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Poor CW Energy Transpher

Craig Macomber 1218071186|%e %b %Y, %H:%M %Z|agohover
in discussion Blogs / Craig's Hurling Blog » Poor CW Energy Transpher

I spent some time today dry firing and taking video. I have to say that with a 5 pound weight (about 8.75 total CW) falling 7 feet, I only got a small portion of the energy into my light weight 2 foot arm. If built correctly with inelastic parts, 100% could be possible, so clearly there is room for improvement.

I have some ideas to help; I'm pretty sure I can get at least half of the energy by modifying some parts, though I will likely have to remake the complex trigger mechanism.

For now, I'm going to fix the few issues (slipping knots and such) then go throw some stuff. In the bright side, this machine could dry fire safely loaded with 50 pounds. A miss fire where the sling actually deploys could be an issue though.

Dry Fires

Craig Macomber 1217994225|%e %b %Y, %H:%M %Z|agohover
in discussion Blogs / Craig's Hurling Blog » Dry Fires

I just did a few no CW dry fires on my treb. Seems to work right, though a few things need adjustments, and needs something to prevent it from falling over forward. I think I just make sure it is not on an uphill slope, and stake the back down or something like that.

As I have progressed with this implementation of the design, I have realized several flaws in my machine that should be changed for future ones. Changes can be made to tolerate elastic parts better at the cost of arm drag for example that would be good for a flimsy machine like mine, and least until I get some less stretchy string. Also, before the CW detaches, the transfer of energy may not be as complete as I want because of the same stretchy string and some minor building errors/choices. Again, the next one will be better in this respect.

I'm quite worried about the sling. With the axle around 3.5 feet off the ground, and a 4 foot sling, things could get ugly. 7 feet of string slapping the ground/treb! Also, the tuning literally chooses the release angle, though the first throw will basically be at a random angle, and the next one should fix it, but a random angle on such a machine is bad as it might just slam the sling and projectile into the ground!

Axle assembly and frame progress

Craig Macomber 1217724045|%e %b %Y, %H:%M %Z|agohover
in discussion Blogs / Craig's Hurling Blog » Axle assembly and frame progress

I just have two uprights to cut and install, and the counterweight arm to cut and install. If all goes well, I might have it finished tomorrow.

The CW came out more compact than I thought, so it should hole a few extra 5 pound disks if desired, but I will have to modify it to work with my planned initial test weight (5 or less pounds) because the CW arm would not properly clear the arm assembly if I simply make it skinner when I remove weights as planned. Also, the primary trigger needs to be designed, but it should be trivial.

Sling and pin finished.

Craig Macomber 1217473689|%e %b %Y, %H:%M %Z|agohover
in discussion Blogs / Craig's Hurling Blog » Sling and pin finished.

I just finished the sling and adjustable firing pin. Adjusts across about 90 degrees of angle. The sling came out to 4 feet long. I have to wonder about the effects of having a 4 foot sling on a 2 foot LA.

I also gathered the remaining parts of the frame, though I still need to locate some hardware and such. I'm really looking forward to getting this thing tested, though I will have to start with just a few pounds of CW so wont out throw my local park. Looks like the treb might actually work!

Triggers work!

Craig Macomber 1215205496|%e %b %Y, %H:%M %Z|agohover
in discussion Blogs / Craig's Hurling Blog » Triggers work!

My new treb may have a complex hacked together unstable trigger system, but it works. I clamped the axle to the work bench and spin the arm around. Even the sling holder and new sling configuration seems to work great. Now I just need full length sling sling lines, a firing pin, and the upper part of the frame.

Now, I think it will work. I always can confidence in the concept, but my implementation of it has left me wondering it it would actually work. Maybe as soon as next week I will be able to get some real throws off.

Springs and things

Craig Macomber 1215056050|%e %b %Y, %H:%M %Z|agohover
in discussion Blogs / Craig's Hurling Blog » Springs and things

I just added the tab that lets the tertiary trigger get released after the secondary has released. I also spring loaded the secondary and tertiary triggers. Now I just need the sling box, and hook that up to the tertiary trigger and the trigger system on the arm will be complete. Well, the firing pin for the sling could be considered the quaternary trigger, and it is not done, but I'm not worrying about it now.

Re: Trebuchet Plans?

Craig Macomber 1214683807|%e %b %Y, %H:%M %Z|agohover
in discussion Site Discussions / Questions? » Trebuchet Plans?

