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All About Retracts - A Tutorial (Hopefully)

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All About Retracts - A Tutorial (Hopefully)

Old 12-08-2009, 10:27 PM
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Flyin Beagle
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Default All About Retracts - A Tutorial (Hopefully)

I am in the process of assembling my Epic LT 1.20, and want to install retracts on this plane. I have never dealt with retracts nor have I looked at an installation on a plane at the field. I have performed several searches on RC Universe trying to find any good basic information on retracts, but I have had very little luck.

Soooo... I thought what better topic for the beginners forum than to ask all of you regulars to pass along your sage advice regarding all things retract to us retract nooobies. The more pictures the better. And if we could get some of those great diagrams from RCKen, and Minnflyer that would be fantastic as well. Hopefully this can become a good enough thread to become a sticky some day.

Some of the questions that I specifically have are:
1. What are the advantages and disadvantages of each of the types of systems (air up/air down, air up/spring down, mechanical, electric actuated etc...)?
2. What are rotating retracts for?
3. How in the great wide world do you connect steering linkage to a trike setup when the steering arm moves with the retract????? (big one for me I cannot figure it out)
4. What are the different ways of connecting gear doors to open? How do you syncronise the timing of them?
5.Are retract servos really necessary?
6.How do you install linkage to keep your wing removable?

I am sure there are many other questions that i do not know to ask, but your help would be greatly appreciated.


Thanks
Old 12-09-2009, 07:20 AM
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MinnFlyer
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Default RE: All About Retracts - A Tutorial (Hopefully)

Wow, you sure ask a lot of questions

1 Advantages to mechanicals is they are more dependable, require less maintenance and are much less expensive, but air retracts are easier if you have a nose gear. The best type of air retracts are subjective, but if you lose pressure, it's nice to have the ones that spring down in case of pressure loss - of course, they're even more expensive.

2 Rotating retracts are for planes where the gear retracts rearward and the wheel rotates 90 degrees to lay flat inside the wing. These are only used for scale planes where the full-size plane had wheels that did that (Like a Hellcat)

3 Steering linkage is done with a pull-pull setup (See pic)

4 Not many people use gear doors due to their complication, but they can also be actuated mechanically or pneumatically. In either case, there is usually an electronic synchronizer to sequence them.

5 Retract servos are necessary for mechanicals. They need the extra torque and the slow movement gives them a scale look as they transition. For pneumatics, a standard servo is used to actuate the air valve.

6 Mechanicals only need to unplug the servo from the Rx, pneumatics only need to unplug the 4 airlines. If you have a mechanical nose wheel, it will need its own servo which will stay in the fuse when the wing comes off.
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Old 12-09-2009, 08:36 AM
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Default RE: All About Retracts - A Tutorial (Hopefully)

Great idea, Flyin Beagle!

MinnFlyer: Don't the pull-pull lines change tension when the gear is up?
Old 12-09-2009, 08:48 AM
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Default RE: All About Retracts - A Tutorial (Hopefully)

Yes.

So what?

You're not going to be steering when the gear is up!
Old 12-09-2009, 11:03 AM
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Flyin Beagle
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Default RE: All About Retracts - A Tutorial (Hopefully)

Thanks for the help, Lets keep this going with descriptions and photos of different types of installations. Please share any tips or lessons learned etc. you have regarding retracts.

Thanks
Old 12-09-2009, 11:10 AM
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MinnFlyer
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Default RE: All About Retracts - A Tutorial (Hopefully)

On of the biggest lessons is: Retracts are a P.I.A. - use them only when really needed

If they weren't so cool, no one would use them. But they DO have a great "Cool Factor" and they DO clean up your plane's lines and increase speed.

The problems you will usually encounter are: Air leaks (with pneumatics) and bent gear wires - which can lead to getting a wheel stuck in the wheel well - not a fun thing when you're trying to land, especially if you're dead-stick!
Old 12-09-2009, 06:32 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

flying beagle, the spring air retracts use a slider arm to steer. when the retract is up the slider arm slides on the tiller arm (or vice versa). sorry, a couple or 3 microbrews have me questioning my verbiage. regardless, it works and it makes sense when you see it. and i'm sure that a lot of other brands use the same approach.
Old 12-09-2009, 09:31 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

This is great timing.

I have the TF b-25 with the robart optional retracts. I've acquired a slow leak only when the gear is up, the tank will drain half a hour, and I think the problem is in the o-ring
in the piston: best way to solve this??? With the gear down, after a couple days the pressure gauge from BVM was practically with the same pressure mark.

