Design Criteria and Vehicle Specifications
PIC Microcontroller Vehicle Design Criteria
Design and build a program-controlled, autonomous and environmentally friendly model vehicle of the future, using a microcontroller to provide in-built intelligence so it can automatically avoid obstacles. The vehicle must include recycled or recyclable components within its design.
In competition, the race winning vehicle will be judged to be one that scores the most points over the three attempts.
Design & Technology National curriculum coverage includes:
Knowledge and understanding of systems and control: statements 5 (a) (b) (c) (d) (e)
Summary: Recognise the elements of systems that can be broken down and the importance of feedback; understand basic principles of electrical, electronic control systems including sensors; understand basic mechanical systems and how these can be linked to other control systems.
Evaluating process and products: statements 3 (a) (b) (c)
Summary: Evaluation of ideas and comparison with original intention; testing and evaluation of prototypes; use of criteria for judging wider fitness for purpose.
Knowledge and understanding of control systems: statements 5 (a) i; ii; iii.
Summary: Knowledge and understanding of control process, design of systems, the concept of feedback and analysis of system performance.
PIC Microcontroller Vehicle Specifications
- Your vehicle must include recycled or recyclable items within its design and the team must be able
to demonstrate features which make the vehicle environmentally friendly.
- All electrical components must have been supplied by Rapid (www.rapidonline.com).
- The starter kit utilises a PICAXE microcontroller. Your final vehicle must use either the PICAXE or GENIE microcontroller system. Other microcontroller systems are not permitted.
- Each vehicle must have an on/off switch which is accessible from the outside which enables the power to the motor(s) to be cut.
- Maximum length (from the furthest point at the rear to the furthest point at the front) must not exceed 300mm.
- Maximum width (from the widest point at left to the widest point at right) must not exceed 190mm.
- Maximum height (from ground to highest point) must not exceed 150mm. (Please note the track walls are 50mm in height)
- Teams may like to use a body shell to improve aerodynamics and aesthetics. This may not exceed the maximum dimensions outlined above.
- All vehicles must have at least three wheels which touch the ground at all times. Roller balls are permitted but these must rotate to be considered a wheel.
- You must demonstrate that your vehicle uses an environmental power source. Solar cells do not have to be used in the PIC Microcontroller class, although teams may like to make use of this energy source.
PIC Microcontroller Vehicle
- Control board and motor/gearboxes
- Computer and software and download cable for developing control program
Vehicles of the future are likely to use renewable energy sources such as solar, wind or hydroelectric power. These can be harnessed and stored as electricity in batteries which can then be used to propel a vehicle. Therefore, very efficient electric motors and gearboxes are required to get the best performance from these batteries.
It is also likely that vehicles will become more intelligent and will, for instance, be able to avoid obstacles to prevent accidents. Microcontroller chips are already being used in vehicles to provide some intelligence such as automatic windscreen wipers that switch on when it rains or ‘Adaptive Cruise Control’ which can control the speed of a vehicle. Autonomous vehicles are already used in situations where it may be inconvenient or unsafe for humans, such as exploration of inhospitable environments or in factory automation.
A microcontroller is often described as a ‘computer-on-a-chip’. It can be used as an electronic brain to control a product, toy or machine. The microcontroller is an integrated circuit (‘chip’) that contains memory (to store the program), a processor (to process and carry out the program) and input/output pins (to connect switches, sensors and output devices like motors).
Microcontrollers are purchased ‘blank’ and then programmed with a specific control program. This program is written on a computer and then ‘downloaded’ into the computer chip. Once programmed, the microcontroller is built into a product to make the product more intelligent and easier to use.
The Toyota STEM Challenge kit uses a PICAXE microcontroller to control two motors to provide movement and steering for the vehicle. The obstacle detection sensors and control program must be developed by the team entering the competition.
Breaking down the task
The first part of the task is to create a chassis for the vehicle. This can either be designed and built from scratch, or the basic board in the kit can be used. Comprehensive assembly information is provided separately in the control board instructions. This can be found in the ‘Downloads’ section. The board is fairly easy to construct but should be attempted only by pupils with good soldering skills.
The second part of the task is to design the vehicle, incorporating the control board and user selected sensors/additional output devices. The microcontroller on the control board provides 5 inputs and 8 outputs. Four outputs (4-7) are pre-configured to drive the motors; all other inputs and outputs are available for the students to use for their vehicle.
The final part of the task is to develop and test the control program for the PICAXE microcontroller. Sample programs are provided in the separate control board instructions, but students will need to further develop their control program to make a competitive vehicle.
Design decision considerations may include:
In its simplest form, two micro switches (Rapid 78-2408) may be used as the obstacle detection sensors. Alternatively, a high resolution sonar range finder (Rapid 78-1085) may be used to detect obstacles before the vehicle hits them. The sonar sensor can be accurately configured to detect obstacles from 3cm to 3m away.
Choice of motor/gearbox
The choice of motor and gearbox, and accuracy of construction of gearbox, can greatly affect the efficiency of the vehicle. Two gearboxes (Rapid 37-0310) are provided in the starter pack, but students may also consider using a more efficient gearbox (such as Rapid 70-2220).
Students may also choose to use alkaline or rechargeable cells. A maximum of 6V is recommended, but which cell size (AA, C etc.) and how many alkaline (1.5V) or rechargeable cells (1.2V) give the best power/weight performance ratio? Keep in mind that you should make your power source as environmentally friendly as possible.