Trouble getting Tricopter build to takeoff

ArduCopter Copter 3.6
1

I am having trouble getting my new tricopter to take off. When I throttle up for takeoff, the tricopter pitches back to such an extent that I need to move my pitch control stick all the way forward to stop it from flipping back. :sob:

I am using a Pixhawk 4 Mini running the stable PixhawkMini version of Copter from here: PH4-mini

I have completed the initial setup and calibration steps in mission planner with no errors.

Here is a screenshot of the horizon from Mission Planner.

10%20pm

As you can see, it is reading (mostly) level.

How would I go about debugging this?

Let me know if you need any more info about my setup.

Cheers.

2

I do not understand what you mean by (mostly) level.

You want the props and the controller to be perfectly level AND plumb. You are going to need a carpenters bubble level for this

To get an accurate level measure, start with a thick flat piece of plywood or fiberboard.

  1. Place the plywood on the ground and level it using a carpenters bubble level (both axis)
  2. With props and spinners off, place your copter UPSIDE DOWN on the plywood so that the motor shafts are resting on the plywood
  3. Using the carpenters level, span arm to arm of your copter and check for level. Rotate the copter 120 degrees and repeat 2 more times.

Plumb check:

  1. With your copter still upside down, mark the location where each motor shaft touches the plywood with a sharpie.
  2. Rotate the copter 120 degrees.
  3. Verify that motor shafts are still over the marks.
  4. Rotate the copter 120 degrees and verify marks again.

Having established your frame is now level.and motors are plumb,
Flip the copter back over into normal resting position to establish right side up leveling

  1. Place the carpenters bubble level across 2 motor shafts . check for level
  2. Repeat 2 more times with the other 2 shafts.
  3. adjust so that all 3 shafts are now level with one another

Finally, place the carpenters level on top of your controller. Verify level in both axis

Now that you are sure everything is level AND plumb, Go into Mission Planner Optional hardware -> Motor test

Follow the documentation to determine motor order and the percent threshold to get motors spinning. Make sure all 3 motors start at the lowest percentage possible and that they are the correct motor!. If one fails to start, pre-spin it just before you run the test. If it spins up, then you have a mechanical issue. It may be simply fixed by running the problem motor for a while. If after warm up it starts by itself at lowest percentage then you should be all set.

If you perform all steps above and you still have an issue, then you will have to start looking at the logs.

Good luck.

3

Hi, thanks for your reply.

By ā€œmostly levelā€, I mean the pitch (the axis I am having trouble with) is reading level in the horizon from Mission Planner. (screen shot).

Thanks for those detailed steps(esp the Plumb check), ill work my way through them soon.

Cheers

4

hey @danacan211, Iā€™ve finally found the time to level and plumb the drone. Still no luck.

Can you please explain what you mean by ā€œstart looking at the logsā€?

Here is a video of what the drone is doing: https://photos.app.goo.gl/N2tzqjQmgSfRKiRP7

5

Also, is this something I need to be worried about and debug ?

https://photos.app.goo.gl/3nMh7E54tUvu88Yq8

6

Are you giving it pitch command attempting to counter that or does it do that with the pitch stick centered? Itā€™s common that pitch needs to be reversed in the Transmitter. Did you do a radio calibration with the radio trims centered? Post a dataflash log of one of those takeoff attempts.
http://ardupilot.org/copter/docs/common-downloading-and-analyzing-data-logs-in-mission-planner.html

7

At :02 I see this:

image

Did you do the Mission Planner Optional hardware -> Motor test ??

You have either an ESC calibration issue or mechanical issue with the aft motor

8

It does that with the Pitch Stick on the transmitter centered.

I have reversed the pitch on my transmitter so that moving the pitch stick forward moves the pitch bar in Mission Planner radio calibration back.

I have done the calibration with the radio trims centered.

Attaching the log file. I can see moto 4(the tail motor) rev up, but it doesnā€™t seem to level the drone. :sob:

40 1-01-1980 11-00-00 AM.bin (167.9 KB)

9

Yup, I did the motor test.

10

After you arm with the stick, all 3 motors should be spinning with the throttle at idle. Your video did not show this. The Motor RPM must be the exact same for all 3 motors at idle.

To isolate the issue, take the props off and put all 3 escs on a servo splitter wire that is plugged directly into your receiver throttle servo

image
image.png415Ɨ662 3.35 KB

When you raise the throttle, all 3 blades should be turning at the exact same RPM. If not, you have an ESC or mechanical issue

11

You are not seeing Motor 4 rev up in the log (RCOU C4) you are seeing it being commanded, big difference, and based on your video itā€™s not responding. I would suspect the ESC or motor. Swap it with one of the others and see if the problem follows the motor/ESC. What motors and ESCā€™s are you using?

12

Sunsky 980KV motors and Hobywing 30A ESCs.

I swapped out the motor the other day, same issue. Like you guys are saying, the ESC is probably bad :sob:

Gona be a pain to swap it outā€¦ :anguished:

Thank you @danacan211 and @dkemxr for looking into this.