Lesson test: Brushless motors

1.[2p]
A brushless motor needs an electronic speed controller because

removing the brushes moves the job of switching the phase currents outside the motor

Correct

it has no permanent magnets

The answer is: removing the brushes moves the job of switching the phase currents outside the motor

it runs on alternating current from the wall

The answer is: removing the brushes moves the job of switching the phase currents outside the motor

it spins too slowly to self-start

The answer is: removing the brushes moves the job of switching the phase currents outside the motor

2.[2p]
A motor is rated at 2400 Kv. On a fully charged four cell battery of 16.8 V, what is its approximate unloaded speed in rpm?

CorrectNot quite: 40320

3.[2p]
Multirotor motors have three wires rather than two because

three phases make a magnetic field that rotates, while two would only flip back and forth

Correct

one wire is a spare

The answer is: three phases make a magnetic field that rotates, while two would only flip back and forth

the third wire carries the sensor signal

The answer is: three phases make a magnetic field that rotates, while two would only flip back and forth

three wires reduce resistance

The answer is: three phases make a magnetic field that rotates, while two would only flip back and forth

4.[2p]
A high Kv motor produces high torque per amp of current.

True

The answer is: False

False

Correct

5.[1p]
In a motor named 2207, the digits mean

a stator 22 mm in diameter and 7 mm tall

Correct

22 poles and 7 phases

The answer is: a stator 22 mm in diameter and 7 mm tall

2207 Kv

The answer is: a stator 22 mm in diameter and 7 mm tall

22 mm propellers at 7 degrees of pitch

The answer is: a stator 22 mm in diameter and 7 mm tall

6.[2p]
Pairing a high Kv motor with a large propeller is dangerous because

the motor drives the big propeller fast, the current soars, and the motor or controller overheats

Correct

the propeller will spin too slowly to fly

The answer is: the motor drives the big propeller fast, the current soars, and the motor or controller overheats

the battery voltage drops to zero

The answer is: the motor drives the big propeller fast, the current soars, and the motor or controller overheats

the motor cannot start

The answer is: the motor drives the big propeller fast, the current soars, and the motor or controller overheats

7.[2p]
Most multirotor motors are outrunners, with the magnets on the spinning outer bell, because

placing the magnets at a large radius gives high torque at the modest speeds a propeller wants

Correct

it makes the motor lighter than any inrunner

The answer is: placing the magnets at a large radius gives high torque at the modest speeds a propeller wants

it removes the need for a controller

The answer is: placing the magnets at a large radius gives high torque at the modest speeds a propeller wants

it allows the propeller to be mounted underneath

The answer is: placing the magnets at a large radius gives high torque at the modest speeds a propeller wants

1.[2p] A brushless motor needs an electronic speed controller because

2.[2p] A motor is rated at 2400 Kv. On a fully charged four cell battery of 16.8 V, what is its approximate unloaded speed in rpm?

3.[2p] Multirotor motors have three wires rather than two because

4.[2p] A high Kv motor produces high torque per amp of current.

5.[1p] In a motor named 2207, the digits mean

6.[2p] Pairing a high Kv motor with a large propeller is dangerous because

7.[2p] Most multirotor motors are outrunners, with the magnets on the spinning outer bell, because

1.[2p]
A brushless motor needs an electronic speed controller because

2.[2p]
A motor is rated at 2400 Kv. On a fully charged four cell battery of 16.8 V, what is its approximate unloaded speed in rpm?

3.[2p]
Multirotor motors have three wires rather than two because

4.[2p]
A high Kv motor produces high torque per amp of current.

5.[1p]
In a motor named 2207, the digits mean

6.[2p]
Pairing a high Kv motor with a large propeller is dangerous because

7.[2p]
Most multirotor motors are outrunners, with the magnets on the spinning outer bell, because