrap the two pencils together in a square pattern.
This makes it easier for them to stay at right angles.
Frap and tie off as you would with diagonal lashings.
I've attached a pencil to one A frame.
I'll do the other off camera.
It's attached.
Now let's add diagonal supports to keep the A frames steady.
I do this using diagonal lashings.
It looks much better, but
the A frames can still rotate around the vertical axis.
I fix this by adding another crossbar and a diagonal support in the horizontal plane.
By now you should be familiar with the techniques I am using.
Now we have a rigid structure.
This is what it looks like after all we have done.
In this video, I am using a rope axel.
I first tie some string to the arm, leaving two ends.
I then tie both ends to my trebuchet frame.
This has surprisingly low friction and is very easy to do.
To figure out how far you need to hang the counterweight,
hold the string where the CW would be at the start and pull straight down.
Once you can't pull straight down anymore,
you are at the counterweight-arm stall point.
Past this point, the counterweight actually pulls against the arm.
Make sure the arm is vertical enough there for you to get a good sling release nearby.
If you want to know more about trebuchet optimization,
just watch my trebuchet physics video.
If this gets enough views, maybe I'll make an office supply mangonel.
Thank you for watching!