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Old 10-27-2011, 12:35 PM   #26
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I asked for servo set-up procedures a few posts back but I don't see that anyone has provided one so I will offer mine. This comes after you have tested all the servos on the bench to insure that they work and that you have matched any that will have to work together.


SERVO SET-UP PROCEDURE


If you are using a computer radio, establish a new model in a new memory slot

Bind the receiver to the radio or memory slot

Mount the receiver and servos

Connect the servos to the receiver


FROM THIS POINT ON THE RADIO AND THE RECEIVER HAVE TO BE ON TO PROCEED


Confirm you have each servo on the correct channel

Confirm it is moving in the correct direction – use servo reverse if it is not.

Connect the servo to the control arm/push rod/pull-pull strings/cable, whatever.

With the radio on, confirm that all the trims are centered.

Check to see that the control surface is centered and the servo arm will move freely
.....check for binding
.....check for flex of the control rod
.....check for restrictions that might block the servo from moving smoothly

If the surface/servo are not properly centered don't go to the radio first, center the servo mechanically as much as possible.
..... Lift the servo arm off the servo and reset it so that the surface is centered
......Don't forget to put the screw back in an tighten it before proceeding.
......Adjust the clevis to center if that adjustment is available

Set your control throw using mechanical linkages as much as possible
...... use the control horn hole that is closest to the surface for the largest throw – furthest to reduce throw
.......use the servo arm hole that is furthest from the servo for the largest throw – closest to the servo for reduced throw

.......Only after doing this should you use the radio's subtrim, ATV/EPA features to do any centering or control throw adjustments.

When you have one servo right, then do the next till you have them all working correctly.

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Old 10-27-2011, 05:53 PM   #27
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Originally Posted by CHELLIE View Post
Hi The Hitec HS-81 is a Great High End Servo, they are about $13.00 to $17.00 Dollars Each
Yikes!!! Do you know what that sounds like to a refugee from the 1980s, where any servo that you'd trust a plane to cost $30.00? $13 to $17? High end? YES!
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Old 10-27-2011, 11:57 PM   #28
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Originally Posted by Rockin Robbins View Post
Yikes!!! Do you know what that sounds like to a refugee from the 1980s, where any servo that you'd trust a plane to cost $30.00? $13 to $17? High end? YES!

I am A refugee from the 70s and that just goes to show you How Cheap I really Am Take care and Have fun, Chellie

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Old 10-28-2011, 02:04 AM   #29
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HS-81s are budget servos at $15

JR DS368s are $65 are high end servos of about the same size.

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Old 10-28-2011, 02:38 AM   #30
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great idea to discuss servos. here's a question..epa ,end point for servo settings on comp tx's.

i thought the settings are for keeping the servo throws from going to 100% or to far and jamming. i set my servos to 95 or 90% EPA and use the holes on the horns to maximize the throws on the surfaces mechanically.is this a correct thing to do and do others do this practice. i don't want to hijack the thread to becoming trimming topics....just curious

there other reasons for different endpoint settings...example:on a glider ,set the down side aileron for less travel so the up side causes the turn with less drag on air flow[or visa versa]. these may be mostly trim questions ,but the servos are paramount to getting things right. so gang..please don;t switch subject do to my miss guided question..lol

just one more question...rockin robbin's! how do i get those cool active smilies...lol,all i can do is eat popcorn.

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Old 10-28-2011, 02:50 AM   #31
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I had a servo learning experience a few weeks ago. I had 4 unexplained nose dives into the ground with my Electrify FlyLite and with all this talk about 2.4 brown-outs and such I thought I was having a Tx/Rx problem. One day while readjusting the servo adjustments, I suddenly had the elevator stick in the fully down position and making a buzzing noise.

I could just see in my mind the Flylite heading straight down into the ground (4 times) as if I had pushed the stick all the way forward - problem found!

Since the nose was pretty rugged looking I ordered a new fuse and I installed two new SG90 servos from HeadsUpRc at $5 each. Even though these probably qualify as cheap servos they were significantly more rugged and of apparent better quaility then what came with the plane.

I had heard the buzzing occasionally when I was flying but thought the motor was on the way out. I guess this is some of the things us new folks need to learn.

I now have nearly 4 hours of flight time on the rebuilt FlyLite and not a hint of a problem or unitended landings.

