Pulley / Fraying - "Mechanical Flower" Project

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SUMMARY

The discussion centers on the "Mechanical Flower Project," where the user Chris is mechanizing flower petals to curl open and close using a Parallax servo horn and braided fishing line. The main challenge is ensuring the string does not fray or break over an extended period of 6-8 months. Key materials include 20lbs Spiderwire braided fishing line and two types of tubes to reduce friction. Expert advice suggests simplifying the setup by eliminating unnecessary wrapping and using a turnbuckle for tension adjustment to enhance durability and functionality.

PREREQUISITES
  • Understanding of servo motors and their operation
  • Knowledge of materials such as braided fishing line and tubing types
  • Familiarity with mechanical tension systems, including turnbuckles
  • Basic principles of friction and wear in mechanical systems
NEXT STEPS
  • Research the use of turnbuckles for tension adjustment in mechanical systems
  • Explore the properties and applications of shape-memory alloys and polymers
  • Learn about effective methods for reducing friction in mechanical setups
  • Investigate alternative materials for string and tubing to enhance durability
USEFUL FOR

This discussion is beneficial for hobbyists, engineers, and designers working on mechanical projects involving motion and durability, particularly those interested in robotics and art installations.

  • #31
Howdy!
The Flexinol wire manufacturers don't have their own design...I've been looking online on how others have managed using the muscle wire and the hooking it up to the PC board, but still no luck ;( The snapping into shape is because there is too much current. Stilll tinkering ...

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  • #32
Fuichris said:
The snapping into shape is because there is too much current.
Are you sure about that? I haven't looked into Flexinol; I've been leaving that up to you. BioMetal, as I mentioned, has a hysteresis loop in its thermal cycle. At low temperatures, you can pull it to about 105% (or whatever disappointingly small percentage) of its normal length and it will stay there. When you heat it, it doesn't react at all until you hit its transition temperature (let's say 150° C as an example, but I really have no idea) at which point it spontaneously snaps back to its "resting" length within a millisecond or two. You can't deform it again until it drops to maybe 120° (again, just an example). I thought that since you had settled on Flexinol, it must be more controllable, but maybe it isn't. Does the literature state that it is, or did you just buy some to experiment with? If the latter, maybe what I was thinking of as the way to go with BioMetal is worth trying. Instead of what you're currently using as a return spring, (I would be using a leaf-type (no, not because you're making a flower, smartass...)) try one that perhaps has a more aggressive progression factor. I don't know whether or not that can be accomplished with a single leaf, or if you would have to go with multiple leaves like in a car suspension system. The bad aspect of that is that unless you have some very tiny shock absorbers in your parts bin, it will uncurl just as rapidly at it would curl without the spring. That would be okay if the flower that you want to model is a Venus flytrap, but your pictures sure don't indicate that. :p The whole issue is why I was hoping that the metallurgy had improved significantly since I dealt with it, so that a gradual transformation could be achieved. It's obvious from that one video that it's possible with some memory substance, but I don't know what it is.
Aw, nuts! Now I'm starting to think that my design won't work either. :(
I'll keep thinking on it.

edit: Actually, I'm currently too tired to keep thinking on it. Instead, I'll resume tomorrow (well, later today).
 
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  • #33
Hey now! I've been over-thinking this thing all along. Would a simple bimetallic strip such as from a thermostat work? Just heat the whole thing and let the differential reactions do the work...