This page (and the treb) still...
This page (and the treb) still...
This trebuchet was inspired by an e-mail from a chap who had found this site, and built a 13 inch tall FAT that could throw a hollow computer mouse ball 57 feet. I was impressed by this, and since the Christmas holiday was almost upon me I decided that a challenge attempt would make a nice little project.
The treb isn't finished yet. The frame is complete apart from mounting a trigger mechanism, and the arm is nearly complete. I'm in the process of getting some custom wheels made for the treb, until then I won't be making much progress 8¬(.
Here are some stats. Note that all heights are from the top of the base:-
|
height to top of arm when at rest |
326 mm |
|
height to top of counter weight guides |
320 mm |
|
height to wheel tracks |
112 mm |
|
drop of counter weight |
241 mm |
|
counter weight |
not yet known, but I'm expecting around 16 ounces |
|
projectile |
hollow computer mouse balls |
|
ratio of counter weight to projectile weight |
not yet known |
|
upper arm/lower arm length |
200 mm/70mm |
|
wheel track length |
83 mm |
|
wheels |
30mm diameter, 12mm wide |
|
base dimensions |
200mm long, 100mm to outside of counter weight guides |
|
sling length |
not yet known, but I'm expecting around 170mm (around 85% upper arm length) |
And here are the results of the best throw that I will have measured:-
|
counter weight |
projectile weight |
theoretical max throw |
actual throw |
efficiency |
notes |
The efficiency is calculated as the ratio of actual throw distance to the theoretical maximum, expressed as a percentage. The theoretical maximum can be approximated as 2 * counter weight * drop of counter weight divided by projectile weight. I've made an assumption/guess/whatever that a hollow mouse ball is going to weigh around 5 grams. A counter weight of 500 grams would therefore give a theoretical throw of 48.2 metres, or over 158 feet (2 * 500gms * 241mm / 5gms). The biggest treb I've got is around 35% efficient, the smallest is around 40%. Assuming that this treb will be 35% efficient then I should get a throw of around 55 feet. It's going to be a close thing.
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A view of the nearly complete frame. All that's missing is the trigger mechanism, which will include finishing the tops of the counter weight guides. The 2 throwing arm guides on the front of the frame are in the wrong position here. They have been repositioned on the current frame since they were found to foul against the arm. |
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A close up of the front of the treb, showing the counter weight guides, the guide spacing blocks and the brace between the front legs. |
If you're interested in seeing more about trebuchets, return to the index for some links.
This page last updated on April 13th, 2004
Created by hand using 1st Page 2000
