The Current Status
The best that can be said about the existing electrical system, or what is left of it, is that it is operational. Since no original schematics were ever left from previous teams, the entire electrical system had to be reverse engineered in order to gain a comprehensive understanding of how the system woorked. Luckily, there was not a whole lot completed by the previous teams so the schematic was easy to trace out and document. The existing electronic components were mounted on a piece of plywood and laid inside the confines of the chassis just behind the compartment where the driver is supposed to sit.
A Road Map to Success
Clearly, any modification to the existing configuration would be an improvement. Therefore, since the electrical system is in such a primitive operational status, the best design approach would be to incorporate the best of all aspects of electronic circuitry, budget allowing. In brainsorming the key problematic criteria of reliability, maintainability, expandability, and accessibility as mentioned in the problem statement, some rudimentary concepts were generated (see Figure - 1). Each particular concept criteria could be satisfied using a printed circuit board design mounted on slide-in rails that are mounted firmly to the chassis.
Figure - 1: Brainstorming Design Concepts
Additionally, since this project is the property of the University of Utah, it only stands to reason that it should also be configured as a learning aid as well. Mechanical engineering students should be able to understand the schematics and be able to expand and upgrade this electrcial system as the program progresses. For this reason, an interfacing architecture that is common, inexpensive and adaptable to the test equipment, power supplies, and other types of electronic support equipment available at this engineering college should be used.
Design Requirements
Location - With operator safety in mind and through the process of team consensus, the region of the chassis aft of the cockpit was chosen as the electrical system cabinet (See Figure −2). Partly because the existing cables were already configured for locating the electronic in that area and partly because it was the only available space where an undisclosed amount of components could be located without running into problems with operator safety, outer shell clearance, suspension interference, etc. Since this location is the region farthest back on the chassis, expansion will be satisfied by adding a cabinet extension to the existing chassis.
Figure - 2: Electronic Cabinet Location
Reliability - Above all, the reliability and integrity of the electronic circuits in this electrical system must be paramount. Like any electronic device, if intermittence in current flow and unsecured contacts exist, the performance of the parent product will suffer. Consistency is a must in any competitive environment. It simply must work the first time and every time. A solid state configuration is desirable.
Accessibility - Having the circuits mounted on plug-in circuit cards accomodates accessibility in two ways. First, it allows the circuit card to be removed and tested on laboratory bench equipment that will probably be located in a different buildings, remote venues, of even far away city during competition. Secondly, modular circuit boards also allow testing of the on-board/chassis mounted peripherals such as the controller potentiometer, toggle switches, solar panel voltage and current, safety equipment to name a few. with only a few connections plugged into where the circuit board would plug into.
Maintainability - One of the many problem experienced with long term project is the leaps and bounds that technology makes in such a short time. This is true especially in the electonic industry where a next generation of products can make all previously procured components(i.e.connectors, accessories, peripherals, etc.) virtually obsolete due to changes in design architecture.
Compounded with the fact that budget constraint do not allow for all procurement to be done at once. A few parts have to be procured this semester while the more expensive parts must wait for additional funding, perhaps next semester. By the time the final parts of a circuit have been procured, the initial components no longer are compatible. Imagine what will happen two semesters when a few more generations of electronics have been introduced.
The key to maintainability is long term supportability. Using tried and trued components that have been used for years is probably the best way to deal with the problems of maintainability and supportability. In essence this school of thinking goes hand-in-hand with the reliability, accessibility, and training aid requirements previously mentioned. Test equipment is a perfect example of components that have been around a very long time. They have to be reliable and consistent for use in laboratories to be able to provide repeatability during experiments. Simplicity is also an advantage when passing electronic schematics to subsequent design teams composed of mechanical engineering students.