With a failed pin, there would now be no shear connection between the servo
hub and the arm other than friction. So, given enough torque it will slip,
and it must have slipped at some point otherwise the pin wouldn't be shear
ed. The earlier servos had a nylon washer under the crosshead screw to help
it slip!
I guess if you take off the arm, the remains of the shear pin may be projec
ting from the hub sufficiently to get a grip on it.
Duncan mcF.
> On 04 January 2023 at 12:21 David Cripps <dpc@knightonweb.com> wrote:
>
>
> Thanks very much for this extra info, Duncan.
>
>
>
> If you can find that spare stop that would be great. I had seen a pic
ture similar to the one you sent of the stops in another aircraft applicati
on.
>
>
>
> Following your comments about the shear pin, I think this is the smal
l brass screw located just above the main central cross-head screw that hol
ds the control arm onto the servo in the photo I=99ve attached here?
I looked at mine more closely and saw that the head of that brass screw app
eared to be slightly loose and with some tapping I could get the screw head
to drop out of the arm. If that is the shear pin you=99re referring
to then it appears mine is already sheared! However, the arm doesn=99
t show any tendency to rotate on the hub? I guess the cross-head screw is h
olding it onto the hub pretty firmly, but I can see that the arm could pote
ntially rotate against the hub without the pin being there (since there is
no positive locking mechanism against rotation), but the cross-head screw w
ould need to be looser than it currently is for rotation of the arm to be p
ossible. Should the arm be free to rotate against the hub without the pin t
here? Question also now is how to get the threaded bit out and the pin repl
aced?!
>
>
>
> Best regards
>
>
>
> David
>
>
>
> I'd not seen before the clip on the servo arm; there was an earlier F
actory 'fix' of Loctited replacement screws. Later servos have a stud and p
inned locknut instead (I guess the stud is held in only by Loctite!).
>
> The control column stops should take priority, as the servo stops are
probably too light to limit enthusiastic control movements by the pilot, b
ut should at least contain a runaway servo or some other breakage in the se
rvo. I might have some spare stops (if I can find them). The stops are half
-visible and annotated 'F' in the photo at: TruTrak-RV10-Roll-Installation-
Guide.pdf (bendixking.com) https://www.bendixking.com/content/dam/bendixkin
g/en/documents/document-lists/downloads-and-manuals/TruTrak-RV10-Roll-Insta
llation-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 an
d polished to the roots of the screw thread.
>
> My own servo is mounted towards the back of the Europa 'tunnel' and c
onnects 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 firew
all and no tunnel ventilation. Subsequently a 'fire blanket' (two thin laye
rs of woven Kevlar with thin fibreglass loft insulation sandwiched between,
rather like Orkotek) placed on the back of the firewall enabled cooler tem
peratures. I've not heard of the standard under-seat servo location getting
too hot.
>
>
>
> 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
replies 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 really be a problem. We hadn=99t planned to have it fly a full r
oute and navigate itself around turning points. I had thought we=99d
be manually changing the selected track at each turning point, and then loc
k the tracking to the new direction required. However, the Skymap III does
have a =98Turn Anticipation=99 feature if we should in the futu
re 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! D
o 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 seem to have any physical stops on the servo arm. It did, however, hav
e the extra alloy =98clip=99 to secure the screw that attaches
the arm to the servo. I=99ve seen that that clip was an LAA requireme
nt too (see photo). For the physical stops, I did see on another forum some
thing that looked like it would do the job on this servo (may even have bee
n a Trutrak part). Does the LAA specify what these stops should look like o
r be made of? Should they be set so that the servo arm touches them at the
same time as the control column reaches its full deflection (if not, then w
hich stop should =98take priority=99 and be hit first)? Does an
yone have a photo of what the stops look like in their setup? I imagine the
m being mounted on the bolts that attach the servo motor to its mounting fr
ame.
> >
> >
> >
> > My servo would be mounted under the pax seat per Mod 75, so the
re is not really any ventilation there. Is it worth adding a little cooling
fan to 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 wel
l, so that might have been a cause' or possibly I have a too low torque set
ting than optimal in order to limit servo overheating). If too many options
of output data are requested in the GPS NMEA output setup then there won't
be enough time 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 pr
eselected.
> >
> > iv). The Europa needs quite a high torque setting (10 or 12 fro
m memory, which can on hot days plus a high 'activity' setting result in se
rvo overheating and shutdown if you have a trigear with 'heated'/unventilat
ed fuselage tunnel and depending where the servo is mounted).
> >
> > The pilot stick force required to overcome maximum torque will
be applied without even thinking about it and in any case there is a necked
brass shear pin (comprising a modified 6-32 brass instrument mounting scre
w) in the servo arm that can be easily sheared (even without knowing it, an
d then you wonder why the AP is not tracking!). I agreed with LAA to replac
e this with a (necked) stainless steel pin in order to provide a little mor
e strength and haven't sheared it since.
