Animatronics/Engineering Question...... OF DOOM

[Mordoc2k]

Hi people,

I'm currently in the planning stages of a project where I need to be able to rotate a horizontal pipe both vertically and horizontally (as per the pic below), while having both ends of the pole free to attach things to (these would be the "weights" aspect of the pic below)

I have seen some "airsoft/paintball turret" projects on youtube and the like where they use servos to achieve something very similar to what I am aiming for, but in all that I've seen, the vertical motion is achieved by a servo running directly into the side of the pole/etc that will be doing the vertical rotation... (example -> YouTube - Laser Controlled Airsoft Turret )

Have been wracking my brain on this for a day or two, and the pic below outlines the only thing that I could think of that would work, but it strikes me as in-elegant, and I'm not sure what kind of lag/power issues I could run into translating power generated by the the servo/motor through the belt/whatever running down the centreline of the picture.

If anyone here has any input on this, it would be greatly appreciated.

 

[brimst0ne13]

whats it for exactly?

 

[Mordoc2k]

whats it for exactly?

Planning on making a Replica Turret from the video game "Portal". (example of one here -> YouTube - The Broken Turret )

While drawing up plans for the body etc, I thought to myself, If I'm going to spend the time and effort to make it LOOK droolworthy... why not go all the way and make it as functional as possible?

other things to add would be an extending/retracting feature to the arm (pipe) length to replicate teh gunpods opening, some kind of nerf/airsoft solution to actually replicate the shooting etc...

but I figure I should walk before I run, and thus, I wanted to nail the mechanical aspect of rotating the arm/side pods to see if it was viable, as if it wasn't, I'd probably ditch the mechanical side of the electronics, and just make it poseable.

Eventually I'd want to make it twitchy enough to follow a moving person as the one does in the previous video... (hurrah for working out some kind of webcam movement based software tracking solution)

Obviously to move the gunpods like this would require torque-y servos etc if I were going that way, and as far as I can see, my current idea would work...
I thought I'd leverage the talent here first however, to see if they had better/different ideas on how to achieve what I want to do.

 

[Wes R]

I'll dig through my book collection, i don't know much about this kind of thing but i have a book of suppliers for stuff you could probably use.

 

[nexnox]

wow, awesome project. Servos seem the way to go for sure; However I think you might be better off with a flat plate (.25" Aluminum) between the center and the two "doors". then a servo in each "door" for it's rotation. If you plan on programing it via a basic stamp, you could also use stepper motors in the "doors" with a limit switch to set home for equal rotation. But servos should be good too.

Are you planning on making it close? Twisting Cam + Linkage (terminology?)!

 

[brimst0ne13]

yea i'd set synched individual arm servos on a ball joint so you get a full half dome of flexibility. and maybe a telescopic arm for the activation effect.

 

[Mordoc2k]

woah guys... I'm pretty sure my eyes just glazed over... lol
(awesome info, but consider me a n00b when it comes to jargon )

Currently I'm making a scaled down version (sans electronics) to work out the dimensions of the main body etc... while doing that, am working on plans for the full "rig" at work, hence roughing out the mechanics/electronics ideas now.

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@ Brimstone
I was thinking much the same thing in regards to the activation effect, telescoping, pipe within a pipe, some sort of groove/rail setup to stop the thing rotating.

in regards to the servos on a ball joint... uhhhh... ?
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@ nexnox
ok... so first of all... by "door" i assume that you mean the gunpod/weights I mentioned on either side of the axle/pipe/thing... if so, you're suggesting that I put the actual servo/s in the gunpod/door and have that rotate on a static pipe in the middle... interesting, I hadn't thought of that...it would make the entire thing much more modular and free up space in the middle... but wouldn't the weight be prohibitive? I'd think that would basically mean the entire "pod/door/weight" would be hanging on the servo...

everything after the twin servo idea is more or less like you're talking in a different language... lol...
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@ cobalt
sweet! thanks dude... I'm down in Oz though, so not sure if the suppliers would be down here too?

 

[Honus]

Exactly how big is this going to be?

I'd use linear actuators to make the side pods open- some of them are even available with servo connectors and take servo signals to operate. The actuators are then mounted to a geared servo driven pan/tilt mechanism. It's pretty simple really.

Linear actuators do take up a fair bit of space and they're certainly not cheap for larger units. Another way you could make the side pods open could be done by using an ACME threaded rod that rotated and drove some ACME nuts. If you welded a RH threaded rod to a LH threaded rod using a sleeve, by turning the threaded rod assembly in one direction the ACME nuts would be driven outward and reversing it would cause the nuts to move inward. The center sleeve is simply supported by two bearings mounted to a pan/tilt mechanism.

The real trick is making everything fit in the required width. If the finished turret is say 12" wide then you won't be able to have the side pods open very far on a telescoping rod due to the support length needed. I'd need to do some sketches as to what would be possible but I think the only way it would fit is to have outboard bearings (or sleeves) support the extension tubes while the center ACME rod rotates. Then the tilt servos are mounted in the pods and the pan (rotation) servo is mounted in the turret body.

Controlling it is a piece of cake. I whipped up a little servo driver board just the other day that would easily control it using a Wii nunchuck as an input device.

 

[tim]

vertical motion is achieved by a servo running directly into the side of the pole/etc that will be doing the vertical rotation.

I actually think this would work fine. You could use stepper motors, having one drive each half of your pipe. You could probably synchronize them well enough by just hooking both motors to the same driver circuit. If not, you could use rotational encoders for better resolution. These steppers would sit on the blue platform, which in turn could be rotated by another stepper, as you've depicted.

Another option would be to replace the belt drive you've proposed with a gearbox. That way you could have one motor drive the entire pipe, eliminating the synchronization issue. You might even be able to get away using a simple DC motor geared down to the right speed, which would simplify the electronics.