Wouldn’t it be nice to have true airspeed in some situations? Maybe a stall-speed warning? Why not make the sensor yourself, does not cost an arm and a leg and very easy to put together!
Jeti Airspeed Sensor
Again, jump to the Ebay-world, components needed:
- Arduino Pro Mini 3.3V 8Mhz (Or equivalent) Example link to Ebay here.
- MPXV7002DP based airspeed module with pitot tube Example link to Ebay here.
- One resistor, from 2.4kΩ up to 4.7kΩ
- Little wire and shrink-wrap.
Nothing else is needed, total cost is under 30€.
Airspeed Sensor Features
- Airspeed to transmitter
- User definable units km/h or mph
- Speedrange ~20 to 225km/h or 20 to 140mph
This is not for jets due the small pressure-range of MPXV7002DP sensor used. I have ordered MPXV5004DP to see if we can get up to 350kmh+ with it. Will update code accordingly later.
Accuracy is simply put astonishing. I tested the sensor while driving a car on highway up to 130kmh (~80mph) and values are pinpoint what car’s GPS displayed. Values given from Airspeed Sensor are smoothed for stability but without suffering update speed.
Connection are simple, do note that I have changed the Jeti EX protocol library so the orange wire to receiver is in another location than on previous sensors.
- MPXV7002DP VCC -> Arduino VCC
- MPXV7002DP GND -> Arduino GND
- MPXV7002DP Analog signal -> Arduino A3
You also need the connection to Jeti receiver:
- Arduino TX0 -> 2.4kΩ to 4.7kΩ resistor AND receiver signal
- Arduino RX1 -> 2.4kΩ to 4.7kΩ resistor
- Arduino RAW -> Receiver positive
- Arduino GND -> Receiver negative
NOTE: Some boards have GRN where my boards have GND. Do NOT use GRN, use GND!
Connection schematic below says it all, really simple:
Really, nothing special here. Only three wires between Arduino and pressure-module. Note that resistor can be anything from 2.4kΩ up to 4.7kΩ.
Really a compact unit:
Put together it could look like this:
Put some shrink wrap around it to keep it tidy and ensure parts cannot move:
Programming Jeti Airspeed Sensor
Go and get the suitable .hex or .ino (Named RCT-Airspeed) file from my Github here. Easiest method is XLoader + .hex-file. With Arduino and .ino you need to use the libraries included in Github repository. For info on how to use these look in RFID-sensor how-to here.
Installation of pitot tube to model
There is a few pointers about installation. The most important thing is to install the tube so it’s not in prop-wash. Pitot tube needs to get “clean air”. So if you have on front-mounted engine best place for pitot tube is most likely a wing. Make sure you install pitot tube with enough distance from fuselage.
Pitot tube’s connection to sensor module is easy, plug in the tubes. You can blow in the end of pitot tube to test function (do not cover the small holes, blow only to the end). If you need to suck to get speed on transmitter turn tube-connection around. Pitot-tubes angled connection goes to sensors lower connection.
Using Jeti Airspeed Sensor with Jeti
Unit comes with default speed-unit of km/h. As usual with RC-Thoughts DIY-sensors this one is configured via Jetibox too. So head on to Jetibox -> MX -> down and you should see the start-screen:
Pressing RIGHT takes you to screen where you can select km/h as unit:
if you need to set this setting press DOWN and you are presented with confirmation screen:
If you instead want to use mph as unit when in km/h-screen go right:
And press DOWN and you have mph as your unit.
Resetting to default values are done in next screen:
Pressing down here will return Airspeed Sensor to it’s default settings showing speed in km/h.
NOTE: After changing unit you need to re-scan your sensors in transmitter:
Displaying speed on main screen
As with any other sensors, select either normal or double-sized telemetry window to show airspeed on your main screen:
And that was it. have fun!
- 1.0 Initial release
Always make sure everything works as it should. Do not use faulty devices. neither RC-Thoughts and/or me are in any way liable or responsible for anything you do with your equipment or to others with equipment used as described here. You should never use LUA-apps for operation-critical functions.
If you find something that is not working or is behaving strangely please let me know. I’m a car-mechanic by training, not a programmer-geek :)
Most important thing
Is to have fun building and using, this will not bankrupt you in any way :)