QAUDCOPTERSAn Industrial Approach

SHREYANSH VATS

11BEE1033

By,QUADCOPTERS( A n i n d u s t r i a l t r a i n i n g r e p o r t )

SHREYANSH VATS(11BEE1033)August, 2014

INTRODUCTION

In the following presentation, I am going to discuss about my experience working on the quadcopters

The main topics for discussion will be APM 2.5 AutoPilot controller, GPS, telemetry, outrunner motors, ESCs, IMU and other sensors onboard, batteries, Turnigy 9 ch remote control, Mission Planner, MAVLink communication protocols and briefly about the PID controller implementation and Kalman filter (basic concept of its implementation)

I am extremely thankful to Omnipresent Robot Tech for presenting me this learning opportunity

QUADCOPTERS

These are four rotor Unmanned Aerial Vehicles (UAVs), classified as rotorcraft (as opposed to fixedcraft), capable of taking flights both by manual remote control as well as autonomously. In recent times, it has been popularized in the recent sectors of Defense, Entertainment, Disaster Management, Farming etc. due to its versatility and ease of handling

The company has produced Garun Mark 1 as its first quadcopter for surveillance as well as search and rescue missions for defense and disaster management sectors

Currently, it is developing a quad for the purpose of crop photography to facilitate the farmers with their farm management

TYPES OF QUADCOPTER

1. Plus (+) configuration 2. X configuration

At Omnipresent, the work was on + configuration.

DYNAMICS OF QUADCOPTERS

Roll/ Pitch Yaw

Throttle

TYPICAL QUADCOPTER LAYOUT

APM AUTOPILOT CONTROLLER

APM WITH ONBOARD SENSORS AND OTHER COMPONENTS

GPS

GPS stands for Global Positioning System

Using satellites, the GPS module triangulates the position of the system on which it is installed

The GPS module used was manufactured by 3DRobotics (GPS uBlox LEA 6)

Top of the GPS moduleLower part of the GPS module

CONNECTING GPS TO APM

TELEMETRY

This refers to the communication between a remotely located system and a ground station form where the system is being controlled and monitored

The remote system (here, the quad) performs the task according to the commands given to it while through telemetry module, the real time feedback comes to the ground station (like position, sensor values, battery level etc)

TELEMETRY MODULES

Ground moduleConnected throughUSB

Remote system module

TELEMETRY MODULE CONNECTED TO APM

OUTRUNNER MOTORS

The quadcopter of normal sizes use outrunner BLDC motors as its rotors

The microquad and nanoquad use normal brushed DC motors as their sizes are too small

The outrunners’ prime advantage is that they don’t have any brushed contacts since the coil is mounted on the inner stator and thus is fixed. So, direct connection can be given to it

Also, they are 3 phase, so their control is really easy as compared to normal DC

The outer case is lined with permanent magnets on the inside

ESCs

ESC stands for Electronic Speed Control

The outrunner motors are 3 phase motors while the onboard supply is normal DC

Thus we need to convert the supply into three phase

ESCs not only supply the motors with power, but also regulate its speed as the signal from APM is channelized to the motor through ESC only

ESC designed by Turnigy

Motor outputs from the APM to themotors through the ESC

IMU

IMU stands for Innertial Measurement Unit

This is MEMS technology chip that encompasses an accelerometer, a gyrometer and a temperature sensor

The IMU employed on the APM is MPU-6000 designed by InvenSense

FEATURES OF MPU-6000

Tri-Axis angular rate sensor (gyro) with a sensitivity up to 131 LSBs/dps and a full-scale range of ±250, ±500, ±1000, and ±2000dps

Tri-Axis accelerometer with a programmable full scale range of ±2g, ±4g, ±8g and ±16g

Reduced settling effects and sensor drift by elimination of board-level cross-axis alignment errors between accelerometers and gyroscopes

Digital-output temperature sensor

VDD Supply voltage range of 2.375V–3.46V; VLOGIC (MPU-6050) at 1.8V±5% or VDD

Gyro operating current: 3.6mA (full power, gyro at all rates)

Gyro + Accel operating current: 3.8mA (full power, gyro at all rates, accel at 1kHz sample rate)

Accel low power mode operating currents: 10µA at 1Hz, 20µA at 5Hz, 70µA at 20Hz, 140µA at 40Hz

Smallest and thinnest package for portable devices (4x4x0.9mm QFN)

MAGNETOMETER

It is used to determine the magnetic orientation of the quad

The magnetometer onboard the APM is HMC-5843 designed by HoneyWell

The magnetoresistive sensor circuit is a trio of sensors and application specific support circuits to measure magnetic fields.

With power supply applied, the sensor converts any incident magnetic field in the sensitive axis directions to a differential voltage output.

The magnetoresistive sensors are made of a nickel-iron (Permalloy) thin-film and patterned as a resistive strip element.

These resistive elements are aligned together to have a common sensitive axis (indicated by arrows on the pinouts) that will provide positive voltage change with magnetic fields increasing in the sensitive direction.

FEATURES OF HMC-5843

3-Axis Magnetoresistive Sensors andASIC in a Single Package

Sensors Can Be Used in Strong Magnetic Field Environments

Compatible for Battery Powered Applications

Small Size for Highly Integrated Products

ALTIMETER

This is the sensor for determining the height of the quad from the ground. Normally for 6-7 m of height, Ultrasonics are used, but beyond that, due to dispersion into air, the ultrasonics fail and that’s where the altimeter comes into picture.

