X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 16 Jul 2013 09:48:12 -0400 Message-ID: X-Original-Return-Path: Received: from omr-m06.mx.aol.com ([64.12.143.80] verified) by logan.com (CommuniGate Pro SMTP 6.0.5) with ESMTPS id 6375088 for lml@lancaironline.net; Tue, 16 Jul 2013 09:25:30 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.143.80; envelope-from=vtailjeff@aol.com Received: from mtaout-da05.r1000.mx.aol.com (mtaout-da05.r1000.mx.aol.com [172.29.51.133]) by omr-m06.mx.aol.com (Outbound Mail Relay) with ESMTP id AE1EB700308CF for ; Tue, 16 Jul 2013 09:24:54 -0400 (EDT) Received: from [10.207.61.52] (mobile-198-228-212-067.mycingular.net [198.228.212.67]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) by mtaout-da05.r1000.mx.aol.com (MUA/Third Party Client Interface) with ESMTPSA id 93CB0E000218; Tue, 16 Jul 2013 09:24:49 -0400 (EDT) References: In-Reply-To: Mime-Version: 1.0 (1.0) Content-Type: multipart/alternative; boundary=Apple-Mail-42AAC0FE-8633-4F2E-9595-C55EEF14502E X-Original-Message-Id: <313B1393-3643-457C-9A74-8DEE0BC8A8FF@aol.com> Content-Transfer-Encoding: 7bit X-Mailer: iPad Mail (9B206) From: vtailjeff@aol.com Subject: Re: [LML] Re: AFS Pilot X-Original-Date: Tue, 16 Jul 2013 06:24:58 -0700 X-Original-To: Lancair Mailing List x-aol-global-disposition: G X-AOL-SCOLL-SCORE: 0:2:486598624:93952408 X-AOL-SCOLL-URL_COUNT: 0 x-aol-sid: 3039ac1d338551e549a16fbf X-AOL-IP: 198.228.212.67 --Apple-Mail-42AAC0FE-8633-4F2E-9595-C55EEF14502E Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Gary, Thanks for the education! Jeff Sent from my iPad On Jul 16, 2013, at 3:27 AM, Gary Casey wrote: > I'm not a true TruTrak expert, but here is an explanation that might add s= omething to the discussion: The TruTrak servos are "stepper motors," distin= ctly different in operation from the servo motors used in other autopilots. = The armature is essentially a collection of permanent magnets and the stato= r creates a magnetic field that attracts the magnets. This field is the "st= epped" around the armature by energizing different coils in succession, and t= he armature follows in phase with these steps. That's why the stick can be o= bserved to move in distinct steps, presumably small enough to avoid it being= obvious. Instead of providing a slip clutch to allow the pilot to overcome= the servo (on other autopilots, you do routinely test the clutch by overpow= ering the autopilot don't you? You don't? You should) TruTrak limited the t= orque capacity of the motor and this can be programmed. Set the autopilot a= nd then overcome it by moving the stick - you can feel it "pop" loose and th= en grab again. Set the torque capacity so that the force to overcome is sig= nificant, but not so much that you would have trouble flying the plane that w= ay, at least until you can reach over and shut off the power to the A/P. >=20 > In flight, the servo produces a distinct characteristic if it is overload= ed and slips. Sort like walking uphill on ice - it progressively moves in t= he commanded direction until the opposing force is too high. When the motor= slips out of synchronization it loses it ability to produce torque (and sli= des downhill). Then when the force drops sufficiently it gets back into ste= p and tries again. It pushes and trips, pushes and trips; a characteristic n= ot at all like simple "hunting," which is smooth and proportional in both di= rections. If, set at the highest torque, it still is overloaded in normal m= aneuvers, you need a higher torque servo. However, in roll you have no clue= as to the force imparted by the trim, and the plane will fly just fine in a= n out-of-trim condition - the servo doesn't care how much torque it takes to= move until it is more than its capability. If it won't bank or level off y= ou might want to first check to make sure it isn't out of trim before blamin= g the servo. >=20 > Finally, the shear pin: It is there to protect against the possibility of= a mechanically locked servo motor. Note that, unlike the "others," the Tru= Trak servo is never disconnected. The controller simply turns off power you= when hand-flying and you simply back-drive the servo motor. If the motor p= hysically jams and won't turn (like from a broken tooth in the gear-train) t= he fix is to apply enough force with the stick to shear the pin. The pin wa= s never intended to shear in any other circumstance. So if your pin shears w= ithout a jammed servo, something is amiss and needs to be fixed. Replacing i= t with a stronger pin isn't what I would recommend, as you may not be able t= o shear it if you have to. A jammed control that can't be overcome is THE w= orst-case scenario. >=20 > For what it's worth > Gary Casey >=20 > =20 > Todd, et.al., >=20 > I have had lots of servo issues with my IV, but solved them with =3D > settings and a screw - explanation below. >=20 > The "micro activity" setting is key for getting rid of the hunting in =3D > the roll axis (in my airplane). With the torque set at its maximum =3D > (255) for both roll and pitch, and the "activity" for each set at around =3D= > 6-7, its a very good balance between being harsh and hunting all of the =3D= > time. I recently had a servo refurbished and when the install was =3D > complete all of these settings were off, and I had to adjust them back. =3D= > But when the mechanic reset everything, he also changed the micro =3D > activity setting to either zero or the max (can't remember). It hunted =3D= > in roll very annoyingly, and I thought it was FUBAR. Adjusting this =3D > along with the torque got me back into the happy place. =3D20 >=20 > As for the screw - there is a shear pin that is designed to break if the =3D= > torque on the servo is too high, presumably to not let the autopilot =3D > over control or fight emergency pilot input. The bad news is that this =3D= > pin was not designed for the high loads in a IV. I have broken this pin =3D= > several times in both roll and pitch, just by letting the autopilot fly =3D= > an approach. The fix was a great idea by my mechanic to replace this =3D > shear pin with a steel screw, essentially locking the servo to the =3D > controls. I deem this safe because there are still 4 other ways to =3D > disable the autopilot (stick button, control head power, on/off switch =3D= > on the panel, and circuit breaker). I wanted to throw that out for =3D > others who might be having this same problem since we are on the =3D > subject. >=20 > Hope this helps >=20 > Bob R --Apple-Mail-42AAC0FE-8633-4F2E-9595-C55EEF14502E Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8
Gary,

