mecanization with electric motors/gearing?

[jpolacchi]

I was wondering if anyone out there has any experience with stepper motors?I have a completely crazy idea that I'm considering to try,and that's animating wings on a large scale model.I have been attemptintg to learn about stepper motors but really...I find myself more and more confused.

The kit I have(of which needs lots and lots of work/modifications) is the large scale WARP Models Klingon Bird of Prey.I have intentions of re-building the main hulls to accomodate electronics as well as "lighten" the kit up because the original kit pieces are not practical.Aside from a world of work involving that,I'd really like to have the wings "mechanized" but I really don't know how to do it?

My lack of understanding electronics,mechanics and engineering are really hampering my efforts.The wings need a "starting" and "stopping" position,and that is turning into a real headache.I was wondering if anyone out there has the know how and /or any other ideas (aside from the use of stepper motors) that might be employed?I'd love to hear the feedback on this and any help,suggestions and assistance would be greatly appreciated.

[jwrjr]

A stepper (or maybe one for each wing) will certainly do the job. The catch is that you will need some way to let the controller know where the limits are. You can designate one end as "zero" and just count pulses (sent to the motor) to establish the other end. But if somebody manually moves the wing, that gets thrown out of whack. Or, you can put switches at each end. Those are usually magnetic or optical.
But there is another alternative that may work better. Radio control servos. They make some extremely powerful servos. Digital servos are the same on the outside as Analog servos (not on the unside, though). And, some of those are much more powerful. But most importantly servos keep track of their positions. So if somebody nudges a wing, no problem.

[macfrank]

I've used steppers to drive a large telescope, and they're great for that purpose, but way too much trouble for a model.

I agree with jwrjr; get an RC servo; either digital or standard. They're simpler to control and would fit this application far better. Futaba makes both digital and standard servos, and they're cheap and easy to find.

Frank

[jpolacchi]

Many thanks guys for getting back to me on this "off" subject.The only other real hurdle is developing the physical mechanics to achieve the motion.I know virtually nothing of electronics,a sad subject for me to admit to.I hadn't really thought of servo's as an option,and radio control is a vauge subject I have knowledge of,which is really much closer to "zero".I originally chose stepper motors because that is what ILM has traditionally used for mechanizing their miniatures or used for other mechanical effects for camera work.

I breifly looked on the web page and certainly the servo's listed have very small demensions,so space shouldn't be a problem.How to give a servo a "start" and "stop" position I don't know.Ideally,I'd like to have a mechanisim that will move both components(wings) simutaneously and uniformally.Maybe that might not be possible?The original castings to this kit are also on the heavy side(particularly the wings).So, I'm seriously thinking of re-building the wings from scratch,re-casting them might be more trouble than its worth?

I'm planing on re-building/re-casting most of the other major components in carbon fiber and laying in with epoxy and some fiberglass.Basically,it would be a brand new kit as opposed to the rough kit parts that come from beat up,burnt out molds.$300.00 is a bit rich for this kit,but what you are getting is the immense scale which is impressive.Anyway,thank you again for you ideas and suggestions,all is helpful.if anyone has anything more to add,for sure i am interested in hearing all ideas and options.

[jwrjr]

There is at least one servo controller available (or I can design one, I was thinking of doing that anyway) that allows you to program in the servo's sequence of movements (up to 4 minutes, I think).The controller that I am thinking of, which is sold be Blue Point Engineering, allows you to to set it for running the sequence once and then stop, or set it to loop.

[jpolacchi]

So, if you use this "servo" you can program it to start and stop in different positions?How many?It can only store 4 minutes of memory,am I understanding this correctly?The only other obstical aside from being able to grasp the concept of servos is the mechanics to make the wings move. I was thinking of borrowing one of the ideas from the aftermarket positionable wing/hinge kit that was made for the AMT/ERTL Bird of Prey.I just need to figure out how to get the mechanics to work?I attempted to e-mail FUTABA but the message was returned.Would a digital servo be better choice rather than one that uses brushes?I also saw "brushless" servos on their web page as well.

[macfrank]

So, if you use this "servo" you can program it to start and stop in different positions?How many?It can only store 4 minutes of memory,am I understanding this correctly?

No. A servo is just a DC motor with some circuitry. You feed it a square wave with a certain pulse width to keep it at zero, and increase or decrease the pulse width to move it to one limit or the other (or any position in between the limits). It's actually a lot easier to do than it sounds. Here's an article that has an excellent description of servos. Look around the Seattle Robotics Society web page; they have tons of good info.

The only other obstical aside from being able to grasp the concept of servos is the mechanics to make the wings move.

You would probably only need (or want) one servo, then come up with a linkage system that pulls both wings up or down at the same time. Should be easier than making or modifying the intermeshed radiators! Remember, most hobby servos are used to move the control surfaces on RC planes; if they can move an aileron in an airstream at 30+ mph, moving a pair of wings on a stationary model shouldn't present a problem.

Would a digital servo be better choice rather than one that uses brushes?I also saw "brushless" servos on their web page as well.

The main advantage of the digital servos is that they produce a greater "push" at the start or the motion, that's about it.

Driving the servo is easy with a computer, a microcontroller (like a PIC or and AVR) or with discrete hardware (off the top of my head, a 555 with a couple of trimpots should do it). Here's an example

Frank

[jwrjr]

Yes but ... You can control a servo with a 555 and a handfull of other parts ... manually. A PIC or AVR can be programmed to control a servo if the builder is a good programmer. Many modelers are not. A pre-made controller is more expensive, but you don't have to be an engineer to use it (if it is designed properly).
One thing to remember with the 4 minute time limit - if you set it to 'loop', it will perform that 4 minute sequence over and over for as long as you want it.

[Sparky]

you can build a 'servo tester'

Which is a nob and a connection to the servo (yes there's some electronics in the box but its the same for all servos)

Turning the pot causes the servo to move to a position. Just like it was in an airplane moving the elevator.

This means that you could wire in the servo(s) so that when you turned the pot the wings would move up or down. You could change the pot value so that the servos don't move to far at either extreme.

Its not automated but it does move.