A Smaller Custom Arduino Quadcopter

The new 13.5" (34cm) custom quad             

  I've enjoyed building and flying my first custom Quadcopter based on an Arduino and FreeIMU, so decided to build another smaller version. The original really needs some wide open spaces to open up and fly, and I wanted something I could fly in more confined areas. This one is quite a bit smaller, measuring in at 13.5" compared to 21" and is much lighter. It is very similar to the first electronically, but uses a GY-86 module and Arduino Nano for the FC board. The IMU module has a gyro, barometer, compass, and accelerometer. It uses the same APC220 transceiver for control, but a standard RC unit is recommended in most cases.

Video from one of the initial test flights 

  As seen in the pics, the FC board is very simple, and I used the complex design method of 'connect the dots'. Just below the orange transceiver, jumpers can be seen which are used to disconnect it from the hardware serial port when connecting to USB for programming. The other pins shown just beside the Arduino are for connecting the ESCs, one of which powers the board. The Nano is mounted on header pins, so can be easily removed. This one was modelled somewhat after the first, but uses 10mm square carbon fiber booms and no aluminium mounts. The setup in MultiWii is pretty much the same, but with the GY-86 chosen under sensor definitions.

  The 1.5mm sheet was cut into two squares measuring 1.75" x 5" for the main body, and holes were drilled through the booms to bolt them directly between the sheets. Drilling through the booms may not provide the most strength, but with a small well balanced quad, I'm hoping it will hold up. The motor mounts required both a top and bottom plate as well due to the thin layer of carbon fiber in the centre of the boom. Drilling through the carbon fiber sheets completely dulled a standard drill bit as well.

  The two quads side-by-side

  A quick test flight with a 3S 1000maH battery and 3-blade 5045 props provided about 6 minutes of casual flight time, but it should be better with a 2S battery and 6" props according to eCalc. The tool also says the props will stall, but it hovers and moves nicely so not sure about that. The FC board is attached directly to the frame using some nylon standoffs, but vibration is minimal after balancing.

  I had a lot of difficulty trying to balance such small props individually, so admitted defeat and went directly to dynamic balancing. I came across laser balancing in this video and I always keep some spare lasers around (who doesn't?) so I tried it, and the balance was the best I've achieved. I balanced the motors before adding the props/adaptors and re-balancing.

 

  I had a few issues with these motors, since the mounts are a bit flimsy, and will break if there is excessive vibration. I've since attached the motors using hard rubber between the metal mounts and the carbon fiber to provide some give, and it seems to be working ok so far. Something also seems to have gotten into one of them, tearing apart the wiring, but it was easy to rewind with new magnet wire. Luckily, I bought 5 motors, but I may need to purchase a different type of motor if troubles keep popping up.

Main Parts List:

Quad:

4X HobbyKing Donkey ST2004-1550kv Brushless Motor

4X Propeller Adaptor (Colet Type) 3MM

2X Counter Rotating Three Blade 5x4.5 Propeller

2X Counter Rotating Three Blade 6x4.5 Propeller

4X Turnigy Multistar 10 Amp Multi-rotor Brushless ESC

2X 1000mAh 3S 25C Lipo Pack

2X 1000mAh 2S 25C Lipo Pack

1X 10mm Carbon Fiber Square Tube - 750mm

1X Woven Carbon Fiber Sheet 300x100 (1.5MM Thick)

FC Board:

1X Arduino Nano

1X GY-86 10DOF IMU Module: MS5611 HMC5883L MPU6050

1X APC220 Wireless Serial Data Module

FC Board PinOut:
pin3: front motor
pin9: rear motor
pin10: right motor
pin11: left motor
A4: GY-86 SDA
A5: GY-86 SCL
TX: APC220 RX
RX: APC220 TX   

Custom Arduino QuadCopter: First Outdoor Test Flights

I've finally had some opportunities to do some outdoor testing, and this is the first such test with a GoPro camera attached. The quad is running on a stock Arduino Mega2560 board, along with some sensors and a digital transceiver. Details of the build are documented here and in previous posts.

This is the first recorded outdoor test-flight, and it goes pretty well at first with some easy flying. I end up trying to do spins and flying around while forgetting to switch from MAG to HeadFree mode, so lose control at the end.

The ESCs are not sealed well from moisture, so needed to be dried out after the snow landing.

