Bryan McDonnel Michael Mize Ryan Taylor (presenter) Miles Whittaker Team 11: RoboSiM Safety and Reliability Analysis Bryan McDonnel Michael Mize Ryan Taylor (presenter) Miles Whittaker

Key Concerns Reliability: Safety Power electronics for both power supplies Motor control hardware (logic and power switches) Microcontroller and supporting hardware Ultrasonic sensor array Safety Battery technology Burn risk Rogue robot

Part Failure Risk λb = 10.368 failures per 106 hours AOD 413 Power MOSFET (6V power supply) λb = 10.368 failures per 106 hours MTTF = 96,450.6 hours to failure Model Used: Transistor, Low-Frequency, Si FET TA8429A H-Bridge Controller (Motor Control) λb = 69.174 failures per 106 hours MTTF = 14,456.3 hours to failure Model Used: Hybrid Microcircuit LM22672MR-ADJ Switching Controller (3.3V power supply) λb = 39.236 failures per 106 hours MTTF = 25,486.5 hours to failure

Part Failure Risk (cont.) TPSB476K010R0250 Capacitor (6V Supply Output) λb = 0.159727 failures per 106 hours MTTF = 6,260,680 hours to failure Model Used: Capacitor, Fixed, Electrolytic, Tantalum, Solid PIC24HJ128GP306 Microcontroller λb = 1.364 failures per 106 hours MTTF = 733,138 hours to failure Model Used: Microcircuits, Microcontrollers

FMECAnalysis: Criticality Definitions Major injuries not predicted Most severe: burn injuries Criticality Levels Low: nuisance failure; no chance of additional damage to parts/part lifetimes Elevated: risk of additional part damage, reduction of part (or platform) lifetime High: definite part damage and part/platform lifetime reduction “+I” Suffix: chance of personal injury or property damage

FMECA: Major Concerns Failure Mode Possible Causes Failure Effect Detection Method Criticality Motor(s) stuck at Vcc PWM failure (hard or software), H-Bridge controller failure One or both motors driven at full speed, excessive heating in motors and 6V components Observation; RoboSiM can’t turn normally or avoid obstacles correctly Elevated; 6V component wear, reduced battery life PuC > 73mW @ 16MIPS Core clock fault, faulty power supply connection, fighting on output pins Heat build-up, decreased part lifetime, glitching in other parts Observation; heat and smell. Potential glitching in LCD or motor control Elevated + I 6V Short to Ground Buck converter diode short, damaged MOSFET, shorted capacitors Excessive current, heat build-up, possible destruction of motor windings and H-Bridges Observation; heat and smoke likely, erratic/no behavior of entire platform High + I 3.3V Short to Ground Buck converter diode short, reset switch stuck closed, destroyed uC or op-amp Excessive current, heat build-up, destroyed parts, RoboSiM loses decision-making ability

Steps to Improve Reliability Conservative derating on capacitors & motors At least one capacitor operating at stress of 0.6 Recommended 20% derating, preferred 50% or higher Over-designing each of the power supplies Exceed expected power & peak current rating (20% or higher) Lowest available temperature coefficients (°C/W) Reduction of environmental factors Reinforced packaging (watertight, low center of gravity, durable) Potting material to reduce humidity and mechanical strain Minimize design weight Less current draw from motors, decreasing power dissipation Bonus: longer battery life

Questions?