ArduIMU Quadcopter part II (mini)

Hi all,
I have finished my second quadcopter with ArduIMU. This time is a "mini" version with only 28cm from rotor to rotor and has the new Jordi´s magnetometer integrated!.
This tiny machine is fantastic, with a great stability. Look at the hands-off part of the video inside house!!
Very funny :-) Video:

Motors: 1811 2000Kv 10grams brushless motors
Props: standard 5x3
ESCs : Turnigy 6A
Batt : 2S610 Lipo
Weight (RTF) : 180grams
Again it´s a very cheap and easy setup. Because I use standard propellers I mounted left and right motors with some twist. I´d really love arduIMU flat hardware...

Look at the PPM output Rx, Is this a new 2.4Ghz receiver form DIYDrones?
No, it´s a "lighweight" (4.1grams) mix between Spektrum AR6110 Rx and Jordi´s PPM encoder. This is nice for DIY projects...

The code is improved from the old version. This one has the magnetometer integrated so now we don´t have drift
on yaw axis, better implementation for the D term on the PID controler (more responsive to user inputs), same safety improvements, fast ESCs update rate (166Hz), new PID tunning...

But this history had an interesting lesson for me... The prototype you see here are really the second one, the first one was a dissaster... (flys bad...)
Do you want to know the "small" difference between them? This:

For the first one, I use an U shaped aluminium arms to save some weight. Well this shape is very bad in torsion and generates a lot of vibrations. This vibrations saturate the gyros (our gyros are quite sensible on vibrations because the low internal resonant frecuency). You could see here a graph of the gyro output value vs Throttle and you can see clearly the effect...

I change the arms to the square shape (8x8mm) and problem gone!! Perfect stability... :-) Vibrations are our enemy (Lesson learned)

Here is the new source code: (see notes.txt inside)
Schematic (conections): Photo1 Photo2
Old post (first version) here

New ArduPilot Mega will be a perfect platform for Quad´s also, so stay tuned...


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  • What is the GPS used for in the standard ArduIMU code(is it required)? and Does the IMU serial output sentences of degrees of attitude(-180 to 180) if not so what?

    Also I've looked at the schematics and board diagram but unfortunately I couldn't figure whether the UART output is the same as the FTDI output? what is currently used for centripetal correction GPS or airspeed sensor?
    But anyways, in the future with ArduIMU+pilot will GPS be connected to IMU then to pilot OR GPS to pilot(in other words is GPS or airspeed sensor used for centripetal correction in the DCM?)
  • Developer
    Andrew, because Spektrum doesn't use traditional PPM signal. All is done with special encoding for digital radios.
  • Very impressive. Congratulations.
  • Nice job..!
  • Ohh, thank you! but why wouldn't you just take the ppm from the receiver directly by tapping into the crystal or something?

    What is the GPS used for in the standard ArduIMU code(is it required)? and Does the IMU serial output sentences of degrees of attitude(-180 to 180) if not so what?
  • Developer
    The receiver does not output PPM. PPM is an internal signal within most receivers. Jose has hacked the receiver to bring it out. This is/was a common technique in the Paparazzi community. If weight is not critical and you don't feel like hacking in to your receiver there is a board that will take the PWM servo outputs and reconstruct the PPM signal.
  • Question: If servos read PWM output then why does this receiver output PPM? I've always thought that receivers output PWM for servos and ESCs.
  • Admin
    Thanks Jose, for details and closeups
  • Developer
    Hi all,
    There are several people asking me for documentation about the construction process of the quadcopter.
    Well, I am very bad making documentation, most of the times I am developing a project and thinking on the next one... This is why I take a lot of photos so people could see by the details...
    Here is a new photo during the construction process. It is really simple (it took me less than 2 hours to construct the frame) Photo

    And some more details :
    I used 8x8x1mm square aluminium tube. I cut one piece of 30cm and two of 14.6cm. Then I use two 7x7cm x 1.2mm plywood with blue vinyl for the uper and lower plates. Distance from motor to motor is 28cm.
    In order to get the correct twist on the right and left motors I used an small piece of 0.6mm plywood.

    There are also some good threads on RCgroups about quadcopter construction...

  • Developer
    Dave, Morli, here are some details about the AR6110 and PPM encoding mix.

    First I remove some pins on the AR6110 (this is really optional, to save weight...) I remove most GND and 5V pins (only left one) and also I left the pins for the bind plug. To remove the pins it´s easy if you remove first the small black plastics that join the 3 pins of each channel.
    So you need one GND, one +5V and all the signal pins from the AR6110. In order to solder to the PPM board you need to bend slightly to fit (there are different spacing between channels on AR6110 and PPM encoder).

    Here are some high resolution photos, so I think you could see this better. Photo1 Photo2

    Hope this help

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