The Trebuchet Project #3: No More Baseball

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Blog entry by William posted 10-20-2010 04:47 AM 4317 reads 2 times favorited 8 comments Add to Favorites Watch
« Part 2: Bucket And Swing Arm Part 3 of The Trebuchet Project series no next part

I got the chute installed. This is what the sling with the tennis ball will ride on.

Then I rigged up the cord for the sling and trigger. Everything is made with 3/16” nylon cord. For the sling, a length of cord run from an eyelet under the swing arm to one side of the sling. Then another length of cord runs from the other side of the sling to a brad nail on the end of the swing arm. The timing of when exactly the sling releases the tennis ball is adjusted by changing the angle of the bend in the nail at the end of the arm. You have to fire it in a trial and error method to fine tune the swing for maximum distance.
The trigger mechanism is a length of cord that runs from an eyelet on the right side of the frame across a nail on top of the swing arm with a ring tied on the other end. That ring sits between two eyelets in the left side of the frame. Another length of cord with a 2” cotter pin on the end of it passes though one of those eyelets, through the ring on the first cord, and through the other eyelet. When the cord is pulled, it pulls the pin out, releasing the cord that is holding back the swing arm, launching the tennis ball.
You may notice the sling lying on the right side of the trebuchet in this photo. It is a 4” wide piece of leather with a grommet installed in each end of it.

Then I slapped on a coat of poly and tried to test it. The problem was, I haven’t actually bought the tennis balls yet. So I aimed it across the road of my shop, where there is nothing but a deep gulley, and put a rock in it. I stood towards the side and yanked the pin. Then I run like hell when the rock launched in my direction. The small rock didn’t stay in the sling too well. After some thought on the matter, I determined you need a projectile about the size of the chute, so the side can keep everything together so it can leave the end of the chute and release properly. If you don’t, you do stupid stuff like have rock launched in your direction (he he).
Then I went to the back yard to see what else I could find. Nope. No tennis ball. A baseball is about the same size though. After careful consideration, my conclusion was that with the baseball being heavier than the tennis ball, it wouldn’t go very far, just will let me know that it works. I was wrong.
I tucked the baseball into the sling. I attached the other end of the sling over the nail. I got back. I yanked the trigger cord. The baseball sailed over the deep gulley. It flew staight across the neighbor’s yard. The last time I seen it, it was going into the deep woods, the one’s that are overrun with cudzu vines, on the other side of the neighbor’s yard.
There will be no more posts on this blog series until I can get some tennis balls and take the trebuchet to a safer location to fine tune it for distance. I need to get somewhere that I won’t be losing all my kid’s toys.


8 comments so far

View HerbC's profile


1756 posts in 2860 days

#1 posted 10-20-2010 06:56 AM

You might want to ensure the new location is clear of breakable items down range…

Great project.

Be Careful!

-- Herb, Florida - Here's why I close most messages with "Be Careful!"

View RonPeters's profile


713 posts in 2881 days

#2 posted 10-20-2010 06:59 AM

And wear a helmet for gosh sakes!

A video would really help in understanding the dialog….

-- “Once more unto the breach, dear friends...” Henry V - Act III, Scene I

View rivergirl's profile


3201 posts in 2839 days

#3 posted 10-20-2010 03:07 PM

Is this some sort or medieval RPG launcher?

-- Homer : "Oh, and how is education supposed to make me feel smarter? Besides, every time I learn something new, it pushes some old stuff out of my brain."

View William's profile


9949 posts in 2843 days

#4 posted 10-20-2010 03:24 PM

It launches tennis balls rivergirl. This is the first one I’ve ever built, but the advertisement for the pattern says it’ll launch them a minumum of 200 feet. It is medieval though. The trebuchet was one of the tools they used centuries ago to knock down castle walls.
RonPeters, once I get everything dials in right, I do plan to try putting up a video.


View zzzzdoc's profile


550 posts in 3004 days

#5 posted 10-20-2010 07:06 PM

My son won a science fair with a trebuchet a number of years ago. They are a hoot to build and shoot.

What are you using for your weights? We used tungsten and lead. The heavier the better.

We found that the length of the string on the sling was very critical. Small changes made the projectiles go backwards instead of forwards.

We had impressive distances. Way out of site (although a potato cannon goes much farther).

Enjoy your foray into Siege Warfare!!!

There are calculators on the internet to determine sling length, arm length, weight, etc…

-- Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you're a mile away and you have their shoes.

View William's profile


9949 posts in 2843 days

#6 posted 10-20-2010 08:47 PM

This one in particular is for my kid’s Christmas. This is what Santa Claus is bringing them this year. It is designed to launched tennis balls a minimum of 200 ft. (advertised distance). With some fine tuning, I am sure we can get a little more.
I’m already contemplating building one for me and the older sons on a bit of a larger scale.


View Jason's profile


659 posts in 3509 days

#7 posted 10-21-2010 04:54 PM

Sounds like fun (minus the rock)! Good luck with the fine tuning.

-- Jason - Colorado Springs

View HalDougherty's profile


1820 posts in 3238 days

#8 posted 10-29-2010 11:42 AM

My son built a trebuchet for a project when he was in middle school. Since it was a school project he made a small one and used marshmallows for ammo when he displayed it for the class.

-- Hal, Tennessee

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