ok here it is i picked up a used plane from a guy he it has a retract servo he said it wasnt working... so i got it all set up with my new futaba 8fg radio. i got all the servos going.
so i figured i would try a flip the the switch for the retract servo and nothing happend then all of a sudden the wheels came put. then i started to get smoke from the wing and so i pulled all the wires and removed the retract servo the bottom of the servo was melted? could this have been a bad setting on my radio or just a bad servo?

Did you use an ACTUAL retract servo?

Retract servos move 180 degrees and stop. Their movement must not be impeded nor must they hit any obstructions until they stop fully.

It could be you did not set up the retracts to permit full movement of the servo, so the motor stalled and burned.

If you did not use a retract servo, then your radio may have commanded the servo to move past the point the retracts permitted it to. An endpoint adjustment may have fixed this.

So remove the burned out servo. It sounds like you have a mechanical setup... so push the pushrods in and out and verify that the retracts work correctly.

Also note how MUCH the pushrods travel. You have to have the mechanics set up so that the servo only attempts to move the pushrods that amount, no less and no more.

Finally is the servo you replaced powerful enough for the job?

Too small of a servo may cause the servo to burn out as it can not produce the force required to move the retracts.

I would make sure that you replace the burned out servo with a retract servo only. Using a regular servo may work, but it is never a good idea. A retract servo does the cycle and then shuts off so it is not drawing on your battery power all the time. As mentioned, the servo needs to be set up so that it only moves the push rods as much as needed both going up and down. It can take some work to get them to work as designed. Good Luck, Dave

yes retract servo...

yes it was a retract servo... and yes I ordered a new retract servo

so do I use end point adjustment ?

no, measure how much travel the push rods need to fully raise and lower the gear, then use a servo arm that has the same amount of travel

Most folks have no end of trouble with mechanical retracts and seldom if ever get them functioning properly the first time around. Its for this reason that is the reason the fellow you got the ship from said the retracts were not working. Its likely they were never setup properly since the ship was new. Its also likely the reason you let the smoke out of the servo by not assureing the proper mechanical linkage before trying to cycle.

The same could happen even to the new servo you ordered if you don,t start over with the linkage. You see as oppose indicated in his post a retract servo is not proportional once triggered it will continue to run its full travel no matter what and when it reachs its full run it will shut off with no drain on the battery if something impedes its journey to full travel, something such as a maladjusted linkage it will keep trying to force it to keep moving and this will tend to dump your flight pack battery or it could cause a motor burnout which seems to have happened to you. A retract servo will not respond to end point adjustment in programing.

The thows of the actuation rods must be adjusted strickly with linkage and this is done normally with either star shaped or round servo output wheels. Betcha never knew what thos round ones were for Huh. The idea is to drill your own holes in the round output arm for the S bends on the actuation rods to acheve just the right total throw or trave of the rod.

John

What retract servo did you order?

again i am new to this so let me ask what probaly is a dumb question.. so say i measure the travel needed by the push rods and it is lets say 1/2 a inch. do i then use a servo arm that is a half inch in lenght from center of servo arm?

this is the new servo i ordered Hobbico CS-63 Servo Low Profile Retract BB U

no, you now need to measure how far the arm travels, your looking for a spot on the arm that moves only a "1/2 inch", this is where a round disk will help as john said,

i'll warn you that i'm horrible at math, if you need 1/2 inch of travel then you should be able to measure 1/4 inch out from the center of the servo arm, this is where you connect to the arm, the round disk usually work best

ok great i have plenty of the round disc i will use one of them.. ok so let me make sure i understand now! ok someonme said that " A retract servo is not proportional once triggered it will continue to run its full travel no matter what and when it reachs its full run it will shut off with no drain on the battery " ok lets say my push rods travel is 1/2 inch to fully retract and extend . But the servos travel is 3/4 of a inch thats when the placement of the hole in the servo disc for the pushrods comes in to play . If i am understanding this correctly ?

Hi rcworld2000,

If you only need 1/2" of travel to lower or raise the retract, you need to set the distance from the center of the servo output shaft to the attachment point of your pushrod to 1/4". Since the retract servo travels 180º, 1/4" 0n 0ne side of the output shaft, measured from the center of the output shaft, will give you 1/2" of travel after completing it's 180º travel. Make sure you use something like an EZ connector on your servo wheel, so you can make small adjustments to your linkage.......

Larry / Instructor

yea your understanding correctly, sounds easy, but as John alluded to, get your story ready, because in a couple of days your going to be setting in the back of a police car trying to explain to the nice officer why a toy airplane made you run down the middle of the street at 2 o'clock in the morning yelling, screaming and pulling your hair out.