As far as using cheap servos, planes such as the FlyLite are good canidates for their application so long as they work. If I was building a TopFlite T-34 I would definately be looking at a more quality product.
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Old 10-28-2011, 04:30 AM   #32
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Originally Posted by stuart View Post
great idea to discuss servos. here's a question..epa ,end point for servo settings on comp tx's.

i thought the settings are for keeping the servo throws from going to 100% or to far and jamming. i set my servos to 95 or 90% EPA and use the holes on the horns to maximize the throws on the surfaces mechanically.is this a correct thing to do and do others do this practice. i don't want to hijack the thread to becoming trimming topics....just curious

there other reasons for different endpoint settings...example:on a glider ,set the down side aileron for less travel so the up side causes the turn with less drag on air flow[or visa versa]. these may be mostly trim questions ,but the servos are paramount to getting things right. so gang..please don;t switch subject do to my miss guided question..lol

just one more question...rockin robbin's! how do i get those cool active smilies...lol,all i can do is eat popcorn.



Rockin

About servos set-up - see post 26
http://www.wattflyer.com/forums/show...9&postcount=26

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Old 10-28-2011, 05:46 AM   #33
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Here is a beginner question. When shopping for Servos I understand the difference bearings, analog and digital but they come in many different sizes I have seen 3 or 4 and have wondered if there were a difference? I assume some would be for micros but what I mean is bigger better?

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Old 10-28-2011, 07:09 AM   #34
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Originally Posted by Fishbonez View Post
Here is a beginner question. When shopping for Servos I understand the difference bearings, analog and digital but they come in many different sizes I have seen 3 or 4 and have wondered if there were a difference? I assume some would be for micros but what I mean is bigger better?
Normally the Bigger the servo is, the more powerful it is, bigger servos are needed in larger Aircraft to move the Bigger control Surfaces. Hope that helps, Chellie

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Old 10-28-2011, 12:36 PM   #35
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Originally Posted by Fishbonez View Post
Here is a beginner question. When shopping for Servos I understand the difference bearings, analog and digital but they come in many different sizes I have seen 3 or 4 and have wondered if there were a difference? I assume some would be for micros but what I mean is bigger better?

bigger may be stronger but it is also heavier and may not fit.

Typically we want to strike a balance between strength, size, weight and cost.


If I need 40 inch/ounces of torque I can go to

A futaba Standard Servo - $11
http://www3.towerhobbies.com/cgi-bin...&I=LXH288&P=ML

Speed: 0.23 sec/60 @ 4.8V
0.19 sec/60 @ 6V
Torque: 44 oz-in (3.2 kg-cm) @ 4.8V
57 oz-in (4.1 kg-cm) @ 6V
Dimensions: 1.6 x 0.8 x 1.4" (1-9/16 x 13/16 x 1-7/16")
(40 x 20 x 36mm)
Weight: 1.3oz (1-5/16oz) (37g)


Hitec HS-85 MG BB servo $30
http://www3.towerhobbies.com/cgi-bin...?&I=LXN685&P=7

L: 29mm x W: 13mm x H: 30mm (1.14" x 0.51" x 1.18")
Transit: 0.16 sec/60 (4.8V) 0.14 sec/60 (6.0V)
Torque @ 4.8V: 3.0 kg-cm, (41.66 oz-in)
@ 6.0V: 3.5 kg-cm, (48.6 oz-in)
Weight: 21.9g (0.77oz)


Hitec HS-81 - $13
http://www3.towerhobbies.com/cgi-bin...&I=LXN676&P=ML
Transit Speed: 0.11 sec/60 @ 4.8V
0.09 sec/60 @ 6.0V
Output Torque: 36.10 oz-in @ 4.8V (2.6 kg-cm)
41.66 oz-in @ 6.0V (3 kg-cm)
Length: 1.17" (29.8mm)
Width: 0.47" (12mm)
Height: 1.16" (29.6mm)
Weight: 16.6g (0.58oz)
Mounting holes on-center: 1.31"(33.27mm)



JR Thin wing digital servo - $69
Size Category:Specialty
Type:Digital
Application:High-performance scale sailplanes, electrics and pylon models
Torque:60 oz-in (4.3kg-cm) @ 4.8V; 75 oz-in (5.4 kg-cm) @ 6.0V
Speed:.16 sec/60 degrees @ 4.8V; .13 sec/60 degrees @ 6.0V
Length:1.18 inWidth:0.43 inHeight:1.14 in
Weight:0.7 oz (20g)
Bushing Or Bearing:Bearing


Three will provide over 40 ounces of torque. The HS-81 is only 36 ounces but, do I really need 40?

