ChRoMicro - Cheap Robotic Microhelicopter HOWTO (EN)
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1. ChRoMicro Cheap Robotic Microhelicopter HOWTO EN Copyright 2005 2006 2007 pabr pabr org All rights reserved RC model helicopter prices have reached a point where all sorts of challenging i e crash prone robotics projects become affordable This document explains how to build a 300 g helicopter with embedded Linux and Bluetooth datalink from off the shelf components for less than 500 EUR http www pabr org chromicro doc READ THE HYPERTEXT VERSION HERE http www pabr org chromicro doc chromicro en html Revision History 1 2 2008 09 07 Bluetooth joysticks 1 1 2006 12 07 Software section moved to pxaRC project Documentation in French 1 0 2005 06 02 First public release 0 2005 05 27 Document created Table of Contents ARTOA Saa test aeons Sat tae RTs e tl 2 DISC AIMEOY acd Gisele ee A ee Ae ee ee ee 3 Off the shelf COMPONENTS 20 ee cece cece cece eee ee cette eee ee aa aaa tent ee ee ceca aaaaceeeeeeeseaeaaaaaaeeeeeseeaeaaaaaes 3 1 Helicopter platform sna aienea cece ee ence ener ee VKE aina a INEA AVARANU ANAA AN VEA aA 3 2 Embedded cOmputlen ico do 3 3 Accelerometers and YYTOS ccccccoccccccnnnocnconnnonnnonnnnnncnnnnnnncnnnnnnnnnnnnnnnnnnnnnnn crearan ida 3 4 Other SQUIPMENE ririo rriei nineyi ind a la t 4 Hardware ua it ee leaves 4 1 Voltage regulator MOd Avarinio EEE EEE E EEES EENEN 4 2 PWM injection Mod creira rici ie enh aA eddie desi weed e2. org chromicro doc http Figure 6 Rear view with connector on I O daughterboard and Table 2 I O daughterboard pin assignments show the connection with the Gumstix daughterboard Table 2 I O daughterboard pin assignments Pin Signal Usage 10 NACRESET disconnected by 5 V CC in cutting the trace on the PCB 16 GND GND 18 GPIO61 6 channel PWM out 7 Operation 7 1 Remote control over Bluetooth or Wi Fi Figure 7 Remote control over Bluetooth or Wi Fi ChRoMicro Cheap Robotic Microhelicopter HOWTO EN In this scenario Figure 7 Remote control over Bluetooth or Wi Fi we simply emulate a regular remote control There are no sensors on the helicopter no complex embedded software and no feedback from the helicopter to the ground station Procedure 1 Startup 1 Start ipre_tx on the PC Connect the battery The GPIO pin will be pulled high while the processor is booting 2 3 Setup networking over Bluetooth BNEP This can be automated with the daemon pand 4 Load the pxa_opwm module The GPIO pin will be configured for output but kept at logic O level 5 Start ipre_rx on the embedded board PPM will be generated as soon as UDP packets are received Procedure 2 Shutdown Either disconnect the battery stop ipre_rx or stop iprc_tx All alternatives should be equally safe Note that with the original remote control it is mandatory to shutdown the receiver or
3. sixlinux en html Battery Elimination Circuit Bluetooth Network Encapsu lation Protocol Collective pitch helicopter Cyclic Collective Pitch Mix ing Duty Cycle Modulation Drone Electronic Speed Controller Fixed pitch helicopter General Purpose I O Global Positioning System Inertial Measurement Unit Lithium Polymer Mode 1 Mode 2 Printed Circuit Board Pulse Code Modulation Glossary A DC DC voltage converter linear regulator or switching converter which is used to power a RC receiver and servos from the same battery as the motors Output is typically 4 8 V or 5 V Provides an ethernet like interface e g bnep0 at each end of a Blue tooth connection Refers to a helicopter rotor design with variable collective pitch Thrust is controlled by varying either the collective pitch or the speed of the main motor or both See Also Fixed pitch helicopter A modulation which encodes an analog signal into the average value of a square wave signal Typically used to drive an electric motor with an H bridge See Also Pulse Width Modulation See Also Unmanned Aerial Vehicle A motor speed controller typically driven by a PWM signal in RC mod els Refers to a helicopter rotor design with cyclic pitch but fixed collective pitch Thrust is controlled by varying the speed of the main motor This causes more inertia than ina CP helicopter Besides FP helicopters cannot fly inverted See Also Collectiv
