Fault Diagnosis

Upon finding the motor circuit was not operating correctly it was decided to trace the fault; so that appropriate action could be taken.
1. Using a continuity tester all the PCB was tested to ensure that no solder had 'tracked' across between lines. Only one case was found and quickly rectified but did not resolve the fault.
2. Using a voltmeter all voltages were inspected. Starting at the main battery pack and traced successfully to the motor circuit board. All voltages entering the motor circuit board were correct but the expected voltages that should have been seen on the motor terminals were not there. This suggests that there is a fault with the motor chip; which willneed replacing.

Final Design

The final and new buggy has been made as a team this weekend. Its chassis built from Durable modelling plastic ,and all the circuit boards soldered up nice and neatly. The jockey wheel has been far improved, and the whole buggy moves in a straight line and does not veer off to one side. The new Sensor array has been made with 4 White LEDS and 3 LDR's placed underneath the vehicle. With testing these appear to work really well giving constant values untill a black line is moved underneath them. However during Testing the motor circuit board has not been working this could either be a fault with the circuit or a blown motor chip.

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Bugguie Design

The intial and secon Prototype was made using a plastic box with some screws and masking tape. It was decided buy the team that the design of the buggies was need to be enhanced to look more professional. The team decided that we should keep the initial design but the chassis will be built by ourselves and wire the circuit boards up neatly.

For this a diagram of a the layout was required. It was drawn using Solidworks on an A3 sheet with 1:1 scale. This makes it easy to use and construct.

The chaise is a block of wood with carefully placed holes for the wiring. The wires will the run through the holes and under the chassis. This makes the wires unseen from the top and increases the look of the organisation.
As well as the wiring being neatened the team decide that the jokey wheel needs to be strengthened. This could possibly be achieved by changing the material used in construction.

A second prototype has been constructed and a few changes have been made. The chassis design has been altered slightly. A plastic container has been used, which has had holes drilled to allow mounting points for both the motors at the front and the jockey wheel at the rear of the buggy. The buggy appears to be able to move straight, left and right, however it only appears to do this while the jockey wheel is mounted at the back of the vehicle, hence why they are that way round. The new motors are a definent improvement, now that they aren't buckled. Additional improvements that can be made are as follows:

- A more stable jockey wheel.
- A better chassis for the buggy to sit in.

After a lengthy group meeting today, we have decided on a few more changes for the buggy as a whole.

- The inner circuitry will be redone and neatened.
- The inner circuitry will be mounted on a semi-removable board for aesthetics and practicality.
- The jockey wheel is to be reconstructed.

Electronics

The electronic circuit has been built as follows from the circuit diagram (Courtesy of Duncan Scriven), currently it resided on a bread board but will eventually be put on a circuit board to aid in weight reduction.The sensor and provisional LED array have also been made. This includes having 3 LDR's evenly spaced 0 0 0 and an ultra bright LED placed next to them to give light (as mentioned earlier more LEDs can be used. (The LED circuit for now has been made seperate to the motor circuit as to not drain the batteries but it can be attached to a pin.) After Testing the sensor array it became apparant that different ambient lighting affected the sesnor array so my sensor array will need to be completely enclosed so as the only light reaching the LDR will be coming from the LED's. It also became apparant that using just digital inputs was a bad idea having to manually change them when the lighting conditions continually change, so we have changed to reading the ADC output of each of the pins keeping the potentiometers at one level.

First prototype.

The first prototype has been constructed. The group decided to base the design on a three wheeled basis, whereby the chassis was to be made out of plastic containers, to give rigidity and light weight. The use of the original wheels and motors help as we know these can be run effectively without too much complication. Despite this Some major problems have surfaced as a result.

• One of the worm gears is not straight and so will have to be replaced.
• There is a distinct lack of speed and manoeuvrability, however it is still able to run , so placing weight nearer the motors may help , especially when turning.
• As the group decided against lego and other "toys" as this does not show originality, the body had to be made ourselves. This is slightly tedious as nothing will fit tightly , however with the use of drills this situation is being remidied.
• Trying to find an appropriate jockey wheel that can fit with the chassis effectively and to which is effecting the turning. At the moment a lego jockey wheel has been constructed but is ideally not suitable.

Proposed Pin Out diagram

This is the proposed pin-out of the actual PIC circuit board;

Output Pins 0-4 are used to control motor 1 or 2. ( 1 being the left hand motor, 2 being the right hand motor respectively looking at the buggy from the front). The Combinations shown are those to drive the motors forward ( i.e the combination of pin0 being high and pin 1 being low will drive the left hand motor forward, while reversing to Pin0 low and pin1 high will drive the left hand motor backwards.)

The sensor posistions are shown are indicated as if looking at the buggy from the front.

Pin 7 turns on a transistor that activates 5 LEDS mounted above the LDR sensors.

Its pretty flexible so if anyone needs anything moved to make their section a bit easier then give me a shout and ill see if it works and if so ill update the diagram.