Category Archives: Quadcopters

HobbyKing AIO – GPS and Bluetooth

I started by connecting the HobbyKing AIO board to the GPS that I bought from HobbyKing for $35 and to the HC-05 Bluetooth module. This allows me to configure the AIO via BT.

IMG_8400

The connections are as follows:

GPS to AIO board

The UBlox Neo-7M GPS comes with a cable that has 2 mini-molex connectors, one with 4 pins and one with 5 pins.

gps connector

Some changes must be made to these connections in order to fit them to the AIO board. Moving the cables between pins is simple – lift the flap that holds the cable inside the connector and pull the cable out. See the photo below.

IMG_8401

The changes to cabling are as follows:

4-pin connector

The 4 pin connector is connected to the i2C connector on the AIO.

It should have the following cable connected to it, from top (leftmost) to bottom:

  1. SCL – moved from pin 2
  2. SDA – moved from pin 3
  3. VCC – moved from the 5-pin connector
  4. GND – moved from the 5-pin connector

5-pin connector

The TX and RX cables from the 5-pin connector must be connected to RX2 and TX2 on the AIO board respectively. So I replaced the 5-pin connector with a 6-pin connector that I had from the AIO package and connected the TX and RX cables at the right slots.

AIO board to HC-05 BT module

The BT module connects to the FTDI port on the AIO as follows:

  1. AIO GND  —> HC-05 GND
  2. AIO VCC   —> HC-05 5V
  3. AIO – RX   —> HC-05 TX
  4. AIO TX is connected to HC-05 RC via a voltage divider in order to protect the HC-05. The HC-05 uses 3.3V while the output of the AIO board may be 5V. The following photo of a crumpled piece of paper shows the two resistors that form the voltage divider.

IMG_8402

AIO external power

The AIO receives 5V power from an external source on the GND and VCC pins.

HC-05 Setup

The HobbyKing AIO that I’m using in this project talks MAVLink with the APM console (or any other MAVLink management console). I decided to use BT for connecting it to the console so I borrowed a HC-05 module from my good friend Tomer.

The HC-05 comes configured for 38400 bps (bits per second) so the first step was to configure it to operate at 115200 bps.

Configuration of the HC-05 is done with a FTDI board. I bought one on Ali express for $2.48.

Here are the HC-05 on the right and the FTDI board on the left:

IMG_8391

This FTDI board has a switch that sets it to use 3.3V or 5V. Since the HC-05 is sensitive to voltages over 3.3 I used 3.3V.

The HC-05 enters configuration mode (via AT commands) when pin 34 is pulled high. On this board pin 34 is connected to “Key”.

The two boards are connected as follows:

  1. FTDI ground —> HC-05 ground
  2. FTDI TX          —> HC-05 RX
  3. FTDI RX          —> HC-05 TX
  4. FTDI VCC       —> HC-05 Key
  5. FTDI VCC       —> HC-05 5V

Now the FTDI board can be connected to a USB port and you can use a terminal program (I used Arduino’s serial monitor) to connect to it. Remember that the connection speed is 38400.

Sent “AT” to the board and it should respond with “OK”.

To change the bit rate send “AT+UART=115200,0,0”. The board should respond with “OK” and it is ready.

The data sheet for the HC-05 can be found here.

Flying by cellular – Project Plan

After a long break while working for a start-up company I’m returning to my main technological hobby – quadcopters.

This time I’m building a quadcopter based on the HobbyKing AIO board:

IMG_8380

My main goal is to control the UAS (unmanned aerial system) over the cellular network. This means that commands will be sent to the UAS over the cellular network and the video feed from the UAS to the operator’s console (a computer, or a cheap PS3 joystick) will also be transmitted over the cellular network.

There is nothing new in this approach by itself and people all over the net are doing it by putting a $50 Raspberry Pi running Linux on the UAS. My angle on this would be to try and achieve this goal with cheap hardware.

My development plan is as follows:

  1. Build a good and stable UAS and get it to fly with the HK AIO controller – using the HK firmware
  2. Compile the firmware from sources, configure it and get it to fly
  3. Transmit commands over the cellular network
  4. Transmit the video feed back over the cellular network

LED Controller – Planning

After learning how to use the various features of the PIC16F1825 controller that I need for building and writing the LED controller it is time for some planning.

First the HW. Following is a schematic diagram that I prepared with the Freeware version of the Eagle application for Mac. Here are the details.

