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Kill Switches / Failsafes - A Rough Guide
Table shows the key features of some of the available kill switch / failsafe devices to date
In summary a 2 channel or auxillary (3rd or 4th) channel kill switch works to automatically shut down the engine in the event ofthe situations listed in the table below. It can therefore help prevent a serious runaway, protecting the Baja from potentially expensive damage and ensuring the safety of those around.

It is recommended that an auto kill switch should be one of the first items to install in a gas / petrol powered rc vehicle such as the Baja.

Additionally, the ability to remotely kill the engine at will (from the associated auxillary channel switch on the hand held transmitter, or in the case of the 2 channel killswitch, the tx power on/offswitch) is a convenient alternative to having to access and manually press the stock kill switch located on the engine. This is of course useful as both a routine off switch and during tuning - allowing the engine to be stopped quickly at various RPMs for a more accurate spark plug colour check.
KILL DEVICE >>>>>>>> DIE-
MASTER PICO		 BATTLE
SWITCH		 TGN PICO AMS KILL SWITCH CBE KILL SWITCH MHZ EKG
SWITCH		 KILLER RC SUPER PICO KILLER RC
KILLER BEE		 KILLER RC
KIT 7		 KILLER RC
 KILLER BEE V2		 KILLER RC
 KILLER BEE V2-S
DESCRIPTION / FUNCTION               DISCONT'D   DISCONT'D    
3rd Ch / Manual Kill YES YES YES YES YES YES NO YES YES YES AUTO (4) AUTO (4)
2 Ch / ('manual kill' only by switching TX off) YES YES

Transmitter (TX) - Switched Off / Low Voltage / Signal Loss / Signal Interference
(1 Second delay)
(MHZ - 0.05secs)

 YES YES YES YES YES YES NO YES YES YES YES (8) YES(9)
Receiver (RX) - 
Low Voltage		 YES YES YES YES YES YES YES YES YES YES YES YES
Receiver (RX) - Switched Off / Total Power Loss (No Voltage) YES YES IF NC NO YES NO YES YES YES YES YES YES YES
Ability to house within Radio box YES YES
(WITH NEAT ARRANGE-MENT)		 YES YES YES YES -
CIRCUIT B
NO - RELAY (see note 1)		 YES YES YES YES YES YES
APPRX. SIZE OF UNIT (mm)
L x W x D		 18 X 15 X 12 32 X 32 X 23 18 X 15 X 12 15 X 10 X 8 18 X 15 X 12 42 x 22 x 6.2
(CIRCUIT BOARD)
42 x 22 x 22
(RELAY)

30 X 25 X 13

 26 X 15 X 12 26 X 15 X 12 28 X 22 X 10 28 X 22 X 10 28 X 22 X 10
Circuit (At Rest) -
(NORMALLY CLOSED)
see notes below*
LED ON = 
Motor can start		 CLOSED CLOSED
OPTION		   CLOSED   CLOSED CLOSED CLOSED CLOSED CLOSED CLOSED CLOSED
Circuit (At Rest) -
(NORMALLY
OPEN)
see notes below*
LED OFF = 
Motor can start		   OPEN
OPTION		 OPEN   OPEN              
Audio Alarm - Buzzer
(24mm diam X 5mm depth)
(see note 2)		                 YES
KIT 5 OPTION		   OPTION OPTION
Externally mountable LED
(see note 3)		                 YES
KIT 4, 5 OPTION		   OPTION OPTION
Pre-wired stock kill switch (red button)                 YES
KIT 3, 4, 5 OPTION		 YES OPTION OPTION
Pre-wired, allowing removal of existing stock kill switch (red button)                 YES
KIT 2 OPTION		   OPTION OPTION
Ability to run 6V LED lights through kill switch to indicate kill status               YES
KIT 6 OPTION		        
Programmable Digital Light Controller & Kill Switch                   YES    
Direct plug in to aux rx channel YES YES YES YES YES YES YES YES YES YES N/A   
Y splitter (3 wire) required for connecting to rx
(when used with 2 channel radio)		                     YES YES
Y splitter (3 wire) to connect switchable lights (NB.light controller required) & kill switch to aux channel. YES (5) YES (5) (7) YES (5) YES (6) (7) (7) YES (5) YES (5) YES (5) YES (4) YES (4)
IMPORTANT - 
It is vital that the radio is set up correctly in order for the kill switch to work effectively as a failsafe - this may involve changes to the 3rd channel settings from the radio handset menu. eg, allocating a 3rd channel switch on the handset, reversal of 3rd ch switch or 3rd channel values +100 / - 100. Refer to the appropriate manuals for details.

