ajvpb

My Feedback: (3)

I'm not sure if I'm missing something, but I am wondering why retract servo's go 180 degrees. The retracts only go 90, so what is with 180. I have no idea about the mechanical linkages, but if someone would spread some light on the subject for me I would appreciate it. Also, is it severly limiting to get a non-proportional one or do you just work with the servo arm on that? Thanks

Alex

JWN

My Feedback: (42)

The idea with a 180 degree servo is that when the gear is locked up, or down, any load on the linkage will be directly in-line with the center of the output shaft of the servo instead of off to one side. What this does is prevent any load, which may be present due to improper linkage setup, from causing the servo wheel to turn and lower or raise the gear when you least want it to. Something else to note about retract servos is that they, for all practical purposes, turn off when after they have cycled the gear. This prevents excessive drain on the battery. They also are not proportional. If you plug one into a channel on your receiver that's controlled by a proportional dial or stick, instead of a toggle switch, you will note that the servo does not move unless the stick is pushed all the way in one direction.

HTH,
John

ajvpb

My Feedback: (3)

Thanks for the response. I'm building a TF 1/7 .60 sized P-51. I plan to use hobbico mechanical retracts and robart robostruts. What would be an appropriate servo for that setup. I have a JR radio. Thanks

Alex

JWN

My Feedback: (42)

My personal favorite retract servo is the Futaba S136. Trim the key off of the connector and it will plug right into your JR receiver. This is a low profile servo with a lot of power. JR makes a good retract servo, but I've never used it. BTW, I fly JR as well so you have nothing to worry about on this servo working with your radio.

John

Thud_Driver

My Feedback: (1)

And, of course, the other reason is to get the total throw required for the retract unit which might not be possible with a regular servo. Some retract servos are proportional and some are just 2 position.

On the Hobbico's, I've used as little as a standard servo with an appropriate arm length. By standard, I mean an Airtronics 94102 50 oz/in with plastic gears, roughly equivalent to a Futaba S-148 or S3003.

Lt. Dan

My Feedback: (21)

I use a Hobbico command CS-63 retract servo in a couple of my planes and they're great. They pull about 90 in oz of torque too!

I tried using a standard, but they seem to groan a lot when a constant load is on them and I worry about battery drain.

I don't understand why the futaba retract servo is so darn expensive myself!

JWN

My Feedback: (42)

Because it says "Futaba" on it

John