Tks for the help, sorry for the hijack
Old 12-10-2009, 08:07 AM
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Default RE: All About Retracts - A Tutorial (Hopefully)


ORIGINAL: MinnFlyer

Yes.

So what?

You're not going to be steering when the gear is up!
Then,

1) Is the gear locked in straight position just before retracting?
2) Must the rudder be straight before retraction or extension begins?
3) Could the wires get tangle while the rudder servo keeps moving during flight?

This is an interesting mechanism.

Thanks, MinnFlyer.
Old 12-10-2009, 08:46 AM
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Default RE: All About Retracts - A Tutorial (Hopefully)

1 no

2 no

3 no
Old 12-10-2009, 12:43 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)


ORIGINAL: lnewqban


ORIGINAL: MinnFlyer

Yes.

So what?

You're not going to be steering when the gear is up!
Then,

1) Is the gear locked in straight position just before retracting? You can do this with mixing from your radio but it isn't required
2) Must the rudder be straight before retraction or extension begins? Well that all depends on the plane. My P-47 require the tailwheel to be pretty straight or it will get hung up. A quick rudder flick will free it though.
3) Could the wires get tangle while the rudder servo keeps moving during flight? Yes they could but again its not very likely. Make sure there are not airlines or servo wires around the wires that they could snag on and you will be fine.

This is an interesting mechanism.

Thanks, MinnFlyer.

I have a P-47 with 2 mains and a tailwheel that retracts. Had an airleak intially but tracked it down and fixed it. You can use a servo to have your gear come up with the airvalve or you can buy an electronic unit that does the same thing without a servo. That costs a tad more on something simple like my plane since the gear doors and connected to the gear so I only need 1 servo to actuate the gear coming up. The valve is adjustable so you can somewhat control the speed of the gear retracting and you can also put restrictors in the air lines.


Now on my F-16 I used a computer controlled actuator because the gear doors need to open first then the gear. Some planes have the gear doors open the gear come out then some or all the doors close again while the gear is out. On scale type planes its about making them look like the real thing as well as drag. Most planes are flying close to stall speed on landing and adding things hanging down increases drag putting you closer to the stall speed. Plus it looks cool. My F-16 nose gear uses a tillar bar for steering. Bascially its a direct linkage to a hollow servo arm. A small piece metalpin sticks throught the tillar arm to control steering. When the gear retract the metal falls out of the tillar arm and the gear rotate to fit in the plane. No chance of binding this way. When the gear extend it is better if the servo is centered so it lines up with the tillar arm and can stick the metal pin back in easier. On this plane I plan to mix steering to the rudder but only have it functional when the gear is retracted. I will be able to fine tune steering with the dial knob on my radio.


Something that wasn't really mentioned is when you use mechanical retracts (where the gear have a wire that you pull/push to make them retract instead of air) the servo needs to be be a Retract servo. They are typically strong but more importantly they have more travel than a standard servo. You need this to fully extend/retract the gear.


Another option that is just starting to take place is failsafes. You can buy the gear that without airpressure extend auto (spring air). But you can also order a computer controlled box that will extend your gear with a specific air pressure. Or you can be like most of us and if you lose pressure you are landing without gear. Retracts require some maintenance that fixed gear don't. Don't think you can just set it and forget it. They need to be tested often and checked for leaks etc.

The last option is the new Lado type gear. This is also just starting to catch on. Basically it is comptured controlled gear or servo powered gear where they are controlled at the gear itself. For instance each gear gets its own servo right at the gear and the servos connect to a power unit that connects to your RX. the powerunit tells all the servos to make each gear extend.

Everything has pros and cons and you have to do research PRIOR to buying your plane to see what company and what type of gear are designed for your plane.
Old 12-10-2009, 01:07 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

I appreciate your responses and explanation, Sweetpea01.

Additional question: is shock absorbing achieved only by a coiled wire gear (similar to fixed front gear), when it is not functional, as shown in post #2 above?
Old 12-10-2009, 01:11 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

Regarding Pull-Pull steering on retractable nose gear.

1. Notice the servo is behind the wheel.
2. Also notice that the cable connections on the steering gear is NOT at the pivot point.
3. In all likelyhood, the nose wheel servo doesn't have as much throw (distance from center of the servo arm, to the point of attachment of control rod - or pull cable) The nose wheel doesn't necessarily need the same amount of travel as a rudder to be effective.

As the gear retracts, the cable mount point moves aft. Thus creating slack in the pull wires.

