TRex - no fail safe

I have the TREX controller set up for RC mode using the original sketch and a Quantum i8 RC controller. No other modifications to the program have been made and the receiver is plugged in to the correct pins on the board. The robot moves fine but the problem is that whenever the power to the transmitter is turned off, the motors turn back on (forward) after a brief pause. If I turn the transmitter back on, the motors go back to a standby state until the joysticks are moved again. I looked through the sketch and experimented with the RCdeadband time( in line 43 of the main TREX_controller tab) to no avail. I read in the notes in lines 82 and 83( that mentioned a weak pull up resistor on the inputs to prevent false triggering). Does this mean I may have to install resistors between the receiver line outs and the TREX? Thanks!


I am not sure what you mean by “the original sketch”, but it sounds like you are using someone else’s software to configure your TReX. Can you clarify what program you are using?

It sounds like your RC receiver is defaulting to outputting some non-neutral signal when it loses its connection with the transmitter, and the TReX has no way of knowing that these particular signals should be ignored since they look the same as valid signals. If you have access to a USB-to-serial adapter, you could connect the TReX to a computer and use our configurator software to see what the RC signals are doing when the transmitter is turned off. Alternatively, it should be easy for you to verify that this is an issue with your receiver just by unplugging the receiver wires and noticing it is a very different effect from the one you are describing.

Have you checked to see if there is a way to configure your RC receiver to change this behavior?


Thanks Grant. Ok, I unplugged the receiver while the Trex was powered on (and the transmitter) --the motors held their position as I needed them to be. So as you said, the receiver is sending a signal back to the Trex after power is lost. I did some research on the Quanum i8 (transmitter/receiver I am using) and found out that when power is lost, it sends a signal for the servo (as they would expect most people to use this system for–not a TRex board) to return to its home position. (I’m guessing 1500pulses which is standard). There does not appear to have any way to reprogram the receiver.

The sketch I am sending is the original one from its creator, Russel (aka Oddbot) from Dagu. I am including a link here to Sparkfun’s site which has a copy of the code to download.

The arduino IDE will open it normally. Take a look particularly at the RC section(tab) of the program as well as the main Trex controller section I am hoping that something can just be tweaked in the sketch to prevent the Trex from acting on the fail safe signal being sent from the receiver. Your help is much apprecitated Grant, thank you!

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