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Old Jul 23, 2012, 06:09 PM
I don't like your altitude
Stupot46's Avatar
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Quote:
Originally Posted by Quick61 View Post
Hold your fire! (if only for a moment)

It would seem that after all the thought and planing of making a rack and pinion system, someone like Richard comes along and thinks of something so simple and easy it takes all the work, er, um, FUN out of it. Great thinking Richard!(IMO) And here it comes again... but, I can see just one little thing with the setup as drawn. That being as the wings increase sweep, the two fixed points on the cable will get farther apart, stretching the cable. Now put that cable on the outside of a radius and the length wont change. pic attached
My brain hurts .Going to bed.More later
Stuart
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Old Jul 24, 2012, 12:45 PM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,280 Posts
The reason my brain was hurting.Took the pulleys and cable,stuck em in a pot with the timing belt,stirred and out came this.The two small pulleys need only be half circles as they do not rotate;I've stayed with the belts as they are virtually stretch free.The shaft is also fixed,so a minimum of moving parts.
See what you guys think,but this could be the one.
Regards Stuart
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Old Jul 24, 2012, 01:05 PM
I don't like your altitude
Stupot46's Avatar
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After Herks comments to Mark about his pod I took another look at mine.It was a bit on the flimsy side,so I've beefed it up a bit.3/16 balsa sides,most of which will get sanded away to a rounded profile.My idea then is to find the two extremes of the weight needed to balance and cut a slot through the pod between these points.A box in the slot to take the weight,thin ply plates outside to keep it in place.A series of holes to mark each position and peg the box in place.
Stuart
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Old Jul 24, 2012, 01:30 PM
Just call me crash for short
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United States, OH, The Plains
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And the engineer lives yet another day! Nice, the way you boiled the different ideas like that. Nothing wrong with minimal moving parts in my book. Funky landing gear and nose on that pod.

Mark

Oh, there just clamps - Never mind.
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Old Jul 24, 2012, 02:34 PM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,280 Posts
Quote:
Originally Posted by Quick61 View Post
And the engineer lives yet another day! Nice, the way you boiled the different ideas like that. Nothing wrong with minimal moving parts in my book. Funky landing gear and nose on that pod.

Mark

Oh, there just clamps - Never mind.
You should see the video
Stuart
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Old Jul 24, 2012, 02:56 PM
I don't like your altitude
Stupot46's Avatar
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I may be over engineering again.Could I use some sort of Kevlar cord or similar?A heavier version of the cord Kent used in his pulley system.
Is there a way I can work out a figure for the load on the system in an extreme flight scenario,ie the required tensile strength of the cord,and size of motor and rod?
Stuart
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Old Jul 24, 2012, 03:33 PM
I don't like your altitude
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Maybe this would do.
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Old Jul 24, 2012, 03:51 PM
less is more
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I don't think that you could break that kevlar cord if you tried. That is the thickest available from ACP Composites. It is braided, so no fraying. You can reduce the stress on the cord by using larger pulleys. A system for tightening the cord is needed.

Been watching the development of this mechanism and my vote is for the worm screw drive system.
  • Zero load on the servo
  • rigid and robust
  • fine adjustment possible
  • It DOES require a special servo

You might find some good plastic worm screw parts in an old copy machine.

Kent
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Old Jul 24, 2012, 04:44 PM
I don't like your altitude
Stupot46's Avatar
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Thanks Kent,I've just had a look at the ACP site.Good price,and crimps included.
Shouldn't be too much stress involved,the only movement is on/off the quadrants.Initial tension could be set using the two inner"pulleys"
The worm screw is the thing I'm not sure about.A static rod/rotating nut will allow the rod to be used to adjust the cord.I think a fine thread driven at higher speed would be best;it would need to be robust enough to take the full strain of the forces on the wings without binding..
Regards Stuart.
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Old Jul 24, 2012, 04:55 PM
Just call me crash for short
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Joined Jan 2011
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What you would need is a winch servo to drive the worm gear / drive nut. Gear reduction is built into the servo. Finding one that is the right size / weight, I'll leave up to you. Best of luck!

Mark
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Old Jul 27, 2012, 07:34 AM
I don't like your altitude
Stupot46's Avatar
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I've been searching for suitable worm gear/motors etc.then realised I have no idea what sort of speed I should be aiming for.As B Matthews pointed out,a direct drive through the motor as in the drawing will be way too fast,but what would be a practical range for flight?Any thoughts........
Regards Stuart
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Old Jul 27, 2012, 07:55 AM
Just call me crash for short
Quick61's Avatar
United States, OH, The Plains
Joined Jan 2011
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Have a look at this video. While it's for a winch on a RC truck, the first part shows how to mod a servo to a variable speed, bidirectional drive motor. Think it would give you the speed and torque your looking for.

Mark

How to make a RC winch for a home made 1/8 scale 4WD truck (7 min 41 sec)
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Old Jul 27, 2012, 08:56 AM
I don't like your altitude
Stupot46's Avatar
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Thanks Mark,my local(ish)store stocks the Hitec HS645mg,I'm going to pick one up and see what I can do with it
Regards Stuart
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Old Jul 27, 2012, 10:54 AM
less is more
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Quote:
Originally Posted by Stupot46 View Post
I think a fine thread driven at higher speed would be best;it would need to be robust enough to take the full strain of the forces on the wings without binding..
Regards Stuart.
You COULD build a worn drive type of mechanism from standard hardware store parts. You may need to braze the tab on to the coupler nut though. For a small plane, big 4-40 linkage would probably be adequate.

Maybe the sketch will get the basic idea across (the pond).

Kent
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Old Jul 27, 2012, 12:45 PM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
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Thanks Kent,that looks promising.All being well I'll pick up enough bits and pieces tomorrow to mock up the pivots and try out the various options.
Regards Stuart
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