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GPS, 3-axis Gyros, 3-axis Accelerometer, 3-axis-Compass, Air Speed Indicator, and Barometer...which one's to choose.

Posted by James Kirkley on July 17, 2012 at 6:38pm

What telemetry systems are usually included in a UAV setups?

There must be a heiarcy of which instrumentation to choose first.

 

I know I want to fly waypoints, so the GPS is a requirement.

Barometers and airspeed indicators are a one off. Get them if you want them.

 

This leaves the sticky wicket:

1. I want a "stability mode".

2. I want an indicator of "the heading" in near realtime.

3. I want an indicator of "pitch", "roll", and "yaw" in near realtime.

 

So which to choose: the 3-axis gyros, 3-axis compass, or the 3-axis accelerometer?.

What are the pros and cons of each?

What are the redundancies?

Maybe a combination is best?

Which gives the best realtime indications?

Which holds it accuracy the best over time.

Which has a tendency to wander?

 

 

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Replies

  • James Kirkley July 18, 2012 at 7:59am

    Thanks guys,

    I think I'm starting to understand a bit better.

     

  • Jake Stew July 17, 2012 at 11:18pm

    You don't have to choose.  Your two good options are STmicro and Invensense.  Both use a two chip solution to give a 9DOF IMU.

    STmicro has a accel+mag chip and a gyro chip.  Invensense has a gyro+accel chip and you can a mag from another vendor.

    STmicro has an actual sensor fusion and AHRS code solution that runs on their STM32 processors.  Invensense has been touting a vaporware solution for years, but no actual sensor fusion processor has materialized and most likely doesn't exist IMHO.

    ST chips are cheaper, but most autopilots have gone with Invensense since they've been making good IMU chips a bit longer.

  • Derek E July 17, 2012 at 10:00pm
    Gyroscopes can tell a change in angle, but they don't 'remember' what angle they are at.
    Accellerometers measure changes in speed and their direction.
    Gyroscopes+Accellerometers gives you real stability. Here is a video thhat explains them both very well: https://www.youtube.com/watch?v=s19W-MG-whE

    I agree, go with the ArduPilot Mega 2.0. It has gyros, accelerometers, barometer, magnometer (compas) and GPS is optional (built in or external).

    If you want to know heading and roll/pitch/yaw from the ground then you will also need telemetry. You can do this several ways. Through video and an OSD (On Screen Display) or with two way radios like Xbee (or 3DR Radio) along with a PC running Ardupilot Mission Planner.
  • Eddie Furey July 17, 2012 at 7:14pm

    Just get the ArduPilot Mega 2.0. It will do everything you want, and more, and is in a convenient and tested package. No messing around joining all the components together yourself.

    That said, afaik...

    Stability requires gyros.

    Heading can be calculated from GPS as long as you're moving, otherwise compass.

    Pitch and roll require an accelerometer. Yaw I guess you'd need to calculate from GPS heading vs compass heading?

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