Wireless Launch Controller

At first I was unable to obtain reasonable range with this control.
However, another experimenter indicated that 1000-1500 ft could be obtained.
The secret was using separate power supplies for the receiver and the relays.
Since then, I've switched to a 12 channel $31.00 control from another company and had very good luck with it.
The new controller has a lot of advantages. I'll update the webpage when my workload permits.

Wireless launch controllers have significant advantages for long cable runs.  Besides wire cost, time deploying and retrieving wire, reliability issues, and wires to trip over, conventional wired systems are less flexible than wireless systems.  For these reasons, this away pad controller is useful for distant and close pads.

This launch controller is based on an 8 channel diversity transmitter and receiver which have unique pre-determined codes selected from over 1 million combinations.  Each channel can be set up for momentary, toggle, or latch.  I used output of the 8th channel in toggle mode for arming/disarming and output of 6 of the other channels in momentary mode for launching.  

The transmitter can be used at short range as is.  Or, the range can be increased to by utilizing an external antennas as shown in the launch control panel interface later in this article and by adding amplifiers to the receiver and/or transmitter.

  Ultra bright clear red LEDs on the launch control provide highly visible indication of the selected pad even in direct sunlight.  A strobe is used at the bank of pads to indicate arming.  Both the transmitter and the receiver should be spaced away from any metal and wiring when mounted.

Launch Receiver/Pad Relay Box

The outputs of the receiver is 100 ma.  Therefore, 12 volt relays are used to provide the necessary 10-15 amps for igniters.

If 120 amps capability for clustering of extremely large numbers of motors is desired, the coil of a "cluster buster" using an automotive solenoid can be driven by the output of a relay in this system.  It is best to house a cluster busters separately so that they may be moved.

The receiver interface is designed so that even with a welded igniter relay, a rocket cannot be launched unless the pad is armed.  Igniter continuity is displayed at the pad array box.  Igniter test current is limited to 10 ma.  This is about 1/20 of the maximum no-fire current for Oxral and Daveyfire e-matches and 1/10 the maximum no-fire current for HiMRI matches.  (For a brighter continuity display, the 1.5 K resister can be replaced with a 660 ohm resistor for 20 ma current.  However, we find 10 ma more than sufficient when the correct LEDs are used.)

The diode located in the left bottom corner of the schematic is there to prevent damage to the receiver if you hook up the power backwards.  Although the receiver can operate on ac or dc, the outputs cannot handle the large current allowed through the spike protection diodes if the control is hooked up backwards for even an instant.  The added diode is placed OUTSIDE of the igniter loop so that it sees only the coil current.

The drawing below will be replaced with a photo:

 Faceplate of Receiver Relay Box 
mounted in 100 crtg .50 cal ammo box

 Mounting Diagrams

A piece of aluminum or steel is bent in an inverted U with legs just high enough to allow space for the relays etc beneath them.  This is placed in the ammo box and allows sufficient space above the panel for the battery jumper cable, zenon flashing light, and some extension cords which are used for igniter leads.  No penetrations to the waterproof ammo box are made.  It is opened for use and an antenna is attached.

Transmitter Launch Control Interface

It is possible to use the unmodified hand held 8 channel transmitter.  When doing so, it is advisable to use channel 8  (activated by pressing top button and button 4 simultaneously) as the arming channel so that the channel will not be armed accidentally.  Range with an unmodified hand held transmitter is limited.

UPDATE:  Adding wires to the existing pushbutton transmitter switches apparently is problematic.  Use of twisted wire and shielded wire on the control did not prevent RF from interfering with the logic of the switching on the transmitter.  I will try adding .001 microfarad bypass capacitors at each switch to see if it fixes the problem.

PLEASE DO BUILD THE TRANSMITTER INTERFACE PANEL BEFORE THIS ISSUE IS INVESTIGATED FURTHER AND RESOLVED AND THIS NOTICE IS REMOVED.

Although a 12 volt supply could be used with dropping resisters, I chose 6 volts supplied by 4 AA cells to protect the transmitter below.  This with a low current circuit board reed relay should provide long battery life.  The 1N4001 diodes are used to protect the circuitry from spikes created by the relays.  The AA cells also eliminate the need for external hookups except for the antenna.

To prevent the possibility of launching channels 1-3 when 5-7 are chosen, the arming button should not be pressed at the same time as the safety and fire buttons.

The circuit diagram below is based on a 12 position switch.  Obviously, the 7th channel should be omitted if a 6 position switch is chosen.   The additional channel which might be used for another pad or to provide arming for 2 banks of 3 pads instead of 1 bank of 6 pads.

Photo of soldering connections to transmitter:

The drawing below will be replaced with a photo:

All modifications above this line are concerned with interfacing with the switches not the transmitter or range of the device.  Keep in mind that the height of the receiver (receiving antenna) is significant to achievable range.  Neither the receiver nor the transmitter can be mounted in a metal box unless an external antenna is used.

Range and Antennas

Replacement of the existing receiver antenna alone will have little effect on the range unless a high gain antenna is used.  Replacement of the transmitter's antenna can result in a dramatic increase in range.  Many antenna options exist.  For use in a large open field, interference with other services should not be an issue.

Note what happens when the impedences of the circuit are
not matched  with the transmission line and antenna - no range.

Diversity receivers like the one in this control use two antennas and have substantially better performance than an ordinary receivers.  When mounting the receiver, I used only one receiver antenna.  The resulting compromised performance was offset by the improved transmitter or receiver antenna.  If maximum performance is required of the receiver, two receiver antennas could be used and they should be spaced at least 9" apart.  This would help with dropouts. The addition of pre-amplifier kit from http://www.rainbowkits.com/kits/wba-p.html with just one antenna increased the range of the receiver.  Without an amplifier, inadequate transmitter power is available for significant range.

Homemade Ground Plane Antenna

The vertical element and radials can be made of no. 12 copper wire or welding rods, coat hanger, etc. The vertical radial (A) should be soldered to the center connector of the SO239. The four base radials (B & C) and (D & E) can be soldered or bolted to the SO239 mounting holes using 4-40 hardware.

The four base radials then should be bent downward to a 45 degree angle. The antenna can be mounted by clamping the PL259 to a mast or even passing the coax through a 3/4 ID PVC pipe and compression clamping the PL259.

Ground plane dimensions:
   radiator - 8  29/32"
   radials - 9  23/64"  (Use 9"would work for radiators if they are horizontal.)

Note: The 1/2 wave vertical is roughly .85 db more gain than a ground plane when mounted 1 ft above the ground but requires a matching coil.  1/2 wave vertical dimensions - 1.49 ft

Coaxial Collinear Antenna (5-10 ft long inside a 3/4" pvc pipe)

TRANSMITTER:  LINEAR DSX-25 - http://www.linearaccesscontrols.com
RECEIVER: DXSR-1508 - http://www.linearaccesscontrols.com

The following rotary switches can be used for the transmitter:

http://www.alliedelec.com/cart/partlookup.asp?ST=AS&PartNumber=747-6730
4 pole 12 position - about $22.20 each

LEDs should have an output of 6,000 mcd at 20 ma.  E-bay is an excellent source.