I'd not seen before the clip on the servo arm; there was an earlier Factory
'fix' of Loctited replacement screws. Later servos have a stud and pinned
locknut instead (I guess the stud is held in only by Loctite!).
The control column stops should take priority, as the servo stops are proba
bly too light to limit enthusiastic control movements by the pilot, but sho
uld at least contain a runaway servo or some other breakage in the servo. I
might have some spare stops (if I can find them). The stops are half-visib
le and annotated 'F' in the photo at: TruTrak-RV10-Roll-Installation-Guide.
pdf (bendixking.com) https://www.bendixking.com/content/dam/bendixking/en/d
ocuments/document-lists/downloads-and-manuals/TruTrak-RV10-Roll-Installatio
n-Guide.pdf
The shear pin is merely a 6-32 screw with a short part of its length (where
this crosses the interface between the mating arm and hub) necked and poli
shed to the roots of the screw thread.
My own servo is mounted towards the back of the Europa 'tunnel' and connect
s to a horn bolted to the rear end of the roll torque tube. This area used
to get hot under certain situations via heat from the stainless firewall an
d no tunnel ventilation. Subsequently a 'fire blanket' (two thin layers of
woven Kevlar with thin fibreglass loft insulation sandwiched between, rathe
r like Orkotek) placed on the back of the firewall enabled cooler temperatu
res. I've not heard of the standard under-seat servo location getting too h
ot.
Duncan McF.
> On 03 January 2023 at 22:30 David Cripps <dpc@knightonweb.com> wrote:
>
>
> Thank you for the comprehensive reply, Duncan, and also for the repli
es from Alan and Peter. I really appreciate the feedback.
>
>
>
> It seems that the Skymap III should work OK for us, despite its 0.5Hz
data refresh rate. A bit of =98hunting=99 shouldn=99t re
ally be a problem. We hadn=99t planned to have it fly a full route an
d navigate itself around turning points. I had thought we=99d be manu
ally changing the selected track at each turning point, and then lock the t
racking to the new direction required. However, the Skymap III does have a
=98Turn Anticipation=99 feature if we should in the future want
it to follow a route, and not overshoot a waypoint. Do most people use it
to follow a full track, and make all the waypoint turns?
>
>
>
> Good to know about the shear pin in the arm as a last resort! Do you
have any drawing of the necked stainless pin that you got the LAA to agree
to?
>
>
>
> The servo that I have came out of an old Europa and didn=99t se
em to have any physical stops on the servo arm. It did, however, have the e
xtra alloy =98clip=99 to secure the screw that attaches the arm
to the servo. I=99ve seen that that clip was an LAA requirement too
(see photo). For the physical stops, I did see on another forum something t
hat looked like it would do the job on this servo (may even have been a Tru
trak part). Does the LAA specify what these stops should look like or be ma
de of? Should they be set so that the servo arm touches them at the same ti
me as the control column reaches its full deflection (if not, then which st
op should =98take priority=99 and be hit first)? Does anyone ha
ve a photo of what the stops look like in their setup? I imagine them being
mounted on the bolts that attach the servo motor to its mounting frame.
>
>
>
> My servo would be mounted under the pax seat per Mod 75, so there is
not really any ventilation there. Is it worth adding a little cooling fan t
o the seat locker to keep the air circulating around the servo?
>
>
>
> Many thanks for all the input!
>
> 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 point, but there were sites yesterday that were GPS-jamming as well, so
that might have been a cause' or possibly I have a too low torque setting t
han optimal in order to limit servo overheating). If too many options of ou
tput data are requested in the GPS NMEA output setup then there won't be en
ough time to output all that data within a faster update period; the GPS se
t will normally tell you if this is going to be the case.
>
> iii). The servo does not care about torque feedback. The servo will p
rovide a force (torque) only up to the maximum value that has been preselec
ted.
>
> iv). The Europa needs quite a high torque setting (10 or 12 from memo
ry, which can on hot days plus a high 'activity' setting result in servo ov
erheating and shutdown if you have a trigear with 'heated'/unventilated fus
elage tunnel and depending where the servo is mounted).
>
> The pilot stick force required to overcome maximum torque will be app
lied without 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 servo arm that can be easily sheared (even without knowing it, and then
you wonder 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 stre
ngth and haven't sheared it since.