The following video is from a 30,000sq ft indoor fly event hosted by Regina Micro-Flyers at the CU EventPlex April 7, 2013:

QuadCopter: Current Summary, Docs and Info 

The quad, controller, and camera

Flight Control Board

The flight control board is based on FreeIMU and built onto an Arduino Mega 2560 running MultiWii. The main goals were to build a customizeable and affordable quadcopter using mainly open source hardware and software, and learn a bit about how it all works. Bugs and design issues seem to have been worked out now, so it looks like this will be the base design for my board. Video

Since it is all open source, adding additional custom components to control lights, sound, servos, etc. is about as easy as it gets. For anybody already familiar with Arduino, it's just a matter of  choosing what customizations to add.

The top picture on the right shows the simplicity of  the FC board, using only a few modules. A previous mock-up of the board was scrapped due to some simple design flaws. The current version attempts to address some of those problems:

a: Although the shield fits tight, secure mounting is a must, and nylon standoffs are used to secure the shield to the Arduino.

b: Here I am using a cheap, single sided prototyping board, but we'll see how long it lasts...

c: The first mock-up used the female header pins as shown on the right of the bottom pic, but they aren't made for Arduinos (too thin), and caused I2C errors and subsequent crashes. The header pins shown on the left are thicker and fit snug every time.

d: The GPS module was left out since GPS nav won't be something I'll be using right away.

The ESCs connect to pins exposed on the top of the board, which are hard to see since the angle of the bottom pic purposely hides my shoddy looking soldering work. The Arduino gets fastened to the frame using rubber mounts taken from broken CD/DVD players to minimize vibration.

Notes:

FC Board:
The board is intially based on a FreeIMU board as mentioned previously, and is actually pretty simple to build at this point, with only 3 modules. The HMC5883L magnetometer module is connected to the aux. I2C lines of the MPU-6050, and running on 3.3V. An APC220 module is connected to the fourth serial port (serial3), and a GPS module can go on serial2 or via I2C if desired. The best part of the flight controller and quadcopter is that it is all based on open source software and hardware, so customization and prototyping like this is actually possible without spending huge amounts of money or time.

FC Board/Arduino Mega Connections:
pin2: front motor
pin3: rear motor
pin5: right motor
pin6: left motor
pin14: APC220 RX pin
pin15: APC220 TX pin
pin16: GPS RX pin
pin17: GPS TX pin
pin18: MPU6050 interrupt
pin20: MPU6050 SDA (I2C)
pin21: MPU6050 SDL (I2C)
pinA0: Voltage divider (battery monitor)
MPU6050: Aux SDA to HMC5883L SDA
MPU6050: Aux SDL to HMC5883L SDL


Main Parts:
1x Turnigy Talon carbon fiber frame
4x Turnigy 20Amp MultiStar ESCs
1x Turnigy ESC programmer
4x NTM Prop Drive Series 28-26A 1200kv/250W Motors
2x Slow Fly 8045 propellers
2x Slow Fly 8045R propellers
1x 4000mAh 3S LiPo battery pack
1x Arduino Mega
1x GY-521 Gyro Module (MPU-6050
1x HMC5883L Magnetometer module 
1x APC220 serial data wireless transceiver
Uses Modified XBox controller for RC (previous post)


XBox Controller:
Prev post. Uses the MultiWii RCSerial protocol
Quad can easily be controled by a PC via RCSerial protocol and APC220 transceiver

Frame/Physical Assembly:

Since the controller and FC board are both custom made, I had to code and then debug the controller during flight in some cases, and had no failsafe at the time. The initial assembly of the central parts of the frame used all nylon bolts. This was to prevent damage to the frame and motors when big crashes happened, since parts would usually break away before breaking or bending much. It currently uses a combination of metal and nylon connectors to provide rigidity and allow for some give on big impacts. As can be seen in the picture above, I have also made my own motor mounts.

ESC Calibration:

One of the problems I ran into in some of the first flights was individual motors cutting out seemingly randomly. The quad uses 20A Turnigy MultiStar ESCs, and gives a choice between slow-down of motors, and hard cutoff when the voltage is low. This caused a bit of frustration since the motors would start cutting out when the voltage was low, regardless of the setting via programming card.

I was confused by the MultiWii calibration code at first since, according to the ESC manual, it would basically just set the programming of the ESCs to the LiPo battery setting, and that hardly seemed like 'calibration':

ESC Programming:
a: Power ESCs on while receiving max throttle signal

b: These ESC will beep accordingly, move throttle to min to select what option to set in the programming 

The ESCs apparently use this interaction for calibration as well, and it made a big difference once I programmed them this way. The motors seemed to sound a bit smoother afterward, and they slow down nicely to force a landing once the battery is low.

Always remove your propellers before uncommenting this line in 'config.h':
#define ESC_CALIB_CANNOT_FLY 

Propeller Balancing:

Another important factor that was initially overlooked was propeller balancing. This made a big difference in the stability of the craft, as well as reducing vibrations. I followed this tutorial and had some good results on my first shot at it. Videos from the previous post show the vibration evident from unbalanced propellers, and a motor wire breaks in the second one, likely related to the vibration issues.

