VCE Systems Engineering cheat sheet

Mechanical advantage (MA) = load force / effort force; ideal MA for a lever = effort arm length / load arm length.

Velocity ratio (VR) = distance moved by effort / distance moved by load; efficiency = (MA / VR) x 100 percent.

Lever classes: Class 1 fulcrum between effort and load; Class 2 load between fulcrum and effort; Class 3 effort between fulcrum and load.

Torque = force x perpendicular distance from pivot; unit newton metre (N m); a couple is two equal, opposite, parallel forces producing rotation only.

Mechanical systems convert motion types: rotary to linear (rack and pinion, lead screw), rotary to rotary (gear, belt, chain), linear to rotary (crank).

Gear ratio = number of teeth on driven gear / number of teeth on driver gear; ratio greater than 1 reduces speed and increases torque.

Equilibrium requires sum of forces = 0 and sum of moments about any point = 0; a body is stable when its centre of gravity lies over its base.

Friction force = coefficient of friction x normal force; static friction coefficient exceeds kinetic friction coefficient for the same pair of surfaces.

Stress = force / cross-sectional area (pascal); strain = change in length / original length (dimensionless); Young's modulus = stress / strain in the elastic region.

Ohm's law: V = I x R; power P = V x I = I squared x R = V squared / R.

Series circuit: current common to all components, voltages add, total resistance = sum of resistances.

Parallel circuit: voltage common to all branches, branch currents add, 1/R total = 1/R1 + 1/R2 + ...

Kirchhoff's laws: current law (sum of currents into a node = sum out) and voltage law (sum of emfs = sum of voltage drops around a loop).

Digital logic: AND output high only when all inputs high; OR output high when any input high; NOT inverts; NAND and NOR are inverted AND and OR.

Truth tables list every input combination; a 2-input gate has 4 rows, a 3-input gate has 8 rows (2 to the power n).

A relay uses a low-power coil to switch a higher-power contact circuit, giving electrical isolation between control and load.

Sensor types: thermistor (temperature, resistance changes), LDR (light, resistance falls with light), potentiometer (position), switch (binary state).

Breadboard rows are connected horizontally in the body and vertically along the power rails; the centre channel separates the two halves.

The design process sequence: identify need, define problem and constraints, research, generate concepts, select, model/prototype, test and evaluate, document.

Design brief states the problem, client, purpose, constraints and criteria; specifications are measurable targets used to evaluate the finished product.

A system is a set of interacting components with inputs, processes, outputs and feedback; open systems exchange mass or energy with surroundings, closed systems do not.

Functional analysis decomposes a system into sub-functions (input, transmit, control, actuate, output) drawn as a function block diagram.

Gantt charts show task duration against calendar time; critical path is the longest dependent sequence and sets minimum project duration.

Isometric drawings show three axes at 120 degrees; orthogonal projection uses front, top and side views with first-angle or third-angle layout.

Australian Standards and legislation relevant to design include AS/NZS electrical wiring rules, work health and safety Acts, and intellectual property (patents, design registration).

Ergonomic design applies anthropometric data such as 5th to 95th percentile reach and height so most users can operate the product safely.

Open-loop control has no feedback; closed-loop control compares sensed output with a setpoint and acts on the error.

PID control: proportional output proportional to error, integral sums past error to remove offset, derivative responds to rate of change to reduce overshoot.

Hysteresis (dead band) prevents actuator chatter when a sensor value fluctuates around a switching threshold.

A microcontroller program follows setup then a repeating loop; inputs are read, logic applied, outputs written; delay blocks other tasks.

Flowchart symbols: oval terminal, parallelogram input/output, rectangle process, diamond decision, arrow flow direction.

Pneumatic and hydraulic systems use compressed air or oil; pressure = force / area, and flow rate controls actuator speed.

Quality control uses inspection, tolerance limits and testing against specifications; quality assurance manages the process that produces the product.

Risk assessment ranks hazards by likelihood and consequence; hierarchy of control: eliminate, substitute, engineer, administrate, PPE.

Testing documentation records test procedure, measured values, pass/fail against specifications, and actions taken for non-conformance.