=
Thanks for the education!

Jeff

Sent fro= m my iPad

On Jul 16, 2013, at 3:27 AM, Gary Casey <casey.gary@yahoo.com> wrote:

I'm not a true TruTrak expert, but here is an explanation t= hat might add something to the discussion:  The TruTrak servos are "ste= pper motors," distinctly different in operation from the servo motors used i= n other autopilots.  The armature is essentially a collection of perman= ent magnets and the stator creates a magnetic field that attracts the magnet= s.  This field is the "stepped" around the armature by energizing diffe= rent coils in succession, and the armature follows in phase with these steps= .  That's why the stick can be observed to move in distinct steps, pres= umably small enough to avoid it being obvious.  Instead of providing a s= lip clutch to allow the pilot to overcome the servo (on other autopilots, yo= u do routinely test the clutch by overpowering the autopilot don't you? &nbs= p;You don't?  You should) TruTrak limited the torque capacity of the motor and this= can be programmed.  Set the autopilot and then overcome it by moving t= he stick - you can feel it "pop" loose and then grab again.  Set the to= rque capacity so that the force to overcome is significant, but not so much t= hat you would have trouble flying the plane that way, at least until you can= reach over and shut off the power to the A/P.

In flight,  the servo produces a distinct characteristic if it is o= verloaded and slips.  Sort like walking uphill on ice - it progressivel= y moves in the commanded direction until the opposing force is too high. &nb= sp;When the motor slips out of synchronization it loses it ability to produc= e torque (and slides downhill).  Then when the force drops sufficiently it gets back into step and tries again.  It pushes a= nd trips, pushes and trips; a characteristic not at all like simple "hunting= ," which is smooth and proportional in both directions.  If, set at the= highest torque, it still is overloaded in normal maneuvers, you need a high= er torque servo.  However, in roll you have no clue as to the force imp= arted by the trim, and the plane will fly just fine in an out-of-trim condit= ion - the servo doesn't care how much torque it takes to move until it is mo= re than its capability.  If it won't bank or level off  you might w= ant to first check to make sure it isn't out of trim before blaming the serv= o.

Finally,= the shear pin:  It is there to protect against the possibility of a me= chanically locked servo motor.  Note that, unlike the "others," the Tru= Trak servo is never disconnected.  The controller simply turns off powe= r you when hand-flying and you simply back-drive the servo motor.  If t= he motor physically jams and won't turn (like from a broken tooth in the gea= r-train) the fix is to apply enough force with the stick to shear the pin. &= nbsp;The pin was never intended to shear in any other circumstance.  So= if your pin shears without a jammed servo, something is amiss and needs to b= e fixed.  Replacing it with a stronger pin isn't what I would recommend= , as you may not be able to shear it if you have to.  A jammed control t= hat can't be overcome is THE worst-case scenario.

For what it's worth
Gary= Casey

 
Todd, et.al.,

I have had lots of servo issues with my IV, but solved them with =3D
settings and a= screw - explanation below.

The "micro activity" setting is key for g= etting rid of the hunting in =3D
the roll axis (in my airplane).  Wi= th the torque set at its maximum =3D
(255) for both roll and pitch, and t= he "activity" for each set at around =3D
6-7, its a very good balance bet= ween being harsh and hunting all of the =3D
time.  I recently had a s= ervo refurbished and when the install was =3D
complete all of these setti= ngs were off, and I had to adjust them back.  =3D
But when the mecha= nic reset everything, he also changed the micro =3D
activity setting to e= ither zero or the max (can't remember).  It hunted =3D
in roll very a= nnoyingly, and I thought it was FUBAR.  Adjusting this =3D
along wit= h the torque got me back into the happy place. =3D20

As for the screw= - there is a shear pin that is designed to break if the =3D
torque on th= e servo is too high, presumably to not let the autopilot =3D
over control o= r fight emergency pilot input.  The bad news is that this =3D
pin wa= s not designed for the high loads in a IV.  I have broken this pin =3D<= br>several times in both roll and pitch, just by letting the autopilot fly =3D=
an approach.  The fix was a great idea by my mechanic to replace th= is =3D
shear pin with a steel screw, essentially locking the servo to the= =3D
controls.  I deem this safe because there are still 4 other way= s to =3D
disable the autopilot (stick button, control head power, on/off s= witch =3D
on the panel, and circuit breaker).  I wanted to throw tha= t out for =3D
others who might be having this same problem since we are o= n the =3D
subject.

Hope this helps

Bob R
<= /div>
= --Apple-Mail-42AAC0FE-8633-4F2E-9595-C55EEF14502E--