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Are mechanical retracts any good?

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Old 12-04-2003, 10:07 AM
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Default Are mechanical retracts any good?

Are mechanical retracts just as reliable as the air types?

I have been told that the mechanical type fail easily and can cause excess flight pack drain if not fitted correctly.

They are required for a 65 ich span Spitfire weighing approx. 7lbs.

The views of current mechanical retracts users would be much appreciated!



Thanks.....
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Old 12-04-2003, 12:58 PM
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Default RE: Are mechanical retracts any good?

Yes, mechanical retracts can be just as reliable as the air retracts, provided that you set them up correctly and don't overtax them. The mechanical type do not necesarily fail easily. If your servo throw is off, then the retracts might fail to lock or might bind, draining your battery. If you use scale struts and heavy wheels, then the retract servo will strain while trying to raise those gear up. I have had good luck with mechanical retracts on .40 size planes and lighter .60 size planes.
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Old 12-04-2003, 01:04 PM
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Default RE: Are mechanical retracts any good?

If you are going to use mechanical retracts go with bigger battery and a higher torque servo. If you have a progamable radio you can adjust the travel on the servo so it wont bind on the lock position.
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Old 12-04-2003, 01:26 PM
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Default RE: Are mechanical retracts any good?

ORIGINAL: cappio777

If you are going to use mechanical retracts go with bigger battery and a higher torque servo. If you have a progamable radio you can adjust the travel on the servo so it wont bind on the lock position.
Mechanical retracts are normally used with retract servos, and they are high torque anyway.

You cannot use the radio to adjust the travel on the retract servo, no matter what type of computer radio you have. Once the servo is activated, it rotates either 160° or 180° from one side to the other. Another word, a retract servo is non-proportional.
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Old 12-04-2003, 02:07 PM
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Default RE: Are mechanical retracts any good?

RichardL & Cappio777....thanks for your advice!

I intend fitting a 7kg torque retract servo with the mechanical retracts. Although I have been building and flying for 20 years this is the first time that I have bothered to fit retracts. I guess better late than never!

They will be fitted to my latest project the Jamara 60 Spitfire ARTF. (using a 4-stroke .91 glow)

Would I be wise to fit a higher capacity/torque flight pack than a standard one in case of excessive in-flight current drain?
I've considered soldering up up a 4 cell pack from some ex-electric flight Sanyo 1700 SCRCs which I could fast recharge at about 2 amps, although there would be an additional weight penalty using sub-c size cells.

Or would I be okay using a standard 800 mAH flight pack on ailerons, rudder, throttle, elevator and retract servo???

Thanks...
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Old 12-04-2003, 02:19 PM
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Default RE: Are mechanical retracts any good?

Yes, it would be wise to fit a higher capacity flight pack. I would go with at least 1100 mAH. Keep in mind that your retract servo only draws current during operation or if it binds. You control the throw of the servo using the correct length servo arm. Just measure the throw of the retracts and choose the servo arm with the proper distance between the two mounting holes for the EZ connector, as in the diagram below:

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Old 12-04-2003, 02:34 PM
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Default RE: Are mechanical retracts any good?

Richard L

Thanks for the info...outstanding!
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Old 12-04-2003, 10:15 PM
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Default RE: Are mechanical retracts any good?

There is a way to use a separate batt. pack for retracts. If I remember right the neg. of both batt are connected. The pos. goes to the servo, and the signal wire goes to the rcvr. Maybe someone could verify.
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Old 12-05-2003, 01:48 PM
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Default RE: Are mechanical retracts any good?

ORIGINAL: Flypaper 2

There is a way to use a separate batt. pack for retracts. If I remember right the neg. of both batt are connected. The pos. goes to the servo, and the signal wire goes to the rcvr. Maybe someone could verify.

Flypaper 2,
I'm sure that there is a way as you say. But, for me, it all sounds a little complicated. Perhaps a high torque 1500 mHA 4.8v pack weighing 100grms, or approx 4 ozs., would be the best way forward for me. For additional safety I could then merely top up the charge after each flight!
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Old 12-05-2003, 03:05 PM
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Default RE: Are mechanical retracts any good?

I am using a 600 mAH battery pack with my mechanical retracts, and I'm good for at least five flights before recharging. Like I said earlier, if your retracts are not binding and you use light wheels, then an 800mAH or 1100mAH battery pack should work fine for at least five or six flights.
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Old 12-05-2003, 05:45 PM
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Default RE: Are mechanical retracts any good?

ORIGINAL: Richard L.

I am using a 600 mAH battery pack with my mechanical retracts, and I'm good for at least five flights before recharging. Like I said earlier, if your retracts are not binding and you use light wheels, then an 800mAH or 1100mAH battery pack should work fine for at least five or six flights.

Thanks again to everyone for all the useful advice!
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Old 12-05-2003, 11:19 PM
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Default RE: Are mechanical retracts any good?

robart mechanicals are the best and with a good retract servo and 1100 pak you will do great
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Old 12-05-2003, 11:56 PM
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Default RE: Are mechanical retracts any good?

ORIGINAL: Richard L.

Mechanical retracts are normally used with retract servos, and they are high torque anyway.

You cannot use the radio to adjust the travel on the retract servo, no matter what type of computer radio you have. Once the servo is activated, it rotates either 160° or 180° from one side to the other. Another word, a retract servo is non-proportional.
You are totally correct, .....my brain fart!
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Old 12-06-2003, 08:31 AM
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Default RE: Are mechanical retracts any good?