So.. while the gear is retracted, there is enough slack in the cables, so any movement by the servo arms never consumes the slack.
Old 12-10-2009, 02:55 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

Yes, most retracts use a coil for shocks. I think there are some that use oil only though.
Old 12-10-2009, 03:04 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

     Great thread Beagle!!!  I have just started a thread in the Kit Building forum for a Tiger 60.  Goldberg used to make a Tiger Deluxe kit but have discontinued that.  BUT, they will still send you the Deluxe addendum (free) and the die cut parts to build it (around 25 bucks w/shipping).  The addendum features Robart air retracts.  I have not decided yet on which I prefer,  air or mech.  There is a company called SpringAir that has an air up/spring loaded down.  Or vice versa, I am not really sure of the sequence.  I have read here in RCU that they can be slow to respond.  The company, not the retracts.   I do not know from personal experiance but I will probably find out.  I have also read here that everyone who has them absolutly love them.  They are supposed to be very reliable.  I do know that their website looks good and their prices are very reasonable.  
       The Tiger that I am building will be a taildragger (fixed) with retractable mains only.  I have a couple of weeks before I have to decide on which type.  I have never installed retracts and even though I have done alot of research I still have many questions.  I will be watching this tread daily until I absolutly have to decide on which type to use.  Oh, and I hope I didnt use too many big words what with you being from Auburn and all.


 Roll Tide!!!

Old 12-10-2009, 05:12 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

I have a P-51D with mechanical retracts. The good thing about them is that they are cheap ($30/pr). The bad thing is that a hard landing means replacing them. [] As stated earlier, they are cool, but you pay the price for cool. I've been flying this Mustang since September, and I'm on my third set of retracts (with 2 extra sets in my shop...just in case).
Old 12-10-2009, 06:13 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

Sweet Pea some photos of your installations would be great to help us understand how your systems are set up. I especially am interested to how your gear doors operate with you landing gear.

thanks for all of your responses.

Stevenmax. I am a displaced Wildcat so your not firing up any tigers here. Last Saturday was a great day in college sports. Wildcats beat North Carolina on the hardwood, and then I got to see Bama make Tebo cry. It doesn't get much better.
Old 12-10-2009, 06:26 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

I came across this thread while doing some searching. About Half way down page 2 there are some good instructions on setting up mechanical retracts.

http://www.rcuniverse.com/forum/m_21...2Cmount/tm.htm
Old 12-10-2009, 08:16 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

Dito on the pics Sweatpea. 
Jeez, the plans the Carl Goldberg give to add retracts to the Tiger 60 totally suck.  There is no other way to say it.  I feel like I am on my own with this one.  Its a constant back and forth from the basic plan to the addendum.  Its my first Goldberg plane and alot of folks like em alot.  Right now I have some bowed wood to fix and I am scratin my head over the retract plans.  I may ditch the plans for this bird.

Igotta give it to ya Beagle.  Wildcat roundball cant be beat.
Old 12-15-2009, 09:29 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

I know there has to be more advice out there on retracts than this.

Does anyone have any experience with these???
http://www3.towerhobbies.com/cgi-bin...?&I=LXET60&P=0

They look like a nice simple way of dressing up wire retracts.

Old 12-16-2009, 07:54 AM
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Default RE: All About Retracts - A Tutorial (Hopefully)

HOW-TO STRUT COVERS:

http://www.robart.com/how_to/Strut%20Covers.aspx
Old 12-16-2009, 10:43 AM
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Default RE: All About Retracts - A Tutorial (Hopefully)

Hi lnewqban. Got your email and I belong to the Bush Pilots RC Club. I have been building custom retracts for about 34 years, so If I can answer any questions, I will be happy to try. Lee Robinson [email protected]
Old 12-16-2009, 12:15 PM
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Default RE: All About Retracts - A Tutorial (Hopefully)

I will offer my opinion here - I have used retracts in my warbirds - mainly mustangs - for over 15 years. I have tried mechanicals and air retracts and have found that the air up/spring down are the easiest to install and keep working. But you need to use a quality brand of retracts. If you go for the cheapest ones you can find you will live with problems.

So for your mustang type retracts (non rotating) I use Spring Air brand retracts. I use a Robart fill valve because this fill valve works easiest with the air compressor I use for them. I use oleos with them - an oleo is a spring loaded gear leg. I do not use wire gear legs, but if I did I would use 3/16 wires, not the smaller 5/32 wires, and I would be sure to get wires made from music type wire, which flex but do not take a set/bend on hard landings.
But the oleos handle the shock of a hard landing better than wire gear legs. So I use retracts that are made to accept the oleo directly into the retract without needing to grind short lengths of wire to go between the retract and the oleo - this is much simpler to adjust and stronger.

