Module/Aeroprobe OTF

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Aeroprobe 3mm 5-hole probe
Aeroprobe On-The-Fly! air data computer
OTF! cable

Overview

The Aeroprobe On-The-Fly! air data computer measures air pressure from a 5-hole pitot tube and can write resulting data to an SD card or transmit it through an UART. It outputs speed, angle of attack, angle of sideslip and altitude. The air data computer input "1" goes to the middle tube of the probe, the longest one. The next shorter one goes to "2", then "3" and so on.

Module name sensors/airspeed_otf
Sensor type airspeed, flow angle
Range (speed) 8m/s .. 63m/s
Range (angle) ±20°
Resolution (speed) 0.02m/s
Resolution (angle) 0.01°
Refresh rate 100Hz

User manual

Hardware

The air data computer needs to be configured by the manufacturer to output data at the desired speed. The serial interface does have original RS-232 levels, that is not compatible with the autopilots 3.3V interface. You need a RS-232 level shifter. Do not use a simple transistor-based converter like the Sparkfun PRT-08780 as it can not safely be driven by the Aeroprobe. Use a integrated converter like the MAX3232 based Sparkfun BOB-11189.

Air data computer/pitot tube supplier: Aeroprobe

RS232 level shifter supplier: Sparkfun

OTF connector supplier: Farnell

Wiring Umarim

Umarim UART1 pin Umarim UART1 Level shifter LOGIC
1 GND GND
2
3 +3.3V VCC
4 RX1 R1OUT
5 TX1 T1IN

Wiring Logger/TWOG

TWOG SERIAL pin TWOG SERIAL Level shifter LOGIC
1 GND GND
2
3 +3.3V 3V-5.5V
4
5
6
7 RXD1 R1OUT
8 TXD1 T1IN


Common wiring

BEC Power supply OTF OTF pin
+ +VCC 1
- GND 2


color Level shifter RS-232 OTF OTF pin
red R1IN TX (data out) 3
orange T1OUT RX (data in) 4
black GND GND 5


Ground usage

This is for the lab only, not for flight. The modem serial port of an Umarim will be occupied by the OTF! compter. Therefore the data is transferred through USB.

File: conf/airframes/myplane.xml
 <firmware name="fixedwing">
    ...
    <subsystem name="telemetry" type="transparent_usb"/>
    ...


To use it load the airspeed_otf module:

File: conf/airframes/myplane.xml
  <modules>
    ...
    <load name="airspeed_otf.xml"/>
  </modules>


The used UART has to be set globally:

File: conf/airframes/myplane.xml
   <target name="ap" board="<my_board_type>">
      ...
      <configure name="OTF_UART" value="UART1"/>


Result message (old)

The output is airspeed (velocity), angle of attack (a_attack), angle of sideslip (a_sidesl) and altitude. The data is secured by a packet counter and a checksum.

File: conf/messages.xml
  <message name="FLOW_AP_OTF" id="179">
     <field name="counter" type="uint32"/>
     <field name="velocity" type="int16" unit="cm/s" alt_unit="m/s"/>
     <field name="a_attack" type="int16" unit="centideg" alt_unit="deg"/>
     <field name="a_sidesl" type="int16" unit="centideg" alt_unit="deg"/>
     <field name="altitude" type="int32" unit="cm" alt_unit="m"/>
     <field name="checksum" type="uint8"/>
  </message>


Sample log file lines

11.522 123 FLOW_AP_OTF 1076 1480 628 1636 -100 2
11.535 123 FLOW_AP_OTF 1077 1457 735 1707 900 29
11.548 123 FLOW_AP_OTF 1078 1451 661 1867 800 19
11.555 123 FLOW_AP_OTF 1079 1422 697 1685 -300 11

Result message (new)

The output is airspeed (velocity), angle of attack (a_attack), angle of sideslip (a_sideslip) and altitude. Dynamic and static pressure are always zero for this sensor. The data is secured by a packet counter and a checksum.

File: conf/messages.xml
  <message name="AEROPROBE" id="179">
    <description>
      Airflow data returned by OTF and uADC 3D probes from Aeroprobe.
    </description>
    <field name="counter"    type="uint32"/>
    <field name="velocity"   type="int16"  unit="cm/s" alt_unit="m/s"/>
    <field name="a_attack"   type="int16"  unit="centideg" alt_unit="deg"/>
    <field name="a_sideslip" type="int16"  unit="centideg" alt_unit="deg"/>
    <field name="altitude"   type="int32"  unit="cm" alt_unit="m"/>
    <field name="dynamic_p"  type="int32"  unit="Pa"/>
    <field name="static_p"   type="int32"  unit="Pa"/>
    <field name="checksum"   type="uint8"/>
  </message>


Sample log file lines

11.522 123 AEROPROBE 1076 1480 628 1636 -100 0 0 2
11.535 123 AEROPROBE 1077 1457 735 1707 900 0 0 29
11.548 123 AEROPROBE 1078 1451 661 1867 800 0 0 19
11.555 123 AEROPROBE 1079 1422 697 1685 -300 0 0 11