The alternatives considered during the design process are represented in this section. In order to have a systematical and detailed feasibility study, the design alternatives are classified in four different sections. There are some sub-sections for making it clear to see the specifications of the alternatives. Necessary drawings for the alternatives are given in Appendix A.

Driving torque from the motor is sent to both of the wheels by means of a differential mechanism located between the wheels.

Advantages: Just one motor is sufficient to drive. Better for straight motion.

Disadvantages: Difficult to manufacture (higher cost). Requires a prime mover for control.

Two different motors drives two opposite wheels. The motors are controlled by different control systems.

Advantages: Can be controlled easily. Simpler to manufacture and operate.

Disadvantages: Requires more energy to operate. Lower probability of motion along a straight line.

Driving torque is given to rear wheels. Front wheels are navigated by an Ackermann mechanism. Appendix A-Figure 5

Advantages: Easier and more precise control.

Disadvantages: Another motor is required for navigation of front wheels. Difficult to manufacture and mount. High precision is required.

Four wheels placed at four corners. Can be either front wheel drive or rear wheel drive. Can be driven by almost all of the drive mechanisms.

Advantages: Simplest and the most stable choice. Easy to manufacture and mount.

Disadvantages: Cause problem during rotation. The non-driving wheels may experience friction during rotation. Rotation time may not be enough to prevent the vehicle from falling.

4.1.2.2 Three Wheels: Two wheels plus an idle wheel.

4.1.2.2.1 The front wheel is the idle wheel. Requires differential drive or step motor.

Advantages: May work both with differential drive or with one motor for driving and a step motor for navigation. Better for rotation (especially if differential drive is used).

Disadvantages: Very unstable. May have difficulties in balancing and navigation.

Bad in straight line motion.

4.1.2.2.2 The rear wheel is the idle wheel and driving torque is given to the front wheels.

Advantages: Better for straight line motion. Works better with differential drive.

Disadvantages: High probability of falling down during rotation (since axis of rotation would be the other front wheel). May have problems in balancing.

Two track mechanisms placed at each sides of the vehicle. It is formed by a belt wrapped around two wheels for each side. Requires differential drive.

Advantages: High stability. Better rotation with minimum risk of falling down (rotation without further movement). Decreased slippage between with the surface.

Disadvantages: Low probability of straight line motion. Requires more power. Difficult to manufacture and mount.

4.2.1 Rack and Pinion Mechanism

Mechanism works by a pinion mounted to a motor and a horizontal rack placed inside a slider. On the rack, there is a needle to hit and drop the cubes, which are placed in a container vertically. Appendix A – Figure 6

Advantages: Higher speed and precision during operation. One motor is sufficient.

Disadvantages: Requires rotation in opposite directions steadily. Probability of locking. Difficult mountage (precision needed), requires a slider additionally.

A horizontal powerscrew rotating makes a slider move along and carry the cubes that are placed in a vertical container to the holes provided.

Advantages: Safe and precise.

Disadvantages: Works slowly. Requires rotation in opposite directions. Heavy.

A solenoid is used to hit and drop the cubes placed in a vertical container (since there are two regions in each side for placing cubes, two of these mechanisms are required). Appendix A – Figure 7

Advantages: Simpler for manufacturing, mounting and operation.

Disadvantages: Two different mechanisms are required for each side. Requires high electrical energy.

A rotating arm connected to a motor hits and drops the cubes. May be both horizontal or vertical.

The cubes are placed in a vertical container and the arm hits the bottom cube to the holes placed at each sides of the container.

Advantages: Occupies less space. Easy to control (may have rotation more than 360° which is crucial if the cube locations on the beam are considered).

Disadvantages: Possibility of locking. Replacing the fallen cube due to effect of gravity may cause alignment problems.

The cubes are placed in a horizontal container and recharged with the help of a spring.

Advantages: Recharging the cubes decreases possibility of locking and misalignment of cubes.

Disadvantages: Occupies much space. Requires springs with proper compressibility.

Mechanism works by a pinion mounted to a motor and a vertical rack placed inside a slider. An arm is joined to the rack, which holds all the cubes in a vertical container. As the arm goes up in each step, the cubes stick to the upper beam. After sticking, the arm moves down to prevent friction between the cubes and the upper beam.

Advantages: Higher speed and precision during operation.

Disadvantages: Requires rotation in opposite directions steadily. Probability of locking. Difficult mountage requires a slider additionally. Appendix A Figure 8

A vertical powerscrew rotating raises the slider, which carries the cubes until contacting to the upper beam and after sticking occurs, comes down in order to prevent friction between the cubes and the upper beam.

Advantages: Safe and precise. Simpler to operate.

Disadvantages: Requires high rotational speed and rotation in opposite directions.

A crank is rotated by a motor at a pre-specified angle in order to raise the cubes up, which are located on the slider link and kept in a vertical container.

Advantages: Little rotation of the motor is sufficient. Appendix A – Figure 9

Disadvantages: High probability of locking. Requires high precision control for rotation of pre-specified angles.

A vertical conveyor belt with a holding arm perpendicularly stuck to the belt used for carrying the cubes upwards. The cubes are placed vertically on the arm and driving motor rotates at a pre-specified angle for each cube.

Advantages: Little rotation of motor is sufficient. Better accuracy in motion.

Disadvantages: High forces occur in contact with the belt. Possibility of jamming of cubes between the beam and the belt. Appendix A – Figure 10

4.4.1.1 Electronic Circuit:

An electronic circuit is a simple device to control the operations carried out in the system. It is composed of electronic units like transistors, resistances, capacitors etc replaced on a main board.

Advantages: Simple. Occupies less space.

Disadvantages: The program can be loaded only once and the whole circuit should be renewed in case of any adjustment in the system.

A microprocessor is replaced on a mainboard with the other electronic components and used for controlling the operation of the system. It should receive signals coming from sensors or encoders and control other units like motors, solenoids etc with respect to these signals.

Advantages: The program to be loaded on the micro processor can be changed replaced or deleted according to changes in operation.

Disadvantages: Expensive. Sensitive (can be affected by electrical or magnetic field).

4.4.2.1 Encoders:

In order to control stopping of the machine at pre-specified locations, an encoder may be placed to the motor shaft. The encoder sends signals to the control unit and actuates the necessary mechanism.

Advantages: Requires trial & error procedure in order to reach necessary solution. Easily assembled.

Disadvantages: Includes expensive parts. May experience deviations in case of slippage.

4.4.2.2 Optical Sensors:

Mainly used for sensing the aluminum foils placed on the beams. After sensing the aluminum foil, gives signals in order to stop the machine and operate the other mechanisms. Could also be used to keep the machine on the beam.

Advantages: Works in high speeds. Better accuracy. High sensitivity.

Disadvantages: Requires more outlets from the micro processor. Expensive. Can be affected by external causes.

4.4.2.3 Micro Switches:

Used for keeping the machine on the beam. Placed at two outermost points at the sides of the machine and connected to the driving motor(s).

Advantages: Does not require connection with the controlling unit. Can be connected directly to the driving units. Simple. Cheap.

Disadvantages: Has probability of deviation from the direction since there is always a friction between the microswitch and beam. Since works mechanically, there is possibility of failing during operation.