How do the direct plug-in electronic retracts sense where the endpoints are?
Do these work proportionally like a servo, or do they only go from endpoint to endpoint?

I have a different application that these might be ideal for.

WinchDoc

Those retracts have two little SMD End-of-travel switches located on their motor driver PCB ...

no proportionnal action at all !!!

but close-to-proportionnal action is found on the electric airbrakes for gliders ...

Alain

They also time-out in that they will only run in either direction for so long before stopping (assuming they are jammed) to prevent running down the power system.

Andy

Some even have over current protection against jamming.

A.

Retracts "jamming"? What are you guys talking about?

Jamming is a common problem with retracts which can become bent on a hard landing. If not noticed, it can cause excessive battery drain if there are no protections built in.

A.

You might want to check out firgelli linear drives. They a RC interface option that is proportional.
http://www.firgelli.com/products.php?id=41
Edwin

Originally Posted by AndyOne

Jamming is a common problem with retracts which can become bent on a hard landing. If not noticed, it can cause excessive battery drain if there are no protections built in.

A.

You didn't see the tongue in my cheek, did 'ja?

If I didn't have retracts on some of my planes, I wouldn't have anything to work on when I got to the field, I'd just have to fly.

Oops sorry, I block all emoticons as I hate anything moving on-screen I find it very distracting.

If you need some extra frustration at the field, bring the gallon or two of fuel you had previously cracked open in the shed for a while. Hours of fun, especially for the audience.

There's always opportunities, dead field box and glow driver battery, leaving the starter, container of LiPos or transmitter at home. The list is endless.........................

I'm curious of the intent of the title to this thread. There have already been several started regarding how they function, (and fail) with solutions to a few common problems. There is really nothing you can do to interfere with their sweep speed, direction or safety features, (such as the previously mentioned bind sensing and/or if they need to see the signal sweep over center once or even twice before the first cycle after power up).

Originally Posted by Cougar429

I'm curious of the intent of the title to this thread. There have already been several started regarding how they function, (and fail) with solutions to a few common problems. There is really nothing you can do to interfere with their sweep speed, direction or safety features, (such as the previously mentioned bind sensing and/or if they need to see the signal sweep over center once or even twice before the first cycle after power up).

What I want to do is build a servo-like device that will move a small (1oz or so) weight so I can change the CG in flight. It needs to fit in a 9" long tube about 3/4" diameter. The worm screw actuators look like they would work but I want positioning like an R/C servo. The Firgelli acuators look useable, but a bit pricey.

WinchDoc

Would a sail winch servo and small pulleys work?

Originally Posted by Cougar429

I'm curious of the intent of the title to this thread. There have already been several started regarding how they function, (and fail) with solutions to a few common problems. There is really nothing you can do to interfere with their sweep speed, direction or safety features, (such as the previously mentioned bind sensing and/or if they need to see the signal sweep over center once or even twice before the first cycle after power up).

I think your confusion is due to a misunderstanding of the type of electric retracts being discussed by some of this thread's posters. They aren't talking about the common "mechanical" retract, one that is operated by a servo and a control rod, as opposed to an air cylinder. "Electric retracts", are a fairly new type of device, and are entirely different.

An electric retract has an electric motor and a gearbox mounted on the retract housing itself, and does not require or rely on a servo to cycle the mechanism. They usually plug into a controller board of some kind, and when the controller senses that the RX has sent it the signal to move, it powers the motor directly, which makes the retract move from one end to the other. A lot of them use a worm gear for smooth operation. There are no control rods to bend or adjust, no servo, it's all made together. The controller board can include a current sensing circuit to tell the mechanism when it's reached the end of it's travel, so power to the motor is shut off, and to prevent the battery from being drained in the event that something is bent or binding such that the mechanism can't move fully from end to end. Others, like the smaller ones sold by Eflight for foamies, have small micro-switches somewhere on the unit that shuts the motor off when it has reached the end of it's travel. And because the motors used are brushed motors being powered directly by the controller, their speed is adjustable for more scale-like appearance. Most of these retracts are for use on giant-scale planes and/or jets, and they aren't cheap.

I understood the type of retracts and in fact run several different makes of servoless. It was more along the lines of what other type of setups this type of system could be used for.

That information may have helped point to what would work.

Originally Posted by winchdoc

What I want to do is build a servo-like device that will move a small (1oz or so) weight so I can change the CG in flight. It needs to fit in a 9" long tube about 3/4" diameter. The worm screw actuators look like they would work but I want positioning like an R/C servo. The Firgelli acuators look useable, but a bit pricey.

WinchDoc

I would take a servo encoder board and motor and use it to run a jackscrew. The centering pot would be replaced by a pair of fixed resistors. As I move the servo's control input farther from center it would go faster in that direction, and when I return to neutral it would stop moving.

Andy