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TruTrak C servo repair/teardown
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Tim Olson



Joined: 25 Jan 2007
Posts: 2841

PostPosted: Tue Jan 05, 2021 5:16 pm    Post subject: TruTrak C servo repair/teardown Reply with quote

Jim,
Thanks for the links.  It's tempting to try one of those.  The things
that stop
me would be:

I don't know the manufacturer at all, or reputation.   And I don't know with
the different wire colors how they'd match up.  I'm sure it would work. 
Your point
about the amps would hopefully be accurate too.   It's just more
comfortable to
buy the exact same part, because then you'd know for sure it would
work.  As it is,
I think if my servo no longer works, I'd try one of these just for
kicks. The price is
right.  But, I also bought the spares now, so I'd probably use that one
and keep
the Amazon one for a spare.   Also, the gear on the shaft is held on by
a small 1/16"
roll pin, so I'd need to drill the shaft on the new one and install a
new roll pin to
use it.  But it certainly is an option.

I measured the height of the servo from the mount base to the top and it's
something between exactly 3" and 3-1/16".  I had a crappy tape measure
near me. Smile

Here are pics of the servo I pulled out, with pics of the guts.

https://www.myrv10.com/N104CD/maintenance/TruTrak_Servo/

I cleaned off the corrosion and lubed the bearings and blew out the
inside after
a light scotchbrite of the inside and rotor and now it's actually more
free than the
brand new one.  In the link above, the pic near the center of the page
is of the
2 new ones I just bought.

Anyway, I posted the pics in case anyone is interested.

Oh, and for any of you guys that offered your servos for sale, let me
know if you
want your info passed on to someone else who's interested. I had a guy
write me
on VAF who's looking for a servo too.

Tim
On 1/5/2021 6:43 PM, Jim Combs wrote:
Quote:


Typically the motors are driven with a constant current driver. It
does not matter that the winding voltage is 4 volts. The drivers will
chop the current to maintain the 1.5 amps. As the motor speed
increases there is a back EMF that has to be overcome. Like I said,
this should be a drop in replacement for that stepper motor.

Just my opinion.

JIm C

On Tue, Jan 5, 2021 at 5:36 PM Tim Olson <Tim(at)myrv10.com> wrote:
> It is a NEMA 23 type. I wasn't having a great time trying to find the exact same servo, however. Maybe you or someone who deals with these things would. I think the best I found was mid-$300's for price. If the motors could be bought for $100 it would be a no brainer. Here's the info off my DSB-C servo. I noticed that the newer ones I got from my friend don't have the manufacturer info. Also, the URLs of most websites I found are either broken, or domains missing.
> Superior Electric
> Slo-Syn Motor
> Impedance Protected Rockford IL
>
> Stepping Motor
> Type KML062F03
> 4.4 VDC 1.5A
> www.slosyn.com
> 200 Steps/Rev
> Connect PER213803
> 044921795
>
> 4 leads, 2.93 ohms, 16.9 mH inductance.
> Bipolar Holding Torque 250 oz-in (177 Ncm).
> Max Overhang Load 15lbs
> Max Thrust Load 25lbs
> Residual Torque 6 oz-in
> Typical Motor Weight 2.3lbs
>
> KML06 = NEMA 23 type
> Maybe that will make it easier to find the match.
> Tim
>
> On 1/5/2021 3:35 PM, Jim Combs wrote:
>
>
>
> Is it a NEMA 23 Stepper or NEMA 17 stepper. These are very
> standardized and are produced in very large quantities. Makes them
> really cheap to replace.
> On Tue, Jan 5, 2021 at 12:28 PM Tim Olson <Tim(at)myrv10.com> wrote:
>
> I'm assuming it's not an issue with short-term removal?
> It would be pretty crazy if pulling it out for 5 minutes reduced the life by a lot.
> I don't intend to keep it out very long. Just enough to clean it up.
> Tim
>
> On 1/5/2021 10:46 AM, David Carr wrote:
>
> Tim,
>
> Some stepper motor rotors will lose a fair amount of their magnetism when removed from their stator. This causes the torque of the motor to be significantly reduced. I don't know if this will be the case with your motor, but it's worth watching out for.
>
> David
>
> On Tue, Jan 5, 2021 at 10:42 AM Tim Olson <Tim(at)myrv10.com> wrote:
>
>
>
> I thought I posted a follow-up post on this but I did tear it apart.
> The base that the
> stepper motor is mounted on contains all the gearing for the autopilot.
> All of that
> was fine. The stepper motor itself was tight at times. I'd turn it and
> after sitting
> for a few minutes, it would usually turn ok for a partial revolution,
> and then get
> tight. I removed the base of the motor, pulled out the center rotor,
> and the bearings
> were fine. Nothing much out of place, but, I did have one of the 4
> screws holding
> the motor together that was corroded, and some corrosion between the bottom
> of the coil area and the base of the motor. There was a little
> particulate on the
> placemat after disassembly. The clearances are pretty tight inside, and
> my guess
> is that it was just corrosion that was the issue. After inserting the
> rotor again,
> everything was much more free again. I didn't get a chance last night
> to clean it
> all up, but I plan to do a 2nd disassembly and cleaning and lubrication and
> assembly and then my guess is that the servo will be fine. I bought a
> spare pair
> from a friend of mine that should show today, but I'll try my old one
> first and if it
> works, I'll just keep using it for the time being.
>
> More to come.
> Tim
> On 1/5/2021 10:17 AM, Jim Combs wrote:
>
>
>
> Are you going to take apart the failed servo and do any kind of
> failure analysis? If not, I would be willing to open and take a look.
> I too am using the same servo's. 10 years of flying and 1400 hours so
> far.
>
> Jim C
>
> On Mon, Jan 4, 2021 at 12:14 AM Tim Olson <Tim(at)myrv10.com> wrote:
>
> Was that when it was still TruTrak, or through Bendix? I'm a little leery of anything but
> the original TruTrak folks, since the stories become less positive after that purchase.
> I would hope that good service will continue, but I'd feel more comfortable if
> the TruTrak guys still do their own repairs.
> Tim
> On 1/3/2021 10:53 PM, David Saylor wrote:
>
> TruTrak overhauled a roll servo for me in Aug 2019. The cost was $380 and it looked <brand new>, including the serial number! They turned it around the same day.
>
> On Sun, Jan 3, 2021 at 16:55 Tim Olson <Tim(at)myrv10.com> wrote:
>
>
>
> Hey all, my 16 year old TruTrack DSB-C type servo in my wing (aileron)
> got tight and binding. Interestingly it releases once in a while like
> the clutch releases but then binds again. So I pulled it out today,
> and will start looking into replacement. I would also like to
> tear it open if it's something that I can do without wrecking anything
> inside, to see what broke. Does anyone have any teardown pics or
> has anyone had a servo rebuilt by TruTrak (I guess now Bendix) before?
> Just interested in how much $$ I'll be out to get it fixed up and
> working again. I'd like to keep one as a spare from here out,
> since I have 2 planes that could use them.
> Tim
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fasilpereira



Joined: 17 Jul 2011
Posts: 72
Location: Brazil

PostPosted: Thu Jan 07, 2021 2:47 am    Post subject: Re: TruTrak C servo repair/teardown Reply with quote

I’m also looking for Trutrak servos at a reasonable price to keep as spares.

If you have any available, please send pictures and asking price to fasilpereira(at)yahoo(dot)com

Thank you,

Fabricio


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