Design and Fabrication of RC PWM compatible Drive for a four wheel differential drive Robotic Platform.

PORJECT CO-ORDINATORCHAIRMAN ELECTRONICS DEPARTMENT

Prof Engr. Rashid Baig

A PROJECT FOR Pakistan Space and Upper Atmosphere Research

Commission (SUPARCO)

Project Members

OWAIS JABBAR (GROUP LEADER)

SYED ZAKIR HUSSAIN ZAIDI

FAHEEM AHMED SHAIKH

MUHAMMAD JUNAID

MUHAMMAD AQIB RAJPAR MUHAMMAD HASSAN

DIFFERENTIAL DRIVE

Differential drive is a method of controlling a robot with two/four motorized wheels.

The term 'differential' means that robot turning speed is determined by the speed difference between the two differentials that is, front and rear wheels of your robot.

The differential drive steering system determines the orientation of movement based on speed of its individual channels.

In a four-wheel differential drive system there are usually two independent channels (right and left channel) on both sides of the robot.

The four wheel differential drive has separate motors driving the left and right sides of the vehicle, which can therefore have differential speeds.

If the speed on one wheel (channel) is same as the speed on other wheel then vehicle either moves in forward or in reverse direction without turning.

The difference in speeds on the channels results in rotation of the vehicle. The vehicle will turn toward the side which has less speed than the speed on the other channel.

If one channel moves forward and the other channel either remains stationary or moves backward then vehicle will spin around the stationary wheel or the center of the axle of the two wheels, respectively.

The rotation of wheels of robotic system is done by the use of DC motors. The speed of DC motors is dependent on the input voltage given to it.

1. Design of Electronic Drive Circuit.2. Capable of driving PMDC up to 60 Volts and 30 Amp per

motor3. Capability to operate the differential drive vehicles via

commercially available RC transmitter receiver 4. Thermal design 5. Drive hardware box 6. Testing on real system.

PROJECT TASK

FLOW CHART OF PROJECT

POWER SUPPLY

RC TX/RX

MICROCONTROLLER

DRIVER CIRCUIT

H-BRIDGE

ROBOTIC PLATFROM

POWER SUPPLY

2 BATTERIES HAVE BEEN USED• Lippo battery 14.8volts• Lippo battery 7.2volts

POWER UNIT The Power Unit or Power supply is capable of

providing two voltage levels: +5 Voltages(7805) +12 Voltages(7812) Two different voltage levels are the

requirements of the project circuitry, the Microcontroller circuit board and Driver IC board requires +5volts and +12 volts for driving H-bridge.

The large main capacitor primary purpose is to suppress transient spikes caused by the motor. Often when the motor accelerates, decelerates, or stops suddenly, an EMF “feedback” voltage will spike on the main battery voltage.

RC TRANSMITTER/RECEIVER Radio control (often abbreviated

to R/C or simply RC) is the use of radio signals to remotely control a device.

The term is used frequently to refer to the control of model vehicles from a hand-held radio transmitter.

 Industrial, military, and scientific research organizations make use of radio-controlled vehicles as well.

MICROCONTROLLER

The signals from RC TX/RX are captured and decoded by the microcontroller and then transferred to H-bridge

Microcontroller used PIC18f45k22

3 CCP and 2 ECCP MODULES

MICROCONTROLLER AS A PWM decoder

RC produces PWM signals that are compatible for Servo motors only

Task is to operate PMDC motors

Microcontroller decodes the PWM signals for PMDC motors using CCP and ECCP modules

CCP & ECCP MODULES

PIC Microcontroller is used in Capture Mode, in this case an event occurs at CCP pin will start 16 bit timer register.

Using Capture Mode for measuring width of pulse given by RC

On every 1st rising edge timer will get start and it will start counting unless next falling edge will come on which timerl will be stopped.

On the basis these calculated values the CCP module will make a scale of duty cycles which are then transferred to ECCP module.

Compare/capture and PWM Enhanced compare/capture and PWM

PULSE WIDTH PROVIDED BY RC

FUCNTION OUTPUT TO ECCP

1ms -1.5ms Acceleration in Forward position 0-100%

1.5ms Break position 0% Duty cycle

2ms Acceleration in reverse direction 0-100%

FUNCTIONS ON DIFFERENT SCALES

DRIVER CIRCUIT (LEVEL SHIFTER)

The IR2110 are high voltage, high speed power MOSFET drivers with independent high and low side referenced output channels.

They operate on bootstrapping principle or floating power supply principle.

Bootstrapping circuit is composed of capacitor & fast switching diode.

Bootstrap capacitor acts as floating power supply for high side mosfet.

CONCEPT OF BOOT STRAPPING

Bootstrapping circuit provides extra voltage at gate of mosfet above than source level so that mosfet switches on.

Gate voltage must be 10 V to 15 V higher than the source voltage. Being a high-side switch, such gate voltage would have to be higher than the rail voltage.

H-BRIDGE DRIVER CIRCUITA link between digital circuitry and mechanical action

An H-bridge is a simple circuit, containing four switching element, with the load at the center, in an H-like configuration.

The H-Bridge is a circuit which can drive a DC motor in forward and reverse. The motor’s direction is changed by switching the flow of current in order to turn the motor one way or the other.

When switches(Mosfet) S1 and S4 are closed the motor gets power and spins. When S2 and S3 are closed the motor gets power and spins in the other direction. Note that S1 and S2 or S3 and S4 should never be closed together in order to avoid a short circuit.

DRIVING ROBOTIC PLATFORM

If Both Motors rotate In clockwise direction. Vehicle moves In forward direction

If both motors rotate In anti-clockwise direction vehicle moves In reverse direction

For turning our vehicle one motor In clockwise direction and other anticlockwise direction

ARE THE GIVEN TASKS COMPLETED ?

Design of Electronic Drive Circuit.The H-bridge consisting of 4 Mosfets and driver circuit consisting of ir2110 IC are required Electronics circuitry.

Thermal designThe Electronic components dissipate heat, which is harmful for circuit to avoid it, each circuit is designed on separate PCB module.

Capability to operate the differential drive vehicles via commercially available RC transmitter receiver Vehicle’s direction and speed can be varied with the help of PWM signals and these signals are obtained from commercially available RC TX/RX

Capable of driving PMDC up to 60 Volts and 30 Amp per motor .The Mosfet which are used in our h bridge are STP75NF75they can bear an output voltage up to 75volts and current up to 75amps

Testing on real System For testing our driver circuit we have design a robotic vehicle.

ROBOTIC PLATFORM

APPLICATIONS

Used in industries for lifting heavy loads( i.e. Automobile industries).

Space vehicles are best example.