Building an autopilot from scratch using a RaspBerryPi Zero : Mini Zee

ppoirier · September 27, 2016, 1:03pm

I finally received my Raspberry Pi Zero, just in time to get into the DIY challenge of building a smart drone with the Pi Zero and APM under 100$. I called this project: MINI-Zee

How this can be done?
Well first of all, thanks to Victor and the team at Erle Robotics for releasing the plans and software of their PXFmini. This is a real inspiration for building my own board, because all the parts are available at a cheap price and are relatively easy to assemble and interconnect using through-hole breadboard, providing you are very experienced with this type of build. Thanks to Mirko as well, for having introduced a real DIY autopilot project that allows us to experiment with a fully working and well supported BeagleBone based ArduPilot Cape called the BBBMINI.

Bill of Material (US$ - Transport & taxes excl.):
Raspberry Pi Zero 5.
MPU 9250 (SPI 9 dof IMU) 8.
MS 5611 (SPI Baro) 9.
PCA 9685 (16 channel PWM Servo Driver) 5.
3.3 v. regulator 1.
BEC 3 amps 3.
Breadboard, Resistors, Connectors, Misc. 7.
AutoPilot: 38.
HobbyKing Spec FPV250 V2 Quad Copter
ARF Combo Kit - Mini Sized FPV 60.
Total: 98.
*This is Banggood price; I had an ADAFRUIT –PWM on hand, and I really recommend going with ADAFRUIT, because of all the effort they put on making a great tutorial and drivers for this product. Note: Just like Erle , the USB WIFI, GPS and the Radio Control are excluded.
Building:

A) Hardest part: Get a RASPBERRY PI ZERO (Where is my Zero site)
B) Hardware - See BOM
C) Board Schematics : Erle pxfmini
D) Board Software: Erle pxfmini
E) LOAD LATEST Raspbian-Jessie
Disable serial Login (Allow GPS on serial Port)
Enable , I2C, SPI , Serial
Disable Console = Auto Log on a shell

F) LOAD RT-PREEMPT
http://www.frank-durr.de/?p=203
Load Test Result: TEST: T: 0 ( 1136) P:80 I:500 C: 100000 Min: 16 Act: 31 Avg: 32 Max: 157

G) MAKE ArduCopter
Special MINI-ZEE release:

The MPU 9250 is mounted on the Z-Axis, so we need to change :
CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_PXFMINI
, _default_rotation(ROTATION_YAW_270) = to ROTATION_NONE
The PCA9585 has no external clock, and the ESC are connected to ports 1-2-3-4, so we need to change:
static RCOutput_PCA9685 rcoutDriver(PCA9685_PRIMARY_ADDRESS, true, 3, RPI_GPIO_27); -to-
static RCOutput_PCA9685 rcoutDriver(PCA9685_PRIMARY_ADDRESS, false, 0, RPI_GPIO_27);
H) Fly the MINI-ZEE == Add these to /etc/rc.local

echo “Starting ArduCopter” >> /home/pi/bootlog
sudo /home/pi/ardupilot/ArduCopter/ArduCopter.elf -A udp:192.168.gcu-address:14550 -B /dev/ttyAMA0 > /home/pi/startup_log &
exit 0
I) FIRST FLY LOG:

Thanks to the damping platform, the vibration level is within specs. Video is available for anyone interested…

Conclusion:
This project took about 20 hours to complete. As you can see, I really enjoyed doing some hardcore DIY to demonstrate that it is still possible to build your own flight controller from a Linux Based system. I do not recommend to try this as a first project, but if you are interested, get a BBBMINI, this is the best introduction to DIY and if you want to fly a Raspberry Pi Zero, it is much easier to buy a PXFMINI.

ppoirier · September 27, 2016, 1:10pm

Here is an update:
Upgraded to latest Raspberry Pi Zero and connecting camera
Had to reduce EMI for the GPS (7 series) using MuMetal shield == Racer Look
Changed the Wifi Dongle for a 5 Ghz + Hostapd so it is working as an Access Point
Changed Motors for more powerful 2206 size.

