Reverse throttle channel and motor interlock

I am running pixhawk 2.1 on a nitro helicopter with a fbl unit downstream. I need to reverse the throttle channel because of the operational direction of my throttle servo. Reversing it either in the tx or through rc8 gives me the motor interlock error and I can not arm. Reversing it through servo8 does not do anything. Unfortunately my fbl unit does not have a reverse option for the throttle. Is there either another way to reverse it I am not seeing or a way to bypass the motor interlock?

What version of arducopter are you using?


Whatever the most recent is, just installed it a few days ago. I apologize I am not at home to look but I believe it is 3.5

So I am assuming that it is probably 3.5.4. So in that version, the min, max and reverse features are handled by these parameter
in this case to reverse the servo you would set H_RSC_PWM_REV to -1

The next release 3.5.5 will have min max and reverse handled by the servo8 parameters.

Great! Thank you! I will give that a shot tonight. Would I be correct to assume I can also use those min and max parameters there to adjust the throw to match my carb instead of in the transmitter?

So I wasn’t following your other thread regarding your set up. It depends what RSC mode you are using. If you are using mode 2 or 3 then yes, you would set up your servo travel using the h_rsc_pwm parameters. I think if you were using mode 1 which is a passthrough then I would set my Transmitter and these h_rsc_pwm min and max parameters the same. It is not truly a straight pwm passthrough. You want to still do your reversing through the h_rsc_pwm_rev parameter.

Perfect, thanks BIll! I am using mode 1 so I can still fly the heli 3d in acro if I’d like to. The reversing I think is that largest concern. Once I set the min and max whether it be in the tx or in these settings it will still see it as full end to end throw as long as I calibrate after correct? Otherwise it would see the shorter end and think throttle is increased.

So here is what it does for passthrough. It sees the range of the transmittter throw (channel 8) as 0 to 1 and it calculates the what the current pwm is as a fraction between 0 and 1. It then uses the pwm_min and pwm_max as 0 and 1 for the servo. It calcates the actual pwm out to the servo based in the fraction and pwm min and max. Hopefully that makes sense. So calibration will only set the RCIN min and max based on the stick throw. So I think this is somewhat arbitrary. What really matters for servo throw is the pwm_min and pwm_max parameters.