The Futaba is cheap, big and heavy. Fine in a 5 pound plane but not in a 1.5 pound parkflyer.

The HS-81 would be comparable to the Futaba but in a micro servo package for only $3 more.


The Hitec HS-85 is half the weight, half the size and 3 times the price but adds BB and metal gears.

The JR Digital is about the same size as the Hitec but twice the price again, and 50% higher torque and digital control.

I would use the first in a big sport plane or one of my Big RES gliders where I was not too concerned about long term centereing and long term performance. I am not saying it is a bad servo but you get what you pay for. If I had big space and I NEEDED weight anyway I might use it.


The second would go in most of my sport planes and gliders. Might be a good choice for a high speed sport plane where strength and size matter. Good balance of size, weight and cost, for me.

The third would go in my compettion gliders. Size, weight and strength and I need absolute accuracy. 6 of these will give me the accurate control I need with plenty of reserved power to handle the strongest launches of an 11 foot wing span winch launched competition glider.

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Old 10-28-2011, 10:28 PM   #36
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The attached file is an Excel based servo calculator that you might find useful.

Select the tab that says "Simple Set-up".

Select your maximum air speed - Box at top

Set the cord and width of your surfaces

Watch the numbers and the graphs change as you do this.

Play with it and it starts to become clear how it works.

I did not write this. I downloaded it from a site in 2005, but that site seems to be gone now.


Attached Files
File Type: zip servo_calculator.zip (95.0 KB, 124 views)

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Old 10-29-2011, 02:10 AM   #37
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Downloaded Thanks AEAJR

Happy flying may your crashes be limited and if they are not limited let them be cool.
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Old 10-29-2011, 02:24 AM   #38
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Originally Posted by AEAJR View Post
The attached file is an Excel based servo calculator that you might find useful.

Select the tab that says "Simple Set-up".

Select your maximum air speed - Box at top

Set the cord and width of your surfaces

Watch the numbers and the graphs change as you do this.

Play with it and it starts to become clear how it works.

I did not write this. I downloaded it from a site in 2005, but that site seems to be gone now.
Doesn't the wgt. of the aircraft have to be taken into account when selecting the servo? Using this graph I did not see anything to do this or did I miss it? Maybe my assumption on the wgt. does not need to play into this.
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Old 10-29-2011, 03:14 AM   #39
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Originally Posted by gramps2161 View Post
Doesn't the wgt. of the aircraft have to be taken into account when selecting the servo? Using this graph I did not see anything to do this or did I miss it? Maybe my assumption on the wgt. does not need to play into this.

Nope, weight of the aircraft has little or nothing to do with it. It is pressure on the control surfaces. But naturally larger aircraft will have larger control surfaces. It is surface area, speed and angle of deflection that matter.

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Old 10-29-2011, 03:50 AM   #40
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Thanks for the lesson seems I know why I haven't stripped a servo in flight. I probably have servos producing more torque than I need. I thought the wgt. of the plane was was a factor in selecting the proper torque of a servo. Learn something new everyday.

I will have to play with this chart some more very informative just like this thread you started. Have to punch in some info on a couple of planes I have setup just to see how close or far off I am on the servos being used in them.
Thanks
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Old 10-29-2011, 09:30 AM   #41
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Better to have too much torque than too little. The closer you run to the limit of the servo the more likely it will fail.


A comment on servo gear material.

For most applications the standard nylon gears work great. They are quiet and they don't seem to wear very fast. And they are cheap to replace.

Where metal gears are indicated is where you might have sudden shocks that are likely to strip a nylon gear. This shock could be caused by something hitting the surface.

Most gliders have no landing gear. If the glider has flaps, they are likely to be deployed on landing. When you land you want to pull those flaps up just before you touch ground. But what if you don't get them up in time. Then the grass, a rock, a stick or something else can hit the surface and produce a shock to the gears and strip them. For this reason glider pilots often use metal gear servos for flaps.

This same logic might apply to your small electric that is belly landed. If you have full span ailerons that are being used as flapperons, they can hit stuff on the ground when you land, so metal gears might save you some damaged servo gears.

