FAKA Trebuchet

FAKA Trebuchet

jmarsh24 03 Nov 2008 02:51

I have created a FAKA trebuchet for my physics class for a golf ball lab. I was wondering if anyone could give me advice on how to solve problems of the arm derailings, the trebuchet going all the way to the end of the tracks, and any other advice in which people can provide. Any advice would be greatly appreciated.

http://www.youtube.com/watch?v=7UNmxO_l2ig

http://www.youtube.com/watch?v=9jyINsWxvqk

Re: FAKA Trebuchet

Craig Macomber 03 Nov 2008 03:32

Are you actually throwing a projectile? I don't see a sling. Without a load, there is no where for the energy to go but smashing stuff together. The one time my FAKA fired without a projectile with a counterweight (the golf ball fell out of the sling), it struck the front and derailed. Never fire any high efficiency treb without a projectile, or it will probably damage something, or at lest respond violently.

J-Buchet, and a few other trebs have made a great improvement to my design, and added a top rail to prevent derailing. Looks like your machine can survive them ok, and it only seems to derail after it should have released, so it should not be too much on an issue.

I'm surprised how fast the design is spreading, but I guess thats what the internet does! I seem to find a new one every day! I need to update the page with more info.

Re: FAKA Trebuchet

Anonymous (76.126.43.x) 03 Nov 2008 05:53

In this video I am not throwing a projectile yet, I just tested this today and am currently trying to create the sling. I have made a few improvements on your design, atleast I didn't see you use what I did. All of the pivot points have ball bearings in them and I tried to stabilize the rocking problem with a solid 12" wide piece of wood. I had a problem with figuring out how to align the railings parrallel, at the moment there is a 3/8 inch difference from one side to the other. If I adjust the back side it will do the same to the front.
I didn't really want to go too all out on this project, so I decided not to do a top bar to the design. My arm design has no problems with anything breaking. I made everything pretty tightly built.
Right now, I'm currently trying to figure out how to keep it from traveling across the whole railing, maybe that will change by adding the golf ball. Also, I'm trying to determine what exactly is the optimal sling length with my arm (40 inches from the pivot point). If you have any advice on how to optimize the trebuchet please feel free to let me know.
If you would like, I have various pictures of our build process and am going to be able to have videos of the trebuchet soon. So if you would like to add some of my material onto your site I would be happy to provide you with whatever stuff you would like. I will soon have my working inventor design, although I haven't figured out how to make a string, so that will be a learning process for me. Do you have an aim or anything of that sort? If you do, I would love to be able to instant message you instead of talking over a forum. Just email it to me if you would like.

Re: FAKA Trebuchet

jmarsh24 03 Nov 2008 06:09

^
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is me btw =P

Re: FAKA Trebuchet

Craig Macomber 03 Nov 2008 06:54

I sent you a message.

Having a projectile will drastically all of the mechanics. The whole point of the machine is to put energy into the projectile. Not having one is like flooring the gas in your car with the clutch in. No where for the energy to go, so stuff gets abused. On small machines this is not so much of an issue (durability is higher for small things for several reasons), but many larger machines have been broken by firing without a projectile, or simply by using one thats the wrong weight. Trust me one this, if your machine will be efficient at all, the projectile and sling will change the tuning completely. Like I said, my only throw without a projectile ended like yours, hitting the end of the frame and derailing, while I have only hit the end on 1 or 2 throws with projectiles, and that was directly caused by an early secondary trigger release. (Tuning can be confusing!)

As far as sling length goes, make it adjustable as you will want to fine tune it. My slings page has details, but I need to update it.

Re: FAKA Trebuchet

Anonymous (69.104.217.x) 14 Nov 2008 02:29

I'm pretty much in the same boat the OP is in. Do you really see a difference with a projectile? I am built a variant of your GBB, using only 2 pictures for reference.

Re: FAKA Trebuchet

Craig Macomber 14 Nov 2008 04:58

Suppose you make a machine (a diving board) to let you make a splash (put kinetic energy in the water). Is it really any different if you leave out the water (projectiles) for the test runs? I feel like it might effect the moving parts (arm, axle/ you falling body) a bit when the energy is disposed of in a rather quick unintended manner.