MMM Circuit Description
Meccano Martian Mission
Control Circuit & Logic - Description & Operation
The complete circuit is shown in schematic form as a “block flow chart.” As a convention current flows from top to bottom. There are three exceptions to this rule, where upward flow is depicted by yellow arrows. Two being the outputs from the “Fuel Relay” (T) the blue wire back up to the PWM boards, and the black wire to the Fuel gauge motor. The third is the Start power output from the latched relay (Q).
The overall circuit is divided into four main areas shown with coloured backgrounds. The yellow area basically shows the main drive components and manual control system. The blue area shows the sensing and logic circuit components. Both these areas are supplied by “continuous power” which is constantly available.
The third area with white** background is supplied by “switched power.” This includes all systems which need to be disabled (switched) as soon as the Lander Module (LM) contacts the ground, thereby freezing and ending the game.
**Within the white (switched) area is the fourth area in green. This area is supplied by “start power.”
Everything within the green area is only powered after the start button is pressed. Doing so energises the Start relay which is latched in the energised state, so the start button only needs to be pressed momentarily to begin the game.
Power Supplies
Power is initially supplied via a set of four “panic buttons” strategically located around the model. If any of these are pressed the entire circuit is shut down to protect the model. “Protected Power” is then fed to the models first power bus bar, which is called the “continuous supply.” Everything is initially if not directly supplied by this bus. A feed from this bus bar goes to the “Drive Disconnect” relay (W). The output from the relay contacts is termed the “Switched Supply.” Any circuits powered from here are disabled on ground contact when the relay is energised by the logic circuits. When this happens, the game is effectively ended.-
Main Drives (Yellow area)
The first four switches at the top (and also the Reset Switch – see later) are the Manual Controls mounted to the rear of the model. These allow direct control of the main drive systems, i.e. the Vertical and Horizontal (V and H) motions. Drive power comes from two high speed “muscle” motors which each drive a friction wheel at a constant high speed. These are switched on manually during the initial set-up. The manual demand switches are used for maintenance - they feed full current directly to the demand motors (when manual mode is selected) and they also control demand direction. The demand motors cause the Friction discs to traverse over the pickup wheels generating a gradually accelerating output drive. The output shaft feeds back into the demand mechanism via a differential to return the pickup to centre, thus gradually decelerating the drive back to zero (when demand is removed) and thereby simulating momentum and air friction.
In auto mode, (set by the Auto/Manual Select Switches) the same function is provided by the PWM boards which divide thrust between V and H according to the attitude of the LM. This is facilitated by the divider pots shown between the PWM boards generating a “conditioned thrust signal.” Demand motor direction is controlled by the direction switches (up/down, left/right) shown in buff and blue respectively. These switches are actuated by the corresponding sensing cams linked to the Attitude motor in the white region, and they control the “Demand Relays” (R) and (S). A smaller third cam (green) operates the “Lander upright” switch which forms part of the logic circuit.
Logic and Sensing Circuits (Blue area)
It might be best to describe this section starting from the bottom up. The game is controlled by two sensing tracks to determine where the LM has landed. When the LM makes ground contact, the appropriate circuit is earthed and a corresponding result is sequenced in response. If the LM lands safely, a LAND Banner is deployed, but if it crashes, a CRASH Banner is deployed instead.
There are two sensing tracks. The LAND sensing track is connected to all level sections of Landscape (Landing Pads). The CRASH sensing track is connected to all sloping sections of Landscape (Mountains)
The two switch symbols labelled “Contact Rails” represent contact of the LM with either of these landscape regions, and they show the earth path via the Land relay (Y) or the Crash relay (X), their corresponding Banner sequencers and the power supply. If one of these circuits is earthed the relay is energised, and so is the corresponding “Banner Release Motor.” The energised relay diverts power to the “Drive Disconnect Relay” thereby disabling the “switched supply.” This will disable all player inputs, as well as the orbit motor, the gravity drive clutches, main drive clutches and the Game Timer.
Basically, everything stops moving.
Looking at the logic circuit more closely, you will see there are three (green) safety sensing switches installed, any one of which will energise the “Crash or Land” relay (Z) in an “unsafe configuration.” In the event the LM contacts safe (level) ground, but is travelling too fast, or is not sufficiently upright, the Crash or Land relay will divert the “LAND” signal to the CRASH Banner circuit.
The Lander Upright Switch is wired to be “unsafe” when closed. The speed switches are centrifugally operated and they are closed in the “safe” condition. They need to generate a positive (unsafe) signal when they are open. To achieve this, when closed (safe) they will energise a “safe speed relay” (U) or (V) which disables the positive signal. When the switch opens at higher (unsafe) speeds, the speed relay de-energises, and a positive signal is sent to the Crash or Land relay (Z)
Switched Supply Circuits - Start Game and End Game (White area)
This bus is further divided into two branches by the Start Button. Before the start button, switched power can still feed the Orbit motor which means that the Landscape will already be in motion (to simulate orbit) before the game begins. This motor only runs at high altitudes and is controlled by the Altitude sensing pot. It becomes ineffective at lower altitudes.
Power will also still go to the vertical limit switches which are used to power the Main Drive Clutches and Gravity Motor. Provided the Vertical element (Tower mounted LM) is within “Gameplay limits” both main drive clutches and the Gravity Motor are energised. If the LM gets too high, both main drives are disabled briefly, but Gravity can still drive the LM down and back into play. If the LM gets too low, (it should contact the ground first however) all drives are disabled.
Start Power and the Start Button (Green Area)
Before the game is initiated by pressing the start button, Gravity select clutches are disabled (so the LM remains in orbit), all Player controls are disabled, and the Fuel / Timer gauges are disabled.
As soon as the Start Button is pressed, all the afore-mentioned circuits are made live, and the game begins.
The Start Latch Relay is energised and latched, maintaining Start Power when the Start Button is released. The player now has full control of thrust and attitude, and the timer immediately begins the countdown. When time runs out, the timer motor stops (no time switch 2) but also thrust is disabled (no time switch 1). There is still a chance for a safe landing, but all you can do is get upright – the rest is left entirely down to gravity and luck!
During active gameplay, thrust demands by the player will energise the Thrust Relay (T). Start Power is then sent via the relay contacts, first to the Fuel motor which drives the Fuel gauge down (as fuel is used), and second, back up to the PWM drivers to energise them. This will enable the “conditioned thrust signal” to be sent to the demand motors as dictated by the LM attitude sensors.
The main drives are disabled on contact with the ground as previously mentioned. They can be re-enabled by pressing the Reset Switch to manually drive the LM off the ground. At this point, switched supply is restored and the reset switch is no longer needed. This switch was fitted as an added optional extra. It is made redundant, because a quick disconnect mechanism allows vertical drive to be temporarily disengaged. Then the LM can be physically lifted back into orbit by hand.