# Tiny Wireless Remote Kill Switch

I attached a tiny electric motor and battery to a small balsa wood glider. I'd like to add a tiny remote kill switch, with a range roughly around 20-40 meters. A switch that requires line-of-sight would be fine. Reliability is not vital (75% reliable would be fine).

I don't want full RC control, just a simple kill switch to shut off the motor remotely.

It needs to be tiny and lightweight and will run off a 3v or 5v battery. Preferably cheap as well, since my whole project has cost about $3 so far. What wireless technology should I be looking for? Bluetooth? Infrared? 2.4 GHz? Something else? • In practice, IR will not work outside, it relies on ceiling reflection. If building something from scratch, using a BLE IC in a non-BLE 2.4 GHz mode (ie, nRF24 compatibility) could be very compact. But if trying to buy something, just gutting a tiny quadrotor drone for the board is likely going to be your best bet at around 2 grams. There are alternate firmwares out there for those based on STM32, GigaDevice and Nuvoton parts, or your could do something like parallel all the motor drivers to largely defeat the control algorithm. Jun 13 '18 at 14:45 ## 2 Answers In practice, IR will not work well for a remote-controller aircraft outside, it relies on ceiling reflection to be usable indoors. If building something from scratch, using a BLE Radio/MCU IC like an nRF51822 in a non-BLE 2.4 GHz mode (ie, nRF24 compatibility) could be very compact. Or use it in BLE mode and use your phone. Note there already is a product for powering/controlling "paper airplanes" that is BLE based. Especially if you use BLE you should make the system cut off the motor on loss of "connection" - and having it cut off after a second or two with no packet getting through at all (losing many packets is normal) would not be a bad idea for any radio mode anyway. If trying to buy something, just gutting a tiny quadrotor drone for the board is likely going to be your best bet at around 2 grams and perhaps$12 including the transmitter and four little motors. Be very careful not to short out or mishandle the lithium battery. There are alternate firmwares out there for those based on STM32, GigaDevice and Nuvoton MCUs with separate radios, or your could do something like parallel all the motor drivers to largely defeat the control algorithm. Though you might still get some surging if it thinks it's tumbling. A little add-on circuitry could probably interpret any PWM motor pulses from the board at all as a command for full power, and their lack off - but reprogramming the MCU is most flexible and not particularly hard if familiar with MCU programming in general and prepared to solder at the scale of ultralight model aircraft (the SWD pins are essentially always broken out, and sometimes even on a labelled connector footprint).

Actually IR reflections are not needed but help when emitter is poorly aimed .

With multiple remote 16kHz detectors( or one well aimed) and LDO a more powerful emitter array (>1A pulses vs 100mA). Ought to reach 50m with <=10deg emitters.

I can get 10m easily with one Emitter at 100mA 16kHz pulses into Sun-filtered Vishay/Sharp IR AGC/BPF TV remote detector. Optical gain improves with narrower beam angle but makes emitter aiming more important which should be easy with aim guide on line of site if aft direction is used on Rx.

This will achieve your weight size cost goals for Rx. But don’t be so cheap on package, battery and number of 25 cent emitters (lol) unless you recycle useless remote controllers with Mods to drive say 10 LEDs or much more.

• Build it, take it outside and try to fly it, and you'll find IR is not what you want. Also, while definitely possible, it's a non-trivial exercise to wire up a detector, tiny SMT MCU to interpret it, and FET to run the motor, and come out with less mass than an off-the-shelf micro quadcopter's readily reprogrammable board. Jun 13 '18 at 15:02
• I was including added weight of battery to power RF Rx. You may be right on if budget is OK and battery weight is acceptable. Jun 13 '18 at 16:02
• The battery usage to power the RF RX is minor compared to powering the motor the poster wants to propel the aircraft with, and which the purpose of the receiver is to switch off. And the cost of the tiny drone does include a small battery of approximately the right capacity and its charger... And they typically feature a low battery cut-off - almost always for the motor, in some for the MCU and radio also in case the main switch gets left on after use. Jun 13 '18 at 16:12
• I agree , why reinvent the wheel! Jun 13 '18 at 16:33