Siege Mista Ballista : 2006 Rope Bundle Reconfiguration

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Mista Ballista : 2006 Rope Bundle Reconfiguration
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In 2005 we broke our fancy fiberglass arms. In 2006 we got the new carbon fiber arms and video taped them in action in the summer at our DVD from the History Channel.')">2006 History Chunk. This led us to discover how much they bounced around the outer stanchions. We were getting multiple recoils after every shot, sometimes back at least 30 degrees. That was also just with 2000 lbs of pullback, which is much less than we expect to use in competition.

This was accounted for in Greek Ballistae by the notch cut out of the outer stanchion. The arm is therefore able to swing forward farther before hitting the outer stanchion, allowing the heel and rope to slow the momentum of the arms. (A feature we failed to account for when we first built our machine.) We decided it was high time to just move our outer stanchions out of the way, as we are not able to put a notch in the steel as occurred in wooden ballista.

First we needed to extract the rope. We did this by banging out the epizygis on whichever side was easiest. Next, we slotted cardboard through the scutula hole so as not to get grease over the rope, and pulled it out.

Then we rewound the rope back onto the spools. Dave's forklift proved quite handy as a spool hanger.

Then we tried to get the rope bundle frame off the trailer. Oops. Kevin grabbed a picture with his camera phone. We continued with two forklifts until the bundles were safely on the ground.

Cutting torches were used to cut out the outer stanchions on one side, and the bolts were taken out of the cast iron side. Dave grabbed a picture of the seemingly naked rope bundle frame.

Dave uses his new magnetic base drill to bore nice square holes into the scutulas so we can tap them for the bolts needed on the cast-iron side of our rope bundles.

Next came the hole tapping. This puts the threads directly into the cast iron so we can bolt the interface plate onto the scutula. (You can't easily weld steel to cast iron.) 14 holes in all.

Next, we bolt in the stanchion. Then flip the bundles, and weld the other side into place.

This picture is nice in that you can see where the original bolt-down location was, and that we are moving the stanchions about 6" forward and slightly outward.

Gratuitous picture of Dave welding the stanchions back in.

The last time we tried lifting the rope bundles onto the ballista we had wound them on the ground, then lifted them with the forklift. Various bad things happened (which is why it's not a pictoral on the website). This lead us to put the rope bundle frame back onto the trailer empty. It worked quite smoothly, though there were a few tense moments. The challenge is that the forklift can't pull all the way up to the scapus since the trailer tongue is in the way.

Grease up the interface between the modiolus and scutula.

Pack in the first row of rope. We get 10 loops of this 1" rope across our first row.

We had trimmed off our extra rope which didn't fit into the rope bundle in the summer. This time, however, we put even less rope into our bundle than last year with a strategy of getting a different power/recovery curve from our bundles. We didn't want to loose the opportunity of using more rope in future years, so we neatly tucked all the extra rope into the newly moved outer stanchion, and tied it all in with a sailing knot.

Also, you can see we've got Mr. B back out in a field for a little more testing. Huzzah!

See the 2006 Punkin Chunk for more on when we competed with them.


Here is the slow-motion video that convinced us to put the project of moving the stanchion to the top of our priority list. This was captured during the DVD from the History Channel.')">2006 History Channel Chunk.

Google Video Service
Mista Ballista slow motion

Slow motion of Mista Ballista firing. Shows the extent of the arm recoil.
18 sec - Jul 8, 2006

Additional Pages for Mista Ballista
Mista Ballista Mista Ballista is _Team Tormentum's_ *Torsion Division* competition catapult.
Mista Ballista : Modiolus and Epizygis In 2008, Dave devised a new system for managing the torsion in Mista Ballista with his friends Karl Hamm and Kevin Cheney. This represents a large investment in our machine in these custom parts.
Mista Ballista : Bowstring The bowstring has been one of the most challenging pieces of our torsion engine. It is the last piece to get right, and has been the most likely part to fail in any given year.
Mista Ballista : Rope Bundles The rope bundles are the main engine of the machine. The framework that holds everything together is about 24 ft long, and 6 feet tall.
Mista Ballista : 2005 Rope bundle Upgrade At the 2004 chunk the main stanchions for the torsion frames were bent by the impact of the arms. You can see the animation of when this happened on the Mista Ballista Arms page.
Mista Ballista : 2006 Rope Bundle Reconfiguration In 2005 we broke our fancy fiberglass arms. In 2006 we got the new carbon fiber arms and video taped them in action in the summer at our 2006 History Chunk. This led us to discover how much they bounced around the outer stanchions. We were getting multiple recoils after every shot, sometimes back at least 30 degrees. That was also just with 2000 lbs of pullback, which is much less than we expect to use in competition.
Mista Ballista : Frame The framework for the Ballista had to be built strong enough to resist the pullback, and to hold up the 2500 pounds we currently estimate of our engine. It must also push it up 16 feet in the air!
Mista Ballista : Trailer One of our goals for the 2003 season is to acquire a dedicated trailer for Mista Ballista.
Mista Ballista : Torsion Mista Ballista's engine operates on torsion from twisted rope bundles. One of the biggest challenges of torsion for this machine has been adding the twist. An onager is pretty straight forward in that a large lever and gravity can be used. With our ballista, the direction of twist is sideways, so an alternate means of twisting is needed.
Mista Ballista : Arms After the failure of our arms in 2007, a new tactic was needed. Dave contacted his friends Karl Hamm and Kevin Cheney about designing and building a set of ballista arms out of aluminum. Aluminum was chosen for its strength and light weight.
Mista Ballista : Deployment To travel to different chunkin' locations, we need to pack the system down onto our trailer. Deploying from the folded up position is challenging and time consuming, taking a day and a half at the 2002 chunk. This year at the 2003 Punkin Chunk, we were done in about 4 hours.
Mista Ballista : Hydraulic and Electric Power Mista Ballista uses hydraulics for lifting the engine to a 45 degree angle for firing, and also for winding the cord bundles. We also like having electricity on hand since Mr. B has a tendency to break, and need on-field repairs. This page describes what we are using to power up the system.
Mista Ballista : Mystery Parts All winter during 2003 we have been collecting the parts we need to accomplish our 2003 chunk goals. Here are a bunch of pictures of these random parts. Can you guess what they are for?
Mista Ballista : Modiolus and Epizygis 2007 This page describes the Modiolus and Epizygis system we used from 2002 through 2007. In 2008 we developed a new system for twisting up Mista Ballista.
Mista Ballista : Torsion 2007 All torsion catapults depend on twisting the rope bundles to create the engine to drive the catapult. Mista Ballista went through many phases as we attempted to add more power every year to our throw. This page describes the obsolete systems we'd used in the past.
Mista Ballista : Arms 2006 - 2007 This page describes the construction of our dearly departed Carbon Fiber composite arms. We miss them.
Mista Ballista : Failed Arms Building an arm for a torsion machine this large has proven to be very challenging. Based on the experiences of our competitors, who also keep breaking arms, we find that we are not alone in this dilemma.

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