MultiWii Config and GUI:

The videos in the previous post were shot using the PID settings shown in the pic to the right and with the low-pass filter enabled for the MPU-6050 at 20Hz in 'config.h'. Higher values for the filter makes for 'tighter' controls, but is more susceptible to vibration and affects PID. Mitigating vibration issues should allow a higher setting. 

MultiWii Code:

Code base is MultiWii_dev_r1240
Uses slightly modified version, but can work with original:

• Supports serial rc cmds with smaller payloads
• Supports failsafe when using serial rc
• Supports basic monitoring during flight via processing gui and existing transceiver (prev. post)
• Still unsure whether to remove or work with test code to control a music player from alarms and controls, so left it in for now (alarm buzzer timing is changed)
• Longer delay for ESC calibration code specific to MultiStar ESCs (see esc manual below)

Reference Material:
MultiWii - Code w/Modifications
MultiWii - Arduino Mega pin layout
MultiWii Wiki

Mag Orientation
Mag Calibration
MultiStar Manual
APC220: Manual  - Software

Quad/GoPro Camera Test

This video shows one of the first test flights using a GoPro camera strapped to my quadcopter. The camera is mounted using the included straps and is free to move around a little bit, so there is some movement and vibration evident in the video. Although way off balance, stability and power aren't much of a problem, but the batteries drain noticeably faster with the camera attached. The throtte is being hard limited to 75% for indoor testing.

Here the camera swings a lot so the video can be hard to watch:

Here the camera is mounted in a more stable way, top-side:

Quad-Copter: Control and Feedback

  The quad has been working well using the MultiWii RCSerial protocol and custom XBox controller for basic flight controls, so it seemed time to add additional capabilities. The controller code now uses the same type of implementation used in the actual MultiWii code for building and sending RCSerial commands, so commands are easy to structure and send. The default failsafe code doesn't currently work with serial commands, so some simple modifications were made to accomodate the serial based control. Additional mods to the protocol are still being made to accomodate some additional commands and features as well.

   
  The flight control board has been updated with a GPS module and connections to monitor the battery voltage. Initial testing shows the quad can handle incoming commands while sending out data , so some initial coding was done using the Static Google Maps API and Processing to receive serial data from the quad, then display it on a map and plot the path taken during flight. 

  The sketch was designed to use the least amount of reasources possible, by passively listening for data to be sent periodically, and making use of the existing APC220 tranciever module on the FC board for communication. Here is a screenshot of the current iteration showing what it looks like in use. Here, the quad is actually sitting still, and the GPS is tracking around way off course for some reason, but it makes for a good demo of the tracking:

The above sketch is intended only for GPS functionality and basic status info, so will be kept fairly simple. It still needs work and requires some minor modifications to the MultiWii code. Right now it does the following:
- Displays location from GPS data
- Displays heading from magnetometer data
- Logs I2C errors with timestamps
- Plays warning sound if I2C errors are detected
- Zoom In/Out

Processing Sketch: 
MultiWiiGPS
Notes:
- Requires minor changes to MultiWii. See the included readme for info.
- Will work with any serial-data based transceiver
- If it stops getting maps, get an API key here
- Requires ControlP5 library
- Ubuntu users require this fix for audio to work
- Designed/tested with MultiWii_dev_r1240

  In addition to the GPS sketch, here is a link to the XBox controller code with initial integration of the RCSerial protocol. It is a work in progress, but the code is very stable, and it works great. See previous posts for details of the controller build.

Arduino Sketch:

XBox Controller RCSerial 

 

Quad-Copter: Free at last

The quad has come a long way in a short time since the previous post. After a fair bit of reading, adjusting and testing, I was finally able to get my custom flight control board working with the MultiWii software, and the initial results are better than expected.

I was able to get it working initially with the flight software by converting the data to PPM Sum at the receiver, and it worked fairly well in testing. This required the use of an additional microcontroller to receive the signal and convert it, so was not ideal.

