APM-2.8 Controller Servo Output lags RC Input

Hardware UnSupported hardware
1

Mission Planner Version 1.3.72
ArduCopter Version: v.3.2.1
Flight Controller: APM-2.8
Default Mode: Stabilize

Hello Team, Need help in figuring out the problem with APM-2.8 controller. Though I know it has been discontinued long time back.

Any pointers would help.

Problem statement: Huge discrepancy in RC Throttle Input and Servo Output. Due to the lag between these two flight is next to impossible.

That is, when quad is hovering even when throttle(step-1) is reduced the copter is still gaining height. after a while(around 5 seconds lag) reduction in throttle done earlier (ref: step-1). leads to copter loosing altitude. At this time throttle is re-applied (step-2) but it doesn’t immediately result in servo’s output to increase and there by increasing the thrust eventually resulting in drone crash landing. Even after crash-landing it take significant time to disarm(step-3) the copter(because the increase in throttle in step 2 is still in play) and subsequently dis-arming kicks in.

Please note the drone is properly calibrated for RC, Accelerometer, Magnetometer via Mission Planner. All The 4 ESCs are calibrated directly using RC receiver. All ESCs are working properly as the increase/decrease in throttle immediately results in corresponding increase/decrease in RPM of motors. So ESC issue is ruled out.

From the log plot it is clear that RC-Throttle Input and Servor-Outpot(1-4) are not in sync and is an issue in APM-2.8 controller. Have attached a sample zipped Log file and a plot of the discrepancy in Throttle Input V/s One-of-the-servo-outputs

Lag observed in Servo Output w_r_t RC Channel Throttle Input
Lag observed in Servo Output w_r_t RC Channel Throttle Input1920×1080 393 KB

2024-11-10 20-20-37.zip (716.8 KB)

2

There is no expected direct correlation between input and output in multirotor control loop. You are testing a closed loop controller in an open loop configuration, this doesn’t work.

I would strongly recommend getting a supported flight controller, it will make working with documentation much easier and pool of people able to help much larger.

3

Thanks for your response. I am with you as far support for APM-2.x is concerned. From technical standpoint of view are you requesting logs with Props on and the quad to fly so that it becomes closed loop. Is there a possibility that the board has some issues. What more logs can I share?

4

Do tests in while flying stabalize mode (all other test are useless)
And reduce vibrations by stiffening the frame and balancing the props, they cause strange altitude issues.

5

A Tlog is of no value for this purpose.