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Old 10-30-2011, 03:25 AM   #42
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Well since the title of the thread is "servo's whatevers on your mind".Can someone explain why digital servos buzz so much.
I could always tell when a analog servo was about to go bad because it would start buzzing.A clear signal to get rid of it.But I just put some digitals in a pitts biplane (sorry I dont have the specs on them right now) & Im just wondering if they'll give any hint of going bad (other than watching your plane smack into the ground)
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Old 10-30-2011, 03:34 AM   #43
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Originally Posted by Rolling Thunder View Post
Well since the title of the thread is "servo's whatevers on your mind".Can someone explain why digital servos buzz so much.
I could always tell when a analog servo was about to go bad because it would start buzzing.A clear signal to get rid of it.But I just put some digitals in a pitts biplane (sorry I dont have the specs on them right now) & Im just wondering if they'll give any hint of going bad (other than watching your plane smack into the ground)
I can't answer your question as to why, but I will confirm that some digitals are very prone to buzzing.

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Old 11-01-2011, 03:05 AM   #44
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I have a question on analog vs digital servos. I flew twice today and both times my Flylite was turning slightly to the right. Each time I gave it two clicks of left trim and it flew straight.

It seems to me the low cost SG90 analog servos I am using are pretending to be digital with the repeat accuracy of the trim required.

The question is what performance does the digital servo provide over the analog? Or maybe I should ask how does an analog device provide seemingly repeatable small increments of movement such as trim.

Thanks AEAJR for starting this thread, very usefull information.
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Old 11-03-2011, 05:44 PM   #45
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Rightfly,

I am not sure I understand your question.

All servos should center properly and come to the same center every time. But in fact some seem to be more consistant than others.

In addition to the servo itself, other factors related to installation can actually be a greater contributor to centering and trim problems.

* Play at the servo arms and control horns
* Flex in control rods
* Friction and/or drag on the control rods
* Weak battery
* Undersized wire
* poor mounting of the servos
* Lack of support or attachment of guides for control rods/cables

Put a top grade servo into a poor installation and you are going to have centering and trim problems.

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Old 11-03-2011, 09:01 PM   #46
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Thank you AEAJR for your reply. I am amazed at how the analog servo's, even the cheap ones, can be adjusted with a computer transmitter such as my Futaba 7c with respect to the trim adjustments as well as the end point set-up adjustments.

My servo experience goes back maybe 25 years or more with industrial type applications that used all kinds of feedback devices to tell a servo valve the position of the device it was controlling. But our little cheap analog servos can be set by clicking a trim button and they respond with a fairly predictable movement without any feedback to the Tx.

So I guess the question is how does an analog device accomplish this?

By the way I appologize for asking about the advantages of a digital servo as when I re-read your post #1, after I had posted, I realized you had clearly covered that. Sorry about that.

Roger
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Old 11-03-2011, 09:06 PM   #47
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No problem.

I can't tell you how the servos work, but I think it has something to do with so many pulses or pulse duration from a reference point which is center. Beyond that I am clueless. I plug them in and they work. Magic!

Ed

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Old 11-04-2011, 01:40 AM   #48
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Originally Posted by AEAJR View Post
No problem.

I can't tell you how the servos work, but I think it has something to do with so many pulses or pulse duration from a reference point which is center. Beyond that I am clueless. I plug them in and they work. Magic!

Ed
AEAJR, There is no way the word clueless could be attached to you, I have been reading your stickys.

Plug and play'm cause they are magic is the best answer for my curiousity.

Thanks,

Roger
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Old 11-04-2011, 03:37 AM   #49
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AEAJR this ought to be a sticky because I have learned a ton on something I never knew to give a lot of thought to.
Thanks
Fishbonez

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Old 11-04-2011, 06:34 AM   #50
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MOUNTING SERVOS

There are a variety of ways to mount servos depending on their function and the stress being put upon them.

Many planes have servo trays that are glued into the plane. You slip the servo into a cutout and screw it down.

There are screw collars that are molded into most servos. Often there is a rubber bushing that goes onto that collar and a brass sleve that goes through the bushing. This creates a vibration dampening system that isolates the servo from vibration of the aircraft.

This vibration dampening mount is primarily focused on glow and gas models were the engines vibrate due to the action of the pistons. This is especially evident on single cylinder motors which are the most common used on glow and gas planes.

