Tuning

This page provides some tips and guidelines for tuning a new aircraft. Be sure to familiarize yourself with the theory of PID Controllers before you begin. Use of the real time plotter may help to visualize and understand the behavior of the control loops.

Sensors

Neutrals

• Put the aircraft in a styrofoam container or completely seal the IR sensors with styrofoam or similar blocks and get a reading of the neutrals for each axis. Also take the gyro neutrals at this time. Update your airframe file, flash the AP and re-check the neutrals.

Directions

• Reverse any servos and make sure no mechanical binding occurs at the limits of travel in Manual mode.
• Take the plane outside and engage AUTO1. Bank and pitch the plane and verify that the controls respond in the correct direction. Note that your body will have a tremendous impact on the measured angles.
• Verify that AUTO1 stick movements respond in the correct direction - important!
• Move the plane rapidly to ensure the gyro response resists motion - increase the gain if needed for better visualization.

R/C, Modem, and GPS

Make sure the GPS signal is strong (outdoors) - you should have a 3-D fix in less than 1 minute and at least some satellite signals above 40dB. The plane should not drift on the map by more than 10 meters. Perform a range test of R/C and modem signals.

Trim

Important: You must never keep any trim, mixers, or rates in your R/C transmitter. R/C trim can be applied in flight but must be corrected and removed on the ground before attempting autonomous flight. Exponential can be useful and will not adversely affect AUTO1 flight but if "low rates" are needed they should be programmed on the same transmitter switch with AUTO1 so that you always have full travel in AUTO1.

• Fly the plane at what you feel is a suitable "cruise" throttle setting and set the trims. Note that setting in the GCS and try to return to that exact setting in subsequent tests. Enter that throttle setting in your airframe file.
• Check maximum pitch and roll response and adjust the mixer parameters or mechanical linkages after landing.
• Land and adjust the linkages. If necessary, the PPM values can be read from the GCS and servo neutrals adjusted electronically, but manual adjustment will produce far better results.
• Fly again to verify trim and control response. If satisfactory, check for any significant throttle-dependent roll. Again, this is best to correct mechanically but can be addressed with the AILERON_OF_THROTTLE mixer in the autopilot. Check also for any odd behavior at full throttle.
• Make sure that GPS and modem data is reliable during these test flights. Note particularly any tendency for the aircraft to appear to fly sideways on the map - this is an indication of weak GPS signals.

Auto 1

• Engage Auto1 and immediately make sure you can turn both left and right!
• Fly at your "cruise" throttle and adjust the ROLL_PGAIN until the plane doesn't quite oscillate
• Adjust the IR roll neutral as needed
• Verify adequate pitch response and adjust PITCH_PGAIN as needed
• Experiment with different throttle settings and tune P and D gains as needed

Auto 2

• Engage Auto2 and you're done!