Siege World Championship Chunk 2012: Mista Ballista

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World Championship Chunk 2012: Mista Ballista
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Mista Ballista returned to Delaware for the 2012 Punkin Chunk. After our big success with bundle pre-tensioning last year allowing us to break the 1000ft mark, we opted to leave good things alone, and instead focus on torquing up the bundles to the max, and compounding the machine to see what it could do!

Our drive to Delaware was hindered by Superstorm Sandy, causing us to arrive late. We planned ahead, and Mr. B left it's field before the storm hit and the field got soft. On the way down, however, the ballista tow vehicle started to run out of gas in Jersey, and the lines were incredibly long. Later we learned many people were in line for 4 or more hours! Fortunately, we had a spare 14 gallon tank for use with our small engines, and we used that to keep going to southern Jersey where the lines were shorter, only a 1/2 hour!

In addition, the storm caused the Chunkin' field to flood, and the WCPCA decided it was not possible to get the field ready for competition on Friday, so Friday was cancelled. Here's a short news spot including Eric Ludlam for Mista Ballista telling some of the story: WMDT on Punkin Chunkin.

Setup Day

Bright and early on Friday we started removing travel bolts holding Mista Ballista in travel mode. In this picture, Dave uses his big drill to drive the front landing gear lifting the machine to maximum.

After lifting the machine, the gray jack stands are placed underneath, the feet are raised back up, and the large cribbing are placed under the landing gear, and the landing gear is bolted to the cribbing.

In this image, junior team member Trevor cranks on the big foot after the cribbing was installed. You can see the jack stands behind Eric's legs in this picture.

Last year during winding, the frames we torque the bundles from flexed dangerously, so this year we welded on some strengthening bars in diagonals across the front. This made everything safer, and we didn't have to invent ways to hold things down.

Next, we drag the bundles to the front of the machine using our winch. We drag it forward to marks we've painted on the machine, and then use a 3-ton come along to tip the bundles up into place. In this picture, you can see the faint orange triangle on the scapus underneath the bundles that mark the tipping point.

Mista Ballista 2012: Tipping bundles

Our Pumpkin Throwing ballista travels down the road with the rope bundles lying in the middle of the trailer. In this video taken by Jr team member Trevor sh...

After bolting the bundles into place, we installed the arms.

Due to pre-tensioning the the bundles, we can no longer just 'put' the arms into the bundles. We must first drive wedges between the two halves of the bundles. Once in place, the arms will slide between the two wedges, and we knock the wedges back out of the bundles.

Once the arms are in position, it is time to crank up torsion engine! We use a big hydraulic cylinder attached to a mega-sized bicycle chain. The chain wraps around a big gear that makes up the modiolus, and when the cylinder pulls, it adds torque to the bundle

Mista Ballista 2012: adding a 1/4 twist.

Adding a 1/4 twist to the bottom of the left bundle on Mista Ballista. Narrated for the new guy. We need to get to 1 full twist on all four corners.

Once everything was twisted up and ready, we put on the bowstring, and then tighten up the arm arrestors, which are the 1" rope that prevents the arms from pushing all the way forward. We use the bowstring to pull back on the arms. while the arms are partially cocked, we use cleats on the back of the machine to tighten up the arm arrestors so that they can slow the arms down gently.

And with that, we called it a day.

Saturday: Shot 1

We arrived bright and early on Saturday morning. On Friday night an email went out requesting that the youth and Torsion lines bring pumpkins to the captains meeting since we'd both be firing first. Turns out that was a typo. It was supposed to be youth and Trebuchets.

Well, that just meant the whole team was there getting the Ballista ready bright and early, and then we got to relax!

Loading the punkin'! Saturday's punkin color was blue, and we had to write our pit number all over it. When fitting a punkin into a ballista pouch, we have to pull back slightly to get everything under tension. We then need to find a punkin shaped just like our last shot of 2011, as we can't adjust the pouch anymore since sewing it all together. I always place the bowline over a ridge to help hold the pumpkin in, and then add a blue seatbelt.

Lock and load! The pumpkin is ready to be shot.

Here you can see our seacatch, our velcro/nylon pouch, the punkin' seat-belt, and bowline separators. The separators ended up being pretty dangerous. Check out the video below and you can see one getting launched backward into the crowd. Good thing there is a giant net back there.

Waiting for the pit-boss to give us permission to fire.

Kevin Johnson manages to snap a picture of the pumpkin leaving the machine.

Mista Ballista 2012: Punkin Chunk Shot 1

Mista Ballista's first shot at the World Championship Punkin Chunk in 2012. 991 ft.

Naturally the thing you do immediately after a successful shot where nothing broke is to start cranking it up even more! We twisted until the hydraulics could do no more. We tightened up the hydraulic pressure limiter until the pump engine stalled. Naturally we then reached into the motor and goosed it to get a few extra HP and PSI and put more into Mr. B than ever before. We wanted tomorrow to be a great day!

