mirror of https://github.com/ArduPilot/ardupilot
412 lines
18 KiB
Plaintext
412 lines
18 KiB
Plaintext
Tuning Overview
|
|
---------------
|
|
|
|
The following instruction assume that:
|
|
|
|
a) your model is trimmed correctly in manual mode
|
|
b) you have done your radio calibration
|
|
c) you have calibrated your airspeed sensor
|
|
d) you have set your APM and transmitter to be able to select FBW-A mode
|
|
e) You have checked your pitch roll and yaw angle on the HUD and
|
|
verified that they match the rotation of the model
|
|
|
|
Ground checks
|
|
-------------
|
|
|
|
1) On the ground select FBW-A mode
|
|
|
|
2) Rotate your model nose up - you should see the elevators/elevons deflect down
|
|
|
|
3) Rotate your model nose down - you should see the elevators/elevons deflect up
|
|
|
|
4) roll the model to the right - you should see the LH aileron/elevon
|
|
go up and the RH aileron/elevon go down.
|
|
|
|
5) roll the model to the left - you should see the LH aileron/elevon
|
|
go down and the RH aileron/elevon go up.
|
|
|
|
6) level the model - the control surfaces should be close to
|
|
neutral. There will be a little bit of offset, but any more than
|
|
10% of your maximum throw indicates that the APM has not been
|
|
leveled or the radio calibration needs to be repeated.
|
|
|
|
7) With the model level apply LH and RH roll stick inputs on your
|
|
transmitter - the controls should deflect in the same direction that
|
|
they would in manual mode.
|
|
|
|
8) With the model level apply up and down pitch stick inputs on your
|
|
transmitter the controls should deflect in the same direction that
|
|
they would in manual mode.
|
|
|
|
6) If you have an airspeed sensor enabled then blow air towards the
|
|
front of the pitot tube and watch the HUD. You should see the
|
|
airspeed reading increase
|
|
|
|
Flight testing
|
|
--------------
|
|
|
|
Ideally you will need a second person to do this - one person to fly
|
|
the plane and one person to adjust the parameters. To follow the
|
|
manual parts of this procedure you need to be a proficient RC pilot
|
|
and have the skills to be able to recover from an unusual attitude. If
|
|
not, then get someone who can to help you.
|
|
|
|
Initial assessment
|
|
------------------
|
|
|
|
1) Takeoff in manual and adjust the trims and throttle to a cruise
|
|
position so that the plane flies straight and level at a speed that
|
|
you are comfortable with. This will normally be somewhere between
|
|
30 and 60% throttle depending on how overpowered your model is.
|
|
|
|
2) With the plane flying away from you switch to FBW-A. It should
|
|
continue to fly wings level and at a fairly constant height (it
|
|
will climb or descend slowly). If it wants to roll or pitch more
|
|
than a small amount then there is a problem with the models trim or
|
|
radio calibration and you need to solve that first before
|
|
proceeding further.
|
|
|
|
3) If the model starts to wag its wings, then the autopilot default
|
|
gain is too high for your model (this is unlikely but could happen)
|
|
and you need to switch back to manual immediately and ask your
|
|
assistant to halve the CTL_RLL_K_P parameter before switching back
|
|
into FBW-A
|
|
|
|
4) If the model starts to porpoise, the default autopilot gain is too
|
|
high (this is unlikely but could happen) and you need to switch
|
|
back to manual immediately and ask your assistant to halve the
|
|
CTL_PTCH_K_P parameter before switching back into FBW-A
|
|
|
|
Roll control tuning
|
|
-------------------
|
|
|
|
Method 1:
|
|
|
|
This method is the simplest, but won't give the best result. For those
|
|
users familiar with tuning the old PID controller gains, the K_P, K_I
|
|
and K_D gains in this controller have the same effect, but there are some
|
|
additional values that can be set by more advanced users.
