I want something small that will throw a golfball or tennis ball an impressive distance. So I was thinking maybe a "King Arthur" style trebuchet (with a fixed axle, not floating.)
Has anyone here built something like that? Maybe I'm at the wrong group, but I don't think so.
How important is it to be able to adjust the amount of counterweight? I was planning to use a sledgehammer for the hanger arm and counterweight. Or maybe a beer can sized block of lead -- about 8 to 10 pounds.
I assume the throwing arm needs to be as light as possible, especially towards the end.
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I want something small that will throw a golfball or tennis ball an impressive distance. So I was thinking maybe a "King Arthur" style trebuchet (with a fixed axle, not floating.)
Has anyone here built something like that? Maybe I'm at the wrong group, but I don't think so.
How important is it to be able to adjust the amount of counterweight? I was planning to use a sledgehammer for the hanger arm and counterweight. Or maybe a beer can sized block of lead -- about 8 to 10 pounds.
I assume the throwing arm needs to be as light as possible, especially towards the end.
Did that about 10-12 years ago with my son, for a science fair project. :-)
Very. For any given trebuchet, there's an optimal ratio between projectile mass and counterweight mass, which results in the maximum throw distance. If the counterweight is too light, the arm rotates too slowly, and imparts too little velocity to the projectile. If the counterweight is too heavy, the arm rotates too quickly, and launches the projectile at too shallow an angle to achieve maximum distance -- and, as we discovered in our experiments, if the counterweight is grossly too heavy, the arm rotates very fast, and launches the projectile after it has already swung past vertical (i.e. launches on a downward trajectory). This leads to a very short throw.
So at least until you discover the optimum ratio for your design, it's critical to be able to adjust the counterweight mass. You also need to be able to adjust the counterweight mass if you will be launching projectiles of significantly different mass.
IIRC, we found the optimal ratios to be approximately 4:1 for length of throwing arm to length of counterweight arm, and about 25:1 for counterweight mass to projectile mass. Don't take that as gospel, but it's probably a good starting point for experimenting.
We used free-weights from a set of dumbbells. The set had two each 2-1/2 pound and 5-pound discs, having a convenient 3/4" diameter hole in the middle. We attached a 3/4" dowel to the counterweight end of the arm, and cross-drilled each end for cotter pins to hold the weights on.
Correct.
We didn't use a sling. The original medieval trebuchets used buckets or baskets to hold the payload; the sling was a later enhancement. Ours emulated the original design, with the role of the bucket played by a kitchen measuring cup duct-taped to the throwing arm.
I built a small one for throwing golf balls. I used a curved hook at the end of the arm and found that adjusting the angle of the hook would adjust the release angle of the sling.
My Boy Scouts and I build a pumpkin chucker every year around halloween and go to Delaware to the contest down there.
Lots of fun...
Never won but there is a lot of satisfaction in tossing a 10 inch pumpkin a
50 to 75 yards.
We started years ago with a traditional catapult but could not get the distance we wanted.
Got a science and physics teacher involved (my son) and have made considerable progress the last year or so with the trebuchet style by playing with the arm and sling length.
This year we tilted the mechanism off the vertical and gave it kind of a sidearm swing. Longer travel, more velocity more distance. Accuarcy suffered a bit but that is a problem for next year.
Do a google search on pumpkin chuckin or chuckers and see what you find.
There are also some neat things you can do with PVC pipe and hairspray in the form of potato cannons. You can also google them.
You could do some damage with a golf ball.
What kind of distance are you looking for?
I was asked this year whay is the secret to being a successful Scout leader and keeping the boys involved.
My answer was projectile weapons and thinking like a 4th grader.....
I've built several, from "peanut throwers" to one that has a 16 pound weight (bowling ball) and throws a 1 pound fishing weight..
This is where I got started:
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first one was a clone of their "cheese chucker"
Don't know about the sledge hammer arm, might want to read a bit first..
I found that the swinging basket for the counter weight not only makes weight adjustment easy, but provides a really good relief for the force generated on the frame.. Early trebs had either a swinging basket or wheels of some type.. Otherwise, they had to re-aim every shot due to movement of the entire treb on the forward stroke..
2 basics... The pivot on the arm should be at a 4-to-1 ratio, or 20% from the front end.. At rest, the throwing arm should be at a 45% angle to the "floor" of the treb..
I would have been much happier with my first couple of trebs if I'd paid attention to those 2 numbers! HAVE FUN!
Thanks for the flashback, Doug.. For most trebs, the counter weight should be roughly 16 times the projectile weight..
The sling is a real trial and error thing.. I used cloth slings and nylon shock cord, one end of the cord is attached to the throwing und of the arm, the other end has a loop to go over the hook at the same end.. I think I started with the entire sling (pouch folded in half and string ends equal) about 3/4 of the arm length and adjusted from there.. It's right when the loop comes off the hook on the forward stroke without tangling, and the projectile actually comes out of the sling..lol When everything is tuned correctly, the projectile should be thrown at about a
I saw a documentary a few years back on a competition between two teams building (full size) trebuchets. The more successful design used a swinging box for a counterweight which allowed them to add or subtract sand to vary the weight as needed. They also found that being able to bend the hook on the end of the throwing arm to adjust the release point of the sling was important.
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