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Topic: Sound installation : Servo & Pendulum Movement (Weight, Dephasing > Break) (Read 132 times) previous topic - next topic

julienn

Hi all,
This is my first message here. I am an arduino newbie.
i am working on a sound installation.
Here is a picture





and a teaser video to see it in action :
https://vimeo.com/112905512

There is a reel to reel loop tape and 2 magnets, placed at the end of rods that are "penduling" just above the tape and erase it.

The top of the rod is attached to a servomotor (a cheap one) and i've programmed a +2°/-2° script via a arduino nano

For now, the magnet is attached to the end of a rod.
My goal is to acheive a continuous pendulum movement.





Problem is magnet's weight and frequencies that are dephasing between top and bottom level of the rod.
Both forces on the servo and at the end breaks the servo.
Other problem is mouvement is almost too large and i would need something like +1°/-1° but then
i am at the limit of the servo techno ( min 1° for what i now) and it loose the fluant effect.

I plan to invest in a better servo, brushless but i am not sure is it enough.

My questions are :
1- Does it exist a kind of "declutched" servo ? I don't need a lot of energy. Just enough to compense the one lost in the friction
2- Is it possible to make degrees variations less than one degree with a brushless servo ?
3- do you see a way a achieve this constant pendulum movement ?

I thought 2 things:
- a "brushless sensored servo" (if it exist) and just give a little hit when servo got a specific position.
But maybe it is science fiction...
-let  the magnet move freely but then i don't know how to "give it a hit" after a while
like on this video but on only 1 axe
https://www.youtube.com/watch?v=yJNmPmV4fpU


If one of you got ideas, it would be greatly apprecied !
Thanks ;)


Julienn

blimpyway

If you only need to give slight pushes to the pendulum you better decouple the servo arm from the pendulum arm, have the servo pull with a spring or a rubber ring between them

MarkT

Definitely add a spring, mount the servo low enough down the pendulum such that the arm movement is about
the same size as the horizontal movement of the pendulum arm at that point. 

You should be applying a force to the pendulum, not a position, and a servo is a position control device,
so the spring translates that to a force.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

julienn

Thanks guys for your replies !
spring definitely seems to be the good idea. i didn't thought about it
Much more easy that all i thought so far ;)

Is this something like that ?



cause i am not sure of understanding that
Quote
mount the servo low enough down the pendulum such that the arm movement is about
the same size as the horizontal movement of the pendulum arm at that point. 
does "arm movement" refers to pendululm's degrees amplitude ?

mich2016

If the end of the servo arm moves 2 cm,   then you want to attach it to the pendulum rod where the rod also moves 2 cm.

If the rod is fixed at the top,   and you want it to swing say 10 cm at the bottom,    then it will be swinging 2 cm about 20% of the way down the rod,  from the top.

julienn


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