World's Smallest Brushless Octocopter?

This is my latest build, the worlds smallest brushless octo-copter (as far as I can tell) running Arducopter (of course) on the kakute f7 AIO.

Build is very simple, custom frame laser cut out of ply. Eight E-Max RS 1106 4500kv with 2.5 x 3.4 four blade props. Two generic blheli32 four in one ESC’s. A Kakute f7 AIO, M8Q-5883 compass from Matek and a FrSky R-XSR.

The f7 processor is the key to this build it allows FrSky telemetry to work without the need for a inverter and it’s versatile pin functionality allows extra pwm outs to be added. A bit of trail and error with the hwdef.dat allowed two extra pwm outs to be added using the led and buzzer pins. The LED pin works straight away however to get the eighth pwm on the buzzer pin you must bypass the amplifier transistor. I soldered a 220 ohm resistor to the left pad of the transistor and the other leg to the esc wire. Resistor is probably not absolutely necessary but are built into most flight controllers for protection. I have all eight motors running Dshot with esc telemetry.

Next step was to get the motor order worked out, test flight and then autotune. It flys very well straight off the autotune giving just over 5 mins on a 1400 mah. It is full capable of doing missions but is missing a full telemetry link.

I’m quite pleased how it turned out, not the most practical of craft but a fun build and good to fly. Not quite race quad power but surprisingly close for such small motors. Some more fine tunning of parameters to be done in the future, maybe i’ll add telemetry, or 3D print a ‘lid’ so the flight controller is less exposed.

14 Likes

Hi,

I’ve spent a lot of time trying to get the two extra PWM outs working on the Kakute F7.
I recompiled the firmware, bootloader, compared them with and without the defines commented out, flashed several times, checked the wiring many times …

Now it works ! Turns out I was missing the BRD_PWM_COUNT parameter !

The steps to get the two extra PWM working on Kakute F7 are :

  • In the file https://github.com/ArduPilot/ardupilot/blob/master/libraries/AP_HAL_ChibiOS/hwdef/KakuteF7/hwdef.dat
    Uncomment the lines
    #PD12 TIM4_CH1 TIM4 PWM(7) GPIO(56) # led pin
    #PD15 TIM4_CH4 TIM4 PWM(8) GPIO(57) # buzzer pin (need to comment out buzzer)
    and comment the line
    PD15 TIM4_CH4 TIM4 GPIO(77) ALARM
  • Configure the project using waf with the setting --board=KakuteF7
  • Compile
  • Upload the firmware
  • Set the parameter BRD_PWM_COUNT to 8 (7 if you are using only one extra PWM)
  • Enjoy your new Servo7 and Servo8 outputs :slight_smile:

Nice build @iampete btw !

5 Likes

what a project Pete,congratulations on getting it to this stage,I have a Kakute F7 mini with the Teko esc and vtx due here tomorrow,my plan was A fully autonomous 3 inch quad will probably do that then look into A project like yours,thank you for sharing