Screen Shot 2015-05-25 at 2.16.42 AM

It is an excellent app and I thank my friend Tomer for telling me about it. The freeware version is limited but completely suitable for my current educational purposes. I will even allow me to design a board if I choose to do so – the freeware version is limited to 10cm by 8 cm boards and this size is enough for my LED controller.

The application is a bit non intuitive, especially with the MAC single-key mouse, but after a bit of practice and watching this video, I managed to draw the whole schematic in about 1.5 hours.

So, here is my schematic diagram.

led-controller-schematic-v1

It looks a bit complicated but it is not. It consists of the following components:

[table id=4 /]

Most of the wiring in this diagram are for the 7-segment display. I think that the rest is self explanatory to some extent and will be clarified in the next posts when I start writing the SW.

I’m aware that this schematic is probably “on the face” as we say in Hebrew, which means very poor and I’m sure I will improve as we go.

Quadcopter 1: Preparing to fly

I’m publishing this post a bit out of order as I already published the post about flying because it was simpler and shorter. However, lets not get hung up on small details. So here I explain the last stages of preparation before flying.

The stages are:
  1. Pair the receiver to the transmitter
  2. ESC calibration
  3. Naza calibration
  4. Attach the propellors  – they must be completely parallel to the ground
  5. Hold it by hand to  see that it responds correctly to RC commands (if it is a small model). Alternatively, you can ask someone to help as I’ll explain.
  6. Find an empty field large enough to fly without crashing into something, or worse, some spectators
All the steps from 1 to 5 should be carried out with the propellors NOT attached to the engines.

 Pairing the receiver to the transmitter

Usually most transmitters and receivers have buttons that place them in pairing mode. Follow the procedure for your devices. I found that my Hitec transmitter works with the Hitec Optima receiver (obviously) and with the cheap Minima receiver.

ESC Calibration

The purpose of ESC calibration is to set the throttle range onto the ESCs. Follow these steps to do that:

  1. Connect the signal cable of the ESC (its color is usually white) to the throttle channel of the receiver. This is usually channel 3 and the signal connector is the upper one.
  2. Turn the transmitter on
  3. Push the throttle to the top most position
  4. Connect the quadcopter power. The receiver should come on
  5. The engine should beep twice
  6. Within 2 seconds move the throttle to the bottom position
  7. The engine should beep 3 times and the ESC should reset itself
  8. Move the throttle up and verify the engine starts. Note the direction in which the engine rotates – clockwise (CW) or counter clockwise (CCW)

The ESC programming instructions are usually the same for all ESCs because they all run the same SimonK firmware. The instructions for my 4-in-1 ESC can be found here.

Note that when the engine starts it should beep several times corresponding to the number of cells in the battery. If one or more engines beep a wrong count then these engines should be programmed. The programming instructions can be found in the ESC manual.

After all engines are calibrated connect the ESC signal cables to the correct engine ports on the Naza controller.

Naza calibration

Naza calibration is guided by the Naza configuration application DJI Naza-M V2 Assistant that runs on Windows and MAC. Here is a screenshot of it’s first screen.

naza first screen

I will not repeat here the information and instructions listed in the Naza-M quick start manual. I will only point out some important points that might be overlooked.

It is important to do all the configuration steps when calibrating the Naza for the first time especially the IMU calibration in the Tools window.

I recommend to do the Naza compass calibration as well. This procedure is described here.

Attaching the propellors

Note that there are two clockwise propellors (CW) and two counter-clockwise propelloers (CCW). The propellors must be attached so that the two CW and the two CCW propellors are at the edges of the diagonals.

You must also ensure that the engines rotate the right way, i.e. the CW propellor should rotate CW and the CCW propellor should rotate CCW. If an engine turns the wrong way then disconnect two of the engine’s three power cables and swap them, meaning that each should be connected to the other lead coming from the engine. This will reverse the engine’s direction.

Hold the quadcopter by hand and run a dry test

This is a risky step and I suggest to do it only if you are a cool headed grown up guy/girl and your model is small enough to hold it with one hand. If the model is large then you should ask someone to help and hold it above his head.

So, hold the quadcopter tightly, arm the system and bring the throttle up until all propellors spin. Be careful not to let go.

Now move the remote control sticks and verify that the quadcopter responds correctly.

Next release the sticks and let them return to their center position. Then hold the quadcopter and tilt it to each side. You should feel the quadcopter resist as it tries to stabilize itself.