|
|
|
|
1) With the model in FBW-A mode, put in a rapid bank angle demand,
|
|
hold it and release. Do the same in the other direction. You want
|
|
the model to roll quickly and smoothly to the new bank angle and
|
|
back again without overshoot or any wing 'waggle'. If the roll
|
|
response is too slow, then progressively increase the CTL_RLL_K_P
|
|
gain in increments of 0.1 until you are happy with the response.
|
|
|
|
2) If during 1) the wings start to 'waggle' and you are not happy with
|
|
the speed of the response, then CTL_RLL_K_D can be increased in small
|
|
increments of 0.01 until the wing waggle goes away and step 1 can be
|
|
repeated. Do not go above 0.1 for CTL_RLL_K_D without checking the
|
|
temperature of your servos when you land as in extreme cases turning
|
|
up this gain can cause rapid servo movement and overheat the servos
|
|
leading to premature failure.
|
|
|
|
Method 2:
|
|
|
|
This method can give a better result, but requires more caution because
|
|
step 2) can produce a high frequency instability that unless reversion
|
|
back to manual is done quickly, could overstress the plane.
|
|
|
|
1) Follow basic method 1) first
|
|
|
|
2) Increase CTL_RLL_K_D in increments of 0.01 until it it starts to
|
|
oscillate, then halve it.
|
|
|
|
3) Reduce CTL_RLL_TAU from the default value of 0.7 for a more rapid
|
|
response if desired and if your aircraft is capable of doing so.
|
|
If the bank angle starts to overshoot or you see wing 'waggle',
|
|
you have gone too far.
|
|
|
|
Advanced:
|
|
|
|
1) Select the tuning box on the bottom of the Mission planers Flight
|
|
Data page. You should get a scrolling black window above the
|
|
map. Double click in the black window and you should get a list of
|
|
parameters to plot. Change the selection until you have the roll
|
|
and nav_roll plotted. Nav_roll is the demand and roll is the
|
|
response. You can use this to look for overshoot and other behavior
|
|
that isn't so obvious from the ground looking at the model.
|
|
|
|
2) Check for any steady offset between nav-roll and roll. If there is
|
|
one you can set the CTL_RLL_K_I to a small value (say 0.01) which
|
|
will allow the control loop to slowly trim the aileron demand to
|
|
remove the steady error. If you want it to trim faster, you can
|
|
increase the value for this gain.
|
|
|
|
3) If you can slow down the rate of roll and make the model bank more
|
|
smoothly by setting the roll rate limit CTL_RLL_RMAX parameter to a
|
|
non zero value. A value of 60 deg/sec works weel for most models.
|
|
The default is 0 which turns the rate limiter off and makes the
|
|
effect of tuning easier to see.
|
|
|
|
|
|
Pitch Control Tuning
|
|
--------------------
|
|
|
|
Method 1:
|
|
|
|
This method is the simplest and but won't give the best result. For those
|
|
users familiar with tuning the old PID controller gains, the K_P, K_I
|
|
and K_D gains in this controller have the same effect, but there are some
|
|
additional values that anbe set by more advanced users.
|
|
|
|
1) With the model in FBW-A mode and the throttle at the cruise
|
|
position, put in a pitch angle demand, hold it and release. Do the
|
|
same in the other direction. You want the model to pitch smoothly
|
|
to the new pitch angle and back again without overshoot or
|
|
proposing. If the pitch response is too slow, then progressively
|
|
increase the CTL_PTCH_K_P parameter in increments of 0.1 you are happy
|
|
with the speed of the response or it starts to porpoise a little. If
|
|
you are happy with the response after this step, you can skip step 2)
|
|
|
|
2) If you get porposising and the response is still too sluggish, increase
|
|
the CTL_RLL_K_D gain in small increments of 0.01 until the overshoot or
|
|
porpoise goes away. If it hasn't worked by the time you have reached a
|
|
value of 0.1 for CTL_PTCH_K_D, DONT go any further until you have checked
|
|
your servo temperatures immediately after landing as in extreme
|
|
cases turning up this gain can cause rapid servo movement and overheat
|
|
the servos leading to premature failure.