ppoirier · September 27, 2016, 1:21pm

Here is another update on conflicting 2,4 Ghz between WIFI and Radio-Control.
,I switched WIFI to an EDIMAX AC600 running as an Access Point on 5 GHZ with the use of HostApd and loading this DRIVER.
Here is a picture of the modified USB Dongle with the micro USB adapter cable soldered directly + a 5volts BEC + a RP-SMA adapter cable to attach the 5GHZ antenna.
So far the tests are good, I’ts flying smoothly and the video is fluid at 640x480 x 20fps up to 500 Meter.

ppoirier · September 27, 2016, 1:22pm

Here is a picture of my routing; Imu on top , Baro bottom, they share the same SPI bus, with different CS (Chip Select), VCC, Ground and X=Not Connected.
Hope it can help

Joao_D_Junior · August 16, 2017, 5:03pm

First of all congratulations for the project, very inspiring, it’s the first one I meet.

I’m starting in the area of drone projects, and I have an idea of making an autopilot for mine, I found your topic interesting and would like to exchange some ideas with you, for example, does the drone follow a preconfigured route? Can he have a reasonable speed?

I am grateful now.

ppoirier · August 16, 2017, 5:27pm

Thank You.

The speed is related to the type of quadcopter, In the model showned here , the speed can be quite good (up to 100 Kmh) in manual (stabilized or acro mode).

I suggest you go through the wiki , you will find answer to most of your questions: http://ardupilot.org/copter/docs/auto-mode.html

And for building, you might consider building a BBBMINI https://github.com/mirkix/BBBMINI this is easier to build and you benefit from a better support.

Joao_D_Junior · August 16, 2017, 5:35pm

Ok, I’m very grateful, it will be of great help, and I already read about BBBMINI, it really supplies all expectations.

Once again, congratulations on the project!

Joao_D_Junior · August 18, 2017, 1:42pm

Could you tell me where you bought the drone structure? I live in Brazil, there are no stores with this material.

ppoirier · August 18, 2017, 1:59pm

@Joao_D_Junior ,
most of my stuff is from China, either Banggood , Aliexpress or HobbyKing

JAR4x4 · December 13, 2018, 3:58pm

@ppoirier , and others…

Hi!
I got inspired by this post a long time ago, and finally I started to build my own version of your project. I understand that the Pi0 isn’t the best option for running Ardupilot, I’m using the Pi0 because to learn both Raspberry and the Ardupilot code.

I’m running Raspian Stretch with kernel 4.14.81-rt47+ (RT patch from the official raspian kernel git) and Arducopter 3.6.3 compiled for PXFMINI with the mods for PCA9685 as you have described. I see that the code has changed a bit since you made your controller.

I have got everything working except the PCA9685. Without the PCA9685 I can start arducopter on the PI, and connect to my GCS. When I connect the PCA9685 it’s not possible to establish an connection with the GCS. It looks like arducopter starts without any errors.

Is the problem the change in the code regarding how ardupilot handles the PCA9685 over i2c?

Best regards
Alex

ppoirier · December 13, 2018, 4:15pm

@JAR4x4 cool, as noted here:

Have you modified these lines ?

github.com

ArduPilot/ardupilot/blob/master/libraries/AP_HAL_Linux/HAL_Linux_Class.cpp#L179


      
          #elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_NAVIO || \
                CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_ERLEBRAIN2 || \
                CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_BH || \
                CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_DARK || \
                CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_PXFMINI || \
                CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_OBAL_V1 || \
                CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_CANZERO
          static RCInput_RPI rcinDriver;
          #elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_ZYNQ || \
                CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_OCPOC_ZYNQ
          static RCInput_ZYNQ rcinDriver;
          #elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_BEBOP
          static RCInput_UDP  rcinDriver;
          #elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_DISCO
          static RCInput_Multi rcinDriver{2, new RCInput_RCProtocol("/dev/uart-sbus", "/dev/uart-sumd"), new RCInput_UDP()};
          #elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_AERO
          static RCInput_SoloLink rcinDriver;
          #elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_NAVIO2 || \
                CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_EDGE
          static RCInput_Navio2 rcinDriver;
          #elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_RST_ZYNQ

JAR4x4 · December 13, 2018, 4:22pm

@ppoirier , thanks for your quick reply!