NOTES

(1) - MHZ - It is recommended that the killswitch relay be mounted outside the radio box to keep radio noise to an absolute minimum.
The  MHZ killswitch was designed and produced by  http://www.isamtec.de/isamtec/Killswitch_NXT_Benzin.html 

(2) - Killer RC kits #1 to #4 & KB2 are all easily expandable to allow connection of a buzzer alarm (as used in kit #5)

(3) - Killer RC kits #1 to #3 & KB2 are all easily expandable to allow connection of an external LED (as used in kits #4 & 5)

(4) -  A 3 wire Y-splitter cable can be used to connect the Killer Bee 2 (KB2) and lights  to a 3 or 4 channel system (NB - a light controller will be needed if switchable light control is required, otherwise lights will remain on - and a separate manual light switch can be installed). In this case the 3rd / 4th channel switch will control the lights and NOT the kill switch. The kill switch can be activated manually by turning off the tx power switch. Auto killing will still take place as indicated in the above table.

(5) -  A 3 wire Y-splitter cable can be used to connect the kill switch and lights to a 3 or 4 channel system (NB - a light controller will be needed if switchable control is required, otherwise lights will remain on - and a separate manual switch can be installed). In this case the 3rd / 4th channel switch will control the lights AND the kill switch at the same time. ie lights on, engine can start / lights off, engine cannot start. Auto killing will still take place as indicated in the above table.

(6) -  As note 5 - though the light controller set up will need to be reversed (check actual switch mounted led for kill status during light set up)

(7) -  Other kill switches may work.

(8) - If the RX has a built in failsafe the KB2 will not work properly. Example: with the Spektrum 2 channel DSM radios, the failsafe will give the Killer Bee2 a signal when the RX is receiving no signal. It defaults to a centre position when the RX is bound to the TX. When the RX loses signal, the Killer Bee2 only kills the engine for 1 second, then it turns back to the run mode. This will only kill the motor if it is at an idle. With any speed to the motor, it will keep running once the failsafe sends a signal to the Killer Bee2 to turn back on. This may very well result in a runaway situation.
Similar problems may be also encountered with other radio systems with a built in failsafe.
This information is based on independant testing carried out using the Killer Bee2 with each of the Spektrum radios (except for the DX3s or the DX3e). Each of the Spektrum receivers (except the SR3300T) was also tested.

(9) -  V2-S - This kill switch works like the
Killer Bee V2
, but its made specifically for Spektrums. You can use this kill switch if you have a 2 channel Spektrum, or if you want to free-up the 3rd channel on your DX3 to control a light controller or 2nd brake servo, etc. Use a Y-splitter cable to let the Killer Bee v2 tap into your Aux or Steering channel. Just turn off the transmitter power to kill the engine.
What makes the V2-S different from the V2 is that the V2-S keeps the engine killed for 5 seconds, allowing the engine to totally shut down, and preventing the Spektrums failsafe from overriding the kill switch before the engine is shut down. Once you turn off the transmitter power and turn the power back on you have to wait 5 seconds before the engine can be started.
Numerous connections and switching options are possible - 5 examples are illustrated below for reference;
 
Use of a Y splitter cable to connect controllable lights and a 3 channel kill switch (see note 5 above)
Use of a Y splitter cable to connect switched lights fed from from rx battery pack
 Use of a Y splitter cable to connect a 2 channel kill switch & servo, with the aux channel (3) used for lights or other secondary device.
 