Sunday: Shot 2

Sunday dawned, and it was an awesome day, partly because daylight savings time gave us a whole extra hour of sleep before the captain's meeting.

To prevent hurling the bowline separator off into the crowd again, Kevin Cheney drilled a 3rd hole into it, and we put a 'keeper line' on it. The line was left loose so it would catch it as it tried to get hurled somewhere. We also applied the universal solution of duct-tape over the ties to see if that might help.

This picture is also interesting in that you can see how the arms are crushing our wooden inner arm stops. These stops had been working well for several years, but they are starting to give up structural integrity with the new more intense bundle winding techniques we're using.

The first Sunday shot color was orange. Naturally we had orange paint on a white punkin. After yesterdays shot, I noticed here that the bit of rope whipped around the pullback lines had melted. When I pulled it off, I discovered that the heat from the friction of firing was so great, the nylon also melted inside the twist. Fortunately the bowline is made of vectran which is very heat tolerant and was not affected. I had to replace the protective rope after only one shot.

Another great picture by Kevin of the pumpkin leaving Mista Ballista.

Mista Ballista 2012: Punkin Chunk Shot 2

World Championship Punkin Chunk 2012. Mista Ballista's second competition shot at 1213 ft.

Launching our pumpkin 1213 feet was pretty cool, but it did a number on our nice throwing pouch. Unlike previous years, we had two shots due today, which meant if we were going to do shot 3, AND try compounding the machine for the first time ever, we had a lot of work to do in a short period of time!

Sunday: Shot 3

Fortunately, Amy had brought her sewing machine! We set her up in the side of the minivan, ran power over from the generator, showed her the damage, and she said "Again?". Inspection showed the thread she had used last year wasn't up for the task, so we borrowed some Kevlar thread from team Ethos. Unfortunately, the needle broke and Amy had to start sewing by hand. Running needles through old seat belts and velcro is pretty tough, and at one point the dull end of the needle stabbed through Amy's finger while she was pushing on it. Ouch! She adopted a hammer, and started using that instead. Fortunately for everyone, she managed to finish the task and get the pouch ready! What a trooper!

While Amy was sewing, Eric was splicing! Eric had simulated Mr. B's geometry in MATLAB to determine how long the bowline extenders for compounding needed to be, but things got a little lost, and we needed an extra 2ft. We pulled some old bowline apart from 2006, and made some extenders for the extenders. On the deck of Mr. B the rope tangle was a challenge as splicing continued.

This diagram shows the basic idea behind compounding Mista Ballista. The pumpkin (the red star) is shown partway up the scapus. The arms (yellow) are about 9ft long from the bundle core. The overall arm sweep will be shorter because the bowline spools around the arm tips, and is extended to, and anchored at the winch at the back. As the arms are pulled back, the rope spools over the arm tips into the middle part of the bowstring, allowing the pumpkin to travel farther down the scapus per degree of arm rotation. If the arms rotate as quickly compounded as normal, that means the pumpkin will be moving even faster!

Kevin Cheney and Eric desperately try to put the just completed bowline onto the machine. The measuring crew was just finishing up the previous machine and was walking over, and our bowline had never been fitted to the machine before! Fortunately, my pinky measures did the trick and everything fit up nicely!

After starting to pull back, Karl noticed that the extender wasn't connected to the anchor bar correctly. It's really hard to see in these pictures, but Karl is trying to get the spliced bowline extender to sit properly on the pulley block mounted on the anchor bar.

Mista Ballista, the first large compounded ballista stands ready for our third competition shot on Sunday.

Mista Ballista 2012 3rd Shot

High speed (210fps) of the third and final shot for Mista Ballista at the 2012 World Championship Punkin Chunk. This shot employed the compounding lines for ...


After 2 days of intense work, here's the end result. Traditional bowstring provided the greatest distance (1213 ft) with our current Scapus length. Once compounded, using the short amount of pullback distance we hindered performance resulting in the shortest shot (813 ft).

Additional Pages for Punkin Chunk 2012
World Championship Chunk 2012 Team Tormentum brought Mista Ballista, our torsion machine to the chunk in 2012.
World Championship Chunk 2012: Mista Ballista Mista Ballista returned to Delaware for the 2012 Punkin Chunk. After our big success with bundle pre-tensioning last year allowing us to break the 1000ft mark, we opted to leave good things alone, and instead focus on torquing up the bundles to the max, and compounding the machine to see what it could do!
World Championship Chunk 2012: Torsion Class The torsion class had a great year with every machine throwing over 1000ft, Chucky III broke 3000 ft again, and spectacular failures on almost every machine on the field.

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