Yes, I have modified that line, just changing true to false, and 3 to 0

running sudo i2cdetect -y 1 shows the address of the PCA9685. I have also tried to run raspbian without the RT patch = same problem

ppoirier · December 13, 2018, 5:35pm

Did you connect the PWM enable (GPIO27) pin 13 to the PCA OE ?

JAR4x4 · December 13, 2018, 5:39pm

Yes, I have tried both with and without PWM enable connected

JAR4x4 · December 13, 2018, 5:46pm

I’m going to check now if the PCA is actually working with the Adafruit python library

ppoirier · December 13, 2018, 5:59pm

Yep, I was about to suggest that and checking with a bus analyser if you have one. Otherwise the code might be broken, I dont think anyone is building pxfmini these days… It’s a ChiBios world with F4 & F7 FC now…

JAR4x4 · December 13, 2018, 6:07pm

Hehe, I know… But I want Linux onboard for the learning… I don’t have a bus analyzer, but i wil hook my scope up to PWM0 and see what happens when i run the python example. I will post back with my results.

I think Erle still is selling the Pxfmini? Maybe they run a custom erle ardupilot flavour?

ppoirier · December 13, 2018, 6:11pm

I think Erle is running an oudated version of ardupilot, … looking at Erle Forum I dont see much activity either…
Anyway, this is still a good primer project for anyone interested in linux integration , as long as the code is not broken and be aware that the PPM routine using the DMA Soft Int has not aged well, it had a tendency to crash on since 3.5

JAR4x4 · December 13, 2018, 6:25pm

Ok, I have seen that, but I will try to compile the erle fork now, and see if that helps.

I hooked my PCA to my scope and ran the Adafruit test code, looks like the PCA works =)

Yes, I have seen that there has been some issues regarding PPM. No problem for me in this project, I’m going to use mavlink for controls over a wifibroadcast setup I’m also working on =)

ppoirier · December 13, 2018, 6:58pm

Might try adding a bus define ? … something like:
#define HAL_RCOUT_RCOutput_PCA9685_I2C_BUS 1
here:

github.com

ArduPilot/ardupilot/blob/master/libraries/AP_HAL/board/linux.h#L269


#define HAL_RCOUT_RGBLED_BLUE     15
#elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_PXFMINI
#define HAL_INS_DEFAULT           HAL_INS_MPU9250_SPI
#define HAL_INS_DEFAULT_ROTATION ROTATION_YAW_270
#define HAL_INS_MPU9250_NAME "mpu9250"
#define HAL_BARO_DEFAULT          HAL_BARO_MS5611_SPI
#define HAL_BARO_MS5611_NAME "ms5611"
#define HAL_COMPASS_DEFAULT       HAL_COMPASS_AK8963_MPU9250
/* HMC5843 can be an external compass */
#define HAL_COMPASS_HMC5843_I2C_BUS 1
#define HAL_COMPASS_HMC5843_I2C_ADDR 0x1E
#define HAL_GPIO_A_LED_PIN        24
#define HAL_GPIO_B_LED_PIN        25
#define HAL_GPIO_C_LED_PIN        16
#define HAL_GPIO_LED_ON           LOW
#define HAL_GPIO_LED_OFF          HIGH
#elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_AERO
#define HAL_INS_DEFAULT HAL_INS_AERO
#define HAL_BARO_DEFAULT HAL_BARO_MS5611_I2C
#define HAL_BARO_MS5611_I2C_BUS 2
#define HAL_BARO_MS5611_I2C_ADDR 0x76