The Modiolus and Epizygis used in Mista Ballista account for a majority of the time spent. The size and detail needed to construct these items in a way that could reliably contain the force of so much rope worried us, and we over engineered them.

Here is Dave learning to weld by building our first Modiolus. The flange in this picture was eventually cut round. We put a grand total of 5 welding passes around the perimeter of the pipe to hold it in place.

Here is a stack of four modiolii in progress. Each modiolus consists of a 3/8 inch plate rolled into a tube and butt welded. Then 1/2 inch plate steel was cut round and hollowed to fit over the tube. After some more welding and machining, these pieces will drop into the hole carriers, and be slotted for the epizygis. These pieces set our rope bundle size at 10.75 inches.

A modiolus is fitted into the hole at the top of our rope bundle. This modiolus has recently had it's pin holes mapped out. All we have to do now is slot them out for the epizygii.

We used the material we had laying around to make the epizygii. That means welding together some 3/4 inch plate and adding some 1-1/2 inch round stock to the top to make our four epizygii. This epizygis is being run through Dave's milling machine getting it's rough edges cut off so it can be welded together efficiently.

Here is an epizygis that has been welded up and milled to accept the round stock. The finished epizygis is about 1.5 x 6 x 18 inches long with a perfect radius on top.

Here is a Modiolus that has been fitted with one of our 1.5 inch epizygii. We milled slots into the side of the steel tube, then cut away the detailed shape using a carbide burr.

Winding the rope bundles was done via this come-along. We could chain one end and then use the come-along to add torque to the machine. In the following image see a high-res picture of the rope bundles and modiolus system (somewhat dirty.)

For more on tightening rope bundles see the Torsion page.

2005 Modiolus /Epizygis Upgrade

As discussed on the 2005 Frame Upgrade page, we had bent the frame. Since we had to disassemble the machine anyway, we decided it was time to upgrade our rope to something a bit larger as well.

First, we extracted the old rope bundle. Our epizygii are not welded in place as some of our competitors have done, so we were able to just push them out the side of the modiolus, and then pull the rope out without any laborious unwinding. The end result (as in this picture) we nicknamed "The Squid".

Next up, we shortened all our epizygii on a band saw. For more information on this, see the Torsion Page which discusses the new torsioning arms for which the long epizygii get in the way.

Our new rope has a much thicker diameter from the old rope, so we needed to widen the tops of each epizygis. Otherwise the narrow epizygii edges could damage the rope under full tension. Jeff found some structural pipe with an inner diameter the same as our current epizygis tops, and slotted out the bottom on a milling machine. Once that was done, we cut them to length, and ground the ends to match up inside each of the modiolii.

Each subsection of pipe now fits neatly inside the modiolus, ready to accept several tons of torsion force.

Additional Pages
Mista Ballista : Modiolus and Epizygis (This Page)	The Modiolus and Epizygis used in Mista Ballista account for a majority of the time spent. The size and detail needed to construct these items in a way that could reliably contain the force of so much rope worried us, and we over engineered them.
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 : Arms	Building an arm for a torsion machine this large has been very challenging. A list of our failures in this area might provide some hints on what not to do.
Mista Ballista : Trailer	One of our goals for the 2003 season is to acquire a dedicated trailer for Mista Ballista.
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 : 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 : Torsion	Mista Ballista's engine operates with 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 alternate means of twisting is needed.
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 : 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.