Practical Catapult

 

Practical catapult primed for firing

Practical catapult primed for firing

This small practical catapult was made for a recent theatrical production. The design was based on a Leonardo da Vinci drawing of a catapult. Modifications had to be made in order for the catapult to operate as required.

The main power for the catapult was a length of rubber cord similar to bungy cord. Two children’s motocross push bikes were recycled (pun intended) for the wheels and steering mechanism. The bike parts were attached to the timber framework with custom brackets which were then lashed with sisal rope to give a more lived in look.

A steel ratchet mechanism was built to ensure reliable operation of the release of the catapult arm. Clicking on the photos below will bring up a larger image.

End view of catapult

End view of catapult

Catapult released

Catapult released

The ratchet mechanism

The ratchet mechanism

Closeup of the release mechanism

Closeup of the release mechanism

Making a Custom Hinge

A commercially available custom hinge can usually be found to suit almost any application. However, sometimes a situation arises when a purpose built custom hinge needs to be made. Such a situation arose when a set of Art Deco security doors had to be installed on the inside of some outward opening courtyard doors. The security doors also needed to be able to open out as well or be left locked while the outer doors remained open.

To enable the inner and outer doors to be totally independent of each other they needed their own hinge but they also needed a common pivot so that they would not foul on each other when opened and closed. This was achieved by making a combination butt/parliament hinge where one flap was longer than the other but they both shared a common pivot flap.

The first step was to find hinges that allowed themselves to be modified into a custom hinge. Eventually a quantity of 90mm butt hinges were found that used 3mm thick steel flaps and had removable finial ended pivot pins. Additional parts to make the extended parliament flap were laser cut in 3mm steel. Once the extension pieces were assembled they could be welded to the required hinge flap. Photos of the installed hinges can be found on the completed installation link.

The pictures below show the steps involved in making the hinges.

Hinge parts

Parts used to make the custom hinge

Disassembled hinges

Two hinges were first disassembled

Making a longer pivot pin

Two pivot pins are joined together to make a longer pin to fit the wider hinge

Joining the two hinges

Two hinges are welded together on one side leaving two independent flaps held in place by the longer pivot pin.

Completed hinge extension pieces

Assembled laser cut hinge extension pieces

Fitting extension piece to one hinge

Fitting an extension piece to one hinge flap

Completed combination hinge

Completed combination hinge

The hinge in two positions showing operation

Hinge operation positions

Mechanical Oriental Fan Props

Prop Oriental fan  mechanism

Prop Fan Mechanism


We have recently completed an interesting project involving the design of X7 large oriental style fan props that can be carried on stage, set in a base support unit and opened on cue by a performer.

After the *business* of the scene is finished the props are closed again and carried off by the performer.

These props had several important criteria with the most important being their weight.

Initially fibreglass batons were considered for the ribs but when compared to equivalent timber parts they were found to be over three times as heavy! All the fan ribs were therefore made from Tasmanian Oak which gave an impressive weight saving as well as excellent strength and flexibility. Additional savings were made using aluminium tube for the support poles and paper for the flags on the fan ribs.

More information and construction photos can be found on this page.

Below is a video showing the operation of the fan props mechanism and how they will be used by the performers.