Flying:

Before flying you should perform the following checklist:
  1. All screws are tight. Especially those that connect the engines to the frame
  2. The battery is attached securely
  3. The propellors are screwed on tightly
  4. The propellors are parallel to the ground
  5. The indicator lights are in their normal state

First flights 

My first flights were catastrophic. I crashed the quadcopter many times and broke many propellors and some engines. So here are some tips to get you started:

Be patient – its takes time for your fingers to learn the controls and respond quickly and correctly.

Start flying in normal mode – be aware where the “forward” direction is and stand behind the quadcopter.

Start with simple flights – lift of and land, lift off, move one meter to each direction and land. And so on …

Don’t start flying in strong winds.

Try to fly the quadcopter circles. I think that if you succeed (in normal flight mode) then you are doing nice progress.

LED Controller – init sequence

Goals

When the controller starts it performs the init sequence. The goals of the init sequence are:

  1. Verify that all LEDs are in working order
  2. Read min/max values from NVRAM
  3. Allow the operator to set the min and max range of the PWM signal
  4. Start normal operation – read the PWM value and set the LEDs

Sequence

The following sections describe the steps of the init sequence. The steps are divided into functional areas.

LED verification

On start up all LEDs should flash for 1.0 second:

  1. Turn all LEDs on with highest intensity (LED State = LEDON)
  2. Enable Timer0
  3. Wait 1000 ms
  4. Disable Timer0
  5. Turn all LEDs off (LED State = LEDOFF)

Load PWM range from NVRAM

  1. Read the min and max values from NVRAM into global variables
  2. If min > max then move to Settings mode
  3. If min > 1023 then move to Settings mode
  4. If max > 1024 then move to Settings mode
  5. If min and max values are sensible then check if settings mode is enabled.

 Check if settings mode is enabled

To enter the settings mode the user should press the push button (SPST switch) during the LED verification stage (1 second).

 Check if the switch is pressed

  1. If the switch is pressed then enter settings mode
  2. If the switch is not pressed then move to normal operation

 Settings mode

Settigs mode allows the user to set the range (max – min) of the PWM value for the LED controller channel

To set the mode the user should move the PWM switch all the way up, wait one second and then all the way down and wait one second.Turn LED 1 on

  1. Start capturing the PWM value.
  2. Enable Timer0
  3. Set counter to 0
  4. While value n+1 is greater than value n set counter to 0
  5. If value n+1 == value n, then check the counter.
  6. If the counter value is 1 secod then:
    1. Store the PWM value as max in NVRAM
    2. Store the PWM value as max in the variable
    3. Turn LED 1 off
    4. Turn LED 2 on
  7. While value n+1 == MAX do nothing
  8. While value n+1 < value n then:
    1. Set counter to 0
  9. If value n+1 == value n then check the counter
  10. If the counter value is 1 second then:
    1. Turn LED2 off
    2. Store the PWM value as min in NVRAM
    3. Store the PWM value as min in the variable
    4. Move to normal operation.

LED Controller Requirements

Introduction

The LED Controller (LC) for quadcopters controls up to 4 high-power LEDs that can be attached to the quadcopter and can be used to make it visible in the dark and/or indicate the status and condition of the quadcopter.

The LC supports multiple configurations of LEDs as described below. It allows the operator to select configurations via the remote control over a dedicated channel.

The blinking interval (the length of time that the LEDs are on or off) can be set by a potentiometer.

The LC may include an optional 7-segment display that shows the LC state.

Hardware

The LC consists of the following HW components:

Component Purpose
PIC16F1825 Application processor – runs the main LC application
PIC16F1826 Optional 7-segment display controller
7-segment display Optional. Displays:

  • the blink interval
  • the PWM min and max values while in settings mode
  • the configuration number (see below) while the user is changing the mode
10K Potentiometer Defines the “blink interval” the amount of time a LED stays on when blinking
Push button – SPST Forces the LC into settings mode
4 Transistors For switching current to the LEDs. One for each LED.
4 High power LEDs

LED Configurations

The LC supports the following configurations:

ID Name Description
1 All off All LEDs are off
2 All on All LEDs stay on permanently
3 All blinking – 1 – High intensity  All LEDs blinking in a fixed rate – on and off
 4  All blinking – 1 – Low intensity  All LEDs blinking in a fixed rate – on and off
 5  All blinking – 2 – High intensity  All LEDs blinking twice and then a break
 6  All blinking – 2 – Low intensity  All LEDs blinking twice and then a break
 7 All blinking – 3 – High intensity  All LEDs blinking three times and then a break
 8 All blinking – 3 – Low intensity  All LEDs blinking three times and then a break
 9 LEDS 1, 2 on and 3, 4 off  
10 LEDs 3, 4 on and 1, 2 off  
11 LEDs 1, 2 blinking 1 – High intensity LEDs 3, 4 are off. LEDs 1 and 2 are blinking in a fixed rate
12 LEDs 1, 2 blinking 1 – Low intensity LEDs 3, 4 are off. LEDs 1 and 2 are blinking in a fixed rate
13 LEDs 1, 2 blinking 2 – High  intensity LEDs 3, 4 are off. LEDs 1 and 2 are blinking twice and then a break
14 LEDs 1, 2 blinking 2 – Low  intensity LEDs 3, 4 are off. LEDs 1 and 2 are blinking twice and then a break
15 LEDs 1, 2 blinking 3 – High  intensity LEDs 3, 4 are off. LEDs 1 and 2 are blinking three times and then a break
16 LEDs 1, 2 blinking 3 – Low  intensity LEDs 3, 4 are off. LEDs 1 and 2 are blinking three times and then a break
17 LEDs 3, 4 blinking – 1 – High intensity LEDs 1, 2 are off. LEDs 3 and 4 are blinking at a fixed rate
18 LEDs 3, 4 blinking – 1 – Low intensity LEDs 1, 2 are off. LEDs 3 and 4 are blinking at a fixed rate
19 LEDs 3, 4 blinking – 2 – High intensity LEDs 1, 2 are off. LEDs 3 and 4 are blinking twice and then a break
20 LEDs 3, 4 blinking – 2 – Low intensity LEDs 1, 2 are off. LEDs 3 and 4 are blinking twice and then a break
21 LEDs 3, 4 blinking – 3 – High intensity LEDs 1, 2 are off. LEDs 3 and 4 are blinking three times and then a break
22 LEDs 3, 4 blinking – 3 – Low intensity LEDs 1, 2 are off. LEDs 3 and 4 are blinking three times and then a break.

Main use cases

The main use cases of the system are:

1. Initialization

When the LC starts it enters the initialization sequence. The init sequence is described in a separate post.

2. Normal operation

In normal operation the LC drives the LEDs according to the currently selected configuration. The LC also monitors the following inputs:

a. Potentiometer – the potentiometer value determines the blink interval – the time that LEDs, in blinking mode, are on and off. In the “blinking 2” and “blinking 3” modes, the potentiometer value determines also the amount of time that the LED is off between blinks. This amount of time is twice as long as the blinking interval. When the value of the potentiometer changes the LC performs the “Setting the blink interval” use case.

b. RC input. If the PWM value on the RC channel changes then the LC performs the “Changing the LED configuration” use case.

During normal operation the 7-segment display, if present, shows  the ID of the current LED configuration.

3. Setting the blink interval

When the blink interval is changed (i.e. the potentiometer value is changed) and if the 7-segment display is present, then the LC displays the new value of the potentiometer for 1 second. After 1 second the display returns to showing the configuration ID.

4. Changing the LED configuration

When the PWM value changes, the LC moves to the newly selected LED configuration. The LC also displays the current configuration ID on the 7-segment display, if present.

 

Quadcopter 1 – Flying

Quadcopter 1 is built with the Naza M V2 flight controller from DJI. It is expensive but worth every penny for the novice pilot because it is very stable and very easy to fly. it will give you the satisfaction that you need so much and the confidence that you can do anything with it. My good friend Misha started flying with an Arducopter controller and quickly gave up.

Here is a recent video (published with permission of the participants) of me flying it in a small parking lot just a meter away from the excited crowd (children are the best crowd for this kind of stuff).

However, I must confess that I do this after relatively many hours of flying the Naza and, I’m not exaggerating, tens of broken propellors, two damaged engines and a fractured carbon fibre frame. DON’T DO YOUR FIRST FLIGHT IN A SMALL PARKING LOT.

My first flight was catastrophic. I bought only 8 propellors and I attached four of them to the engines in a random way. I remembered Misha laughing about people who buy ready made coppers like the Phantom, who don’t even know which way the propellors are attached, but I didn’t understand what he means and I didn’t know what to ask. So I attached the propellors, took it to a large parking lot at night, armed the controller, moved the throttle up and the quadcopter flopped on its head breaking two propellors. I replaced the propellors and tried again, same result with one broken propellor. I took it home and started reading the configuration instructions carefully I soon understood how to attach the propellors correctly (see the “Preparing to fly” post).

