Force hard drive actuator to stay in one position

Hi!
I making my cheap lasershow with two hard drive actuators, but before mouting all, i need to know if I need modifications to do this:
Well, I want to know if I can force the hard drive to stay in one position with help of audio signals.. Why this question? Because when i do for example a 20Hz signal, it vibrates and not stays in just one position.. I think i need to do another kind of signal, but i dont know what kind exactly


Thanks

Look at the other threads about people using hard drive parts for "galvos." The take-home message: you need some position feedback to be able to control the mechanism to get any kind of position control, and for such hardware you need to come up with it yourself because there aren't any ready-made solutions. Assuming you have soem sort of position feedback you can use a PID circuit to control your apparatus to a specific position.

I am conscient that I using very open loop mechanism, so I dont want to control the position exactly because I dont want to do a precise lasershow (like drawing or so)..
I want to make like random positions like here: YouTube - My homemade X/Y laser scanner

Can I do it with only different kind of signals or i'm forced to use PID Circuit?

Thanks

Well you could try attaching a spring to it, so that the signal is dampened and it don't just jump to the rails. That's probably what's happening in yours. You'll need feedback in some form, even if that means you have to tune the circuit to do it beforehand (using your eyes as the feedback).

No, a spring forces the actuator to stay in just one position, but i want to make it to go for one to other position randomly, like the video...

well you could get yourself an old servo, the radio controlled type and remove the motor and fit the HDD voice coil to that with the pot inside the servo attached to the pivot point on the HDD arm, just of the top of my head....

Eh? Can you explain better?

stepping back to your original question:
to help fix your arm to a position the easiest way is to use an elastic band to center the arm (google it, lots of pics and peoples work in that area) and use D.C. current to control its position, this would also work for an audio source (as in you want to produce a squiggle pattern)
another idea you could EXPERIMENT with to help control the position, is to add some D.C. offset to the audio signal.

also:
looking at the video you linked to, say you have a 20hrtz source (to make a tunnel effect with two galvos, one on a 90' phase) and you want to modulate on a whim the AMPLITUDE of the signal, adding a centering mechanism like an elastic band would probably help a lot and lets face it, ITS CHEAP and VERY EASY to TEST

or maybe you do no understand what hertz is?
take a look at this image

if the horizontal center line represents 0V D.C., at 20hertz it will swing that signal between +/- V 20 times a second, the vertical line showing the amplitude of the signal. so the more amplitude the more energy, or in your case the bigger the arm will swing. ( and yes im struggling to explain this )

as for the servo idea be a resourcefulgeek and research radio controlled servos and there dissection to see how they work, else im going to put you into the troll category.

Noo you don't understand mee
I don't want to do the circle o center the actuator
I'm actualling using ruber bands for centering it, but, as you can see in the video, i want to make random positions! What kind of signal or what i need for doing random positions? Not circles!

try playing with "this (click)", its free software

to stop the motor/galvos and let the beam settle to a fixed postion, you could use a "sample and hold circuit", basically op amps in feed back and very simple to make,
or
just use the software i suggested, if that does not work then you may need to use the "sound card DAC mod" thread as its controller, i dont think you'll need to amplify the signal, but experimentation would be required.

the software basically turns a sound card into a variable D.C. output (Digital to Analogue), not quite sure what the sound card mod does however and i guess it maybe required, although i doubt it myself.. a sound card must be used though as it is used as the software output.

to create files for the lfiplayer3d get Spaghetti software

EDIT:::

as you are center pinning you arm, you should not need to do the sound card mod, just the raw output from the lfiplayer should be enough, you will suffer bounce as the arm settles.

You'll just have to tune your driver to have that level of control. He's probably just feeding it random values within a range after he tuned it.