A retract servo shuts off completely when it get to the end travel. Just a safety feature, that, if the servo"s slighty loaded, there would be no servo buzz, and battery drain, as you would get with a stock servo. These guys are thinking afterall. I've had them in a 25 size Zero for about 10 yrs. When they're that small,and a gear hangs up, things start bending, but the servo goes to the end.
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Old 12-10-2003, 05:20 AM
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Default RE: Are mechanical retracts any good?

ORIGINAL: Flypaper 2

There is a way to use a separate batt. pack for retracts. If I remember right the neg. of both batt are connected. The pos. goes to the servo, and the signal wire goes to the rcvr. Maybe someone could verify.

I have researched your suggestion of using 2 battery packs as a backup and this is my understanding of this method!

Two flight packs with an equal number of cells are used in parrallel, say 2 x 4.8v 800mAH receiver packs. These are wired up to 2 seperate flight switches. One switch is plugged into the rx. battery slot and the other into a spare rx. slot. The packs must still be charged seperately and switched on independantly of each other for testing before flight ( obviously both packs switched on when flight commences).
If the voltage on one pack drops the power is then drawn form the backup pack. One pack cannot drain into the other as the small voltage difference is insufficient to cause one pack to charge the other. Some reports suggest that diodes are fitted on the 2 flight leads near the rx to eliminate this possibility but from what I've read this has proved to be unnecessary.
However if a cell failed in one pack and a serious voltage drop occurs then it appears feasible that the other pack would charge the failing pack and a fire could result.
Regular maintenance and cycling of packs is required therefore and flight packs should not be left in a model connected and switched on in damp conditions for lengthy periods of time..

Perhaps the 2 pack safety option is more feasible for expensive and large models and smaller models should continue to use a single higher capacity pack as suggested on this thread?
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Old 12-12-2003, 10:21 AM
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Default RE: Are mechanical retracts any good?

A flight pack back-up!
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Old 12-13-2003, 02:53 AM
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Default RE: Are mechanical retracts any good?

I've now decided to fit a set of mechanical retracts to my .60 size Spitfire and see what transpires?
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Old 12-18-2003, 07:55 AM
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Default RE: Are mechanical retracts any good?

I've opted for a pair of low cost mechanical retracts at £20. If a leg is bent during a heavy landing it's easy enough to loosen off the allen screw, remove the damaged leg and replace with equivelant guage piano wire. Whether these will be strong enough for a 7 1/2 lb Spitfire is debateable!).

(The equivalent Robart types are 4 times more expensive at around £80 but of obvious superior quality).
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Old 12-18-2003, 10:36 AM
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Default RE: Are mechanical retracts any good?

You can bend a strut back while it is still in the wing with a Super Strut Tool: [link]http://www.centralhobbies.com/Tools/alignment.html#CG%20machine[/link]

You can also remove the bent strut, put it in a vise, and bend it back without replacing it.
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Old 12-18-2003, 10:53 AM
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Default RE: Are mechanical retracts any good?

ORIGINAL: Richard L.

You can bend a strut back while it is still in the wing with a Super Strut Tool: [link]http://www.centralhobbies.com/Tools/alignment.html#CG%20machine[/link]

You can also remove the bent strut, put it in a vise, and bend it back without replacing it.

Richard L

Thanks for the info. I've never heard of this u/c alignment tool but it appears to be very useful. Must see if I can get one this side of the pond!
Any advice on how to make the coil in a replacent leg?
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Old 12-18-2003, 12:34 PM
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Default RE: Are mechanical retracts any good?

That coil will be a pain in the butt to make. I would just get a new strut with the coil already in place. Robart sells those struts and Central Hobbies sells titatium struts with coils.
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Old 12-18-2003, 12:55 PM
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Default RE: Are mechanical retracts any good?

ORIGINAL: Richard L.

That coil will be a pain in the butt to make. I would just get a new strut with the coil already in place. Robart sells those struts and Central Hobbies sells titatium struts with coils.


....sounds like good advice!
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Old 12-19-2003, 10:16 AM
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Default RE: Are mechanical retracts any good?

Time to put the theory into practice!
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Old 12-24-2003, 12:07 AM
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Default RE: Are mechanical retracts any good?

I've been flying a set of World Models mechanicals in a 10 pound P-82 all season - I'd say the gear is flawless, but my landings are so bad that I work them over pretty well. I am also building a 64" Spit, and just got done putting Dave Brown retracts in and a low profile retract servo. I found that actuation was a problem, since the gear are set up for the actuating rod to run down the landing gear wire on this set. In other words, to get a stright shot to the two gears from one servo, the wheels must tuck up inward, not outward like in the Spit. So I was forced into a bellcrank approach to allow the servo to be in the middle, but the actuation rods to come from outboard. Hopefully, this makes sense to you - did you have a similar problem?
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Old 12-26-2003, 06:07 AM
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Default RE: Are mechanical retracts any good?

ORIGINAL: Lightning Fan


.......I found that actuation was a problem, since the gear are set up for the actuating rod to run down the landing gear wire on this set. In other words, to get a stright shot to the two gears from one servo, the wheels must tuck up inward, not outward like in the Spit. So I was forced into a bellcrank approach to allow the servo to be in the middle, but the actuation rods to come from outboard. Hopefully, this makes sense to you - did you have a similar problem?

Lightning fan,

The wheels on my 65 inch span Spit also tuck up inwards towards the fuz. as the wing chord is too narrow to close outwards. The retract actuating wire rods will just clear the well mouldings when fitted to the low profile retract servo with no binding being evident!

(Also, although not to scale, with the u/c gear opening outwards this will make for a wider track and more stable landings).
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