>
> I also think that when the servo gets very hot (as above) it's intern
al voltage regulator starts to shut down (as many are designed to do). Agai
n, there 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 s
tops are 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 an
d can do a much better job than the pilot, especially in turbulent conditio
ns.
>
> Have you found a setting on your Skymap that allows adjustment of the
pre-emptive steering sensitivity (or "turn anticipation")?
>
>
>
> Duncan McF.
>
> > >
> > On 03 January 2023 at 13:10 David Cripps <dpc@knightonweb.com m
ailto:dpc@knightonweb.com > wrote:
> >
> >
> > So, I've slowly been making some progress on this, having mocke
d up the 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 tra
ck signal). See attached photo. However, I now have a couple more questions
/observations!
> >
> > i) It seems that the Skymap III that I used in these tests work
s in terms 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 GPS info every 2 seconds, rather than the once every second that the Tr
utrak recommends to avoid 'wandering'. Peter, in your post you mentioned th
at you were using a Skymap III - have you ever had a problem with this (ass
uming your A/P is the Trutrak Digitrak too)? Alan, is the Garmin 196 that y
ou've mentioned as suitable, able to be set to give data at the 'once per s
econd' rates, as from 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 displayed 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 correct direction when there was a small deviation between what was
set on the Trutrak and what we were tracking. However, because our roads a
re not straight, there were frequently occasions when the actual track from
the Skymap was miles away from that set on the Trutrak. In that situation
the servo 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 i
s not creating the sort of aircraft track change that it had expected, that
it just moves the servo even further in order to try to get aircraft to do
something?
> >
> > iii) Clearly my mock-up does not provide any sort of 'force fee
dback' to the servo control arm (ie the arm is completely free to rotate as
it likes). In an aircraft, would this be taken care of by aerodynamic feed
back via the aileron torque tube? What happens to the servo when it reaches
the full movement 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 manoeuv
re! I see that there are settings that can be adjusted in the Trutrak set-u
p menus that control activity level and also control maximum torque. What v
alues have people set in theirs? I note that when I have set the recommende
d value of 12 for the torque, it is almost impossible to override the servo
arm when the A/P is engaged (though I appreciate that with no control colu
mn attached the leverage I can apply to the servo arm with my fingers is ve
ry low. I also appreciate that normally if one wanted to override the A/P y
ou would 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 r
eally working correctly before I contort myself to fit it into the aircraft
itself!
> >
> > Best regards
> >
> > David
> >
> > On 19/11/2022, 16:26, "Alan Burrill" <owner-europa-list-server@
matronics.com mailto:owner-europa-list-server@matronics.com <mailto:owner-e
uropa-list-server@matronics.com mailto:owner-europa-list-server@matronics.c
om > on behalf of alanb@dpy01.co.uk mailto:alanb@dpy01.co.uk <mailto:alanb@
dpy01.co.uk mailto:alanb@dpy01.co.uk >> wrote:
> >
> >
.uk mailto:alanb@dpy01.co.uk <mailto:alanb@dpy01.co.uk mailto:alanb@dpy01.c
o.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|- bu
t maintains 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 y
our 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 numb
er appears which if you press the button you can increase or decrease after
the AP locks on the numbers disappear and you have the -|=94|- on th
e 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 t
he right 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 put out any messages, even the position message for driving a Transpon
der ADS-B output, unless there is a track in the GPS. That was how some of
the older version worked, GARMIN 430 and possible the early AVMAP were guil
ty of that.
> >
> >
> > Hope that helps.
> >
> >
> > Alan
> >
> >
> > Sent from my iPad
> >
> >
> > > > >
> > > On 10 Nov 2022, at 10:52, D McFadyean <ami-mcfadyean@talk
talk.net mailto:ami-mcfadyean@talktalk.net <mailto:ami-mcfadyean@talktalk.n
et mailto:ami-mcfadyean@talktalk.net >> wrote:
> > >
yean@talktalk.net mailto:ami-mcfadyean@talktalk.net <mailto:ami-mcfadyean@t
alktalk.net mailto:ami-mcfadyean@talktalk.net >>
> > >
> > > Digitrak only needs basic positional information from the
GPS on a regular 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 different commands being set at the Digitrak control head to enab
le this), so long as the GPS is also putting out the crosstrack error signa
l; not all of them do.
> > >
> > > Duncan McF.
> > >
> > > > >
> >
> >
> >
> >
> > s.com/Navigator?Europa-List>
> > ion>
> >
> >
> >
> >
> >
> >
> >
> > >
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