Very interesting. KENT would not have been a variable-leverage-remote-drop-vlr (another kind I invented) would it? A wheel-trebuchet is more likely.

Thanks.

Re: Trebuchet Plans?

Shinigami_San 1214683179|%e %b %Y, %H:%M %Z|agohover
in discussion Site Discussions / Questions? » Trebuchet Plans?

We finally competed, the trebuchet performed well during our test runs. But of course, everything goes wrong at the day of. We made the throwing arm out of a fiberglass hockey stick, and it ended up fraying, so efficiency went down a lot. It was a fun experience. More people know about this site now. The winning team had a very efficent design. seeing as how they didn't design it and it was a raytheon engineer. they call it the KENT trebuchet (Kinetic Energy Neo-Trebuchet) Kinda lame if you ask me. It was a totally different trebuchet, seeing as how the counterweight was attached via string. We believe that it broke all the rules, but the Judges didn't do anything about it. Maybe you'll take a look at the design if they post it somewhere, I have no pictures of it. Who knows? maybe you can build and perfect it for another pumpkin smasher.

Treb Construction Progress

Craig Macomber 1214001613|%e %b %Y, %H:%M %Z|agohover
in discussion Blogs / Craig's Hurling Blog » Treb Construction Progress

Yesterday I built most of the arm, and designed the sling holder. Today I started building the secondary and tertiary trigger assembly (they are timed separately). When discussing the design with my dad yesterday, I think we came up with a better way to hold the sling, and also a possible design modification. This thing is complex enough that I'm having trouble visualizing it working. Mathematically it may be the simplest treb, but mechanically it is quite the opposite. On a related note, I think I finally understand how to model arms and slings mathematically.

Re: Trebuchet Plans?

Shinigami_San 1212721716|%e %b %Y, %H:%M %Z|agohover
in discussion Site Discussions / Questions? » Trebuchet Plans?

Ok thanks, you really are a guru when it comes to this kinda stuff. We finished the frame and all we needed was an arm ratio to make an arm. Thanks for clearing that up for us.

Re: Trebuchet Plans?

Craig Macomber 1212720873|%e %b %Y, %H:%M %Z|agohover
in discussion Site Discussions / Questions? » Trebuchet Plans?

Cool! Today we started building the trebuchet, but the model is definately scaled down. I have a question about the formula for mass ratio and beam ratio concerning Phssthpok's Rule ( MR = 20*BR)

Can we use that equation to determine the arm ratio for the FAKA? (1.5k/4g = 20 * BR) or is the FAKA's arm ratio fixed?

I assume you mean 1.5 kg/40g. Anyway, you are looking at a mass ratio a tiny bit higher than K'nex FAKA, and much lower than GBB's max. GBB's 1:4 arm ratio seems to work through a very wide range, 50:1 to 150:1. I would recommend something between 3:1 and 4:1. Maybe 3.7 or so, but really with an FAKA, it does not need to be too precise. I'm guessing that anywhere from about 2:1 to 5:1 would actually work well.

Re: Trebuchet Plans?

Shinigami_San 1212717506|%e %b %Y, %H:%M %Z|agohover
in discussion Site Discussions / Questions? » Trebuchet Plans?

Cool! Today we started building the trebuchet, but the model is definately scaled down. I have a question about the formula for mass ratio and beam ratio concerning Phssthpok's Rule ( MR = 20*BR)

Can we use that equation to determine the arm ratio for the FAKA? (1.5kg/40g = 20 * BR) or is the FAKA's arm ratio fixed?

Re: Trebuchet Plans?

Craig Macomber 1212702360|%e %b %Y, %H:%M %Z|agohover
in discussion Site Discussions / Questions? » Trebuchet Plans?

I haven't made a page for it yet, but K'nex FAKA is small and threw 72 feet. You can see video of it on the FAKA page. One of the best things about the FAKA is that it works well from low mass ratios (30:1 on K'nex FAKA) to high mass ratios (150:1 on GBB). For the triggers, you can do something like I did on mini-ka. Also, for tuning, I strongly recommend an adjustable length slings.

Based on the rules, I think you will have to consider the whole hanger as the CW, so take that into account. A FET is the same as an FAT without the vertical CW guides. To keep the axle from derailing, you need some rollers like on an FAKA.

Because you seem to have some experience with F-series trebs, you can probably just go straight for the FAKA.