Use of a Y splitter cable to connect a 2 channel kill switch & servo, with switched lights fed from a secondary Y splitter from rx pack
Use of a 4-way Y splitter cable to connect several devices off the battery/4th channel. Lights are controllable via the controller unit. Kill switch / servos each have dedicated channels.
Image Library
Diemaster Modified Pico / Pico - http://www.dimensionengineering.com/PicoSwitch.htm  
-
Battle switch - http://www.dimensionengineering.com/BattleSwitch.htm
-
TGN Pico image
TGN Pico
-
A-M-S 'Failsafe Engine Emergency Stop'
http://www.a-m-s.ch/shopenams/tuning-grossmodelle/fg-tuning/failsaves/failsave-engine-emergency-stop.html 
-
Custom Baja Electric (CBE) Baja Kill Switch 
-
MHZ (image courtesy MHZ USA)
-
EKG (Engine Kill Guard) - Warehouse Hobbies Inc.
-
KillerRC.com  Killer Bee Range (replaces the Pb2themax Pico range - see options below)
- 
 
*NOTE

It's important to know the concepts of "normally open" and "normally closed". 

NC - normally closed switch will conduct electricity until it is pressed. (contacts are together at rest making an electrical circuit)

NO - normally open switch won't conduct electricity until it is pressed down - (contacts are separated at rest with no electrical connection)

Normally open contacts would represent relay contacts that would perform a connection upon receipt of a signal. Unlike open contacts, with normally closed contacts a signal will interrupt a contact, or turn a relay off.

Further Reading  - Failsafe Design
A Note on the modification of Picos

Pico - The relay is normally open when unpowered (at rest). The Picoswitch has a status LED on the bottom. The LED will light up when the relay switch is on (active), and vice versa, subject whether it has been modified. 
It will also tell you if your radio link is too weak by flashing repeatedly.

A modified Pico can be altered to having a status of normally closed (NC).

A standard Pico, which is effectively an electronic switch, can be modified to function as an engine kill switch / failsafe device.
An unmodified Pico can adequately serves as a manual kill switch, but will not be capable of shutting down the motor in case of power or signal loss.

The modified Pico is a failsafe and an engine switch in one - the extent of modification and radio set up is what will determine how it will function.

The BattleSwitch is the larger version (10A) of the popular 1A Picoswitch by Dimension Engineering. It also has options for both NC ond NO connections. In theory, that switch can perform two functions at the same time. Eg when "on", the engine can run, and you can also have lights. Turn it "off", and the engine and lights turn off.

CBE kill switch is basically similar hardware to the Pico. The NO status is the same as that of an unmodified Pico, though the operating program has been changed to enable failsafe tasks.

The Diemaster Pico involves the removal of the relay from the u/s of the printed circuit board (PCB) in order to remove one of the pin terminals to the relay. A jumper wire is then soldered to the u/s of the (PCB), prior to the relay being re-soldered back to the original position. The result is that the NO status is changed to NC. It is then protected with clear heat shrink wrap. More details and photos on the process here.

Similarly, in the former Pb2themax Pico the status was again changed from NO to NC, however the voltage route differed slightly from the DM Pico, and involved two areas of soldering to the top side of the PCB and no relay removal.
An open circuit was created by cutting the copper trace on the upper face of the (PCB), a similar result to the Diemaster mod of cutting the terminal pin on the connecting face of the relay.

A jumper wire was soldered to go from the NO (Normally open) relay terminal to the position where the screw-down terminal was soldered to the board underneath. It was then checked with a Fluke meter, prior to an engine kill test. It was then protected with clear heat shrink wrap prior to distribution.

The former range of the PB Kill Switches came in a number of wiring options. The range has now been replaced with a completely new design known as the Killer Bee from Killer RC and also comes in a number of wiring options as shown below.

Images & Text below courtesy of Killer RC

The Killer Bee Kit 1 contains just the Killer Bee kill switch. You must provide the wiring necessary to connect it to the engine’s ignition coil.