4. SCs It must accept 3 3 V signals The helicopter must be strong enough to lift at least 30 g of payload ChRoMicro Cheap Robotic Microhelicopter HOWTO EN The battery must be able to supply 200 mA of additional current 3 2 Embedded computer We use a Gumstix single board computer with the following features e 200 MHz XScale PXA255 processor ARM core plus I O functions e 4 MiB flash with factory installed Linux 2 6 10 and utilities e 64 MiB SDRAM General purpose I O pins I O daughterboard with 2 54 mm pads e 2C bus Bluetooth module and antenna e Comprehensive software development environment Some features are not used Dual channel hardware PWM generator Intended for driving the brightness and contrast of a LCD display Eventually we will need more than two channels e USB client interface Intended for PXA255 based PDAs usbnet is convenient for logging into the board but we can use Bluetooth instead 3 3 Accelerometers and gyros Gyros which measure angular rate of rotation are commonly used in RC model helicopters MEMS accelerometers are now routinely found in mass market devices such as camcorders hard disks and cars Accelerometers can also be used as inclinometers in stationary applications 3 4 Other equipment e Linux computer with USB and Bluetooth e Xbox compatible controller e 12 V 5 A regulated power supply 10 MHz analog oscilloscope recommended 4 Hardware 4 1 Vol
5. die 4 3 Xbox controller MOA ii Se KRAKAU EENEN SOMO A A ae ln ie eee ie ee gt Systemuintegration ir de tatae adia a e ees inate ened Operations nit Ni ee ii eee ear hee 7 1 Remote control over Bluetooth Or Wi Fi ooo ieee cece een eeee ceca eeeeeeaaeeeeeaaeeeeeeaaeeeeeeaaeeees 7 2 Remote control with a Bluetooth joystick oooocooonncccnnnncccccnnnacicononaccnnnnnncnnnnnancncnnnanccnnns 8 SROAGIMADy iii 81 SCNSOIS ainiai ee eke een a wie eee a eee de 8 2 Flight control SOMWare oo Tea eina Ra AAA LAUKAA EENE Sa R ESENES BID OT APOYA a A beet ae seu A aa A a a hace evi eect vind a e aa aaa S he Riuar dered hee mk NY O oO 1 Introduction RC model helicopter prices have reached a point where all sorts of challenging i e crash prone robotics projects become affordable This document explains how to build a 300 g helicopter with embedded Linux and Bluetooth datalink from off the shelf components for less than 500 EUR As a proof of concept we provide software which allows the helicopter to be remotely controlled over Bluetooth with a PC joystick Future work will focus on the integration of sensors IMU altitude magnetic compas GPS camera and flight control software either third party or dedicated 2 Disclaimer Use these instructions and the related software at your own risk e This is an experimental project with none of the fail safe features one could expect in a commercial product e Remote contr
6. disconnect the battery before stopping the transmitter 7 2 Remote control with a Bluetooth joystick Figure 8 Remote control with a Bluetooth joystick In this variant Figure 8 Remote control with a Bluetooth joystick we take advantage of the fact that some modern wireless joysticks are compatible with the Bluetooth HID Profile and can therefore connect directly to the on board Linux computer with Bluetooth module Instructions for using the PS3 SIXAXIS controller can be found in SIXLINUX 8 Roadmap 8 1 Sensors e Inertial measurement unit 6 DoF 12C interface e Digital video camera e Magnetometer compas I2C interface e Pressure altitude airspeed 12C interface 8 2 Flight control software e Assisted flight stable hover 3D e Waypoints e Autonomous takeoff and landing Autonomous navigation in interior environments Bibliography PXA255_DEVEL Intel PXA255 Processor Developer s manual 27869302 pdf ChRoMicro Cheap Robotic Microhelicopter HOWTO EN PXA255_ USER ntel XScale Microarchitecture for the PXA255 Processor User s Manual 27879601 pdf PXA255_ ELEC ntel PXA255 Processor Electrical Mechanical and Thermal Specification 27878002 pdf PXARC pxaRC R C and robotics software for Linux PXA255 PXA270 http www pabr org pxarc doc pxarc en html SIXLINUX Using the PlayStation 3 controller in Bluetooth mode with Linux http www pabr org sixlin ux
