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Lunar Lander

As a teenager I was captivated by the NASA Apollo missions to the moon and still have many newspaper cuttings of the day, although the mice in the loft have probably made a nest of them by now! I really wanted to feature this in a big way and decided this would be the main feature to be located under the clock behind the two doors. I remember making a plastic model of the Apollo Lunar Excursion Module (LEM) and decided I would track down on the internet the largest plastic kit I could find. This turned out to be a 1/40th scale kit made by a Japanese company call Aoshima. It wasn’t cheap or quite as large as I would have liked but it would do.

Around the same time as the first manned landing on the moon, Stanley Kubrick released his film "2001: A Space Odysey". I was enthralled by this film and the ideas behind it and wanted to incorporate this into this part of the clock. The idea, as explained earlier, was that the music “Also Sprach Zarathustra” by Richard Strauss, and featured in the film, starts and builds to its first crescendo in anticipation.  As  the second section

Apollo Lunar Excursion Module

of music starts, the two doors at the bottom of the main tower gradually open and an internal light illuminates a diorama of the lunar landscape with a solitary black monolith (again from the film) standing at the back. The final section of the music then builds to its tumultuous climax as the model of the LEM slowly descends from above and touches down on the lunar surface. You can hear the music here.         A model of an astronaut will then appear from behind the monolith and “hop” around the LEM – more on this later. When the clock sequence has completed and it is the turn of the LEM to close, the top part of it, the ascent stage, will rise up out of sight leaving the bottom part, the descent stage, remaining on the lunar surface. The doors will close. Once closed the ascent stage would then lower again to join the descent stage safely on the “surface” in its parked position. It was my aim that a single geared motor should control all of the LEM motion. I devised a cunning mechanism to do this but also decided to give my son Alex, who is a mechanical engineer, an opportunity to devise a mechanism. He came up with exactly the same scheme as me! So here it is:

Various stages of the LEM descent and ascent.

Proof of concept mock-up.

As this was a rather abstract notion, after producing this diagram, I made a crude Heath Robinson mock-up using a couple of small blocks of wood, some string and a flower pot!. Yes it all seemed to work OK!

The ascent stage and descent stage are two separate parts. Two sets of holes are drilled vertically through the two parts as far from the centre as possible and either side of the centre. Two very thin transparent nylon fishing lines are threaded through these holes and attached to the top and bottom of the clock tower. Springs are located at the top to keep the lines in tension. The whole LEM is free to move up and down these lines, the function of which is to act as guide wires stopping the assembly from rotating and generally swinging around. They are depicted in blue in the diagram.

Bicycle wheel for controlling the LEM.

Another hole is drilled vertically through the centre of the ascent stage and another transparent nylon fishing line passed through this and attached to the top of the descent stage centrally. This is shown in red in the diagram and controls the motion of the descent stage. Another fishing line is attached right next to  the  central  hole  in

the  top of the ascent stage. This is shown in green and controls the motion of the ascent stage. So, by pulling the ascent stage line (green), the ascent stage will rise, and by pulling the descent stage line (red), the descent stage will rise lifting the ascent stage with it if it is not already raised.

Motor and drive belt.

Position sensing microswitch

The two control lines pass over two pulleys at the very top of the tower, then travel horizontally to two eye hooks at one side of the tower. They then descend to the rim of a large bicycle wheel attached to the central side frame of the tower. The latter I found in a skip at the back of Halfords and took with their  permission.   It  is  shown  above  in the 

completed frame. The picture also shows the weatherproof control cabinet at the rear. Around the rim of the wheel is some plastic dual channel moulding which fitted perfectly as a press-fit. One channel holds the fishing lines and the other takes a 4mm polyurethane drive belt. A geared motor with a large Meccano wheel attached is mounted in the top and the drive belt wrapped around the two wheels. Three microswitches will be arranged around the bicycle wheel to be activated by cams on the edge of the wheel. These will be used to determine the positions where the motor has to stop rotating the bicycle wheel. The key fact is that the ascent stage line is attached to the top of the wheel and the descent stage line to the bottom as shown in the diagram as “Stage 2”. The lunar landscape base will be mounted on the rails just above the base bottom to allow room for the astronaut mechanism underneath and the door-opening mechanism. The proposed and revised order of operation is as follows:

  • In the rest position when the clock is not performing, the entire LEM will be wound down to sit on the base as shown in the diagram as “Stage 2”. This is to stop it swinging about in transit and to reduce stretching of the lines. Just before the clock starts its sequence, the motor will turn the wheel clockwise in the diagram causing both lines to be wound around the wheel pulling both ascent and descent stages up to the top and out of sight. A microswitch will signal when this position has been reached and the motor will stop. This is now shown as “Stage 1” ready for the sequence to begin.

  • At the appropriate time, the motor will drive in the other direction, turning the wheel anti-clockwise in the diagram, thus unwinding both strings and lowering both parts of the LEM together. After a pre-determined time, the motor will be pulsed on and off fairly quickly to give the impression of the descent slowing down just before touchdown. This will continue until the ascent stage line is at the top of the wheel. At this position another microswitch signals to stop the motor. The LEM has landed.

  • When the sequence needs to be completed, the motor will continue in the same direction. As the (green) ascent stage is at the top, this will be wound up, raising the ascent stage. However, the (red) descent stage line will continue to unwind as it has about half a revolution before it has fully unwound. A weighted pulley at the top will take up the slack produced. A third microswitch signals this position. We have now reached “Stage 3” in the diagram. The ascent stage has departed to dock with the imaginary command module (orbiting the moon) leaving the redundant descent stage on the moon.

  • When the doors have finally closed, the motor will reverse to Stage 2 lowering the ascent stage back on top of the descent stage in the parked position.

So I made the plastic model, painted it referring to various images from the internet for authenticity and covered parts of it in gold foil used for wrapping Rolo confectionary. It looks good but is very delicate. It even has sprung shock-absorbing legs!

Plastic model  of LEM on temporary base.

After trialling this mechanism for a while, I decided I would add a stay and limit switch just above the highest point the Ascent module would rise to, which is about 2/3rds the way to the top. This stay, bolted to the wheel axle support, holds the two guide lines closely in position to stabilise the LEM from swinging about when it is elevated. The limit switch is a normally closed microswitch in series with the motor. If any of the microswitches on the rim of the bicycle wheel fails to operate for any reason, the top of the Ascent stage will hit the microswitch lever and operate it thus cutting power to the motor. This would prevent the motor driving the LEM into the top of the tower and causing damage to the model - it nearly happened once!

Stay added to stabilise LEM and  prevent catastrophic overrun

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