A Bulletproof Failsafe, Switchable Power Supply, and Cutoff Switch for $10

A Bulletproof Failsafe, Switchable Power Supply, and Cutoff Switch for $10

 

After getting my plane stuck in a tree three times now thanks to Google Maps elevation errors, I wanted a way to shut down my aircraft remotely. My latest mishap resulted in my plane being held hostage overnight and over-discharging a perfectly good battery. The relay control with APM is no longer supported, but with the help of Chris Anderson I found a cheap solution.

To complete this project, you will need two relays, and a RC Switch. Instructions for wiring the RC Switch can be found here.

I am no electrical engineer, so please forgive my scratchings (see drawing below). This is the diagram for the power cutoff switch:



The basic principle for a cutoff switch is this:

1. A 5V power supply runs through the USB port to power the APM.

2. The main battery is connected to the normally open NO side of relay.

3. Control and power for the RC Switch comes from the APM analog rail, in my case, servo A10.

3. The coil of the relay is controlled by the LOAD circuit of the RC Switch. When the RC Switch energizes the coil by a command from the APM by moving the servo to the HIGH position, power from the main battery is sent to the ESC, BEC, and power module.

4. Disconnect the 5V power. When you get your plane stuck in a tree, you can disconnect the main battery with a servo command from your ground control station, by setting A10 to the LOW position.

Here it is in real life:



What is really cool about this is that you could operate the RC Switch directly from the receiver for a failsafe. In the case of a fly-away a Spektrum receiver goes into failsafe mode (assuming you set it up) and the PWM to the RC Switch could be set to the OFF position in failsafe mode, cutting all power to the aircraft. In this case it would be beneficial to keep your 5V power supply attached to the APM to power your telemetry. If you wanted to be super cool, you could wire a third relay or controller to a chute that deployed when the failsafe activates!



A switchable power supply would only have a small variation, with no 5V power supply for booting up the APM. A second battery would be used instead. I have not tested this, but I remember another user stating a need for it earlier this year. See below:



Every time I have been stuck in a tree, it has been because of a map error, not a map reading error. Batteries are expensive, and this simple, $10 device can save you a whole lot more in batteries. It could also save your craft from an expensive or dangerous flyaway. I hope this helps somebody out. 

FONTE:A Bulletproof Failsafe, Switchable Power Supply, and Cutoff Switch for $10 - DIY Drones