Below is a short video showing the Quad-Copter while I attempt to learn the controls and work out some of the details on my custom controller. There are many things that still have to be tweaked, tuned, adjusted, and implemented but at this point, it is looking pretty promising for a custom rig:

After some more looking at the RCSerial protocol built into MultiWii, I was able to build it into my sketch and communicate directly with the flight control board using serial data via APC220 radio module, and my customized XBox controller. I had some troubles finding examples of direct control using the RCSerial protocol, so here is the working but incomplete sketch I have been using. In the next video, the flight control board is closer to completion, with the rf module, gyro/accel and magnetometer all soldered into place, and is using the 'Angle' and 'Mag' modes in MultiWii:

This mode is a lot easier to fly in, and after a few more flights like this, I'm comfortable that this setup is going to work pretty well, especially after some tuning and adjustments. As can be seen, the motor mountings are bent a bit, and the propellers also have some big cracks in them due to previous crashes, but it flies fairly well regardless. The throttle is being hard limited to 3/4 just for safety indoors, and I'm not getting close, so it will be interesting once this thing is outside. Additional features like low battery detection needs to be added, and some extras like GPS, a barometer, or an LCD screen may be added too, but a few bugs need to be worked out first. And yes, that is in fact a breadboard plugged into the Arduino Mega like a shield in the first video.


Details of flight controller on Summary Page:

Building a Quad-Copter

Why a quad-copter? Time spent working on various projects involving robotics and automation have led me to a single conclusion: Flying Robots!

My first searches on the subject turned up various projects that offer pre-built units you can simply buy, connect, and fly, but the point here is to build a unit with interchangeable and customizeable Arduino-based flight and radio controls, and hopefully learn a few things along the way. This will also allow me to build, tweak, add or modify any component as required.

After receiving the main components: frame, motors, ESCs, battery, etc., the first thing I did was test out a single motor and ESC using DIY speed control (An Arduino). I have some 20A Turnigy MultiStar ESCs, so connected the orange wire to pin 9, brown to ground, and left red unconnected. Then, with the power connected to the battery, and using the servo library, I was able to get the motor going by using servo.writeMicroseconds(700); and ramping it up to about 800 to hear the beep indicating it is ready to go, and then up to 900 to get the motor turning. Ramping it up higher increases the RPM, so it seems pretty simple to control. Later experimentation showed that starting at 1000 and ramping up from there seems to work the best.

Setup for spinning motors up and first liftoff:

The initial testing was done using commands sent over the serial port, and the next step was to use wireless remote control so, of course, I used the newly customized XBox controller from the previous post to acheive that. The controller sends a variable and/or a value, (such as "S 1000" for a speed of 1000) and reception is as simple as Serial.read(); etc. Since there are multiple rotors, two must spin the opposite direction of the other two, along with having reversed propellers. The ESCs come with a simple programmer, so direction is easily controllable electronically. Along with the servo library, I was able to spin up all four motors and get the quad-copter airbourne for the first time, if just for a few seconds.

Next is final assembly of the unit and to try for some DIY flight stabilization. My first attempts at flight control will use the Proportional-Integral-Derivative (PID) library which takes an input (pitch,roll, etc) and adjusts an output (motor speed) to maintain a constant reading. This is the same type of thing the line-following-junkbot code attempted to do. Currently, I have an MPU-6050 gyro/accellerometer module connected, which I hope is enough for some simple stabilization. Prior testing required the device to be strapped to the floor with a few inchess of slack, just enough for it to get airbourne, and the same setup will be used here. As luck would have it, my frame kit is lacking in nuts and bolts, so I had to scrounge some up from various broken electronics, and the "feet" are not connected.

First stabilization attempt

Above is the video showing the initial flight using untested and untweaked settings for the PID library and stabilization. Without PID enabled, the quadcopter lurches and jumps when the ropes pull tight, so this flight demonstrates that the stabilization is at least somewhat effective. Next will be to tweak and tune the PID, timing, and associated code for more stable flight, then probably on to controlling its movement.

This next video shows the quad once the PID settings are tuned a little bit better, as it demonstrates some actual stability. It is connected to the board via a large elastic, so whenever it pulls taught suddenly, there is a tendancy to jerk to the side, which the copter succesfully counteracts to a large degree. It took a fair bit of work to acheive this much stability, so a pre-bought flight control board is starting to look appealing.

More progress towards stabilization

Judging by its stability when under load and encountering some additional outside forces (from the tether), it may be time to start working on movement controls. They would simply adjust the balance point for the yaw and pitch, allowing me to direct its movements, and do some more fine tuning on the PID adjustements.

The MPU-6050 will be used in conjunction with an HMC5883L, which pretty much gives me the equivalent of the FreeIMU v0.4 board, minus the barometer. I've run the FreeImu GUI software, and succesfully calibrated my device, but the MPU-6050 library below seems to provide much more accurate readings, so I've been sticking with that. Since it works fine with the FreeIMU library, I attempted to use the MultiWii libraries, but have not had any luck. The sketch below is pretty basic, and only uses yaw, pitch, and roll readings for stabilization.


Libraries and Sketch:

Rough sketch
MPU-6050 library
Modified PID library


Hardware info on Summary Page