|
|
|
|
3) Now roll the model to maximum bank in each direction. The nose
|
|
should stay fairly level during the turns without significant gain
|
|
or loss of altitude. Some loss of altitude during sustained turns
|
|
at constant throttle is expected, because the extra drag of turning
|
|
slows the model down which will cause a mild descent. If the model
|
|
gains height during the turns then you need to reduce the
|
|
CTL_PTCH_K_RLL by small increments of 0.01 from the default value
|
|
of 1.0. If the model descends immediately when the model banks (a
|
|
mild descent later in the turn when the model slows down is normal
|
|
as explained earlier) then increase the CTL_PTCH_K_RLL by small
|
|
increments of 0.01 from the default value of 1.0. If you need to
|
|
change the CTL_PTCH_K_RLL parameter outside the range from 0.7 to
|
|
1.4 then something is likely wrong with either the earlier tuning
|
|
of your pitch loop, your airspeed calibration or you APM's bank
|
|
angle estimate.
|
|
|
|
Method 2:
|
|
|
|
This method can give a better result, but requires more caution because
|
|
step 2) can produce a high frequency instability that unless reversion
|
|
back to manual is done quickly, could overstress the plane.
|
|
|
|
1) Follow Basic Method 1) first
|
|
|
|
2) Increase CTL_PTCH_K_D in increments of 0.01 until it it starts to
|
|
oscillate, then halve it.
|
|
|
|
1) Reduce CTL_PTCH_TAU from the default value of 0.7 for a more rapid
|
|
response if required and if your aircraft is capable of doing so.
|
|
If the pitch response starts to overshoot, you have gone too far.
|
|
|
|
Advanced Options:
|
|
|
|
3) Increase CTL_PTCH_K_I from the default value to more rapidly trim
|
|
out errors in pitch angle (you will need to monitor the nav_pitch
|
|
and pitch in the tuning graphs window to do this).
|
|
|
|
2) The maximum nose down and nose up pitch rate in degrees/second can
|
|
be constrained by setting the CTL_PTCH_RMAX_D and CTL_PTCH_RMAX_U
|
|
parameters to a value other than 0. These parameters can be
|
|
used to limit the amount of g produced during a pull-up or push
|
|
down.
|
|
|
|
Yaw Control Tuning
|
|
------------------
|
|
|
|
The yaw control loop can be configured either as a simple yaw damper
|
|
(good for models with inadequate fin area) or as a combined yaw damper
|
|
and sideslip controller. Because control of sideslip uses measured
|
|
lateral acceleration, it will only work for those models that have
|
|
enough fuselage side area to produce a measureable lateral
|
|
acceleration when they sideslip (an extreme example of this is an
|
|
aerobatic model flying a knife-edge maneuver where all of the lift is
|
|
produced by the fuselage). Gliders with very skinny fuselages and
|
|
flying wings cannot use this feature, but can still benefit from the
|
|
yaw damper provided they have a yaw control of some sort of yaw
|
|
control (rudder, differential airbrakes, etc)
|
|
|
|
Tuning the yaw damper:
|
|
|
|
1) Verify that the CTL_YAW_K_A and CTL_YAW_K_I gain terms are set to
|
|
zero, the CTL_YAW_K_RLL gain term is set to 1.0 and the CTL_YAW_K_D
|
|
gain term is set to zero
|
|
|
|
2) Roll into and out of turns in both directions and observe the
|
|
yawing motion as it rolls into the turn. If the nose yaws away from
|
|
the direction of roll, you need to increase the KFF_RDDRMIX gain
|
|
until the yaw goes away.
|
|
|
|
3) Increase CTL_YAW_K_D in small increments of 0.05 until the tail
|
|
starts to 'wag'. Halve the gain from value at which you start to
|
|
see the tail 'wag'.
