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1.0 Introduction

The study describes the different phases executed during the demand to proving phases of “ Grimblebot ” . The automaton was two-wheeled and was capable of equilibrating itself by agencies of the provided feedback system. The undertaking was divided into two phases chiefly based on the two chief challenges faced:

  • How to do the automaton aware of its place
  • How to reconstruct the automaton so that the wheels stay under its Centre of gravitation thereby accomplishing balance

An supersonic detector was at the nucleus of the feedback system. The signals from the supersonic detector was read and interpreted. Following this, the angle made by the automaton with the land was calculated. From the angle, the rotary motion required to equilibrate the automaton can be calculated.

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The circuit design used to interact with the detectors, the manner the signals were interpreted and processed and eventually the manner stableness was achieved by changing the motor velocity and way will besides be described in the approaching subdivisions.

2.0 GRIMBLEBOT OVERVIEW

Grimblebot is made up of chiefly four functional faculties which are

  • Supersonic Sensor
  • The Ultrasonic PCB Board
  • Main Motherboard
  • Motor

2.1 Operation Process

The detector on the Ultrasonic PCB detector works on a request-respond footing. The reading from the detector is sent back as pulsations to the Ultrasonic PCB board receiving system when a petition is received from the Ultrasonic PCB board. The Ultrasonic PCB board, upon having the signal from the detector, converts the standard signal to a digital value and passes it on to the main/mother board. The motherboard does the calculation and sets the motor speed, way and rotary motion angle to obtain balance.

2.2 Ultrasonic PCB Board

The signal transmitted/received to/from the detector to place Grimblebot is generated/interpreted by the Ultrasonic PCB. The Ultrasonic PCB board is functionally composed of two chief constituents:

  • Supersonic Sender
    & A ; uuml ; Ultrasonic Receiver

2.2.1 The Sender

The chief constituents of the sender faculty are a microprocessor, a CD4000 and 6 1.2V batteries. The signal produced by the sender is amplified by the CD4000 bit. The 6 batteries connected in series produces a cumulative electromotive force of 7.2 V. This is required chiefly because the microprocessor produces a 50 KHz signal which is merely 3.3V.

This signal is farther amplified by differential signalling before being fed in to the transducer.

2.2.1.1 Differential signalling:

In differential signalling of a two-base hit ended system ( i.e. with a positive and negative Voltage Vs and -Vs ) , a electromotive force VS represents the high electromotive force degree and the low logic degree is 0 V. The difference between the two degrees is hence VS – 0V = VS. Now consider a derived function system with the same supply electromotive force. The electromotive force difference in the high province, where one wire is at VS and the other at 0 V, is VS – 0V = VS. The electromotive force difference in the low province, where the electromotive forces on the wires are exchanged, is 0V – VS = – VS. The difference between high and low logic degrees is hence VS – ( – Volt ) = 2VS ; twice the electromotive force of the system

This means the possible difference across the transducer will be 7.2V- ( -7.2V ) = 14.4V.

In consequence, the signal has been doubled and can now be fed through the transducer.

2.2.1.2 Level shifting:

The 3.3V produced, by the Microprocessor is beneath that of the logic Gatess voltage threshold and therefore needed to be level shifted to the 7.2V required. This is done utilizing transistors as shown in the circuit below.

Here the transistor acts as a switch. If the microprocessor outputs a low signal i.e. transistor off, the electromotive force of the input will be pulled high to the 7.2V rail electromotive force, and this is interpreted as a logic 1by the NOT gate.

When the microprocessor outputs a high signal, the transistor turns on and the electromotive force drops to zero. This is interpreted as a logic 0 by the NOT gate.

2.2.2 The Receiver

The receiving system is responsible for observing the reflected signal from land. The standard signal is translated to voltage and amplified and sent back to the microprocessor. The comparator on the motherboard compares the two end product signals and finds the bigger signal.

2.2.2.1 The Op-amp Filter:

The Op-amp used has a addition of 50. It has a cut-off of 70KHz and Acts of the Apostless as a low-pass filter.

The undertaking utilized the TLV2772 double op-amp.

2.2.2.2 The Comparator:

The comparator is used when there are two electromotive forces or current to be compared. The end product of a comparator is the larger of the two input electromotive forces. The comparator in the below given figure wo n’t give an end product until the electromotive force exceeds 2 V is generated by the Op-amp. Until so the end product wo n’t travel high.

2.2.3 Assembly of the Ultrasonic PCB

When the end product from the circuit matched with the expected values, the Ultrasonic PCB development was complete. Then the girl board was soldered on to the motherboard.

2.3 Microprocessor and Motor Driver

2.3.1 Microprocessor

The microprocessor ‘s chief map was to accept the signal being reflected from the land and being sent by the receiving system. The clip taken for the signal to have the microprocessor was used to cipher the angle made by Grimblebot with the land. This clip could be calculated by cognizing the clock frequence and the standard signal. The algorithm pre-pre-programmed in to microprocessor was adapted consequently after test and mistake trials.