Good luck! I'm glad my site has been of some use.

Re: Trebuchet Plans?

Shinigami_San 1212683890|%e %b %Y, %H:%M %Z|agohover
in discussion Site Discussions / Questions? » Trebuchet Plans?

I GET IT NOW! The arm design for the FAKA does have two triggers, I thought that they were both on the arm where the Primary was. This trebuchet; however is going to be on a smaller scale. Do you think that it can perform well under the size restrictions?

Re: Trebuchet Plans?

Shinigami_San 1212683306|%e %b %Y, %H:%M %Z|agohover
in discussion Site Discussions / Questions? » Trebuchet Plans?

Oops, didn't log in I was so excited. That previous post was by me, in case anyone else was wondering. Of course the Admin would know, but for future reference. Thanks again! This site is awesome.

Re: Trebuchet Plans?

Anonymous (67.41.224.134) 1212683126|%e %b %Y, %H:%M %Z|agohover
in discussion Site Discussions / Questions? » Trebuchet Plans?

Thank you for responding.

Based on the state Director's Interpretation, the arm cannot roll off of a wheel not attached to it, such as the F2k Series. This rule was added because we used an F2K design, which was totally unexpected. (Most people there had the traditional trebuchet design, therefore we were scoring way higher than they could of.) They then disqualified us on the spot and we went home sad. Determined to build a trebuchet with great efficiency, we build a FAT and took State. We now qualify for nationals, and have been searching around for a better trebuchet design.

I like your idea of an FET, but I haven't found any pictures or information on how to build it. I'm assuming that it has the basic frame that of a FAKA, and the arm contains no special moving parts but the horizontal moving wheels at the pivot. Please Correct me if I'm wrong.

Thanks again for helping us, we enjoy your site and we find it very useful. We'll be sure to advertise it at the competition and help it grow.

Re: Trebuchet Plans?

Craig Macomber 1212636874|%e %b %Y, %H:%M %Z|agohover
in discussion Site Discussions / Questions? » Trebuchet Plans?

Looking through the rules, an FAKA does seem to be legal though the meaning of this is unclear to me:

14. The rotating arm must include its own pivot point. External pivot points are prohibited. There mustonly be one pivot point.

Anyway, if you haven't built trebuchets before, I strongly advise you don't build an FAKA. They are one of the most complex designs, and require video analysis and extensive tuning experience to get to work to their potential. That said, if you have lots of time, an FAKA might be an ok choice. Based on the rules, a floating-arm-trebuchet-fat a great choice. I would actually go for the floating-everything-trebuchet-fet. If that goes well, you can convert it into an FAKA (well, just make an FAKA arm for it so you can use which ever works better). An FET is basically an FAKA without most of the hard parts (complex tuning, and multiple triggers), and still gives great performance. I would put a lot of emphasis on keeping the arm very light, and even more emphasis on tuning it well.

I think you should find sufficient trigger details on king-arthur-ka. Make sure to look at the large version of the images. Once you understand what the triggers need to do, the designing is up to you, but my pictures provide some examples.

Trebuchet Plans?

Shinigami_San 1212631925|%e %b %Y, %H:%M %Z|agohover
in discussion Site Discussions / Questions? » Trebuchet Plans?

Hi, my friends and I are in a competition regarding trebuchets. The rules can be googled: MESA 2007-2008 Trebuchet Rules (California). We found this site to be very helpful in trebuchet designs; however, we are looking at designing a FAKA, this seems to be the most efficient. In order to build this, we need to know how the arm operates. (How we build it to have a primary and secondary trigger.) If we can get some help, that would be GREAT!

We are also looking at other suggestions at trebuchets. (F2K Series disqualified)

Thanks!

Re: Next Treb

Craig Macomber 1211502943|%e %b %Y, %H:%M %Z|agohover
in discussion Blogs / Craig's Hurling Blog » Next Treb

Here is a rendering of part of my design (Click for very large size). It came out a bit more complicated than the original plan, but it should make the timing easier. Feel free to speculate about that how it will work. Now, this is not the final revision, but it should be close. Also, I made a few of the parts pictured, and will continue with construction soon. I really hope it works.

Re: Next Treb

Craig Macomber 1205640015|%e %b %Y, %H:%M %Z|agohover
in discussion Blogs / Craig's Hurling Blog » Next Treb

Pictures here.