Door opener

kerick · Post by **kerick** » Sat Mar 27, 2010 3:03 pm

I'm considering a project with a large hinged hanger door. Is there some sort of servo or other device to open it at a slow speed? About 3 seconds to open 90 degrees would look very much in scale. I thought about an RC aircraft servo if it can be hard wired to a switch.
Thanks for any thoughts on this.

Scott Hasty · Post by **Scott Hasty** » Sat Mar 27, 2010 6:05 pm

Are you looking for a push a button to open and push again to close, or total control of the door by use of a "knob?"

modelnutz · Post by **modelnutz** » Sat Mar 27, 2010 8:39 pm

Look into a device called a "jack screw"....used a lot in the RC world for doing retractable landing gear on RC planes.
Picture a long screw mounted to a small motor...that assembly is rigidly mounted to the model with a support holding the end of the screw stationary....now, picture a nut mounted on the screw...this nut is trapped on 2 sides by some sort of channel which prevents it from rotating....all it can do is move it's way up and down the length of screw as the motor turns. You can easily solder a connecting link or cable to the nut so that you now have an "automatic door opener"....works well in both directions.
get the picture ?

Another idea.... if you have an old disk drive...you can find a very nice rack and pinion setup in the door operating mechanics. Slow linear movement.

macfrank · Post by **macfrank** » Sat Mar 27, 2010 9:35 pm

Most RC motors use PWM (pulse width modulation) so a simple switch will not work. You would need a circuit to generate the correct pulses to open and close.

If you don't want to build a PWM circuit, another option is to use a DC motor with a reduction gearhead. Something like this or even better this one which probably does close to what you need with no extra circuitry, and low voltage (3-6V).

Frank

kerick · Post by **kerick** » Sat Mar 27, 2010 10:06 pm

The jack screw sounds like my garage door opener, only much, much smaller of course. Interesting ideas, thank you all.
"Another idea.... if you have an old disk drive...you can find a very nice rack and pinion setup in the door operating mechanics. Slow linear movement."
I know of a computer shop close by that may be able to help with this.
Something I can open and close with a switch, possibly built into the model, is what I'm looking for. I will try these suggestions to see what fits best. Thanks again.

Kylwell · Post by **Kylwell** » Sun Mar 28, 2010 12:50 pm

You could also try the spring & string method. Spring load the doors open & use a small motor with a spool on it to reel & unreel the fine cable pulling the door closed.

kerick · Post by **kerick** » Tue Mar 30, 2010 9:32 am

I wonder if fishing line would work for the cable? I just took apart some old electronic junk that had two nice springs in it. Hmmmmm....

NNYGamer · Post by **NNYGamer** » Tue Mar 30, 2010 10:59 am

If you want a small reversible geared motor, just find an old video camera! There are small ones that drive the focus and zoom on them, Run at lower power to get the right speed.

kerick · Post by **kerick** » Tue Mar 30, 2010 2:54 pm

Found a screw drive in an old Walkman type CD player that has been laying around the basement for years. It's the part that moves the CD laser reader across the disc. Small enough to fit where I need it and runs on 3 V. Been scraping out a bunch of old electronics laying around the basement. I have all kinds of motors and greeblies of every description.
I just threw out a camera that my wife was holding when she fell into a pond while on vacation. Ruined a camera and a cell phone on that little splash. Almost had to go to a doctor to look at my ribs I was laughing so hard. (until we had to pay for the new phone.

)
Thanks for all the suggestions, this will keep me busy for a while.

MillenniumFalsehood · Post by **MillenniumFalsehood** » Sat Apr 03, 2010 2:35 am

That one won't work. The drives in CDs for the laser are always stepper motors, which require an oscillating circuit to drive them. The reason is that the laser needs absolute precision in it's position, and stepper motors have very fine 'step's that allow this.

kerick · Post by **kerick** » Mon Apr 05, 2010 9:19 am

MillenniumFalsehood wrote:That one won't work. The drives in CDs for the laser are always stepper motors, which require an oscillating circuit to drive them. The reason is that the laser needs absolute precision in it's position, and stepper motors have very fine 'step's that allow this.

I hooked it up staight to D cell batteries and it ran well. Reversing the polarity reversed the direction also. Could you explain further?

MillenniumFalsehood · Post by **MillenniumFalsehood** » Sun Apr 25, 2010 1:09 am

Hm. Perhaps I was wrong then. Wouldn't be the first time.

Anyway, I just thought of something: airplane servos *can* be used, *if* you are willing to virtually destroy them.

If you take off the casing and remove everything that isn't a motor or a gear, then connect the motor terminals to the circuit, it will operate just fine.

Scott Hasty · Post by **Scott Hasty** » Sun Apr 25, 2010 7:37 am

MillenniumFalsehood wrote:Hm. Perhaps I was wrong then. Wouldn't be the first time.

Anyway, I just thought of something: airplane servos *can* be used, *if* you are willing to virtually destroy them. If you take off the casing and remove everything that isn't a motor or a gear, then connect the motor terminals to the circuit, it will operate just fine.

No destruction necessary...

kerick · Post by **kerick** » Sun Apr 25, 2010 11:18 pm

MillenniumFalsehood wrote:
Anyway, I just thought of something: airplane servos *can* be used, *if* you are willing to virtually destroy them. If you take off the casing and remove everything that isn't a motor or a gear, then connect the motor terminals to the circuit, it will operate just fine.

I may look into that. New might be more $ then I want to spend just to take it apart. Must be stuff out there some one doesn't want any more. Thanks for the info.

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Mon Apr 26, 2010 3:35 am

MillenniumFalsehood wrote:Hm. Perhaps I was wrong then. Wouldn't be the first time.

Anyway, I just thought of something: airplane servos *can* be used, *if* you are willing to virtually destroy them. If you take off the casing and remove everything that isn't a motor or a gear, then connect the motor terminals to the circuit, it will operate just fine.

Many people do that to make operating radar drives...
Of course I usually use a servo where the electronics have already
stopped working. ... They are a bit noisy though.

http://video.google.com/videoplay?docid ... 4993245944#

You would need a double pole double throw switch to cross over the
power for Up/down direction, and maybe wire in some limit switches.

.

kerick · Post by **kerick** » Mon Apr 26, 2010 10:00 am

Many people do that to make operating radar drives...

A spinning radar thingie on top! More good stuff!
I'm just getting started on all this electrical stuff, not much use for it on 1/72 jets. Thanks to all!!!!!!

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Tue Apr 27, 2010 3:06 pm

Oh, I f you are keeping the gears, for the slow rotation, don't forget to
trim the gear stop on the final gear... I imagine you know it when you see it...

http://www.rcgroups.com/forums/showpost ... stcount=40

Here is are some more typical mod for continuous rotation and then used as an ESC (Electronic Speed Control)

http://www.mhsd.org/model/howto/servo.htm

http://buildingmodelboats.blogspot.com/ ... sions.html

I proposed, to one person, that he fit a threaded rod into the the servo
pinion and build his own linear actuator. A matching nut, or threaded
insert could be run over the rod and attached to the piece being animated.

There are also these gear head motors...
http://www.gizmoszone.com/shopping/agora.cgi

I have a couple of these... very nice, have to watch the voltage though.

kerick · Post by **kerick** » Tue Apr 27, 2010 9:14 pm

Thanks for the suggestions Umi. More ideas to consider, a nice problem to have!!