Using Retracts in Subs?

[terry weber]

I like to from time to time go throught my back issues of the SR magazine and re-read the articals. In Issue 49 on pages 50-55, author Gary Hethcote talked about using "Retracts" to build a balist tank for his robbie U-47. I got to thinking that someing like this could be used to rise and lower a periscope on a Model Sub? Has anyone trid this before? Can anyone give me more info on these "Retracts"?
Also I herad someone talking about using something called a "Push and Pull" in an R/C Airplane for the control surfaces. Can Anyone give me more info about them too?
Thanks,
Terry Weber

[raalst]

The retracts are (if i'm

The retracts are (if i'm correct)
retractable landing gear for larger r/c planes
driven by pneumatics,
sold under the brand Robart.

[interpol]

Not all retracts are pneumatic,

Not all retracts are pneumatic, some are electro mechanical. The "push-pull" they are talking about is probably a linear actuator. A linear actuator takes electric current and transforms it into linear motion. Think of it as a rod attached to a box, and the rod moves in and out depending on what kind of power is connected to it.

There are LOTs of different linear actuators, but unfortunately, the ones in a reasonable price range normally only have a maximum stroke length(distance the rod can move) of about 1 inch. There are some screw-type actuators that have strokes of around 3" that are about $80.

Whether or not you want to use and electric or pneumatic actuator depends on a lot of factors, like size of apparatus, amount of stroke needed, speed of the stroke, and holding power. Pneumatics are capable of more power, obviously, but if the lose pressure you lose your stroke. Some of the electric ones ( the screw types in particular) will hold their position if power is lost, which is in alot of cases a very good thing.


If you want to look at a lot of different actuators and solenoids, McMasterCarr has a good selection of them. I suggest looking there and checking the prices on them before getting any ideas, though, as most are in the $200 and up range.