Most of my planes are 60 size mustangs. For those I use Spring Air (www.retracts.com) 700 series 85 degree retracts with 7/16 Robart oleos, and similar oleos that are sturdy. I recently bought a set of Robart air up/spring down 700 series retracts which look strong but I haven't flown them yet. I NEVER have air leaks with Spring Air retracts - for the 10 plus years I have used them.

I have a couple of giant scale mustangs also, and I have used the same type of retracts (air up/spring down Spring Air 400 series) in one of those giant scale mustangs. For the other I bought Robart 622-5 air up/down retracts - but only because the air up/spring down retracts are not available that fit the Top Flite giant scale mustang directly.

I will look for pictures of my retracts, but if I get the chance I will take a couple of pictures of some that are not installed.

I avoid mechanicals because the ones I tried were hard to set up properly and when you include the cost of the retract servo they were about the same cost as the air up/spring down retracts. In addition to my knowledge the only mechanical retracts available that will carry oleos are the ones Hangar 9 uses on their planes and those don't have the offset oleos that the mustang uses.

Recently there have been lot of retracts advertised made in China and I haven't tried many of them. This is because the Spring Air retracts have been flawless and I don't see much reason to mess with them. I suppose if I found a set that I could look over before buying them I might try them if they looked like a good design, but the part that you can't see from looking is the type of aluminum that they are made from and how good the seal design is. So at this time I will stick to Spring Air and maybe Robart.

For rotating retracts Robinaire and Sierra seem to make good quality retracts. Rotating retracts are used on planes I don't fly so I don't have anything more to say about them.

Ed
Old 12-19-2009, 07:13 AM
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Default RE: All About Retracts - A Tutorial (Hopefully)

ORIGINAL: Flyin Beagle

I am in the process of assembling my Epic LT 1.20, and want to install retracts on this plane. I have never dealt with retracts nor have I looked at an installation on a plane at the field. I have performed several searches on RC Universe trying to find any good basic information on retracts, but I have had very little luck.

Soooo... I thought what better topic for the beginners forum than to ask all of you regulars to pass along your sage advice regarding all things retract to us retract nooobies. The more pictures the better. And if we could get some of those great diagrams from RCKen, and Minnflyer that would be fantastic as well. Hopefully this can become a good enough thread to become a sticky some day.

Some of the questions that I specifically have are:
1. What are the advantages and disadvantages of each of the types of systems (air up/air down, air up/spring down, mechanical, electric actuated etc...)?
2. What are rotating retracts for?
3. How in the great wide world do you connect steering linkage to a trike setup when the steering arm moves with the retract????? (big one for me I cannot figure it out)
4. What are the different ways of connecting gear doors to open? How do you syncronise the timing of them?
5.Are retract servos really necessary?
6.How do you install linkage to keep your wing removable?

I am sure there are many other questions that i do not know to ask, but your help would be greatly appreciated.


Thanks
Answers to your questions in order asked.

(1) Both air up/air down and air up/spring down retracts offer easy setup and control of retraction & extension speeds, but the air up/air down have more areas that can develop leaks versus air up/spring down. They require more plumbing over the air up/spring down retracts. Both are dependable if a good air tight system is maintained with the air up/spring down having the advantage of getting the gear down if a leak develops plus slightly lighter weight. There are fail safe devices for air up/air down retracts that will lower the gear if air pressure falls below a set target....downside is extra weight & expense.

Mechanical retracts versus air are generally harder to setup than air retracts and require a retract servo and perfect linkage setup. You want an extra battery pack that is dedicated to the retract servos so that in the event that a bind occurs where the servos are stalled, you do not drain your receiver battery. The upside is they do not require the items associated with air retracts...air tanks, fill valves, air lines or air control valves.

Electric retracts generally are dependable but have the downside of being heavy. Again, extra batteries which equals weight. You definitely want to keep either mechanical or electric retract power systems isolated from your flight system.

(2) Rotating retracts are generally used in military type aircraft such as Corsairs, Hellcats... etc:. The strut tire/wheel assembly will rotate as the gear retracts/extends.

(3) Nose gear steering can be accomplished several different ways. The one most widely used is the pull/pull system where cables are used on both sides of the steering tiller arm and run to the steering servo horn. You then have a push/pull system where a shaft/pin is attached to the tiller arm and a mechanical link is used between the steering arm & servo horn. The best way to describe the later setup is with a photo...