7. e pitch helicopter The PXA255 has 85 general purpose pins which can be independently configured for input or output or connected to integrated peripheral functions e g serial ports and LCD driver Accelerometers translation and gyros rotation Most popular layouts for axes on a RC helicopter transmitter Refers to a digital transmission in contrast with PWM or PPM ChRoMicro Cheap Robotic Microhelicopter HOWTO EN See Also Pulse Width Modulation Pulse Position Modulation Pulse Position Modulation Refers to a multiple channel differential PPM signal in RC terminology See Also Pulse Width Modulation Pulse Code Modulation Pulse Width Modulation A modulation which encodes an analog signal into variable duration digital pulses Typically used to drive RC servos See Also Pulse Position Modulation Duty Cycle Modulation Unmanned Aerial Vehicle Note An unmanned vehicle is not necessarily autonomous See Also Drone 10
8. e rotor design Unfortunately current commercial implementations are too small to carry mainstream sensors and embedded com puters However due to its passive stability this design will probably turn out to be the preferred choice for hovering robots which do not require high maneuverability Another alternative is the quad rotor helicopter which is more silent mechanically more robust safer with ducted rotors and probably easier to control than a single rotor swashplate design Potential weaknesses include the overall size of the aircraft for a given payload the energy efficiency of four small motors versus a larger one providing the same lift and the impact of usually fixed pitch rotors with high inertia on maneuverability For this project we use a microhelicopter kit containing ChRoMicro Cheap Robotic Microhelicopter HOWTO EN A pre assembled helicopter with variable collective pitch rotor two brushed motors and three minia ture servos e An all in one controller package with BEC 6 channel RC receiver yaw gyro and ESCs A 41 MHz 6 channel RC transmitter with hardwired CCPM mixing e A 11 1 V lithium polymer battery A battery charger The aircraft has a mass of 270 g and can lift about 50 g of payload Figure 1 Contents of the integrated controller in a typical commercial microhelicopter kit An all in one controller package connects all the components together This is in contrast with larger model h
9. e signals This modification can be done in such a way that the original functionality is restored simply by discon necting the CPU board and inserting a jumper 4 3 Xbox controller mod Xbox controllers are widely available inexpensive and have well defined functionality unlike PC joy sticks They can be connected to a PC by replacing the proprietary connector with a USB type A plug Just connect the four wires with matching colors and ignore the extra yellow wire Alternatively any USB joystick a k a joypad or gamepad with two dual axis analog sticks can be used In this case the mixer configuration file must be adjusted to match the layout of the axes see ipre_tx in PXARC 5 Software The software developed for this project is now packaged separately See PXARC Figure 3 Mixer configuration xpad_ccpm120_mode2 mix wT SEPIA 4 IN ies F Y a A if iJ Creisser i JE A po f IRE ig 5 MOTOR A E Figure 4 Coefficients for 120 CCPM mixing for reference Depending on the type of helicopter used it might be necessary to configure iprc_tx to perform the CCPM mixing An example can be found in Figure 3 Mixer configuration xpad_ccpm120_mode2 mix ChRoMicro Cheap Robotic Microhelicopter HOWTO EN 6 System integration Figure 5 Helicopter ARM Linux _ 5y REGULATOR BLUETOOTH ANTENNA Q he o E fa re S s a o www pabr