|
|
|
|
4) Now roll the model into and out of turns in both directions. If the
|
|
model has a tendency to yaw the nose to the outside of the turn,
|
|
then increase the CTL_YAW_K_RLL gain term in increments of 0.01
|
|
from its default value of 1.0. Conversely if the model has the
|
|
tendency to yaw the nose to the inside of the turn on turn entry,
|
|
then reduce the CTL_YAW_K_RLL gain term in increments of 0.01 from
|
|
its default value of 1.0. If you have to go outside the range from
|
|
0.8 to 1.2, then there is something else that needs to be sorted
|
|
and you should check step 2), the airspeed calibration and accuracy
|
|
of the bank angle measurement.
|
|
|
|
Tuning the sideslip controller (advanced):
|
|
|
|
1) Tune the yaw damper first
|
|
|
|
2) Set the CTL_YAW_K_I gain term to 1.0. If this causes the tail to
|
|
'wag' then reduce this gain until the wag stops
|
|
|
|
3) Bring up the tuning graph window in the mission planner and plot
|
|
the lateral acceleration ay.
|
|
|
|
4) Roll the model rapidly from full bank in each direction and observe
|
|
the lateral acceleration ay. If the lateral acceleration sits
|
|
around zero and doesn't change when you roll into or out of turns
|
|
then your model is very well trimmed and no sideslip control is
|
|
required. You can change the CTL_YAW_K_I gain term back to zero.
|
|
|
|
5) IF you see that the y acceleration is offset or spikes up during
|
|
turns, then progressively increase the CTL_YAW_K_A gain in steps of
|
|
0.5 until the error goes away or the tail starts to wag. If the
|
|
tail starts to wag, then halve the gain from the value at which the
|
|
wag appeared.
|
|
|
|
|
|
Control Parameter Descriptions
|
|
------------------------------
|
|
|
|
The default values for each parameter are shown.
|
|
|
|
Pitch control parameters:
|
|
|
|
Main Parameters:
|
|
|
|
CTL_PTCH_K_P = 0.4
|
|
This is the gain from demanded pitch rate to demanded
|
|
elevator. Provided CTL_PTCH_OMEGA is set to 1.0, then this gain works
|
|
the same way as the P term in the old PID and can be set to the same
|
|
value.
|
|
|
|
CTL_PTCH_K_I = 0.0
|
|
This is the gain for integration of the pitch rate error. It has
|
|
essentially the same effect as the I term in the old PID. This can be
|
|
set to 0 as a default, however users can increment this to make the
|
|
pitch angle tracking more accurate.
|
|
|
|
CTL_PTCH_K_D = 0.0
|
|
This is the gain from pitch rate error to demanded elevator. This
|
|
adjusts the damping of the pitch control loop. It has the same effect
|
|
as the D term in the old PID but without the large spikes in servo
|
|
demands. this will be set to 0 as a default. Some airframes such as
|
|
flying wings that have poor pitch damping can benefit from a small
|
|
value of up to 0.1 on this gain term. This should be increased in 0.01
|
|
increments as to high a value can lead to a high frequency pitch
|
|
oscillation that could overstress the airframe.
|
|
|
|
CTL_PTCH_K_RLL = 1.0
|
|
This is the gain term that is applied to the pitch rate offset
|
|
calculated as required to keep the nose level during turns. The
|
|
default value is 1 which will work for all models. Advanced users can
|
|
use it to correct for height variation in turns. If height is lost
|
|
initially in the turn this can be increased in small increments of
|
|
0.05 to compensate. If height is gained initially then it can be
|
|
decreased.
|
|
|
|
Advanced Parameters:
|
|
|
|
CTL_PTCH_RMAX_D = 0
|
|
This sets the maximum nose down pitch rate that the controller will
|
|
demand in (degrees/sec). Setting it to zero disables the limit.
|
|
|
|
CTL_PTCH_RMAX_U = 0
|
|
This sets the maximum nose up pitch rate that the controller will
|
|
demand (degrees/sec). Setting it to zero disables the limit.
|
|
|
|
CTL_PTCH_OMEGA = 1.0
|
|
This is the gain from pitch angle error to demanded pitch rate. It
|
|
controls the time constant from demanded to achieved pitch angle. For
|
|
example if a time constant from demanded to achieved pitch of 0.5 sec
|
|
was required, this gain would be set to 1/0.5 = 2.0. A value of 1.0 is
|
|
a good default and will work with nearly all models. Advanced users
|
|
may want to increase this to obtain a faster response.
