Sistemi Mobili. Differential wheeled robots. Angelo Trotta

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1 Sistemi Mobili Differential wheeled robots Angelo Trotta

2 Differential drive wheeled robots Very common robot type Easy model

3 Components - Arduino Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It's intended for artists, designers, hobbyists and anyone interested in creating interactive objects or environments.

Components Motor driver The TB6612FNG motor driver can control up to two DC motors. Two input signals (IN1 and IN2) can be used to control the motor in CW and CCW.

4 Components Motor driver The TB6612FNG motor driver can control up to two DC motors. Two input signals (IN1 and IN2) can be used to control the motor in CW and CCW. The two motor outputs (A and B) can be separately controlled, the speed of each motor is controlled via a PWM input signal. The STBY pin put the motors in standby mode.

5 Components Motor driver Power supply voltage: VM=15V max, VCC= V Output current: Iout=1.2A(avg) / 3.2A (peak) Standby control to save power CW/CCW/short brake/stop motor control modes Built-in thermal shutdown circuit and low voltage detecting circuit All pins of the TB6612FNG broken out to 0.1" spaced pins Filtering capacitors on both supply lines

6 Components Motor driver A01-A02 = Motor A output B01-B02 = Motor B output AIN1-AIN2 = Motor A input mode PWMA = Motor speed (PWM) BIN1-BIN2 = Motor B input mode PWMB = Motor speed (PWM) STBY = Standby pin

7 Components Motor driver

8 Components - Chassis

9 Components - Chassis Max Motor Voltage: 6VDC No Load Speed: 90±10rpm No Load Current:190mA (max.250ma) Torque: 800gf.cm Stall Current: ~1A 65mm Diameter Wheels (30mm Wide) Plastic Rims with Solid Rubber Tires

10 Connections

11 EMF (Electromotive Force) EMF (Electromotive Force) is basically current that is generated (in this case) when inertia keeps a motor spinning after its power has been cut. The motor effectively becomes a generator, and the current it generates "kicks back" into the circuit potentially causing damage to the components.

12 Back EMF (Electromotive Force) Protection

13 Ultrasonic distance sensor Working Voltage = DC 5 V Working Current = 15mA Max Range = 4m Min Range = 2cm Measuring Angle = 15 degree

14 Ultrasonic distance sensor 10uS pulse to the Trigger input to start the ranging The module will send out an 8 cycle burst of ultrasound at 40 khz The Echo is a distance object that is pulse width and the range in proportion

15 Experiment Follow the light Connect two eyes (light sensors) Go towards the sensor that sense more light.

16 Experiment Some code 1/3 void move(int motor, int speed){ //Move specific motor at speed and direction //motor: 0 for B 1 for A //speed: 0 is off, and 255 is full speed digitalwrite(stby, HIGH); //disable standby if(motor == LEFT_MOTOR){ digitalwrite(ain1, LOW); digitalwrite(ain2, HIGH); analogwrite(pwma, speed); }else{ digitalwrite(bin1, HIGH); digitalwrite(bin2, LOW); analogwrite(pwmb, speed); } } void stop(){ digitalwrite(stby, LOW); //enable standby }

17 Experiment Some code 2/3 void updatesensorsvalues(void){ lightleftvalue = analogread(light_left); lightrightvalue = analogread(light_right); } void updatemotorsvalue(void){ motorrightvalue = map(lightleftvalue, init_left+offset, LIGHT_MAX, 40, 150); motorleftvalue = map(lightrightvalue, init_right+offset, LIGHT_MAX, 40, 150); if (lightleftvalue < init_lightleftvalue+light_offset) motorrightvalue = 0; if (lightrightvalue < init_lightrightvalue+light_offset) motorleftvalue = 0; if ((motorleftvalue == 0) && (motorrightvalue == 0)) robot >sendcommand (Robot::STOP, 0); else robot >sendcommand (Robot::AHEAD, motorleftvalue, motorrightvalue); }

18 Experiment Some code 3/3 long readfromdistsens(int triggerport, int echoport){ //porta bassa l'uscita del trigger digitalwrite( triggerport, LOW ); //invia un impulso di 10microsec su trigger digitalwrite( triggerport, HIGH ); delaymicroseconds( 10 ); digitalwrite( triggerport, LOW ); long durata = pulsein( echoport, HIGH ); return (0.034 * durata / 2); } void updatedistancesensors(void){ distleftvalue = readfromdistsens(pin_left_trigger, PIN_LEFT_ECHO); distrightvalue=readfromdistsens(pin_right_trigger, PIN_RIGHT_ECHO); }

19 Hints of Control Theory System = Something that changes over time Control = Influence that change

20 Thermostat example

21 Thermostat example

22 Thermostat example

23 Thermostat example

24 Thermostat example

The Basic Building Blocks State = Representation of what the system is currently doing Dynamics = Description of how the state changes Reference =

25 The Basic Building Blocks State = Representation of what the system is currently doing Dynamics = Description of how the state changes Reference = What we want the system to do Output = Measurement of (some aspects of the) system Input = Control signal Feedback = Mapping from outputs to inputs

26 Dynamics: Change Over Time Laws of Physics are all in continuous time: we need derivatives with respect to time Continuous time (differential equation): dx =f (x,u) x =f ( x, u) dt

27 PID-Controller introduction

28 PID-Controller introduction

29 PID-Controller introduction

30 PID-Controller

31 PID-Controller

32 PID-Controller

33 PID-Controller

34 PID-Controller

35 PID-Controller

36 PID-Controller

37 PID-Controller

38 PID-Controller

39 PID-Controller

40 PID-Controller examples

41 PID-Controller examples

42 PID-Controller examples

43 PID-Controller examples

44 Robot model { R x = (v r + v l )cos(φ) 2 R y = (v r + v l )sin(φ) 2 R φ = (v r v l ) L }

45 Unicycle model We want a more familiar model Input: v, ω Dynamics: { x =v cos( φ) y =v sin( φ) φ =ω }

46 Connect the models Implement the robot model but design with the unicycle model { } { x =R /2(v r + v l )cos ( φ) x =v cos (φ ) y =R / 2(v r + v l )sin( φ) a n d y =v sin (φ ) φ =ω φ =R / L( v r v l) 2v+ωL vr = 2R 2 v ω L vl = 2R }

47 Control design P regulator In our robot we have two reference value: v and ω The velocity can be constant; For the angular velocity, we use the P-regulator (part of the PID controller) r =φ d ; e=φ d φ ω=k P e

48 What's next? Go-to-goal Drive a robot to a specific location. { x =v cos( φ) y =v sin( φ) φ =ω (xg,yg) (x,y) } r =φ d ; e=φ d φ ω=pid(e) y g y φ d =arctan( ) x g x

49 Position estimate - Wheel encoder It's important to know where is the robot. Wheel encoders give the distance traveled by each wheel

50 Position estimate - Wheel encoder Each wheel has N ticks per revolution

51 Used materials references on-line course: Control of Mobile Robots by Georgia Institute of Technology book: "Thinking in Systems [Donella H. Meadows; Diana Wright]

52 SISTEMI MOBILI Angelo Trotta Department of Computer Science and Engineering

POLITECNICO DI MILANO

POLITECNICO DI MILANO Final Year Bachelor Project PIXYBOT Mentor: Prof.Andrea Bonarini Author: Rohit Prakash Contents 1. Introduction....................... 1 2. Components....................... 1 2.1