10. elicopters where the connections between the receiver gyro BEC and ESCs are exposed and documented Integrating all these functions reduces size weight and cost but makes modifications harder Fortunately in some commercial microhelicopters the all in one controller can be tinkered with fairly easily lt actually consists of two boards connected back to back with a 2x3 pin connector see Figure 1 Contents of the integrated controller in a typical commercial microhelicopter kit e A generic RC receiver board with seven 3 pin PWM servo outputs e A power gyro board with BEC gyro fail safe and ESCs Table 1 RC receiver PWM outputs lists the PWM outputs of the receiver board two of which are routed internally to the power gyro board Table 1 RC receiver PWM outputs Channel Usage 1 Right servo 2 Front servo 3 Main motor internally connected to the power gyro board 4 Tail rotor internally connected to the power gyro board Unused Left servo Unused 12 ms sync pulses Any similar helicopter can be used The main requirements are The controller board must use PWM signals Generating PCM signals would require more work es pecially if proprietary encodings are used The controller board must expose the multiplexed PPM signal between the FM radio receiver and the demultiplexer see Section 4 2 PWM injection mod or at least the PWM inputs to the motor E
11. olled aircrafts are not toys They are usually operated by properly trained hobbyists on dedicated airfields in compliance with any applicable regulations with adequate liability insurance Due to their mechanical complexity and large moving parts helicopters are among the most danger ous aircrafts Experimental robotic aircrafts tend to wander in unpredictable ways Ensure you have enough room Software dumps core Hardware crashes figuratively Flying hardware crashes into the ground or worse Lithium polymer batteries are known to burst in flames when damaged or misused Bluetooth radio range is 10 m This is not appropriate for outdoor remote controlled flight Unlike 41 72 MHz R C radio equipment Bluetooth and Wi Fi products use shared radio spectrum which can be jammed by various sources 3 Off the shelf components 3 1 Helicopter platform A number of inexpensive microhelicopters are now available to RC model hobbyists Ikarus Piccolo MS Hornet Carboon Dragonfly Honeybee Hummingbird Tiny Aerohawk Blade CP Sky Lark These are essentially scaled down versions of regular model helicopters made possible by advances in battery technology Some models have a rotor head with fixed collective pitch FP while others have both cyclic and collective variable pitch CP Most have a dedicated tail motor rather than a variable pitch tail rotor A recent radical innovation is the ProxFlyer self stabilizing deformabl
12. tage regulator mod The power gyro board has two 5 V voltage regulators labelled CX1117 5 0 and mounted in parallel Current is 50 mA when idle and ranges from 3 to 5 A while flying Since this 5 V rail is exposed on each servo connector including the unused ones the CPU board can be conveniently powered from it In order to accomodate the extra current 100 to 200 mA it might be necessary to replace the two voltage regulators with a larger externally mounted regulator ChRoMicro Cheap Robotic Microhelicopter HOWTO EN 4 2 PWM injection mod Figure 2 RC receiver board details and modifications in red In order to control the helicopter we modify the RC receiver board so that the board can inject its own PPM signal into the PPM demultiplexer Why not get rid of the receiver board entirely and generate five PWM signals with the CPU board 2 The proposed approach has several advantages No need to build a custom PCB e Only three wires between the CPU board and the original controller GND 5 V and one multiplexed PPM signal e The PPM demultiplexer adds one layer of electrical isolation between the CPU board and the power circuits Figure 2 RC receiver board details and modifications in red shows details of a typical RC receiver board and the modification Simply cut the correct PCB trace s and connect both ends to a 2 pin con nector outside of the plastic enclosure Chronograms should help locate th
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