Glad I wasn't drinking anything when I read this. it is so true. retracts will give you such fits, no matter what kind they are, and I have tried them all. When they work right on a scale plane the cool factor can make it seem all worth it. Another thing to watch out for is the voltage requirement of the servo. My buddy burned out 2- $40 JR retract servos on 6 v before reading the specs on the box that said 4.8v only

heres the specs towerhobbies has on the new servo i made the specs for a 6v red. im guessing with there beeing specs for 6v then it can be used with my 6v battery. i dont know about the one i burnt up...
Torque @ 4.8V: 92 oz-in (6.69 kg-cm)
Torque @ 6V: 114 oz-in (8.29 kg-cm)
Weight: 1.23oz 35g
Speed: .5 sec @ 60°
Length: 1.73"
Width: .9"
Height: 1.0"

The typical total actuation rod travel for most mechanical retracts is not a half inch it is three quarter inch and you will find the secret is using a round or star servo output wheel then not starting at rest with the S bend inserted in the output wheel lined up with the actuation rod but of to the side somewhere between twenty and forty five degrees.

And yes as I posted last nite I have never run across any retract servo that was proportional and all I have ever worked with will seek to run to the full limits of their travel regardless even when fighting binding linkage and transmitter endpoint adjustments do nothing.

All retract servos will have a full travel of just a hairs breath over 180 degrees. And the reason is you will find that is what it takes to acheve the full travel of the actuation rods into the zone where the gear locks on each end. The problem fellows always run into with standard servos is the typical travel of most of those is around 120 degrees (this varies slighty) and that is not enough to complete the full travel of the actuation rods. And when the fellows run into that and use very long arms them the power of the sevo is compromised an can not fully raised the gear.

Now some thoughts on the up as well as down locks. Both locks are at a tiny bit of travel at each end but the servo and the adjustment must be sufficient to move the actuation rod it full travel and into this small lock zone. How do you know you are fully gear locked on each end? Easy there will be a slight bit of wiggle both in the up and down position and this indicates the adjustments are correct and the gear is locked. This is the simple way to check your gear anytime both on the bench and at the field just extend the gear and wiggle each gear and feel for that play, then retract the gear and grap each wiggling slightly and feeling for that play.

If you feel no play or wiggle both retracted or extended then the servo is pull/pushing the actuation rod either to far and binding that will cause servo to use excessive current or the linkage has not move the rod far enough which means the gear is not locked down or will not retract far enough.

The Wiggle test is important both on the bench and at the field. Now some retracts provide a strategically located screw for minimizing the wiggle when in the down position but don,t get carried away with this as you will not be able to do the test. A slight wiggle of the mains when in the down position is not a problem for the airplane when landing.

Hope I have not confused but it is a difficult installation as I posted the first time.

John

I'm just curious, what size plane have you got? The reason I'm asking is the 1/2" of travel for the retract to fully cycle you mentioned, every 40 - 60 size mechanical retract I've delt with required 23 to 25 mm of travel. I remember reading an article here on RCU that described the proper way to set up mechanical retracts, I wished I had seen it when I set up my first set of retracts in 1993, I would probably have more hair now.

if I may offer a little advise, I've been flying retract equipped airplanes for decades, they are really not that difficult to set up.
for future reference, purely mechanical retracts such as you have are typically more difficult to set up than are pneumatic or 'servoless' retracts.

here's the part that I've seen people miss: with the mechanical retracts physically disconnected from the servo, cycle the gear manually with your hands.
(push / pull on the pushrod) with the airplane / wing upright as it would normally be in flight. this will give you a very good idea of the amount of force the servo will need to produce.
if it's hard to move with your hands, it'll be hard for the servo to move. so first, check and correct anything that may be binding the mechanism.
while you've got the gear and servo disconnected, put a piece of tape on the gear's pushrod and try as best you can to get a ruler next to the pushrod so you can accurately measure exactly how much the pushrod needs to move.
do the same for the retract servo itself, measure how far the servo does actually move when attached to a pushrod.
from here you've at least got a starting point. you could easily burn out a couple servo's (or drain a flight battery) if the mechanics themselves are binding, or otherwise being picky.

do whatever you need to do to make those pushrods as straight and effortless to move as possible first.
make sure the servo moves the appropriate amount next,
refine as required and check again till they're right.

I do not remember the last time I had an issue with retracts not coming down properly
hope that helps.

It's a size 60 and the Half inch was an example I'm at work haven't measured travel yet

Can i get maybe a few pics of of examples of the servo wheel with pushrods attaches

http://www.rcgroups.com/forums/showthread.php?t=1015996

ound this thread.. see if you guys thinks it will be helpful