Lesson test: ESCs and turning DC into three phases

1.[2p]
In sensorless commutation, the controller finds the rotor's position by

measuring the back-EMF on the phase it has left floating

Correct

reading a Hall sensor on the shaft

The answer is: measuring the back-EMF on the phase it has left floating

counting pulses from the flight controller

The answer is: measuring the back-EMF on the phase it has left floating

timing the battery voltage

The answer is: measuring the back-EMF on the phase it has left floating

2.[2p]
A brushless motor is most likely to stutter or fail to start because

at very low speed there is too little back-EMF for the controller to read the rotor

Correct

the battery voltage is too high

The answer is: at very low speed there is too little back-EMF for the controller to read the rotor

the propeller is too light

The answer is: at very low speed there is too little back-EMF for the controller to read the rotor

the three phases are shorted together

The answer is: at very low speed there is too little back-EMF for the controller to read the rotor

3.[2p]
An ESC sets the motor's speed by

pulse width modulation, varying the fraction of time the driven phases are switched on

Correct

changing the number of poles

The answer is: pulse width modulation, varying the fraction of time the driven phases are switched on

reversing the battery

The answer is: pulse width modulation, varying the fraction of time the driven phases are switched on

adding resistance in series with the motor

The answer is: pulse width modulation, varying the fraction of time the driven phases are switched on

4.[2p]
A pack reads 15.0 V and the ESC is commanded to 60 per cent throttle. What average voltage, in volts, does the motor see, ignoring losses?

CorrectNot quite: 9.0

5.[2p]
DShot is preferred over the old servo-style pulse signal mainly because

it sends the throttle as a checksummed digital value, immune to electrical noise

Correct

it uses fewer wires

The answer is: it sends the throttle as a checksummed digital value, immune to electrical noise

it needs no power supply

The answer is: it sends the throttle as a checksummed digital value, immune to electrical noise

it makes the motor quieter

The answer is: it sends the throttle as a checksummed digital value, immune to electrical noise

6.[2p]
Heating in an ESC's transistors rises with the square of the current, so doubling the current roughly quadruples the heat.

True

Correct

False

The answer is: True

7.[2p]
An ESC's most common way of destroying itself is

being driven past its current rating by an aggressive motor and propeller until its transistors overheat

Correct

receiving too low a throttle signal

The answer is: being driven past its current rating by an aggressive motor and propeller until its transistors overheat

being mounted too far from the battery

The answer is: being driven past its current rating by an aggressive motor and propeller until its transistors overheat

spinning the motor backwards

The answer is: being driven past its current rating by an aggressive motor and propeller until its transistors overheat

1.[2p] In sensorless commutation, the controller finds the rotor's position by

2.[2p] A brushless motor is most likely to stutter or fail to start because

3.[2p] An ESC sets the motor's speed by

4.[2p] A pack reads 15.0 V and the ESC is commanded to 60 per cent throttle. What average voltage, in volts, does the motor see, ignoring losses?

5.[2p] DShot is preferred over the old servo-style pulse signal mainly because

6.[2p] Heating in an ESC's transistors rises with the square of the current, so doubling the current roughly quadruples the heat.

7.[2p] An ESC's most common way of destroying itself is

1.[2p]
In sensorless commutation, the controller finds the rotor's position by

2.[2p]
A brushless motor is most likely to stutter or fail to start because

3.[2p]
An ESC sets the motor's speed by

4.[2p]
A pack reads 15.0 V and the ESC is commanded to 60 per cent throttle. What average voltage, in volts, does the motor see, ignoring losses?

5.[2p]
DShot is preferred over the old servo-style pulse signal mainly because

6.[2p]
Heating in an ESC's transistors rises with the square of the current, so doubling the current roughly quadruples the heat.

7.[2p]
An ESC's most common way of destroying itself is