2.3.2Motor Driver

H-Bridge circuit was used to drive the motors in the undertaking.

6 1.2V V batteries were connected in series to bring forth 7.2V in entire. The motor thrusts clockwise if Q1 and Q4 are closed and Q2 and Q3 are unfastened. The reversal of this causes the motor to revolve anti-clockwise.

Q1

Q2

Q3

Q4

Consequence on Motor

1

0

0

1

Moves it to the right

0

1

1

0

Moves it to the left

0

0

0

0

Undesired province

0

1

0

1

Brake systems

1

0

1

0

Brake systems

The chief aim of microprocessor was to execute the calculation and bring forth the coveted signals to maintain Grimblebot in equilibrium. But the signal produced by the microprocessor is non high plenty to drive the motor. And it is besides necessary that parallel end product is given to the motor.

Digital signals are non good plenty to revolve the motor because that would render the bot unstable. Alternatively, the current passed to the motor must change as per the feedback obtained so that stableness is attained.

PWM is capable of rendering a scope of current to a coveted device. So as per the demand, the current supplied to the motor is varied between nothing and full power.

The frequence of the current passed on to the motor is maintained a changeless. Alternatively, the breadth of the signal is varied so as to supply intermediate phases of power. The square moving ridge used in Grimblebot was 20KHz.

2.4 Power Rails

To circuit is powered by: –

  • 6 1.2 V batteries connected in series to bring forth 7.2 V.
  • 5V connexion to power the female parent board.
  • 3.3 V to power the Ultrasonic logic board.

2.5 The Motherboard

The completion of the girl board ( Ultrasonic logic board ) was followed by soldering the board on to the motherboard. The motherboard ‘s mill scenes and layout were non modified for the undertaking.

2.5.1 Assembling the Motherboard:

Soldering of the constituents was followed by heating the full board in the oven. This ensured that the constituents were decently fixed. Once the motherboard was assembled, the transducer circuit was added on.

3.0 Simulation consequences

All the sub-circuit were simulated and tested on OrCAD before implementing on the existent device. The board design, the constituent evaluations, PCB layout were all performed every bit good to avoid ambiguity subsequently on. The PCB layout was done with both proving and wiring in head so as to utilize the infinite most expeditiously.

3.1 The consequences for the simulation of the Ultrasonic Transmitter

3.1.1 Fake consequence of Voltage across Output at R4:

Readings from R4 was used to cipher the differential electromotive force in the circuit.

3.1.2 Fake consequences of Op-amp/low base on balls filter of the Receiver

As a consequence of the addition bandwidth, cut-off frequence was manner lower than 70KHz. This was the cut-off value derived for Op-Amp.

3.2 Testing

3.2.1 Testing the Power Rails

In order to prove the power tracks, the croc cartridge holder was shorted with the land pin and checked the electromotive force evaluation on C11 capacitance. The end product obtained as a consequence is given above.

The graduated table at which the CRO was set was non right and this was the ground for the above end product. Once sorted, the expected end product was obtained.

3.2.2 Power Rails to Daughter Card

When the Ultrasonic PCB was connected and electromotive force measured the below given was the end product obtained.

3.2.3 Microprocessor to Ultrasonic Board

The signal sent from the microprocessor and the one obtained on the girl board were the same and the graph below confirms the same.

3.2.4 Ultrasonic Board to Microprocessor

3.2.4 Ultrasonic Board to Microprocessor

3.2.5 Transistor Testing

When every constituent on the board was tested to happen out the ground for the wrong end product electromotive force, it was found that the transistors were non soldered decently. The mutual opposition scene was incorrect and this was the cause of the job. The constituent had to be taken and re-set in the right manner. That solved the job of incorrect end product signal ( 3.3 V ) and the moving ridge below was obtained.

4.0 Performance Evaluation

Grimblebot was tested in two conditions. On carpeted floor and on smooth floor every bit good. The 1 on carpeted floor was done in G26. The other trials were conducted outside G26.

4.1 Method

In order to turn on Grimblebot, it should be manually supported in a perpendicular place for around 12 seconds. This is required for the different constituents of Grimblebot to interchange signals and modulate its steady position. Once the potentiometer stabilizes the speed and angle of the motor, Grimblebot will equilibrate itself.

4.2 Testing the Grimblebot

4.2.1 Test One

Time ( in hours ) : 0:14

Detailss

During the first trial, Grimblebot was unable to equilibrate itself. It would fall forwards or backwards neglecting to swing back to equilibrium. The potentiometer seemed to be able to put the motor in merely one way and so stopped.

4.2.2 Test Two

Time ( in hours ) : 3:00

Detailss

During the 2nd trial, it was realized that the consequences in the first trial were chiefly due to the wrong signals as input to the Ultrasonic PCB.. The signal received was non the square moving ridge as required. Alternatively it seemed to be greatly affected by some external noise somehow.