The sensor used in the APM altimeter is MS5611-01BA. It’s a new generation of high resolution altimeter sensors from MEAS Switzerland with SPI and I²C bus interface. It is optimized for altimeters and variometers.  

FEATURE OF MS5611-01BA

The sensor module includes a high linearity pressure sensor and an ultra low power 24 bit ADC with internal factory calibrated coefficients.

It provides a precise digital 24 Bit pressure and temperature value and different operation modes.

A high resolution temperature output allows the implementation of an altimeter/thermometer function without any additional sensor.

The MS5611-01BA can be interfaced to any microcontroller.

The communication protocol is simple, without the need of programming internal registers in the device.

It has very small dimensions of only 5.0 mm x 3.0 mm and a height of only 1.0 mm.

This new sensor module generation is based on leading MEMS technology and consists of an internal oscillator only.

BATTERY

LiPo (Lithium- Polymer) batteries are used for powering the quadcopter as they are reliable, rechargeable and very compact

Specifications are for the cell nos. (3S, 4S etc), capacity (in mAh), discharge rate, weight, size etc

The battery used to power the quad at Omnipresent was manufactured by Turnigy

For making the connections, XT60 connectors are used. The 5 wire ribbon is used for measuring the voltage and current levels of the battery using battery level indicators.

FEATURES

Minimum Capacity: 5000mAh

Configuration: 4S1P / 14.8v / 4Cell

Constant Discharge: 30C

Peak Discharge (10sec): 40C

Pack Weight: 556g

Pack Size: 144 x 49 x 36mm

Charge Plug: JST-XH

Discharge plug: 5.5mm Bullet-connector  

9 CHANNEL RADIO CONTROL

This is to give the attitude control to quadcopter manually

This set contains a pair of transmitter and receiver. While the transmitter is responsible for generating the signal, receiver is connected to the APM and communicates the instruction to the quadcopter

The operating frequency is 2.4 GHz

The leading products in this field are Futaba and Turnigy

This is used for manually giving the controls (Roll, Pitch, Throttle, Yaw and 5 other instructions as it is a 9 channel radio control).

Each channel is assigned the specific control using the Mission Planner software depending upon the connections made by the receiver to the APM.

Apart from the regular Roll-Pitch-Throttle-Yaw controls, other commands like Loiter, AltHold etc could be assigned to other channels. Each control on the transmitter associated with a particularly assigned channel generates a PWM

Turnigy transmitter module

Turnigy receiver module

Turnigy receiver module connections

MISSION PLANNER

It is an open source platform for controlling all kinds of the unmanned systems

It was designed and developed primarily by Michael Osborne

MAVLINK COMMUNICATION PROTOCOL

MAVLink stands for Miniature Aerial Vehicle communication protocol

It is the protocol for communication with small unmanned vehicles like quads with the ground station. It was first launched by Lorenz Meier under LGPL license. It’s primarily used for transmitting the orientation of the vehicle, its GPS location and speed.

MAVLINK PACKET STRUCTUREField name Index (Bytes) Purpose

Start-of-frame 0 Denotes the start of frame transmission (v1.0: 0xFE)

Pay-load-length 1 length of payloadPacket sequence 2 Each component counts up his

send sequence. Allows to detect packet loss

System ID 3 Identification of the SENDING system. Allows to differentiate different systems on the same network.

Component ID 4 Identification of the SENDING component. Allows to differentiate different components of the same system, e.g. the IMU and the autopilot.

Message ID 5 Identification of the message - the id defines what the payload “means” and how it should be correctly decoded.

Payload 6 to (n+6) The data into the message, depends on the message id.

CRC (n+7) to (n+8) Check-sum of the entire packet, excluding the packet start sign (LSB to MSB)

The payload from the packets described above are MAVLink messages. Every message is identifiableby the ID field on the packet, and the payload contains the data from the message. The MAVLinkprotocol helps in identifying the type of vehicle the GS is communicating with, the type ofsignal being sent (i.e. the instructions for execution by the on-board controller).It is implemented through the telemetry.

PID CONTROLLERS

PID (Proportional Integral Differential) controllers are used for controlling the system by reducing the error factor in its expected output due to noise depending upon the past, current and possible future values from the various sensor inputs

In any remotely operated system, PID controllers are the major deciding factor of its performance

APM, through Mission Planner implements the PID controller and through extensive testings the optimal values for the quadcopter is obtained

The Mission Planner has a setting mode for establishing the values of PID for different channels of the controller

KALMAN FILTER- A BRIEF THEORETICAL OVERVIEW

Kalman filter, also known as linear quadratic estimation (LQE) is an algorithm that uses a series of measurements observed over time, containing noise (random variations) and other inaccuracies, and produces estimates of unknown variables that tend to be more precise than those based on a single measurement alone.

The algorithm works in a two-step process.

It is a mathematical procedure which operates through a prediction and correction mechanism. In essence, this algorithm predicts a new state from its previous estimation by adding a correction term proportional to the predicted error. In this way, this error is statistically minimized.

In the prediction step, the Kalman filter produces estimates of the current state variables, along with their uncertainties. Once the outcome of the next measurement (necessarily corrupted with some amount of error, including random noise) is observed, these estimates are updated using a weighted average, with more weight being given to estimates with higher certainty.

Because of the algorithm's recursive nature, it can run in real time using only the present input measurements and the previously calculated state and its uncertainty matrix; no additional past information is required.

KALMAN FILTER MODEL

THANK YOU