The next day I went to the parking lot again, this time with the propellors attached correctly. I armed the controller, moved the throttle up and the copter lifted off the ground, took a wide angle and crashed into a lighting pole. Two propellors broken again and I couldn’t continue flying. I went home and ordered a large number of propellors (I think 20) from a supplier in China but I couldn’t just sit and wait a month for them to arrive. So I went the next day and bought 2 propellors from an importer in a nearby city for six times the chinese price.

After a few more careful flights I could lift it off the ground an land. I decided that I must now start practicing on moving it sideways a bit. So I went to a large field, lifted off and it started flying away, assisted by the strong winds (I live in a mountain region, 800 meters above sea level with strong winds). I couldn’t understand how to make it return to me, so I panicked and switched to the RTH (return to home) mode. In this mode the Naza copter first climbs up to 20 meters and then heads “home”. I saw it climbing up then starting to fight the winds in order to return to the home position, suddenly something snapped and the copter fell from 20 meters to the ground not far away.

I ran to the crash spot and was amazed to see that 3 propellors were broken, one engine shaft was bent but the carbon fibre frame was intact apart from a very small dent. Now I really had to wait a month for new engines to arrive. When I inspected the copter I found the reason for the crash – the screws attaching one engine to the frame came loose, and the engine snapped off. This is something you don’t want to happen in mid-air, especially since I’m writing this post in an airplane on the way to the London Heathrow airport. Not a bright thought at all.

I now had some time to think and I understood that I must perform all the calibration steps and, most importantly, make sure that the propellors (and engines) are completely horizontal. If they aren’t then the copter will rotate or simply fly away. It is easy to detect which engine is not horizontal – it will be hotter than the other engines.

The next time I flew it, it lifted off cleanly, kept its position and height and responded to commands beautifully. Here is a video from that period.

After some more practice I became so confident that I let friends fly it with no training at all. I would give them the transmitter, stand behind them while holding their fingers, and show them the basic movements. They could fly it very nicely just like that without any practice. I stopped doing that after someone panicked and turned off the engines in mid-air and someone else borrowed it for a few days and returned it with 2 broken propellors.

Here is a video (published with permission) of some 2-legged friends and 4-legged friends flying my Quadcopter 1.

 

So, the main point is that anyone can fly a Naza and I strongly recommend paying more for a Naza at least for the first quadcopter.

An expensive evening

I’m a strong believer in putting my money where my mouth is and since I consider my Naza based quadcopter easy to fly I let my friends fly it. We meet almost every evening in our local dog park that doubles sometimes as a tennis court.

So this evening I let A. fly it for his third or fourth time and he did a great job. We even let E. fly it for the first time for a few minutes. By then the battery almost ran out, the red warning light was blinking, and we were going to land. Just at this moment Johny joined us and asked for a short ride. He flew it several times already so I said ok.

Johny lifted the quad into the air and flew it a few meters away. Suddenly, and I still don’t know the reason for it, the quad rolled at a steep angle and fell from about 3 meters right on the tennis net.

At first it seemed undamaged, but when I tried lifting off again it flew away to the right and I saw immediately that one engine shaft was bent.

A bent engine shaft

A bent engine shaft

This was the second accident this evening. Just before that I flew my quadcopter 2 which has a Hobbyking multicopter flight controller and I still struggle to learn to fly it.

In my last flight for today I lost control over it completely, it flew fast and downwards and hit a stone fence. One of its arms was broken.

Broken quadcopter arm

Broken quadcopter arm

So right after this sentence I will try to glue the broken arm and straighten the bent engine shaft. I believe none of these fixes will work  😦

Quadcopter 1: Assembly

Quadcopters are relatively easy to assemble but it took me the better part of a month to assemble Quadcopter 1 – my first quadcopter.

Figure 1 below shows the components of Quadcopter 1 and their connections to each other. In the following sections we explain how each sub-system is assembled.

Figure 1: Quadcopter 1 schematic diagram

Figure 1: Quadcopter 1 schematic diagram

The black lines in figure 1 show the power connections and the yellow lines show the control connections.

Figure 2 shows the assembled quadcopter.

quadcopter1-assembled

Figure 2: Quadcopter 1 – assembled

Frame assembly

The frame arrived as a set of flat carbon fibre pieces and a small bag of screws and spacers. I had to study carefully the photos of the assembled frame on eBay in order to understand how to assemble it. Here is one photo for example.

