TCSP – Reliability and Safety

Reliability AnalysisReliability Analysis• Major component chosen for analysis:Major component chosen for analysis:

• Switching Regulators (LM2679SD-5.0, LM2679SD-Switching Regulators (LM2679SD-5.0, LM2679SD-3.3)3.3)

• Hottest running componentsHottest running components

• Microcontroller (MCS12A64CFUE)Microcontroller (MCS12A64CFUE)• Most complex componentMost complex component

• Quad 2 to 1 Multiplexer (SN74CBT3257)Quad 2 to 1 Multiplexer (SN74CBT3257)• Failure leads to crashingFailure leads to crashing

• Linear Amplifiers for thermopiles (AD8626)Linear Amplifiers for thermopiles (AD8626)• Failure would cause unstable flight, possibly crashingFailure would cause unstable flight, possibly crashing

FMECA FMECA Criticality LevelsCriticality Levels

• High – Could cause personal injuryHigh – Could cause personal injury

• Medium – Inhibits ability to fly Medium – Inhibits ability to fly autonomouslyautonomously

• Low – Inhibits ability to take photos or Low – Inhibits ability to take photos or other inconveniencesother inconveniences

FMECA FMECA Block A - Block A - MicrocontrollerMicrocontroller

FMECA FMECA Block A - Block A - MicrocontrollerMicrocontroller

Failure No.

Failure Mode Possible Causes Failure Effects Method of Detection

Criticality Remarks

A1 Microcontroller outputs no data

Out of spec supply voltage, U1 failure, clock failure, PLL failure, software bug, bypass caps shorted

No display on LCD, does not work in autonomous mode

Observation Medium-High

This failure would be elevated to high criticality if a shorting component caused excess heat dissipation

A2 Some pins are always 0 or 1

Over-voltage on pin could have burned up the driver, software bug

Erratic system behavior, excessive heating of the microcontroller

Observation Medium-High

This failure would be elevated to high criticality if a shorting component caused excess heat dissipation

FMECA FMECA Block B - RegulatorsBlock B - Regulators

FMECA FMECA Block B - RegulatorsBlock B - Regulators

Failure No.

Failure Mode Possible Causes Failure Effects Method of Detection

Criticality Remarks

B1 Vout,5 = 0V or

Vout,3.3 = 0V

Failure of U6 or U7, Shorted capacitor in Block B, no feedback, external short

System shows no operation

Observation High If a short is causing the lack of output, excessive heat is being generated which could injury the user

B2 Vout,5 > 5V or

Vout,3.3 > 3.3V

Failure of U6 or U7 Could damage any of the ICs on the board, system probably non-functional

Observation High Possibility of injurious heat dissipation

B3 Vout,5 or Vout,3.3

not regulated enough

Failure of a capacitor in Block B that becomes and open circuit

Erratic microcontroller failure, perhaps repeated resetting

Observation Medium Unlikely to cause harm, but results in non-flyable plane

B4 Vsense > 5V R20 fails and causes a short

Microcontroller reports unreasonable battery voltage

Observation Low - Medium

Probably just a nuisance which would fry a port pin, but could also cause the entire microcontroller to fail.

FMECA FMECA Block C – Radio and Block C – Radio and ServosServos

FMECA FMECA Block C – Radio and Block C – Radio and ServosServos

Failure No.

Failure Mode Possible Causes Failure Effects Method of Detection

Criticality Remarks

C1 Autopilot / Manual multiplexer signal incorrect

U18 failure, or failure of any of the resistors or capacitors directly before it

Plane does not properly switch between manual and autopilot

Observation High If this failure arose during a flight, the plane could crash, possibly injuring a person

C2 Inputs do not propagate through multiplexer

U13 or R40 failure Servo motors do not respond to manual input or autopilot

Observation High This would cause the plane to crash, possibly injuring someone

C3 Multiplexer always output either manual or autopilot values

S pin of U13 shorted to Vcc or ground

Cannot switch operating modes

Observation High Could cause injury if the drive motor powered up unexpectedly on the ground

FMECAFMECA Block DBlock D – Thermopile – Thermopile AmplifiersAmplifiers

FMECAFMECA Block DBlock D – Thermopile – Thermopile AmplifiersAmplifiers

Failure No.

Failure Mode Possible Causes Failure Effects Method of Detection

Criticality Remarks

D1 Vref = 0V U14 failure, could also have its input or output shorted to ground

Thermopiles do not sense sky properly, unstable flight

Observation High Could cause injury if crash induced

D2 Vref > 2.5V U14 failure Thermopiles do not sense ground as well, jittery flight

Observation High - Medium

Could lead to crashing

D3 Amplifier output is very small

Failure of U9 or U10, Failure of any of the resistors in Block D such that they become shorts

Plane cannot stabilize

Observation High Would lead to crashing in autopilot mode, and possibly injure the operator

D4 Thermopile values read in are erratic

Connection to thermopiles could be faulty

Jittery flight Observation Medium Could lead to crashing

FMECA FMECA Block E – GPS and Block E – GPS and MicroSDMicroSD

FMECA FMECA Block E – GPS and Block E – GPS and MicroSDMicroSD

Failure No.

Failure Mode Possible Causes Failure Effects Method of Detection

Criticality Remarks

E1 Unable to communicate with MicroSD card

Failure of U2, U3, or U4; Any resistor in the SD circuit becomes open; SD card corrupt; software

System unable to read MicroSD card, displays error message

Observation and BIST

Medium No risk of injury, but the plane cannot operate autonomously

E2 Unable to communicate with GPS receiver

Failure of U15, U16, or U17; resistor in GPS circuit becoming open; faulty cable; software bug

System unable to get a GPS lock, waits indefinitely and will not allow autonomous flight

Observation and BIST

Medium No risk of injury, but the plane cannot operate autonomously

FMECA FMECA Block F – Camera and Block F – Camera and LCDLCD

FMECA FMECA Block F – Camera and Block F – Camera and LCDLCD

Failure No.

Failure Mode Possible Causes Failure Effects Method of Detection

Criticality Remarks

F1 LCD_TX signal always idle

Failure of U12, short or open circuit of any of the capacitors or resistors connected to U12

LCD is always blank

Observation Low This is a nuisance, but the plane will operate properly

F2 Camera shutter trigger always open

Failure of U11, software malfunction

Camera never takes photos

Observation Low The plane will fly, but no photos will be taken

Questions?