> >
> > I also think that when the servo gets very hot (as above) it's
internal voltage regulator starts to shut down (as many are designed to do)
. Again, there is no way of knowing when this happens until realisation tha
t the AP is not tracking!
> >
> > v). The LAA will insist upon the stops on the servo, although t
hese stops are not particularly robust and the set up would be better adjus
ted so that the stops never have to resist the pilot's stick inputs.
> >
> > Otherwise, the Trutrak system and its dynamics work extremely w
ell and can do a much better job than the pilot, especially in turbulent co
nditions.
> >
> > 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 mailto:dpc@knightonweb.com > wrote:
> > >
> > >
> > > So, I've slowly been making some progress on this, having
mocked up the whole system out of the aircraft. I have now been able to te
st it in the workshop and yesterday in a car (it needed to be moving to get
a track signal). See attached photo. However, I now have a couple more que
stions/observations!
> > >
> > > i) It seems that the Skymap III that I used in these test
s works in terms of making the servo move and display a track on the Trutra
k, 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 Trutrak recommends to avoid 'wandering'. Peter, in your post you mentio
ned that you were using a Skymap III - have you ever had a problem with thi
s (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 seconds?
> > >
> > > ii) I noticed when testing in the car, that when the trac
k that was displayed in the Trutrak was close to what we were actually trac
king (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 wh
at was set on the Trutrak and what we were tracking. However, because our r
oads are not straight, there were frequently occasions when the actual trac
k from the Skymap was miles away from that set on the Trutrak. In that situ
ation the servo went a bit crazy and rotated its arm by many more degrees t
han it could ever do in the plane. Is this to be expected in this rather 'o
ffline' mode? I can imagine that when the Trutrak senses that its control i
nput is 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 'for
ce feedback' to the servo control arm (ie the arm is completely free to rot
ate as it likes). In an aircraft, would this be taken care of by aerodynami
c feedback via the aileron torque tube? What happens to the servo when it r
eaches the full movement that the aileron would allow (the point when the c
ontrol column hits its roll stops)?
> > >
> > > iv) I can imagine that I wouldn't want the servo ever app
lying full aileron to create a turn as that would make for a very violent m
anoeuvre! I see that there are settings that can be adjusted in the Trutrak
set-up menus that control activity level and also control maximum torque.
What values have people set in theirs? I note that when I have set the reco
mmended 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 contro
l column attached 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 would disengage it first).
> > >
> > > v) Lastly (for now!) has anyone fitted physical 'stops' t
o 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 applie
d?
> > >
> > > Apologies for all the questions but I want to make sure i
t is really working correctly before I contort myself to fit it into the ai
rcraft itself!
> > >
> > > Best regards
> > >
> > > David
> > >
> > > On 19/11/2022, 16:26, "Alan Burrill" <owner-europa-list-s
erver@matronics.com mailto:owner-europa-list-server@matronics.com <mailto:o
wner-europa-list-server@matronics.com mailto:owner-europa-list-server@matro
nics.com > on behalf of alanb@dpy01.co.uk mailto:alanb@dpy01.co.uk <mailto:
alanb@dpy01.co.uk mailto:alanb@dpy01.co.uk >> wrote:
> > >
> > >
y01.co.uk mailto:alanb@dpy01.co.uk <mailto:alanb@dpy01.co.uk mailto:alanb@d
py01.co.uk >>
> > >
> > >
> > > Ok I=99ve had a. Ha ce to fly mine with the GPS fee
d off.
> > >
> > >
> > > As Duncan says below the display drops to show -|
=94|- but maintains the track last set or you are holding when you switch i
t 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 press the button you can increase or decrease
after the AP locks on the numbers disappear and you have the -|=94|-
on the display.
> > >
> > >
> > > Useful if you have a GPS failure but wouldn=99t wan
t that as normal mode of operation so my suggestion is you need a GPS feed
with the right NEMA message set to get the most out of the AP and the abili
ty 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 Tr
ansponder ADS-B output, unless there is a track in the GPS. That was how so
me of the older version worked, GARMIN 430 and possible the early AVMAP wer
e guilty of that.
> > >
> > >
> > > Hope that helps.
> > >
> > >
> > > Alan
> > >
> > >
> > > Sent from my iPad
> > >
> > > > > > >
> > > > On 10 Nov 2022, at 10:52, D McFadyean <ami-mcfadyea
n@talktalk.net mailto:ami-mcfadyean@talktalk.net <mailto:ami-mcfadyean@talk
talk.net mailto:ami-mcfadyean@talktalk.net >> wrote:
> > > >
-mcfadyean@talktalk.net mailto:ami-mcfadyean@talktalk.net <mailto:ami-mcfad
yean@talktalk.net mailto:ami-mcfadyean@talktalk.net >>
> > > >
> > > > Digitrak only needs basic positional information fr
om the GPS on a regular basis. It will use this information to fly the trac
k 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 t
o 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>
> > > ion>
> > >
> > >
> > >
> > >
> > >
> > >
> > > > >
> > >
>
>
>
|