(4) Hinging and operating doors is a PITA. The ways of opening/closing the doors can be accomplished either through electrical, mechanical or pneumatic methods. The method of operation can be dependent of the door you wish to operate. For instance, a main gear door may be simply rigidly mounted to the strut, while an outer or inner door is operated by a servo, air cylinder or mechanical linkage.
Let's take for an example the main gear doors of a MIG 15. There are three doors on each main gear that have to open and close in sequence. First photo is of all three gear doors closed. The center door is considered the main door and is attached rigid to the retract strut. The inner door at the bottom of the photo is operated by an air cylinder which can be seen in the second photo while the outer door at the top of the photo is operated by a mechanical link shown in the third photo.




(5) Retract servos are necessary regardless if you use air or mechanical. For air, the servo is used to operate the retract valve while mechanical will use the servo to drive a rod attached to the retract pivot.

(6) For air retracts where the mains stay in the wing and the wings are removable, you will need disconnects for the air lines where they exit the fuse/wing joint. Same for mechanical retracts except you will be mating an electrical connection...just like plugging a servo lead into an extension.


As for keeping the nose retract straight when retracting and you are using a high end radio with multiple mixing capabilities, a mix can be implemented for the nose gear steering so that it is inhibited when the gear switch is activated. You will still have function of the rudder but the steering servo will remain stationary until gear down is activated.

Pull /pull steering cables need to have some means to hold the cables out of the way so that when the gear is retracted and the cables go slack, they do not get tangled and keep the nose gear retract from extending. Some do this by means of rubber bands, elastic cords or zip-ties.
Old 12-20-2009, 03:51 AM
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Default RE: All About Retracts - A Tutorial (Hopefully)

ORIGINAL: sweetpea01


ORIGINAL: lnewqban


ORIGINAL: MinnFlyer

Yes.

So what?

You're not going to be steering when the gear is up!
Then,

1) Is the gear locked in straight position just before retracting? You can do this with mixing from your radio but it isn't required
2) Must the rudder be straight before retraction or extension begins? Well that all depends on the plane. My P-47 require the tailwheel to be pretty straight or it will get hung up. A quick rudder flick will free it though.
3) Could the wires get tangle while the rudder servo keeps moving during flight? Yes they could but again its not very likely. Make sure there are not airlines or servo wires around the wires that they could snag on and you will be fine.

This is an interesting mechanism.

Thanks, MinnFlyer.
Now on my F-16 I used a computer controlled actuator because the gear doors need to open first then the gear. Some planes have the gear doors open the gear come out then some or all the doors close again while the gear is out. On scale type planes its about making them look like the real thing as well as drag. Most planes are flying close to stall speed on landing and adding things hanging down increases drag putting you closer to the stall speed. Plus it looks cool. My F-16 nose gear uses a tillar bar for steering. Bascially its a direct linkage to a hollow servo arm. A small piece metalpin sticks throught the tillar arm to control steering. When the gear retract the metal falls out of the tillar arm and the gear rotate to fit in the plane. No chance of binding this way. When the gear extend it is better if the servo is centered so it lines up with the tillar arm and can stick the metal pin back in easier. On this plane I plan to mix steering to the rudder but only have it functional when the gear is retracted. I will be able to fine tune steering with the dial knob on my radio.

Hi there guyes and sorry for interfearing but i think that there is no need to buy expencive stuff since there is an easy way that costs no more than 15$ to make a sequencer for the gear doors to operate as you wish together with the retracts.
I will try to explain:

Lets suppose that you have eg. robarts install in your plane and you need to scale open and close the doors.
In the first case lets say your gear is up and the doors closed.
You need your doors ofcourse to open first in order to let the gear extend.
Those doors can easily been driven by 1 or some times 2 small servos.
You also have a servo that drives the valve that either extends or retracts the gear which take the command from the receiver.
NOW WATCH THIS!!!
install on your eg. nose gear a magnetic proximity switch like the ones we use for the house allarm systems (costs like 1$ a piece!!)
the magnet goes to the gear while the switch is installed on the ceiling.
The 2 wires coming out from the magnetic switch will be conected in series to the signal white (or yellow) wire that goes on the servo that operates the doors.
if you connect with a Y cable the channel for the retract valve and the servo that operates the door you have a sequencer.
The Servo is faster so the door will open and then the gear will extend.
When you want to retract the gear will start to retract but the doors wont close untill the magnet installed on the gear reaches the switch to energise it.
I know it's dificult to imagine so thats why i am going to upload this exact setup i used on my CANADAIR CL-415

http://www.aeromodelismos.gr/index.p...,1925.220.html read from post #231 its in english as well!!

NO NEE FOR EXPENCIVE SEQUENCERS AND OTHER MANY $$$$$$$ SPEND!!!! ITS CHEAP EASY AND SINCE I TESTED IN IN MANY FLIGHTS........RELIABLE!!!!!

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