(Dumb?) Linear servo question

[crazygary]

I'm looking into using a linear servo to operate a plunger for a piston tank I'm trying to come up with.

My question is: can a servo be made to stay all the way to one throw limit, and return to the opposite limit when "told" to?? (Kind of like a linear actuator with limit switches.) Don't want it to return to its neutral position.

Or am I whizzin' into a fan, here??

Many thanks for any input!!

crazygary

[He Who Shall Not Be Named]

Just use one of the two-position toggle-switches on the transmitter. 'Landing Gear' is a good candidate.

Problem solved.

M

[crazygary]

Rookie problem has been solved!!

Many thanks, M!!

[Subculture]

What size piston tank are you trying to actuate- bearing in mind that servos are a bit fast, and hence might not give the torque requirement unless the tank is very dinky.

[crazygary]

Not quite sure of the tank dimension yet, but will most likely be made from 1" diameter polycarbonate tubing with a .062" wall thickness. I'm looking to devise something viable to put into a section of my 1:144 Trumpeter Kilos' WTC.

Am currently just "taking a shot-in-the-dark" with a linear servo. Have a couple of "long-throw" servos on order, for R&R purposes, which advertise .9 grams of torque.

I am also looking at model aircraft landing gear retracts ( Thank you, Tom Chalfant) as an operator. The main concern is the length of throw of any of these type units. The longer the available throw, the smaller diameter I can make the piston tank, there by, hopefully, requiring less torque to move the piston. I will be machining the piston from an acetal plastic known as delrin, and utilizing double o-rings for sealing.

Still in "what-if" mode right now, so am open to any suggestions as to possible components. If I can manage to come up with something somewhat "bullet-proof", I will most certainly share my findings.

[He Who Shall Not Be Named]

Time out, CrazyGary!@!@!!!!!....

... have you built and operated an r/c submarine yet?

M

[crazygary]

G'Morning, Brother David!!

In answer to your question, nope!! Am currently a self-imposed "victim" of way too many years of
"engineering-on-the-fly"!! I seem to have this underlying need to have all my proverbial "ducks-in-a-row"
before embarking on a project.


Many things on my "work-in-progress" shelf became "works-in-progress" at
the whims and desires of "She-Who-Must-Be-Obeyed"!! Cold and/or wet weather shall stay me not from
completing the duties as assigned by the dreaded "honey-do" list!!


However, I have managed to begin work on my little Skippy as per your Cabal reports, which contain an immeasureable
wealth of information. Thanks to you for your detailed accounts. Much appreciated!

Am planning her maiden voyage for early spring as our pool is always available for purposes other than swimming, which due to local temperatures at this time of the year, is not on this old pharts "to-do" list!!!

Any "torquey" suggestions from you would be most welcome!!

[He Who Shall Not Be Named]

I ask because you are already sweating small details. STOP DOING THAT!!!

At this point in the game you should be taking the 'road-most-traveled'; you need to keep things simple and follow the path already beaten for you by guys like Skip Asay, Mike Dorey, Norbert Bruggen, me, and the other pioneers, guys who have done the heavy lifting for those in our wake.

Drop the detailed questioning, finish that SKIPJACK, and get it into the water successfully (with our help along the way).

Only after that first successful r/c model submarine under your belt ... and only then ... start sweating linear servos, piston type trim/ballast sub-systems, Interoceters, Klystron Relays, and the Heisenberg Uncertainty Principle.

Crawl, stumble, and walk first .... in that order ... and only after all that, run!

You ain't ready to run yet, pal.

M

[gantu]

You can get from Becker Fm http://www.becker-fm.de/shop/group/Servos/Linearservos

[crazygary]

Yeah, I know!! I'm planning on the Skippy for a first completion, but have this thing about looking too far ahead for what's down the road!! Sounded pretty intriguing.

Tha Skipjack build ia pretty much a "no-brainer" what with all that you have published for us crazy newbies!! Hah!! Pretty sweet little sub, to!! She will, indeed, be the first to carouse the depths of our pool!!

But!!! What about the flux capacitors??? Ya gotta include da flux capacitors?????

[crazygary]

Hi, Gantu!!

Many thanks for the link!

Unfortunately, my Deutsche(sp?) is nowhere near what it used to be!!

OOps! Hold that thought!! Ah, yes! Italian!! That's what I studied in high school!! Hah!!
Silly me!!

They certainly look as though they'll function as needed! Now if I can figure out how to run a translator program,
that would be a big plus!!

Thanks, once again for your help!!

[Subculture]

Okay. Something not right with the figures you gave above- 9 grams of force from the servos? That's bugger all.

[crazygary]

Sorry! That may have been a "typo"!
That servo is rated at .9 grams-that is "point-nine"!!
Thanks for the reality check!

[Subculture]

No that's even worse. May I suggest the torque may be 0.9kg or 900 grams, which sounds more realistic for a small servo.

Unfortunately this will still be too weak for your application.

I expect the motor and servo amplifier board are up to the job, but you need more reduction to slow things down and convert RPM into torque. Most servos will operate over their range in about a fifth of a second or less, you ideally want the tank to work over a three or four seconds.

[crazygary]

Thank you, once again, Subculture!

I went to the manufacturers website and they show it rated at 9.6 oz., or 227 grams of torque. Not sure exactly where I came up with .9???
Realizing that it is, still, much too small for what my needs may be, I am just researching
possibilities. I'm sure I can always use this servo for another purpose!