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'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.

The twisted ropes are held in place via a Modiolus and Epizygis. You can read about how we built them on the Modiolus and Epizygis page.

Come-Along Twisting

At the 2002 Punkin Chunk, and for initial winding at the 2003 Punkin Chunk, winding the rope bundles was done via this come-along. We could chain one end and then use the come-along to add torsion power to the machine.

Using a 2 ton come-along is very limiting, and does not provide much torque. But it's useful for initial tightening to get the arms held in place.

Hydraulic Ram Twisting

For the 2003 Punkin Chunk, we opted to use a Hydraulic Ram to do the tightening for us. See the chunk page for stories on the disasters that ensued. This section describes how we did it.

First, Dave added some Clevis Hooks onto the chain loops used last year. This let us dangle long chains from the ram, and hook onto them at convenient locations.

A hydraulic ram was then strapped into place. The chain on both sides let us twist both rope bundles at the same time. You can see this same ram on the mystery parts page during initial testing.

We had two of these red rams. One on the bottom, and this one which was lofted up on top of the rope bundles. Here Jeff is configuring the chains used to tighten the bundles on the top.

A testament to the strength of the twisted ropes, Dave stands on the arm while working the hydraulic twister.

After a hard weekend of chunking, we unwound the rope bundles, and took out the arms. The rope had stretched so much the modiolus fell right out the bottom.

Torsion extension arms

For the 2004 chunk, we built two torsion arms. The arms had special teeth that interfaced with the modiolus pin-down holes, and also bolted into place, forming a very strong bond to the modiolus. The hydraulics from last year could then be used to tighten them.

To make them interface, we needed to get the three pegs to line up with the modiolus holes. Jeff made eccentric pegs which fit into the rough-cut holes in a piece of channel. They would then be forced into the holes of a modiolus and twisted to get a perfect fit. This was then tack-welded into place.

Here Jeff is adjusting a pin so that it will mesh into the modiolus.

Eventually, the top of the channel was cut off, and welded onto an extension beam. The extension beam then had a hole on the end for attaching the hydraulic ram. Here you can see the pins have grabbed onto the holes in the modiolus, and a bolt is used to hold it on.

Here the hydraulic cylinder is attached to a torsion arm on one side, and the scutula on the other. The hydraulic hose is running up to it. Dave is checking the fit.

In 2005, we decided it was important to add some flexibility to the pin-point for the hydraulic cylinder. At the 2004 chunk, it took some careful adjustments of the hydraulics to get stuff to line up. This year, we got some mega-chain from a scrap yard, and cut it into short lengths. These will be shackled onto the torsion arms, and make it easier to bolt onto the hydraulic rams.

We even got the torsion arms painted. Huzzah!

Video

With hydraulic winding comes problems. We found that the rams were much stronger than other materials in the system. This video shows just how much force is being applied to break the chains, and the scariness of the rope bundle unwinding.

No one in this video was hurt by the flying metal shards, nor rapidly spinning modiolus. After the bundle was unwound and idle, the arm fell, and konked Dave and Jeff on the head.

Google Video Service Mista Ballista - Failure of first torsioning system

Information: At the 2003 Punkin Chunk, Mista Ballista was using a new hydraulic system for tightening the rope bundles. This shows the system in action, then breaking to disastrous effect. 8 sec - Nov 20, 2007

Later we improved our winding using specially made torsioning arms.

Google Video Service Winding Mista Ballista

Information: Roger and Dave working on winding the machine with the hydraulic ram. Shot during 2004 Punkin Chunk 9 sec - Jun 25, 2006

Next, we added trunnion mount hydraulics, and a remote way of controlling the hydraulic valves.

Google Video Service 2007 - Adding Torsion to Mista Ballista

Information: Using hydraulics with an electric valve on a long lead, Roger can tighten our rope bundles and get a good view of when the holes line up. 9 sec - Nov 5, 2007