David,
i). The Trutrak will work on a Europa at 0.5Hz update frequency (i.e. every
2 seconds). Sometimes the AP will hunt gently (yesterday was a case in poi
nt, but there were sites yesterday that were GPS-jamming as well, so that m
ight have been a cause' or possibly I have a too low torque setting than op
timal in order to limit servo overheating). If too many options of output d
ata are requested in the GPS NMEA output setup then there won't be enough t
ime to output all that data within a faster update period; the GPS set will
normally tell you if this is going to be the case.
iii). The servo does not care about torque feedback. The servo will provide
a force (torque) only up to the maximum value that has been preselected.
iv). The Europa needs quite a high torque setting (10 or 12 from memory, wh
ich can on hot days plus a high 'activity' setting result in servo overheat
ing and shutdown if you have a trigear with 'heated'/unventilated fuselage
tunnel and depending where the servo is mounted).
The pilot stick force required to overcome maximum torque will be applied w
ithout even thinking about it and in any case there is a necked brass shear
pin (comprising a modified 6-32 brass instrument mounting screw) in the se
rvo arm that can be easily sheared (even without knowing it, and then you w
onder why the AP is not tracking!). I agreed with LAA to replace this with
a (necked) stainless steel pin in order to provide a little more strength a
nd haven't sheared it since.
I also think that when the servo gets very hot (as above) it's internal vol
tage regulator starts to shut down (as many are designed to do). Again, the
re is no way of knowing when this happens until realisation that the AP is
not tracking!
v). The LAA will insist upon the stops on the servo, although these stops a
re not particularly robust and the set up would be better adjusted so that
the stops never have to resist the pilot's stick inputs.
Otherwise, the Trutrak system and its dynamics work extremely well and can
do a much better job than the pilot, especially in turbulent conditions.
Have you found a setting on your Skymap that allows adjustment of the pre-e
mptive steering sensitivity (or "turn anticipation")?
Duncan McF.
> On 03 January 2023 at 13:10 David Cripps <dpc@knightonweb.com mailto:dpc@
knightonweb.com > wrote:
>
>
> So, I've slowly been making some progress on this, having mocked up t
he whole system out of the aircraft. I have now been able to test it in the
workshop and yesterday in a car (it needed to be moving to get a track sig
nal). See attached photo. However, I now have a couple more questions/obser
vations!
>
> i) It seems that the Skymap III that I used in these tests works in t
erms of making the servo move and display a track on the Trutrak, so that's
progress! However, I note from the Skymap manual that it only gives its GP
S info every 2 seconds, rather than the once every second that the Trutrak
recommends to avoid 'wandering'. Peter, in your post you mentioned that you
were using 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 from the manual it seems it may too default to once every 2 seco
nds?
>
> ii) I noticed when testing in the car, that when the track that was d
isplayed in the Trutrak was close to what we were actually tracking (as rea
d from the Skymap), that the servo was more or less static, and moved in th
e correct direction when there was a small deviation between what was set o
n the Trutrak and what we were tracking. However, because our roads are not
straight, there were frequently occasions when the actual track from the S
kymap was miles away from that set on the Trutrak. In that situation the se
rvo went a bit crazy and rotated its arm by many more degrees than it could
ever do in the plane. Is this to be expected in this rather 'offline' mode
? I can imagine that when the Trutrak senses that its control input is not
creating the sort of aircraft track change that it had expected, that it ju
st moves the servo even further in order to try to get aircraft to do somet
hing?
>
> iii) Clearly my mock-up does not provide any sort of 'force feedback'
to the servo control arm (ie the arm is completely free to rotate as it li
kes). In an aircraft, would this be taken care of by aerodynamic feedback v
ia the aileron torque tube? What happens to the servo when it reaches the f
ull movement that the aileron would allow (the point when the control colum
n hits its roll stops)?
>
> iv) I can imagine that I wouldn't want the servo ever applying full a
ileron to create a turn as that would make for a very violent manoeuvre! I
see that there are settings that can be adjusted in the Trutrak set-up menu
s that control activity level and also control maximum torque. What values
have people set in theirs? I note that when I have set the recommended valu
e of 12 for the torque, it is almost impossible to override the servo arm w
hen the A/P is engaged (though I appreciate that with no control column att
ached the leverage I can apply to the servo arm with my fingers is very low
. I also appreciate that normally if one wanted to override the A/P you wou
ld disengage it first).
>
> v) Lastly (for now!) has anyone fitted physical 'stops' to the servo
body that the servo arm would hit to ensure that the servo can never try to
move the pushrod beyond the point where full aileron is applied?
>
> Apologies for all the questions but I want to make sure it is really
working correctly before I contort myself to fit it into the aircraft itsel
f!
>
> Best regards
>
> David
>
> On 19/11/2022, 16:26, "Alan Burrill" <owner-europa-list-server@matron
ics.com mailto:owner-europa-list-server@matronics.com <mailto:owner-europa-
list-server@matronics.com mailto:owner-europa-list-server@matronics.com > o
n behalf of alanb@dpy01.co.uk mailto:alanb@dpy01.co.uk <mailto:alanb@dpy01.
co.uk mailto:alanb@dpy01.co.uk >> wrote:
>
>
ilto:alanb@dpy01.co.uk <mailto:alanb@dpy01.co.uk mailto: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 main
tains the track 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 co
mpass/DI to show that.
>
>
> If you press the left or right =A4=B5=EF=B8=8F buttons then you ca
n alter the track the AP is following either left or right and a number app
ears which if you press the button you can increase or decrease after the A
P locks on the numbers disappear and you have the -|=94|- on the disp
lay.
>
>
> Useful if you have a GPS failure but wouldn=99t want that as no
rmal mode of operation so my suggestion is you need a GPS feed with the rig
ht NEMA message set to get the most out of the AP and the ability for it to
follow a track you have programmed in is a bonus.
>
>
> One word of caution, I have come across some GPS that don=99t p
ut out any messages, even the position message for driving a Transponder AD
S-B output, unless there is a track in the GPS. That was how some of the ol
der version worked, 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 <mailto:ami-mcfadyean@talktalk.net m
ailto:ami-mcfadyean@talktalk.net >> wrote:
> >
alktalk.net mailto:ami-mcfadyean@talktalk.net <mailto:ami-mcfadyean@talktal
k.net mailto:ami-mcfadyean@talktalk.net >>
> >
> > Digitrak only needs basic positional information from the GPS o
n a regular basis. It will use this information to fly the track that has b
een set on the Digitrak.
> > If a route is programmed in to the GPS, it will fly that too (w
ith different commands being set at the Digitrak control head to enable thi
s), 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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