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16396 - Integrated Design

Group M7Six Legged Locomotive

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ObjectivesAimTo build a six-legged walker, capable of travelling in a straight line, over rough

ground.

Performance Criteria• The robot must cover a distance of approx. 10m.• It must walk this distance on 6 legs without falling over, or self-righting if it does

fall.• It must walk in a straight line, which may require correctional steering.• It must walk at a speed of approx. 0.03 m/s.• It must be able to operate for about 30 min.• It must be able to walk across horizontal rough ground.

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DesignThe final design was selected because it had:• A stable leg arrangement.• A minimal number of motors which reduced cost.• Potential to incorporate 360 steering.

The material chosen was Perspex because it was:• Light and strong.• Easy to manufacture parts quickly and accurately.• Cost effective.

Wireless remote control was chosen:• To reduce costs.• To simplify the design.

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Design - System Block Diagram

These sections were then delegated to different group members:

• Remote Control – Lewis & Niall

• Mechanical Linkage – Iain & Niall

•Driving Mechanism – Tom & Nicola

Design - Prototypes

• The prototypes allowed a greater understanding of the leg mechanism to be gained.

• They also allowed the scale of the dimensions to be more accurately determined.

• However, it was time consuming and failed to model the movement.

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Design - 3D Modelling

The next stage was to produce drawings so that the leg mechanism could be manufactured by DMEM.

All these parts were created and assembled in ProEngineer allowing dimensions to be optimised.

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Implementation - Leg Mechanism

DMEM Pieces

Small Structures

Complete Leg Mechanism

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Design - Remote Control•Researched alternate methods of remote control. Decided that radio frequency remote control would be best for our application.

•Selected paired AM transmitter and receiver units and also the corresponding encoder and decoder chips.

•Implemented a logic circuit and motor driver chip to supply the motor with the required 24V.

•Relays were used to protect the motor driver chip and also allowed the motor to be driven in both directions.

Implementation - Remote Control

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Transmitter and receiver unit tested on protoboard. Problems with transmitter connections prevent transmission at first but were soon fixed.

Inverter chip, motor driver and diodes were added to the protoboard once stable transmission had been achieved. The complete circuit was tested without connection to the motor before the transmitter and receiver circuits were implemented on PCB’s.

Problems with ground connections on the receiver board prevented the motor driving in both directions. This was soon fixed and tests confirmed that the complete system operated as expected.

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Design - Driving MechanismThe motor had to be linked to the central point of all the legs via a shaft which had to be kept vertical.

Thus, two designs were produced as shown, and the one on the right was chosen due to its simplicity.

The motor was selected based upon torque calculations carried out using values of the leg mechanism mass.

The gears were chosen based upon the dimensions of the leg mechanism and the motor shaft.

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Implementation – Driving Mechanism

Two gears were connected to a driving gear on the motor shaft. There was also gearing within the motor to provide the required torque and reduce speed.

The connection between the driving gear and motor was the first problem found during testing. Without a strong connection no power was transferred.

The gears had to be drilled to allow the drive shaft to be attached. The correct positioning of these holes was vital as the gears must be in phase to reduce shearing.

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TestingTesting was carried out in stages prior to integration. Once each section was found to be working individually they were joined in stages and tested.

Problems found:•Weak connection between driving gear and motor shaft.•Weak connections on two of the legs.•Poorly positioned drive shaft separated motor housing from legs.•Stress crack caused a leg piece to break.

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EvaluationAchievements: •The solution was produced on time and within budget.• The six-legged walker successfully walks in a straight line.• The six-legged walker can be remotely controlled and made to walk both forwards and backwards.

Improvements:• Steering could be introduced.• Larger batteries could extend operation time.• The design could be adapted to handle rough terrain more effectively.

ConclusionWithin the budget and time constraints, the specification has been mainly satisfied. However, with additional resources more features, such as steering, could be included.

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