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Previous Page – App Note 33

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OpenTX - Application Note 34

RPM & Temperature Sensor

This application sets up the RPM sensor. This telemetry sensor also has two temperature sensors. It is compatible with any of the X4R, X6R X8R or S6R receivers via the smart port.

 

 

 

RPM Sensor

  Connecting The Sensor

  Configuring The Sensor

Temperature Sensors

Taranis Transmitter Configuration

  Search New Sensors

  Data Logging

  Telemetry Screen Display

  Temperature Value Announcement

Flight Test

  Temperature Alarms

RPM Sensor

Connecting The Sensor

 

The RPM sensor is connected to any two of the motor wires. I made connectors that can be connected in line between the ESC female connectors and the motor male connectors.

 

 

A short length of 14AWG wire joins the male and female connectors which are butted up against each other.

 

Once a wire is soldered to the joined connectors, a sleave of shrink wrap is placed over them.

 

 

Using these makes it easy to move the RPM sensor from one model to the next

Configuring The Sensor

To scale the number of pulses detected by the RPM sensor to motor RPM, the sensor needs to know how many poles the motor has. The RPM sensor uses four LEDs and a pushbutton to set the number of poles.

 

 

 

 

The magnets in a brushless outrunner indicate the motor’s number of poles. The magnets are in pairs on opposite sides of the rotor.

 

The blue dots in the photo show one pair of magnets. This motor has seven pairs of magnets so it has 7 poles.

 

To place the sensor in configuration mode, press and hold the pushbutton until one or more of the LEDs turns on and then release it. The number of configured poles is displayed in binary by the four LEDs. Press and release the button until the required number is displayed on the LEDs. Turn the power off to retain the selected configuration.

Temperature Sensors

The temperature sensors range is -20 to 250°C and does not require any configuration. I placed temperature sensor 1 on the heat sink of the ESC.

 

 

I placed temperature sensor 2 on the base of the motor. (The sensor is held in place but is not squashed by the washer.)

 

Taranis Transmitter Configuration

Search New Sensors

Turn power on the receiver. On the Taranis telemetry set up screen, select “Discover new sensors” and press Enter. The following three telemetry variables are defined, “Tmp 1”, “Tmp 2” and “RPM”. Press Exit to end the new sensor discovery.

 

 

To enable logging of these variables, edit each one and tick their “Logs” boxes.

Data Logging

To log data on the SD card, I created the following special function to enable data logging when switch SC is in the middle position.

 

Special Function

Source

Function

Par 1

Par 2

Check Box

SF10

SC-

SD Logs

0.1s

 

Telemetry Screen Display

I set up telemetry screen 2 to display the current values and the maximum values.

 

Temperature Value Announcement

To monitor the temperatures during flight, I created the following special functions to announce the value of temperature sensors 1 and 2 every 5 seconds when switch SC is in the middle position. (Same as data logging.)

 

Special Function

Source

Function

Par 1

Par 2

Check Box

SF11

SC-

Play Value

Tmp1

5s

SF12

SC-

Play Value

Tmp2

5s

Flight Test

The motor has a spinner, which inhibits airflow through the motor, but it has good airflow over it from an air scoop that directs air from the inlet vents around the motor to exhaust vents on top of the cowl.

 

 

I found during a flight that the ESC temperature rose from 19°C ambient to 40°C, a temperature rise of 21°C. The ESC has very good airflow over its heat sink. This is well within the ability of the ESC to continuously operate with.

 

 

The motor temperature rose from 19°C to a maximum of 55°C, a rise of 36°C.

 

Temperature Alarms

On days when the ambient temperature is 30°C, the ESC temperature would get to 51°C and the motor temperature would get to 66°C. Some motor manufacturers have said that motors should not operate above 80°C or the magnets can become demagnetised.

Based on these graphs, I chose to set an ESC temperature warning alarm at 50°C and a critical alarm at 55°C. Also, I chose to set a motor warning alarm at 65°C and a critical alarm at 70°C. With the alarms in place, the temperature announcements described above are changed so that the temperature is only announced if it is above the warning alarm.

 

Logical Switch

Function

V1

V2

AND Switch

Duration

Delay

LS10

a > x

Tmp1

50

---

---

---

LS11

a > x

Tmp1

55

---

---

---

LS12

a > x

Tmp2

65

---

---

---

LS13

a > x

Tmp2

70

---

---

---

 

Special Function

Source

Function

Par 1

Par 2

Check Box

SF11

L10

Play Value

Tmp1

5s

SF12

L12

Play Value

Tmp2

5s

SF13

L10

Play Track

t1walm

1x

SF14

L11

Play Track

t1calm

1x

SF15

L12

Play Track

t2walm

1x

SF16

L13

Play Track

t2calm

1x

 

“t1walm” is an audio file which says “ESC temperature warning”.

“t1calm” is an audio file which says “ESC temperature critical”.

“t2walm” is an audio file which says “Motor temperature warning”.

“t2calm” is an audio file which says “Motor temperature critical”.

These audio files were created and placed in the folder [SOUNDS]/[EN] of the SD card.

 

On hot days or if something goes wrong, the alarms will tell me that something is hotter than it should be and to land before something fails.

 

Phantom Divide

 

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