Electrics, on the other hand, don't have this motor vibration. If the prop is balanced the motor does not vibrate much. As a result many electric pilots may skip the rubber bushing system and just screw teh servo to the wood or plastic servo frame in the plane. And in foam planes, the whole fuselage is a vibration damper so the bushing are really unnecessary. But they do make for a nice tight mounting system.

In small electrics, especially when using micro and sub micro servos, some people use double sided foam tape or squares to mount servos. The common 3M white foam double sided tape shown at this link has not worked as well for me. I find the servos come loose.
http://www.staples.com/Scotch-1-Moun...product_130476

There is a heavy duty version that works better
http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053

I found a really strong heavy duty gray foam tape that has a red removeable covering. I think this is used for automotive applications. This stuff is wicked strong. If you give it a solid surface and a clean micro or sub micro servo it holds very well. I belive this is what I am using. I cant remember where I bought it but I think it was home depot.
http://3mcollision.com/products/tapes/attachment-tapes

There are also a variety of servo frames that are sold. A search on TowerHobbies finds a wide variety of servo frames.
http://www3.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=servo+frame

You can glue servos into your plane. Goop works well but be carful as it may damage some foams. It holds well but you can cut through it with a hobby knife if you need to remove the servo. I have seen people embed a piece of thread into the goop and use that to cut it by pulling both ends through the Goop. That works well for blind areas.
http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053

Epoxy also works well for this. However if you ever have to remove or replace the servo, getting it out can be a pain and may damage the plane. For this reason I often wrap the servo in heat shrink tubing, the size used to cover battery packs. Shrink the tubing to the servo then glue it in with epoxy. If you need to remove the servo, just cut the heat shrink and pop the servo out. Once the servo is out the heat shrink can usually be peeled off the epoxy leaving a smooth clean surface to glue the replacement servo.

In foam planes there may be servo pockets molded right into the plane. If your servos fit tightly you may not need any other mounting but I often put the screws in as extra insurane. If they do not fit tightly you can shim them with pieces of balsa or some of that double sided foam tape mentioned earlier.

Potting a servo is where you use epoxy to make a pocket that holds the servo, but you don't actually glue the servo in. You can think of this as a custom formed servo frame. This works especially well in foam where the foam might loosen up over time. By potting the servo you create a much more secure and durable mounting.

When potting a servo you cover the servo in wax paper or wax it, put in a glob of epoxy and embed the servo. When the epoxy sets, you can remove the servo and you have a perfectly formed pocket to hold the servo securely. just place the servo and tape it in place. This is also a good way to fill around a servo in a foam plane where the foam pocket is too big or has become to soft. Done right, you can seat the servo, and just tape it into place.

Potting a servo may take a large glob of epoxy which can add up in weight for several servos. To reduce weight you can use microballoons as a light weight filler. You mix it with expoxy and it makes up a very light weight paste that is great for potting servos.
http://www3.towerhobbies.com/cgi-bin...?&I=LXHZ15&P=7

For wing mounted servos, it may be impossible to screw the servo in place. Here a servo frame can be helpful. Potting the servo may work too. Another approach is to install a piece of wood as a flat plate and filler. Space it so that you can use double sided tape to hold the servo laying down in the wing. Get the servo even with the surface of the wing. Then, tape across the opening with clear packing tape so that the servo is secured by the foam tape on one side and the clear packing tape on the other. This works very weill and the tape acts as a servo cover to close the opening.


No matter how you mount your servos, be sure they are secure.

If that servo moves it will change your trim. If it breaks loose you may lose control of your airplane. If you are having problems with your trim drifting, check your servo to see that it has not broken loose or that the mount is not loose.

The servo might be secure to a servo tray but the servo tray may have broken lose. Check that too. I have had this happen in my gliders where a wood servo tray has been glued into a fiberglass fuselage. The servos look solid but the servo tray has broken loose. Wiggle that servo with your hand and see if the tray moves.

Mount them right and you will have trims that hold and consistent response from your servos. Do a sloppy job and you may be picking up pieces as you blame the servo maker, the airplane maker or someone. But the person at fault is the one who installed the servos or failed to check them before the flight.

Clear skies and safe flying!

Long Island Silent Flyers
www.lisf.org
Eastern Soaring League
www.flyesl.org
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