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Open Music Labs Forums • View topic - Adjusting the spindle motor speed.

Adjusting the spindle motor speed.

Re: Adjusting the spindle motor speed.

Postby mcanulty » Sun Oct 16, 2011 10:44 pm

Woah, good find!
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Re: Adjusting the spindle motor speed.

Postby Paleorama » Thu Oct 20, 2011 3:31 pm

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Re: Adjusting the spindle motor speed.

Postby Paleorama » Thu Oct 20, 2011 7:34 pm

I'm drawing a complete diagram of how I want to build this bastard, I got to the stage of the signal bias and read your post and illustration - thanks a lot BTW! - I'm not sure I really get the drawing you've made but I think the main issue would be summing the signals without some weird impedance-loss and all this bizzare stuff that I'm not that educated on yet, but I think my conclusions for my build is:

RLC oscillator for the bias! (easy to build and pretty neat for producing a fixed sine wave signal)
OMP-AMP for summing the signals (as it's inverting the phase, afaik)

wadd'ya say?


EDIT:

Okay, seems like it'll be no problem as I'm already planning on driving my input to the FDD heads through a OP-AMP circuit, and as far as I can tell, it just requires a few resistors between the bias signal and the OP-AMP input!
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Re: Adjusting the spindle motor speed.

Postby zool » Mon Apr 09, 2012 3:22 pm

the way i went about adjusting the brushless motor was to probe around with a potentiometer, usually on a capacitor or resistor close to the speed control chip and tied to ground

(not all drives are going to be the same)

it will change the speed of the motor from 0~150rpm i think and you can add a switch to go back to 300rpm if you want

at low rpms the motor is a little jerky and the sound is not smooth either.
i would be interested if you could slow the motor down so that it has a very low rpm yet still runs smooth, i'm not sure if it's even possible with the type of brushless motors in floppy drives
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Re: Adjusting the spindle motor speed.

Postby Paleorama » Fri May 11, 2012 8:56 pm

Oh yeah, I could imagine the motor running yerky with a low frequency in the pulses. Still interested to do it though!
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Re: Adjusting the spindle motor speed.

Postby Paleorama » Wed Oct 03, 2012 4:54 pm

Update:

I now managed to adjust the motor speed by following the guide i provided at page 1 (bottom), I simply cut the SPD wire, and scaled the drive voltage with a pot. It adjusts the speed to what I think is nearly 50% but there's a steep drop all of a sudden from high to low speed. Any suggestions what I might be able to do? I tried several potentiometers, all from 1K to 1M. