The Turnigy 9x doesn't have a failsafe function when used with the 2.4ghz receiver. Instead, when the radio signal is lost, the receiver "freezes" all channel signals to the last received value.
Add a heartbeat function.
Pick a channel, alternate between high and low PWM signals over some period. As a concrete example, on channel 7 transmit a 1200 ms followed by an 1800 mhz signal, each for 1000 ms.
We can upgrade the Turnigy 9x to use er9x and add the code there.
In the arduino software, we can add a check in the 1 hz event loop. Compare the current values with the previous values, and save the current values for the next check. If after some number of comparisons we don't detect a change in any values, invoke the failsafe routine.
- Is the timing fine-grained enough? If not, we can increase the frequency of the checking rate.
- Open source is wonderful.
Update: some discussion of this idea over at the 9x forums.