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Old 04-17-2014, 06:36 PM   #1
needlenoses
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Default Dynam Servo replacement

If I am in the wrong spot, let me know.

I am replacing the servos on my Dynam Pitts Model 12. I am hoping to find someone else who had done this. I am having trouble loosening the servos from the fuselage. It feels like they are glued in place with some sort of adhesive. two screws have been removed, but no luck. Obviously I don't want to break away a chunk of foam in the process.

Any ideas please.
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Old 04-17-2014, 07:16 PM   #2
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Yes the servos tend to get glued in due to installing them rapidly after glueing in the mount.

You may have to pull the mount, remove the servo from that then glue the mount back in.

In other models they glue the servos to the foam and don't bother with a mount. In those cases you have to just pry the old servo out and then fill the damaged foam. (I use gorilla quick setting (Dries White) polyurethane glue to fill and cover a servo in plastic wrap, clamp in place to control the expanding foam glue. The plastic wrap peels easily from the glue. Install the servo using your desired method afterward.
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Old 04-17-2014, 08:35 PM   #3
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Welcome to the world of crap servo installations !

Yes ... you will prise that servo out ... a chunk of foam will come out as well.

You can do as fhhuber does .... use a foam glue as a replacement medium or as I do ... I run 5 minute epoxy in which then fills and levels out - creates an excellent base to then set new servo onto once set.
The epoxy puts back more strength for very little weight. It flows into all the nooks and crannies and then is much harder to rip out when doing next servo.

Nigel

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Old 04-18-2014, 12:25 AM   #4
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Default servos

Managed, with a bit of nervous sweat, to pull the first servo out of the fuselage. It was like removing a tooth from a Hippo. I actually think it was stuck to some of the paint that was on before the servos were installed. No damage done. Last time I flew this plane I had it in a sharp bank to the right and it wouldn't respond to inputs. We could actual hear a ratcheting noise. Managed to get it back on an even keel to land. So I am replacing all four servos with Hi-Tech Metal Servos.
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Old 04-18-2014, 01:26 AM   #5
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Ratcheting noise usually means stripped teeth on servo gear.

If the servos are known label - you can get gear sets to replace the stripped ... usually either the output or last intermediate gear ... packet contains full gear set and the first gears are rarely needed.

Trouble is most out of box models - the servos are unlabelled or have the model brand on them, not the servo brand - so you have no idea of their real origin.

A useful piece of kit to have is a Servo Tester ... you can get them for less than $10 from Hobby King etc. It is a useful piece of kit especially for installing servos - you can power up and centre a servo for installation without need for radio ... you can test servo for proper movement etc. etc.

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Old 04-18-2014, 01:39 AM   #6
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Dynam's servos are passable... but that's about it. They put in right at minimum for the job.
I haven't had one fail without a good cause and I have a bunch of them from their ARF/RTF planes.
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Old 04-18-2014, 02:44 AM   #7
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I think that most servos that have failed for me have been elevator servos with rudder coming in second. Heavier throws in my case and more stress due the larger surface areas. Striped three on my fleet of Stryker's, but I use hand-made evevons that are larger and have longer throws.
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Old 04-18-2014, 04:02 AM   #8
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Most models can in fact survive with smaller servos than we usually fit. The common 9gr is surprisingly able.

OK - some will disagree with me and tbh ... it's only an idea I have.

A flying machine when flying needs force exerted on a surface to deflect it and therefore change flying machines attitude / direction etc. The force is momentary as surface resists deflection. But once the model starts to act as consequence of the surface deflection - the pressure against the surface reduces and force needed reduces. It peaks again when we stop the change of flight by dab of opposite command ...

Moving on from that - this then to me indicates that speed ... size of surface and amount of deflection has direct impact on servo required. But maybe not in way that is initially thought.

Let's take a 3D machine with over large control surfaces. It may be that greater servo force is needed at slow 3D speed and when flying fast, but at models aerodynamic ideal cruise speed - may be less. I did say I may be wrong ... but my thinking is based on aerodynamics and airflow ... and my racing of yachts !! When a yachts sail is optimum size and speed - control of the yacht and sail is easier than when pressed harder or when slow .. a strange phenonemum ...

Lets look at stripped gears ... I think many will agree that usually stripped gears is due to external force having been applied ton the surface - such as landing in grass ... hitting that door frame when taking model to car ... absentminded trying to move a surface against a servo by hand ... we've all done it ! Rarely is it due to aerodynamic forces overcoming the servo gears ...

...................

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Old 04-18-2014, 01:55 PM   #9
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Many airplanes really need more servo power than we put into them also...

http://www.radiocontrolinfo.com/RCca...culator.php#WL

Inadequate servo power leads to stalled servos which leads to extreme current demand. That can lead to the RX shutting down from low voltage.
Going from 60 in-oz servos in one of my planes to 90 in oz cut the average current demand in flight by HALF.
We just got away with it due to the 72 mhz RX's instant recovery when voltage recovered.

Sure, many of our smaller planes may have more servo power than needed... but any .60 size model (and some .40 size) using "standard" 42 to 45 in-oz servos is very likely to not have adequate servo power.
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