dc-motor-control-DSPIC30F4011

Implementing a basic control system for an autonomous ground vehicle.

A microcontroller board is connected to two motors, forming a differential drive. Let l = 0.5 m be the distance between the wheels, and r = 0.2 m the radius of the two wheels. The microcontroller receives desired reference values for the speed and the angular velocity of the robot. These reference signals are sent through a serial interface. The microcontroller sends feedback messages back to the control PC to report a few status information.

Board Description

dsPIC30F4011 Enhanced Flash 16-bit Digital Signal Controller

dspic30f4011 kit

Parametrics

• CPU Type: dsPIC® DSC
• Program Memory Size(KB): 48
• Operation Voltage Min.(V): 2.5
• Operation Voltage Max.(V): 5.5
• Pin Count: 40
• Segment LCD: 0
• LCD/Graphics Interface: No

Peripheral Features

• High current sink/source I/O pins: 25 mA/25 mA
• Optionally pair up 16-bit timers into 32-bit timer modules
• 3-wire SPI™ modules (supports 4 Frame modes)
• I2C™ module supports Multi-Master/Slave mode and 7-bit/10-bit addressing
• Addressable UART modules with FIFO buffers
• 1 CAN module, 2.0B compliant

Hardware specifications

• Each motor can run from -50 to +50 RPMs

• The motors are controlled through a PWM signal.

• The frequency must be 1 kHz.

• 50% duty cycle corresponds to 0 RPM, 0% corresponds to -60 RPM and 100% corresponds to 60 RPMs.

• A dead time of at least 3 microseconds should be used to prevent problems with the H-bridge controlling the motors.

• Running the motors above +-50 RPMs can damage them and should be avoided.

Firmware requirements

The control systems should compute the desired RPMs of the wheels using a differential drive kinematic model. The control system must never generate PWM signals outside of the specifications of the motors.

• If the requested speed and angular velocities of the robot are such that the necessary motor RPMs are outside the maximum specifications, the system should saturate them to the minimum/maximum allowed value.
• An alert message (MCALE) should be sent at 1 Hz until the desired references are changed again and fall below the threshold.

If no references (i.e., the MCREF command) are received from the PC for more than 5 seconds, the firmware should enter a timeout mode:

• Both motors velocity should be set to zero.
• Led D4 should blink at 5 Hz to signal timeout.
• When a new reference is read, then the led D4 should stop blinking and commands should be given again to the motors.

The firmware must support receiving references at least at 10 Hz frequency (through a proper choice of baud rate).

• The firmware does not reply with an ack to reference messages.
• The frequency should be guaranteed even in case of ENA messages (assume at least 1 per second)

The firmware must refresh the PWM value at least at 10 Hz frequency. The firmware must acquire the temperature sensor at 10 Hz frequency and average the last 10 readings. The averaged value is sent to the PC at 1 Hz frequency with the MCTEM message. The firmware must send the feedback message MCFBK at 5 Hz frequency. The control system should blink led D3 at 1 Hz to always signal a correct functioning of the main loop, regardless of any state. Given the chosen UART baudrate, the firmware should never lose a message due to its implementation (i.e., proper dimensioning of buffers), even with full use of the bandwidth If button S5 is pressed, the firmware should enter a safe mode:

• Motors are stopped immediately, and reference signals are ignored until the microcontroller receives an enable message (HLENA).
• After exiting safe mode, the motors should be set to zero. Motors should move only after receiving a new reference. Once an enable command is received, the firmware should send a positive ack to the PC.

The firmware should write on the LCD

• First row: “STATUS: x”, where x = H/T/C (halt/timeout/controlled)
• Second row: “R: n1; n2”, where n1 and n2 are the applied RPM (e.g. “R: -20; 33”)

If the button S6 is pressed, the data displayed on the LCD changes as follows:

• First row: “STATUS: x”, where x = H/T/C (halt/timeout/controlled)
• Second row: “R: omega; v”, where omega is the reference angular velocity, and v is the desired linear speed for the ground vehicle

If the button S6 is pressed again, the data displayed toggles again to the first one.

Messages from the PC

$HLREF,omega,speed* where omega (rad/s) is the desired angular velocity and speed (m/s) is the desired linear velocity for the robot.

$HLENA* enables the firmware to send references to the motors (to exit safe mode)

Messages to the PC

$MCFBK,n1,n2,state* where n1 and n2 are the applied RPM values and state is 2 if the microcontroller is in safe mode, 1 if it is in timeout mode, 0 otherwise.

$MCALE,n1,n2*, where n1 and n2 are the compute wheel RPM values that are outside the maximum allowed values.

$MCTEM,temp* where temp is the temperature

$MCACK,msg_type,value* where msg_type is the command (e.g. ENA, SAT), and value is 1 if the message was applied and 0 otherwise (example: $MCACK,SAT,0* for a negative ack to the saturation command)

Authors and contact

• Ali Yousefi *email: aliyousefi98@outlook.com

• Mohammad Reza Haji Hosseini *email: mrhhosseini75@gmail.com