So, I've slowly been making some progress on this, having mocked up the who
le system out of the aircraft. I have now been able to test it in the worksh
op and yesterday in a car (it needed to be moving to get a track signal). Se
e attached photo. However, I now have a couple more questions/observations!
i) It seems that the Skymap III that I used in these tests works in terms o
f making the servo move and display a track on the Trutrak, so that's progre
ss! However, I note from the Skymap manual that it only gives its GPS info e
very 2 seconds, rather than the once every second that the Trutrak recommend
s to avoid 'wandering'. Peter, in your post you mentioned that you were usin
g a Skymap III - have you ever had a problem with this (assuming your A/P is
the Trutrak Digitrak too)? Alan, is the Garmin 196 that you've mentioned as
suitable, able to be set to give data at the 'once per second' rates, as fr
om the manual it seems it may too default to once every 2 seconds?
ii) I noticed when testing in the car, that when the track that was display
ed in the Trutrak was close to what we were actually tracking (as read from
the Skymap), that the servo was more or less static, and moved in the correc
t direction when there was a small deviation between what was set on the Tru
trak and what we were tracking. However, because our roads are not straight,
there were frequently occasions when the actual track from the Skymap was m
iles away from that set on the Trutrak. In that situation the servo went a b
it crazy and rotated its arm by many more degrees than it could ever do in t
he plane. Is this to be expected in this rather 'offline' mode? I can imagin
e that when the Trutrak senses that its control input is not creating the so
rt of aircraft track change that it had expected, that it just moves the ser
vo even further in order to try to get aircraft to do something?
iii) Clearly my mock-up does not provide any sort of 'force feedback' to th
e servo control arm (ie the arm is completely free to rotate as it likes). I
n an aircraft, would this be taken care of by aerodynamic feedback via the a
ileron torque tube? What happens to the servo when it reaches the full movem
ent that the aileron would allow (the point when the control column hits its
roll stops)?
iv) I can imagine that I wouldn't want the servo ever applying full aileron
to create a turn as that would make for a very violent manoeuvre! I see tha
t there are settings that can be adjusted in the Trutrak set-up menus that c
ontrol activity level and also control maximum torque. What values have peop
le set in theirs? I note that when I have set the recommended value of 12 fo
r the torque, it is almost impossible to override the servo arm when the A/P
is engaged (though I appreciate that with no control column attached the le
verage I can apply to the servo arm with my fingers is very low. I also appr
eciate that normally if one wanted to override the A/P you would disengage i
t first).
v) Lastly (for now!) has anyone fitted physical 'stops' to the servo body t
hat the servo arm would hit to ensure that the servo can never try to move t
he pushrod beyond the point where full aileron is applied?
Apologies for all the questions but I want to make sure it is really workin
g correctly before I contort myself to fit it into the aircraft itself!
Best regards
David
=EF=BBOn 19/11/2022, 16:26, "Alan Burrill" <owner-europa-list-server@matronics
.com <mailto:owner-europa-list-server@matronics.com> on behalf of alanb@dpy0
1.co.uk <mailto:alanb@dpy01.co.uk>> wrote:
alanb@dpy01.co.uk>>
Ok I=99ve had a. Ha ce to fly mine with the GPS feed off.
As Duncan says below the display drops to show -|=94|- but maintains the tr
ack last set or you are holding when you switch it on.
The are no heading digits on the display so you will need use your compass/
DI to show that.
If you press the left or right =A4=B5=EF=B8=8F buttons then you can alter the
track
the AP is following either left or right and a number appears which if you p
ress the button you can increase or decrease after the AP locks on the numbe
rs disappear and you have the -|=94|- on the display.
Useful if you have a GPS failure but wouldn=99t want that as normal mode of
operation so my suggestion is you need a GPS feed with the right NEMA messa
ge set to get the most out of the AP and the ability for it to follow a trac
k you have programmed in is a bonus.
One word of caution, I have come across some GPS that don=99t put out any m
essages, even the position message for driving a Transponder ADS-B output, u
nless there is a track in the GPS. That was how some of the older version wo
rked, GARMIN 430 and possible the early AVMAP were guilty of that.
Hope that helps.
Alan
Sent from my iPad
> On 10 Nov 2022, at 10:52, D McFadyean <ami-mcfadyean@talktalk.net <mailto
:ami-mcfadyean@talktalk.net>> wrote:
>
.net <mailto:ami-mcfadyean@talktalk.net>>
>
> Digitrak only needs basic positional information from the GPS on a regula
r basis. It will use this information to fly the track that has been set on
the Digitrak.
> If a route is programmed in to the GPS, it will fly that too (with differ
ent commands being set at the Digitrak control head to enable this), so long
as the GPS is also putting out the crosstrack error signal; not all of them
do.
>
> Duncan McF.
>
s.com/Navigator?Europa-List>
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