Introduction to BADI Engineering Year 2

1. Introduction to BADI Engineering Year 2 For BA Design for Industry 2nd year

2. Simple electrical engineering projects

3. Students suggestions • Investigative ‘hands on’ exercises • Simple electricity and electrical components • Related to practical designs • Building a general appreciation of common components and their interconnection & use.

4. My Approach • Students will be asked to work in groups to construct a working electrical device • Using only found material • And demonstrate it to the class • Students will keep a brief record of their progress, issues and observations.

5. Project ideas • Buzzer / vibrator • Weighing machine (load sensor) • Electric Thermometer • Current meter (electromagnetic) • Current meter (hot wire) • Electric generator • Motor • Battery • Electric Clock • Barograph • Seismograph

6. Tuneable buzzer/ vibrator • Wind an electromagnet • Fasten a strip of springy steel near it (armature) • Make a contact to touch the free end • When the current flows the electromagnet • pulls the steel, which • opens the contact & suspends current flow • releases the steel, which springs back • closes the contact & restores the current How can you change the rate it buzzes at?

7. Weighing machine (load sensor) • Get an electric fire element or pare down one side of a fat pencil • Arrange a brass or copper contact to it that can slide up & down • Apply a voltage from a battery across the ends of the element • The contact ‘picks off’ part of that voltage – so voltage is related to contact position • Use a spring to bias the contact to the zero volts end of the element • The output voltage will be proportional to the load

8. Load sensor (alternative) • Make a buzzer • Use a lever arrangement to move the contact closer to or further from the electromagnet depending on the load, or • Mass sensor: attach the mass to be measured to the armature • The rate at which it buzzes is dependent on the load.

9. Temperature measurement • Temperature sensors on cars often use a heater arrangement and a contact that moves depending on the temperature. • One arrangement is to use a bimetal disk and a heater coil. Current flows and the heater warms up the disk, which flips. Contact is broken and the disk cools. The time taken for it to cool depends on the surrounding temperature, so the average current is a measure of temperature.

10. Current meter (electromagnetic) • Wind a coil of wire (electromagnet) on a piece of plastic tube • Find a piece of iron or steel (a slug) that will slide inside it. • When a current is applied the slug will be pulled into the tube • Connect a string to the slug and arrange for a pointer to indicate how strong the pull is.

11. Current meter (hot wire) • Needed: resistance wire (electric fire element) • When a current passes through a wire it gets hot • When it gets hot it expands • Build a rig that will allow this (small) expansion to be indicated by turning a needle on a dial

12. Electric generator • When a magnet is moved near a coil of wire a current is generated • Build a rig to allow a coil to be turned near a magnet or vice versa • Connect a torch bulb across the ends of the coil to show when a current flows • Experiment with different layouts

13. Generator (2) Motors and generators have similar construction.A common feature is that they have a part that turns, called a ROTOR; and a part that stays still, called a STATOR In this design the rotor carries a coil, and magnets are attached to the mounting frame rotor Stator

14. Generator (3) • If the coil is turning the wire ends will twist. • The current can be picked off in two different ways • Slip rings • Commutator • What difference does it make which you use?

15. Generator (4) One use of a generator is a wind turbine, often used to keep batteries charged on a boat. One design uses a car brake disk with magnets mounted around the periphery. A coil is placed near the disk and when the disk rotates a voltage is generated Its an ac voltage and needs to be rectified (converted to dc) before it can be used to charge the battery coil

16. Motor • Wind a short coil of wire onto a plastic former that has a rod through the middle (short axis) • Place this between the poles of a magnet so that it can pivot on the axle • Pass a current through the coil (use a car sidelight bulb to limit the current) • The coil will move

17. Motor (2) • You need to interrupt or change the direction of the current regularly so that it keeps turning. • How can you do this? One way is to use the inertia of the rotor to keep the rotor spinning, and feed current pulses to the electromagnet. There are many ways of doing this, all based on detecting when the rotor is at the right point for the electromagnet to attract it to the next position. • It’s a bit like the way a four stroke car engine works.

18. Motor (3) : Don’t do this Last year some students tried to build a motor to this design, using an air-cored coil suspended by wire ends. Mostly these don’t work because • The magnetic field path through the air is too long, and • Its hard to get the coil balance exactly neutral • The rotor has very little inertia Also you can’t take any power out – it wont drive anything so its no practical use.

19. Battery • When two dissimilar conductors ( metal or carbon) are placed in an acid solution (lemon juice, vinegar etc) a voltage is generated. • Does the voltage depend on the strength of the acid? • Does it depend on the size (surface area) of the metals? • What easily obtainable metals work best? • BE SAFE: DON’T USE STRONG ACIDS!

20. Clock A pendulum, a pair of rotating balance weights or a balance wheel on a spring, a tuning fork …will all give repeatable timing. All you need is to keep them going by applying a pulse at the right time. You could use an electromagnet for this. Read about Harrison’s clocks

21. Barograph or seismograph • You need a motor to drive the paper chart – either a strip or a circle. Use a ready made geared motor. • Now you need to adapt this chart to record (with a pen) the barometric pressure or seismic vibrations. • Lots of ideas on the web

22. General Resources • http://scitoys.com/ • http://www.howstuffworks.com/ • http://www.skillbank.co.uk/ For course notes useful links etc.