Hello, I recently mounted an AP and I keep tweaking the settings. (MGL servos and explorer). I can confirm that certain copy of efis have problems with vibrations indeed. I mounted 2 different ones on my plane, one of wich was completely ou of ajustment. So it could be a good idea to test it with An SP7.
Concerning The course tracking, I noticed a few times difficulties to follow it. I continue my tests.
Do you have autotrim function enabled ?
Why Doesn't The Autopilot Do Its Job Properly?
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Re: Why Doesn't The Autopilot Do Its Job Properly?
I have had time to test the new SP7 fitment. I spent quite a bit of time making sure the bracket was solid and isolated from vibration, particularly High-frequency vibrations.
I did this by fitting it inside a cube of Medium Density foam.
The result was chalk and cheese compared to the inbuilt AHRS of the Explorer lite.
It is now rock solid in turbulence and where I was getting 50-100 feet altitude changes, which I wasn't particularly worried about, it is now more like 10-20 feet altitude changes.
And tracking to waypoints is spot on, no more deviation off track and follows the HITS perfectly.
I only wish I had done it sooner.
I did this by fitting it inside a cube of Medium Density foam.
The result was chalk and cheese compared to the inbuilt AHRS of the Explorer lite.
It is now rock solid in turbulence and where I was getting 50-100 feet altitude changes, which I wasn't particularly worried about, it is now more like 10-20 feet altitude changes.
And tracking to waypoints is spot on, no more deviation off track and follows the HITS perfectly.
I only wish I had done it sooner.
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Microhornet
- Posts: 1
- Joined: Wed Jun 08, 2022 6:48 pm
Re: Why Doesn't The Autopilot Do Its Job Properly?
Hi following this thread my auto pilot all mgl explorer light ,xtrem,sp6,sp7,extender,radac map,2 mgl servos
without sp7 autopilot functions ok
with sp7 the pitch starts off ok in flat calm conditions after a few minutes it starts oscillating in pitch progressively getting worse +/- 500+ft
The sp7 has had a verity of mountings and several different locations with same result even just running the horizon
The a/c is a sportcruiser with all the factory supplied mountings for the servos
The explorer and xtrem share the same can bus could this be causing the problem with the sp7
Has anyone got a photo of the sp7 mountings that work please thanks
without sp7 autopilot functions ok
with sp7 the pitch starts off ok in flat calm conditions after a few minutes it starts oscillating in pitch progressively getting worse +/- 500+ft
The sp7 has had a verity of mountings and several different locations with same result even just running the horizon
The a/c is a sportcruiser with all the factory supplied mountings for the servos
The explorer and xtrem share the same can bus could this be causing the problem with the sp7
Has anyone got a photo of the sp7 mountings that work please thanks
Re: Why Doesn't The Autopilot Do Its Job Properly?
Yes connecting the XTreme onto the same bus as the iEFIS can lead to issues - even if the XTreme is not setup to control the AP it still sends out messages containing velocity which is used by the SP-7 to help with AHRS aiding. Later versions of XTreme firmware can be set to not send this message.
Simple test is to disconnect the XTreme and see what happens...
Usually what you describe is caused by the servo not being able to feed in small corrections as they don't get through to the control surface. Usually this is caused by the shear screw not having been set with a drop of locktight and similar for the large grub screw of the servo boss (the big round thing that holds the servo arm). If this is not done during installation either will loosen - just a matter of time.
I have once seen a case in a Pipistral Sinus - the servo was mounted to the (very thin) aircraft skin. When the servo changed position - the first thing that happened was the skin would flex - no movement at the elevator at all. Needless to say that pitch control was an adventure.
Finally make your your servo magnitude is set correctly for your aircraft and coupling to the control surface. The magnitude dictates the amount of servo movement for a given amount of needed correction. If that is too low - your AP falls behind the aircraft as it is not allowed to react in a measured way to what is needed - at first all is well until bigger corrections are needed - then it simply is not fast enough and the pitch oscillations grow with each cycle.
A correct setting would give the AP a little more control than is needed - the AP is able to "learn" from it's inputs in this case and will settle to a nice even control able to compensate for calm or turbulent conditions.
If the magnitude is too high it will over-control - this is similar to the case of the setting too low - but much more rapid.
Check that with AP engaged on the ground you cannot move the elevator by hand even a little bit (that would indicate play in the coupling) - you should be able to see and feel every step the servo does on the elevator control surface.
Here is the way pitch control works on our systems:
The AP uses your airspeed as primary input. It also takes your vertical speed. This creates a triangle if you are climbing or descending. We can work out the angle of this. We then look at the AHRS - we are not interested in the actual pitch angle. But lets say we are climbing at an angle of 1 degree but really we want to descend by an angle of 1 degree. So we know we need to change the angle difference between our flight path angle and that the AHRS is showing us. We are only interested in the difference. So the AP will now move the servo in proportion to that difference. That now feeds into the airspeed (in this case the nose will drop so we will gain) - so we recalculate the whole thing. We do that ten times per second. Eventually we will arrive and hold the desired angle of climb or decent which is calculated in another part of the system (in the flight director you can also enable for display on your EFIS).
Simple test is to disconnect the XTreme and see what happens...
Usually what you describe is caused by the servo not being able to feed in small corrections as they don't get through to the control surface. Usually this is caused by the shear screw not having been set with a drop of locktight and similar for the large grub screw of the servo boss (the big round thing that holds the servo arm). If this is not done during installation either will loosen - just a matter of time.
I have once seen a case in a Pipistral Sinus - the servo was mounted to the (very thin) aircraft skin. When the servo changed position - the first thing that happened was the skin would flex - no movement at the elevator at all. Needless to say that pitch control was an adventure.
Finally make your your servo magnitude is set correctly for your aircraft and coupling to the control surface. The magnitude dictates the amount of servo movement for a given amount of needed correction. If that is too low - your AP falls behind the aircraft as it is not allowed to react in a measured way to what is needed - at first all is well until bigger corrections are needed - then it simply is not fast enough and the pitch oscillations grow with each cycle.
A correct setting would give the AP a little more control than is needed - the AP is able to "learn" from it's inputs in this case and will settle to a nice even control able to compensate for calm or turbulent conditions.
If the magnitude is too high it will over-control - this is similar to the case of the setting too low - but much more rapid.
Check that with AP engaged on the ground you cannot move the elevator by hand even a little bit (that would indicate play in the coupling) - you should be able to see and feel every step the servo does on the elevator control surface.
Here is the way pitch control works on our systems:
The AP uses your airspeed as primary input. It also takes your vertical speed. This creates a triangle if you are climbing or descending. We can work out the angle of this. We then look at the AHRS - we are not interested in the actual pitch angle. But lets say we are climbing at an angle of 1 degree but really we want to descend by an angle of 1 degree. So we know we need to change the angle difference between our flight path angle and that the AHRS is showing us. We are only interested in the difference. So the AP will now move the servo in proportion to that difference. That now feeds into the airspeed (in this case the nose will drop so we will gain) - so we recalculate the whole thing. We do that ten times per second. Eventually we will arrive and hold the desired angle of climb or decent which is calculated in another part of the system (in the flight director you can also enable for display on your EFIS).