1. 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

2. 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

3. Part Failure Risk λb = 10.368 failures per 106 hours
AOD 413 Power MOSFET (6V power supply)
λb = 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 = failures per 106 hours
MTTF = 14,456.3 hours to failure
Model Used: Hybrid Microcircuit
LM22672MR-ADJ Switching Controller (3.3V power supply)
λb = failures per 106 hours
MTTF = 25,486.5 hours to failure

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

5. 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

6. 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

7. 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

8. Questions?