Main Doors

I wanted the doors at the bottom of the central clock tower to be very close in appearance to those of the original. Guinness kindly gave me permission to use their Sea Lion character balancing a pint of Guinness on its nose. This is the only (discreet) reference to Guinness advertising on the entire clock.  There are very few colour photos showing the original clock with the doors closed. Working from this photo below, I created two gothic arched doors from wooden frames, eventually to be covered on the front with Foamex.

I enlarged the image in Photoshop to create a template for the Sea Lions and copied this onto more Foamex. I then cut out the two shapes using a very fine electric jig-saw. With the aid of an electric file, I rounded off the edges and gave it three-dimensional sculpturing. I painted the Sea Lions metallic gold, like the original, and painted the beer glasses black with a good white head, as shown here – thirsty work!

I managed to track down some door handles and screw-on shoe studs on the internet to mimic the handles and square-headed nails of the original. Like many parts of the clock, they came all the way from China. I could not find any hinges identical to the original but eventually managed to find some similar in style and about the right size AND made in the UK. After painting the front of the doors a bright yellow, I marked out and drilled the holes for the square studs. These were then screwed on from behind. I glued the door fronts to the door frames using a wood glue, but this did not really work. A bit of research on the web suggested a product known as Gorilla Glue. You apply a thin coating of this treacle stuff to one surface and spray water onto the other and push the two surfaces together. I clamped the fronts and frames with loads of G-clamps and waited. The glue reacted with the water and expanded into a sort of very tough foam. This worked perfectly, and I used the same glue for gluing other pieces of Foamex to the main frame around the doors.

I also used the Gorilla glue to stick the Sea Lions in place, and then screwed on the door handles. The hinges were also added, but because I had angled the front of the doors, the arch frame on the right was narrower than on the left which meant the right hinges would stick out beyond the frame. Unfortunately, I had to move these hinges towards the left a little resulting in the pivot not being in line with the edge of the door. The hinges also needed a little packing behind to enable the door to operate freely – a bit of a bodge! You can see them here before the door opening mechanism was added.

Just behind the top of the right door I screwed a small microswitch to the arch frame so when the door was closed the switch would operate. Like the switch in a ‘fridge, I used the normally closed contacts to switch an LED spot light on as the doors opened. This light I positioned inside the main tower near the right-hand loudspeaker and angled down to illuminate the base of the lunar landscape.

The original door-opening mechanism is shown here. There was a single reversible motor driving a leadscrew, the nut on which operated the upper and lower chains, driving sprockets which ran freely on vertical shafts at the two sides of the compartment. The upper sprocket on one side and the lower on the other were provided with crank arms, which operated the door hinges through connecting links, all rather complicated. For this to work, it relied on the fact that the entire tower was placed on top of a larger plinth which housed some of the mechanism. My tower does not have a plinth as such, another reason for not adopting this approach.

Original doors detail

My Guinness Seal

Door furniture

Completed doors

Original door - opening mechanism

Early door - opening mechanism design

I scratched my head as to how I might reliably operate the two doors with either a single motor or one motor per door. One approach was to use a single geared motor with a cranked arm and linkage to drive the left door and cross-coupled with a tensioned toothed belt to a similar cranked arm to operate the right door. Microswitches operated by the crank would control the motor actuation. A plan view of such a design is shown here. The red shows the closed position and the green the open position. The motor gearing would be arranged to operate the doors in ten seconds, similar to the original clock. I did some experimenting with this but was not entirely happy with it; for one thing the speed of the doors opening was not as uniform as I would have liked, and also the direction of forces on the door frame were not ideal. 

Another problem with this arrangement is that some of the linkage mechanism would be visible. However, at some stage I must have decided to use two motors, one per door, and so ordered two 4 rpm geared motors.

Realising the limitations of not having a plinth, I bit the bullet and decided I would have to create a faux plinth at the front. I could then use a mechanism utilising one motor per door, rotating a metal rod directly beneath and in line with the hinge pivots. Having previously ordered up two 4 rpm motors, I realised this new design would open the doors too quickly. So, to increase the opening time, I bought two sets of 16-toothed and 24-toothed pulleys coupled via a 300mm long toothed drive belt to give a slight reduction gearing. Too late, I discovered the motors were actually 3 rpm and were no longer available! In practice this means the doors take about 13 seconds to open. As the music that is played during the opening is at least this long, I could live with this.

Final door - opening mechanism design

The entire mechanism is fixed to a metal base plate located beneath the lunar diorama base and completely out of sight. The axle for the 24-toothed pulley is extended vertically through a watertight orifice in the faux plinth and fixed to the front of the door via a short horizontal bar welded to the top (shown in red and orange respectively). The bottom of the axle rotates in a phosphor-bronze bearing. I had to make a small cut-out in the door frame to allow space for the pulley below the bottom of the door. To cover the pulleys I made the faux plinth (a small box section running the width of the door arches). It did not need to extend beyond the sides as the original did. Two microswitches are used to control the stopping of the motor, one on the base of the door frame and activated by the door itself when closed; the other near the motor and activated by the gear-fixing screw when in the ‘door opened’ position. These switches directly control the stopping of the motor. A current sense circuit is mounted in the controller to detect when the current through the motor has stopped. This sends a signal to the microcontroller to indicate end of travel has been reached. A similar arrangement is used for the right hand door.

Below is a video of one door mechanism operating, followed by a video of the clock as it currently is, showing the doors opening and closing in test mode.

Left door mechanism

Right door mechanism

Faux plinth

Video of door - opening mechanism

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