Arducopter 3DR build documentation problems

I finished building the 3DR quadcopter about a week ago and encountered several issues in the assembly documentation, so I figured I would post my issues and recommendations here with the hope that they could be incorporated into the official documentation.

The main problem regarded the connection of the motors/ESCs. Based on tracing the signals through, testing, and finally flying, I claim that the instructions are flat out wrong and the copter will not fly based on the documentation. Phasing is always an issue in control systems and the arducopter is no exception. This is an area where extreme care should be taken during the initial assembly, and then extensive testing should be performed to verify the assembly. The ground testing worked very well to verify the system, but the assembly documentation basically didn't address this at all.

When all was said and done, channels 1 and 2 were swapped compared to the documentation, so the PWM channels have to cross the PDB This seems to be due to the direction the PDB is installed (down vs. up).

Rather than trying to explain exactly where the issues were, I would suggest the following:

  • Add silk screen markings for each channel (1-4) to the PDB where the 4-wire harness is connected and where each channel goes to the ESCs
  • After the user installs the PDB onto the baseplate, have them write on the baseplate which channel is which. If they don't do this, it's not obvious which channel each ESC should be connected to.
  • When connecting the arms, have the user mark which channel each arm represents. This way, it is easy to connect motor 3 to channel 3 on the PDB.
  • Add a note that says the ESC PWM cables should be installed with the black/ground wires towards the center of the frame. It is not possible to see which direction they should go once the PDB is installed inside the frame.
  • Add a note to ensure correct polarity of the 4 wire harness from the PDB to the APM. After it is properly connected, put some white-out across the connectors to help with plugging it in in the future.
  • Ensure that the polarity is properly described and maintained for the 2 wire harness for the PDB. Also use red/black for the wires to simplify connections
  • Provide mounting holes in the 3DR plate that actually line up with the APM. The diagram in the instructions is incorrect. It is not possible to mount using all 3 APM holes in the "+" orientation.
  • Provide better documentation regarding ESD safety. I'm surprised that more boards have not been fried due to non-chalance regarding ESD.
  • ESCs shouldn't be zip-tied until all of the ground testing is complete, since signals may have to be swapped.
  • Pitch direction of the transmitter is swapped in the ArdupilotMegaPlanner software. There is no documentation that says the GUI should move opposite the stick movement, but that's what I read in the forums and that's what I had to do to get it working.
  • The testing that involves listening to the motor speeds with the props off is very difficult, since its tricky to hear small changes in motor speeds when they are all running. I wound up bailing on that test and moved on to the equivalent tests with the props and and was immediately able to verify the directions of all the axes.

 

Pat Brown

 

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Replies

  • Thanks for the suggestions, Pat. We've already put several of them in place. The reversing error in the documentation has been fixed. Also, check out this picture of the new PDB - some of the silk is hidden by wires but you can see it's got more descriptive writing. Hopefully it will be easier for users to assemble in the future and I apologize that it was so rough around the edges when you got yours.

    DSC06025.JPG

  • I agree with everything you pu there (I just finished my 3dr; and my biggest issue was with where to connect the ESCs to the PDB). I thought it was correct especially since I ran the motors command on the CLI a bunch of times and every time it ran fine but when I tried doing a hand test with around 1/3 throttle the roll axis was reacting well but pitch wasn't. It was only after swapping the motor servo cables around was I able to get a good hover. I will check what the motors command does now but for a while I thought that it would confirm the signals are connected to the right motors but that isn't the case necessarily. I obviously had also checked the sensors using APM planner and it confirmed my sensor orientation was ok the whole time. Also, I agree that the documentation can do a better job of stating how transmitter commands should match to copter reaction. In other words, not just saying increasing pitch should tilt copter on pitch axis but rather that pushing pitch stick upwards should make copter nose go up or down (not sure which it is yet since I have only done a hover test and my controls could still be reversed).
  • Moderator

    Just read about the channel swapping... thanks for pointing that out. I also faced the same issue. I also think that has to be corrected. 

    Japi

This reply was deleted.

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