The launch controller was designed to the safety standard for launch controllers in that it is armed by a removable arming key (the term key is used in general it can just be a pin), It had to be capable of sufficient current to ignite the highest current igniters and be safe to use with flash bulbs i.e. draw minimum current during the continuity check. It had to be a Relay launcher with the battery at the Rocket side of the controller so as to minimise the current drop if having the power at the operator end.
The following is the circuit diagram for the Launch controller.
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The component list for this circuit is as follows.
K1 = Relay with 12v Coil and 12V 5A terminals SPNO
K2 = Relay with 12v Coil and 12V 5A terminals SPNO
K3 = Relay with 12v Coil and 12V 5A terminals SPNO
K4 = Relay with 12v Coil and 12V 25A terminals SPNO
R1 = 56 ohm (dependant on length and resistance of cable used)
R2 = (Voltage/0.025) - Coil Resistance of K3
R3 = 110 ohm
R4 = 750 ohm
R5 = 750 ohm
D1 = High Brightness Diode
D2 = High Brightness Diode
D3 = High Brightness Diode
S1 = Non latching Switch SPNO
S2 = Key switch Key Removable only in off position SPNO
S3 = Power Switch SPNO
S4 = Non Latching Switch SPNO
J1 = Suitable (min) 5 pin connector and socket (FCC68)
J2 = Suitable (min) 5 pin connector and socket (FCC68)
T1 = Terminal Post to connect ignitor leads
T2 = Terminal Post to connect ignitor leads
F1 = Fuse (13A) and fuse holder
The cable and plugs for the controller to the igniter were Silicon extra flex so as to withstand some of the blast from the engines when igniting and allow them to fall clear easily, the part used for these cables are listed below.
Silicon 32A Extra Flexible wire (Red)
Silicon 32A Extra Flexible wire (Black)
Standard Crocodile Clip (Red)
Standard Crocodile Clip (Black)
To connect the battery to the control unit it was decided to use a cable with a plug on it and a socket in the controller this would make the transportation of the unit easier, the connector for this had to be keyed in such a way that the battery could not be connected with reverse polarity easily it was for this reason that a Telefunken plug and socket was chosen. This will of course need connectors on the opposite ends of the cable to connect to the battery these connectors should be suitable for the type of battery you choose to use (see below for details of the battery).
FT9
Telefunken Plug FT98G £1.29
2 Core Mains Cable 1 Meter XR47B £0.39
Power is supplied by a 12V Gel Cell the stronger cell the better but no less that 12maH or a Lead acid battery i.e. a car battery.
A stand for the 100M role of cable can easily be built as shown in the Picture below, this incorporates a winding handle to ease winding the cable back onto the drum, Also to stop the FCC68 connector from having its clip a Cone was constructed that the FCC68 connector is tucked back into for cable recovery to enable a smooth pull of the cable and stop the connector getting caught in the grass see picture below.
If you wanted to make a circuit board for the main controller then the following component layout has been worked out for this, however it is advised to use the terminals on the top of the 25A power relay not using the circuit board for the high power link to the igniter, also the track providing power to the relay from the battery would need strengthening.
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Notes on Design:-
The value of R2 is calculated such that the current flowing through the ignitor when doing a continuity check is 25mA. This value makes it safe for most ignitor type including flashbulbs which require 50mA to ignite.
The value of R1 is dependant on the resistance of the cable conecting the relay box to the hand unit, the purpose of R1 is to reduce the voltage through the cable but if the resistance is too large you will find that the relay K1 will not switch and arm the unit.
Connection directly from the battery's positive terminal to K4's teminal should be suitable to carry large currents hence heavy duty wiring and thick tracks if PCB mouning.
Connection directly from K4's teminal to T1 should be suitable to carry large currents hence heavy duty wiring and thick tracks if PCB mouning.
Connection directly from the battery's negative terminal to T2 should be suitable to carry large currents hence heavy duty wiring and thick tracks if PCB mouning.