Figure 3: Zoom in on the top and front part of the frame

I used 2 mm and 2.5 mm hex screw drivers.

Figure 4: Hex screwdrivers

Battery and the power distribution board

I decided to connect the battery with cable ties to the bottom of the frame because I’m not planning to use quadcopter 1 for photography and I will not connect a camera at the bottom.

Figure 4: Battery connection

Figure 4: Battery connection

After some trial and error I decided to use a double-sided PCB for the power distribution board. I soldered two 1.5 mm cables to both sides of the PCB and the two other ends to a Deans plug.

Note that the the power cables must be thick enough to allow the high power consumption of the ESC. At first I soldered thin cables that overheated very quickly and started to melt the plastic cover of the Naza flight controller at the point where they touched it. I then replaced the thin cables with 1.5 mm cables.

Engines and the 4-in-1 ESC

I soldered gold plated plugs to the three leads from each engine. I also soldered an extension of 1.5 mm cable to each of the cables that came with the 4-in-1 ESC because the original cables were too short for my large frame. I covered all the solder points with heat shrink tubing.

I passed the cables from each engine through the hollow engine arms.

The 4-in-1 ESC fits nicely on the center of the frame under a small cover that is screwed to four spacers. Figure 5 shows the ESC assembly.

Figure 5: ESC assembly

Figure 5: ESC assembly

The ESC is held in place by velcro on it’s bottom and the cover piece with the text: “WTOTOY”

Naza components

The Naza system consists of the following components:

  • Flight controller
  • GPS
  • Power management unit (PMU) – distributes power to the components of the system.
  • LED module – indicates the system status and connects the controller to a PC for configuration.

I followed the assembly instructions in the Naza-M Quick start manual but I made a few changes in the location of the components as follows:

  • The flight controller is not exactly at the centre of gravity (CG) of the vehicle. It is located astern of the ship (on the back).
  • The GPS is also not at the center of gravity but on the bow (forward) of the airship. In the beginning I used the pole that came with the package and glued the GPS case (the white plastic protector around the GPS unit) to it right at the CG. However, after the first few crashes I realized it will be much safer if I attach it to the frame itself.

At first I connected the flight controller and the GPS with velcro strips but then I realised (I realised many things during the process  🙂 ) that the velcro allows the flight controller to move and shake a bit and this is certainly not good. Therefore I replaced the velcro with double sided glue strips similar to these – some were provided by DJI in the Naza package but I bought a few more myself.

50Pcs Double-Sided Adhesive 3M PE foam Sticker Size 25MMx40MM For RC Model Gyro

This glue is very strong after it bonds, but it is always possible to pry it off with a knife.

The receiver

I attached the Hitec Optima receiver with velcro strips to the back side of the frame near the flight controller. The choice of location was mainly because of the short servo cables that I had for connecting the Naza to the receiver. A side advantage is that it is also protected by the strong carbon fibre frame.

optima-receiver

Figure 6: The Optima receiver

Landing gear

The landing gear that came with the frame has very long plastic “legs”. It looked really good when it stood on these legs on my desk but they were too elastic, so often when the ship landed not completely softly it would bounce up and land on its back or side. This went on for quite a long time and through many crashes.

Luckily, if I may say so, I once completely lost control over the quadcopter and turned on the RTH (return to home) feature. When a Naza goes into RTH mode it first climbs to a height of 20 meters and then heads home. On that particular occasion the winds were very strong and the screws holding one of the engine to the frame became loose during all the crashes. So suddenly the engine broke loose and the ship crashed from 20 meters to the ground. Amazingly, all the carbon fiber parts were almost not damaged but one of the plastic legs broke. I didn’t have a replacement so I decided to cut the other three legs to the same length and suddenly I realised that this is perfect. The short legs are not elastic any more and when the craft lands it sets squarely on its legs and doesn’t bounce at all.

So I definitely recommend using a non-elastic landing gear. I am not planning to install a camera under the frame so I am not going to replace the legs that I have even though they are quite short.

Marking the “front”

In the basic flight mode the operator must be aware which side of the quadcopter is the front. Therefore I marked the front of the vehicle (the front legs and the front engine arms) with white tape as can be seen in the next photo.

Figure 7: Marking the front of the quadcopter

Figure 7: Marking the front of the quadcopter

Propellors

The propellors must be installed at the very last step of preparing the quad copters for its first flight. So I will describe the propellor installation in the next post on “Preparing to fly”.