The Killer Bee is the heart of all kits #1 through #5



The Killer Bee Kit 2 allows you to eliminate the stock kill switch. This kit connects the Killer Bee in your battery box directly to the ignition coil on your engine. The wires are securely soldered to the connectors and then heat-shrinked. To kill the engine you just flip off the 3rd channel switch on your transmitter, or turn off your transmitter. This kit includes the Killer Bee, 20” wiring & zip ties. 

The Killer Bee Kit 3 comes with wiring that is soldered to the connectors of the CY push button kill switch, and it's heat-shrinked and zip tied. This kit is compatible with Zenoah and Chung Yang engines. This kit includes the Killer Bee, heat resistant wiring with new CY kill switch & zip ties.

In Killer Bee Kit 4 comes with pre-soldered wiring and new CY push button kill switch, remote status LED with 7” wiring for mounting LED in the battery box lid. To mount LED, simply drill a 1/4” hole in the lid, insert the clear LED cover in the hole, and fit the LED into the lens, and add some glue around the base of the LED. The LED will glow on/off and flash, showing the status of the Killer Bee kill switch.

 An optional buzzer (as shown in kit 5 below) can be ordered in place of the LED if desired.




The Killer Bee Kit 5 comes with pre-soldered wiring and new CY push button kill switch, alarm buzzer, remote status LED with 7” wiring for mounting LED in the battery box lid. To mount LED, simply drill a 1/4” hole in the lid, insert the clear LED cover in the hole, and fit the LED into the lens, and add some glue around the base of the LED. The LED will glow on/off and flash, showing the status of the Killer Bee kill switch. Alarm buzzer will sound when engine is killed, reminding you to flip your 3rd channel switch before trying to start the engine. The alarm buzzer will also sound if you have turned off your transmitter power but left the receiver power on, reminding you to turn off your receiver power and prevent fail safe mode from damaging your servo’s.

DISCONTINUED -The Super Pico Kill Switch Kit 6, does two jobs at once. It will power 6v LEDs and also kill the engine, all without the need for Y-splitters and stuff that clutters up your battery box. When the lights are on the engine can run. When you kill the engine the lights will shut off. With the Super Pico, your headlights will work like a status indicator for the kill switch, letting you know if the engine can be started or not.







Super Pico Kill Switch Kit 6 - shown connected to 4 LED lights

DISCONTINUED - The Kill Switch Kit 7 is a Digital Light Controller & Kill Switch built into one unit. This kit is all you need to put on an impressive light show with the LED lights on your RC vehicle. Use your home computer to create a custom light sequence that you design, and then upload it to the light controller. Lighting sequences can be saved, deleted, changed, and even emailed to other light controller users.

The Digital Controller also has a built-in engine kill switch. It will shut down your engine in case of radio signal loss, or you can kill the engine via the transmitter any time you want. To control the light controller from your transmitter all you need is a 3 channel radio that has variable trim control on the 3rd channel. Click HERE for more info on the Digital Light Controller & Kill Switch kit.

Killer RC have teamed up with Dimension Engineering to bring you this light controller which is based on their smaller DELight Controller. The Digital Light Controller uses the same proven software that comes with the DELight. A major difference is that the PB’s light controller has beefier components to handle more current, and it also has a built-in kill switch. The DELights controller was designed mainly for RC airplane use, but the Digital Light Controller is designed for RC car use, but they both use the same software.

 ~For Light Controller manuals, tutorials, and software, check out the Killer RC Downloads page~


The Killer Bee 2 is designed for those running 2 channel systems. The beauty of this switch is that it can share a channel with either the steering or throttle servo. It can be placed on any channel that does not have a failsafe set up activated on it. With the aid of a 3 wire Y-splitter cable, the kill switch can be connected to the chosen channel.
The kill switch can be activated manually by simply turning off the transmitter.

This switch can also be used as part of a 3 or 4 channel system. In this instance a 3 wire Y-splitter cable can be used to connect the switch and lights (via a light controller) to the spare or auxiliary channel.

 
Understandably, as the market is realised, more and more killswitch options (including modified Picos) will become available through local hobby shops and various on-line sources. Though the choice will inevitably increase, the fundamental principles outlined above will  remain similar.
Rev 6 - 24 March 2010  

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