|
|
|
|
Roll Control Parameters:
|
|
|
|
Main Parameters:
|
|
|
|
CTL_RLL_K_P = 0.4
|
|
This is the gain from demanded roll rate to demanded aileron. Provided
|
|
CTL_RLL_OMEGA is set to 1.0, then this gain works the same way as the
|
|
P term in the old PID and can be set to the same value.
|
|
|
|
CTL_RLL_K_I = 0.0
|
|
This is the gain for integration of the roll rate error. It has
|
|
essentially the same effect as the I term in the old PID. This can be
|
|
set to 0 as a default, however users can increment this to enable the
|
|
controller trim out any roll trim offset.
|
|
|
|
CTL_RLL_K_D = 0.0
|
|
This is the gain from pitch rate error to demanded elevator. This
|
|
adjusts the damping of the roll control loop. It has the same effect
|
|
as the D term in the old PID but without the large spikes in servo
|
|
demands. This will be set to 0 as a default. This should be increased
|
|
in 0.01 increments as too high a value can lead to high frequency roll
|
|
oscillation.
|
|
|
|
Advanced Parameters:
|
|
|
|
CTL_RLL_OMEGA = 1.0
|
|
This is the gain from roll angle error to demanded roll rate. It
|
|
controls the time constant from demanded to achieved roll angle. For
|
|
example if a time constant from demanded to achieved roll of 0.5 sec
|
|
was required, this gain would be set to 1/0.5 = 2.0. A value of 1.0 is
|
|
a good default and will work with nearly all models. Advanced users
|
|
may want to increase this to obtain a faster response.
|
|
|
|
CTL_RLL_RMAX = 60;
|
|
This sets the maximum roll rate that the controller will demand
|
|
(degrees/sec). Setting it to zero disables the limit. If this value is
|
|
set too low, then the roll can't keep up with the navigation demands
|
|
and the plane will start weaving. If it is set too high (or disabled
|
|
by setting to zero) then ailerons will get large inputs at the start
|
|
of turns. A limit of 60 degrees/sec is a good default.
|
|
|
|
Yaw Control Parameters:
|
|
|
|
Advanced Parameters:
|
|
|
|
CTL_YAW_K_A = 0.0
|
|
This is the gain from measured lateral acceleration to demanded yaw
|
|
rate. It should be set to zero unless active control of sideslip is
|
|
desired. This will only work effectively if there is enough fuselage
|
|
side area to generate a measureable lateral acceleration when the
|
|
model sideslips. Flying wings and most gliders cannot use this
|
|
term. This term should only be adjusted after the basic yaw damper
|
|
gain K_D is tuned and the K_I integrator gain has been set. Set this
|
|
gain to zero if only yaw damping is required.
|
|
|
|
CTL_YAW_K_D = 0.0
|
|
This is the gain from yaw rate to rudder. It acts as a damper on yaw
|
|
motion. If a basic yaw damper is required, this gain term can be
|
|
incremented, whilst leaving the K_A and K_I gains at zero.
|
|
|
|
CTL_YAW_K_I = 0.0
|
|
This is the integral gain from lateral acceleration error. This gain
|
|
should only be non-zero if active control over sideslip is desired. If
|
|
active control over sideslip is required then this can be set to 1.0
|
|
as a first try.
|
|
|
|
CTL_YAW_K_RLL = 1.0
|
|
This is the gain term that is applied to the yaw rate offset
|
|
calculated as required to keep the yaw rate consistent with the turn
|
|
rate for a coordinated turn. The default value is 1 which will work
|
|
for all models. Advanced users can use it to correct for any tendency
|
|
to yaw away from or into the turn once the turn is
|
|
established. Increase to make the model yaw more initially and
|
|
decrease to make the model yaw less initially. If values greater than
|
|
1.1 or less than 0.9 are required then it normally indicates a problem
|
|
with the airspeed calibration.
|