Huge quadcopter shaked heavily and then crashed immediately after taking off

ArduCopter Copter 4.5
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1

Hello, experts.

We have a huge copter:

  • 4-Axis
  • 56 inch screw
  • 18s LiHV battery
  • 80A ESC with PWM signal
  • 45KV motor
  • CUAV X7 Autopilot with ArduCopter 4.5.7
  • CUAV NEO V2 Pro GPS

We have some experience assembling small copters (smaller than 15inch and 6s), but we got a big trouble with this huge copter.

We set everything and every parameters well, then takeoff. But the vehicle start to shake heavily and crashed just seconds later. We cannot control it at all but force disarming it from the ground station.

We tried to change the sensitivity, from 0.05 to 0.4, but nothing get better. We also level the motors again and again but that did not help.

Here are two samples of our flights. Please note, the two flights are in the same file (we did not power off the vehicle between the two flights), so there is a time gap.

or download here:

The videos are as below:

We suspect that the ESC is responding too slowly, or that the ESC’s PWM signal wire is being interfered with.

Please help, thank you. Also, sorry for my poor English.

2

You should be testing initial flight in Stabilize not Loiter. And set these properly for 18S:
MOT_BAT_VOLT_MAX
MOT_BAT_VOLT_MIN

And you will probably have to raise the Pitch/Roll Rate D-term. Double it and see what happens.

Or better yet take @amilcarlucas advice!

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3

Use ArduPilot methodic configurator to fix the issues and configure it in a safe sequence of steps.

The software will let you do the changes @dkemxr said.

But only in the step that they make sense.

On such a big expensive and dangerous vehicle it’s irresponsible to not use that software.
You are very lucky that it did not cause more damage

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