4.2.3 Test Three

Time ( in hours ) : 3:00

Detailss

In this session, it was identified that the transistor had been soldered with incorrect mutual opposition in topographic point. Subsequently on, it was reset in the right manner as per the design diagram. This greatly affected the public presentation and took a large pace forwards. Following plentifulness of test and mistake trials, Grimblebot was able to accomplish stableness after standardization values obtained from consequences. The detectors were non at the right angle ab initio and this besides caused jobs during the proving procedure.

4.2.4 Test Four

Time ( in hours ) : 3:00

Detailss

In this session, the detectors and batteries were changed. After seting the motor, Grimblebot was able to remain steady for 68 seconds on carpeted floor. When it was set up in an unsupervised and uncarpeted floor, Grimblebot balanced itself for 97 seconds.

5.0 Points to take a note off:

Improper bonding led to constituents giving incorrect or wrong readings.

Presence of solder Fe on the PCB at wrong topographic points led to resound and affected the public presentation of the full circuit. Advancement in the undertaking was hindered as a consequence and had to be removed before go oning.

When one of the constituents was wrongly placed during the soldering procedure, taking the constituents led to the Cu tracks checking thereby cutting off the signal flow. Later, a wire was merely inserted into the cleft and the signal flow was restored as a consequence.

5.2 Placement:

Ideally the decoupling capacitance is to be placed near a peculiar constituent. The uncoupling capacitance reduces the noise produced in the circuit. During proving, it was found that the placement of the transistor and comparator were non proper and as a consequence had to be removed and resoldered. The circuit had to be designed so that the IC was placed so as to cut down on wiring every bit much as possible.

5.3 Batteries:

Lack of sufficient power besides affected Grimblebot doing it to neglect in keeping the balance.

5.4 Using incorrect Intelligence community:

Wrongly utilizing an IC alternatively of a comparator besides caused circuit to give no end product at all. This job was solved by subsequently on replacing it with the right comparator.

5.5 Tolerance:

Tolerances of the constituents vary and exact end product values are hard to cipher.

5.6 Detectors:

The detectors were calibrated by altering the angles after executing plentifulness of test and mistake trials. The angle it was set subsequently on was besides dependent on the sensitiveness of the detectors every bit good. Initially Grimblebot used to travel off balance in malice of working decently for twosome of rhythms.

6.0 Decision

Even after puting up as per the specialisations, it required batch of test and mistake trials for Grimblebot to eventually accomplish equilibrium.

The whole circuit was ab initio simulated on OrCAD and this helped to plan the circuit and place the chief issues that might happen during the development procedure. Once the PCB was done from abrasion, and constituents attached, the system was tested. The end product electromotive force from the microprocessor was 3.3 V and that from transistor was 7.2 V as required. This was plenty to bring forth a 50KHz signal from the detector. This signal was subsequently amplified.

Once it was made certain that Grimblebot design and end product values were as per specification, it was initialized and had to be held up for a continuance of around 12 seconds. This gave the system clip to exchange signals and initialise them. Once the potentiometers were calibrated, the motor velocities adjusted themselves until Grimblebot balanced itself.

7.0 Recommendations

7.1 Excessive wiring can be avoided by puting constituents which require more interconnectednesss closer.

This could hold been taken attention of the design phase of the undertaking itself. As a consequence of communications with other boards as good, there were wires running across the boards besides. Even though an effort was made to cut down on the figure of wires, there was a definite bound to the result because of clip restraints chiefly.

7.2 Move the decoupling capacitance closer to the microprocessor:

When the decoupling device was kept at a distance from the constituent, it was noticeable that the signals were non expeditiously filtered before making the microprocessor. Filtering seemed to be much better when it was kept nearer to the device.

7.3 Larger dial for a potentiometer:

Initially the potentiometer used was non plenty to supply sufficient item for finer motions of Grimblebot at phases where it about reached equilibrium. This was because of deficiency of information provided by potentiometer when it moved towards stableness. Replacing the potentiometer with a larger dial, helped to supply more information to the motor.

7.4 Transducer circuit board with increased country:

Trying to do the circuit board compact resulted in set uping all the constituents in really limited country. But this had a positive side of seting lesser weight on Grimblebot. But it resulted in congestion on the board because of plentifulness of wiring. Increasing the country of circuit board could hold led to neater agreement of constituents and lesser wiring every bit good. A board layout of 9 * 11 alternatively of 9 * 7 is suggested.

7.5 Testing surfaces:

The calculations performed by Grimblebot are chiefly based on the clip taken by the signal to acquire reflected back to the receiving system. When Grimblebot was tested on uncarpeted surfaces, this response clip was less and Grimblebot seemed to accomplish equilibrium faster. Meanwhile, when placed on carpeted surface, the reflected signal got distorted chiefly because of the nature of the surface of the rug. This delayed the clip taken by Grimblebot to stabilise itself

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