Pulpit and Umbrella

Original pulpit and umbrella.

The original pulpit, shown here, had a vertically rising umbrella raised on a wire wrapped around a drum on the rear of the rotating sun. However, I imagine that because of the effects of wind upon this arrangement, it was redesigned to be hinged at the back and to tilt backwards. My umbrella will also be hinged at the back for the same reason.

The pulpit contained the zookeeper. Mine, however, will contain a manikin of Dr Bob Moog and a replica of a Moog three-tier modular synthesiser (as depicted by Arturia Modular V software), complete with flashing lights. This necessitates having a relatively larger diameter pulpit than in the original.

I made the pulpit and umbrella from 1.5mm thick sheet aluminium, and the tube at the base from a steel flue for a wood-burning stove. The design and calculations for these parts are quite complex and lengthy and I refer you to my eventual book for more information.

The actual pulpit cylinder was straightforward to make from a sheet of aluminium rolled into a cylinder and pop-riveted at the rear. The cone was likewise pop-riveted to both the upper and lower cylinders using the tabs which were bent to shape to fit just inside the cylinders. To strengthen the structure, a circular wooden former disc was cut from thick plywood and screwed into the bottom of the cylinder where it was joined to the top of the cone; it can be seen in one of the images below (you can see we didn't get much rain for the grass that summer!). A sturdy steel ring was fabricated by our local blacksmith and pop-riveted into the top of the cylinder to give it strength. Any gaps in the structure were filled with car body filler.

Pulpit cone showing wooden former.

Four right-angle steel brackets were screwed to the bottom of the structure enabling it to be bolted to the wooden base, as can be seen in a picture below. The base was fitted with four castor wheels, as per the other main assemblies.

Pulpit cone (inverted)

To create the umbrella, I needed to cut eight identical petal shapes from the aluminium sheet. The calculations for the shapes are again relegated to my book. However, before cutting the aluminium, I made a trial run with a reduced-size paper version to check I had got my calculations correct. You can see this version in the image here. Having established that the shape was correct, I cut the eight pieces, and each segment was curved by 90° by rolling a steel tube over it while the segment was placed on a rolled-up cloth, as shown below - not an exact science, but it worked. Each piece had a series of tabs on one side. These tabs were bent back by 45° to eventually make a complete circle. The segments were then pop-riveted together using these tabs and any gaps filled with car body filler. A round disc was riveted inside and outside at the apex to cover the points where all eight segments joined.

Paper model of umbrella

Aluminium "petals" for umbrella

Curving process of umbrella parts

The umbrella was attached to the top of the pulpit cylinder by fixing it with two door hinges to a block of wood attached to the top of the outside at the rear. This picture shows the finished pulpit attached to its base by the four right-angled brackets. The connecting structure to join with the main tower has not yet been added. The pulpit and umbrella were then etch-primed and then spray painted, the colours being similar to the original, with the inside of the umbrella being yellow. It is interesting to note that the spiral pattern on the pulpit varied hugely between the various original models.

The mechanism to open and close the umbrella I based on the original mechanism as shown highlighted in the picture below. It uses a geared motor coupled directly into the bottom of an M12 lead screw supported top and bottom by ball bearings. The motor was chosen to have a speed of around 840 rpm. This meant that it would take between 8 and 10 seconds to fully raise the umbrella, a time similar to the original. On the leadscrew is a nut welded to a cross arm, which is in turn coupled to the inside of the umbrella by two linkages, as shown in the other picture below. There are two limit switches positioned so as to cut the supply to the motor when the umbrella is fully opened or fully closed. The former is actuated by the rising of the cross arm. The latter one is fitted just inside the top of the pulpit at the front and is actuated by a bracket attached to the inside of the umbrella. This bracket is also used to take the weight of the umbrella onto the pulpit rim when in the closed position. The motor turned out to be somewhat noisy, so was encased in some polystyrene foam in an attempt to dampen the noise. This is not shown in the picture.