Throttle Jumps from Min to Max with TX16S - No Gradual Control

[anshul]

Hi all,

I’m running into a frustrating throttle issue with my drone setup on ArduPilot.

When I move the throttle stick on my TX16S, the motors either stay at minimum or jump straight to maximum (100%) with no gradual control in between. It’s acting like a binary switch-either off or full throttle-with no smooth response.

My Setup:

• Radio: TX16S with EdgeTX and ExpressLRS (ELRS) module
• Receiver: RadioMaster RP1 2.4GHz ELRS Nano Receiver V2
• Flight Controller: Pixhawk 4
• Software: ArduPilot , QGroundControl.

The Problem:

• Throttle input doesn’t scale smoothly. It’s either at minimum or jumps abruptly to 100%.

Steps I’ve Already Tried:

1. RC Calibration:

• Disarmed the drone and recalibrated the radio in QGroundControl.
• The Radio tab shows Channel 3 (throttle) moving smoothly from ~1000
  us to ~2000 us as I move the stick.

2. Throttle Channel Mapping:

• Checked the TX16S Mixer menu—throttle is correctly mapped to Channel 3.
• The output increases properly in the radio’s channel monitor as I raise the stick.

3. Transmitter Endpoints:

• Adjusted endpoints in the TX16S to ensure a full range of 1000 us (min) to 2000 us (max).
• Confirmed this range is reaching the receiver correctly.

Despite these steps, the issue remains unchanged. The drone’s motors still jump from idle to full power with no intermediate control.

Additional Details:

• I’ve temporarily disabled arming checks to get past sensor errors, but l’d like to fix the root cause.
• Motors and ESCs seem to work fine individually (tested via motor test in QGroundControl).

Also the motors start spinning from -19, and at +20 it reaches max, nothing in between.

logs
[15:03:07.025] Critical: EKF3 lane switch 0
[15:03:07.037] Warning: EKF primary changed:0
[15:03:18.621] Critical: EKF3 lane switch 1
[15:03:18.621] Warning: EKF primary changed:1
[15:03:31.623] Critical: EKF3 lane switch 0
[15:03:31.624] Warning: EKF primary changed:0
[15:03:44.626] Critical: EKF3 lane switch 1
[15:03:44.627] Warning: EKF primary changed:1
[15:03:46.087] Critical: Vibration compensation ON

sometimes i also get
[15:04:34.520] EMERGENCY: Potential Thrust Loss (4)
but when i check motor 4 manually in motors setup, it seems to work fine.

Any suggestions for further troubleshooting or fixes would be hugely appreciated. Thanks in advance for your help!

[amilcarlucas]

This is with props or without props?

Is the drone on the bench? Or is it flying free?

Which flight mode?

[anshul]

it’s laying on table without props.

[amilcarlucas]

Then that is normal and expected behavior.

This is a closed loop control system and you are testing it in an open loop configuration. It’s expected that it behaves like that.

There are about six similar posts with this question per month on this forum. You can look it up if you want confirmation or more information.

The correct way to test the motors is to use the “motor test” function in mission planner.

[anshul]

thanks brother, and for other details you asked

flight mode - i am using SA switch, and it has 3 modes i think - defualt, alt hold, stabalize,

default - same problem
althold - same problem

so should i directly fly?, I am scared .

[amilcarlucas]

If the “motor tests” in Mission planner work correctly and the motor order and directions are correct, yes you should fly.

If you are unsure if you did all the steps correctly and want a step-by-step guide and checklist, see this presentation you will learn something.

[xfacta (Shawn)]

“default” doesnt make sense, there’s no such mode.

Stabilise should give some level of control, but as amilcarlucas said, that is expected behaviour since the copter thinks you are telling it to take off, and so it is trying to.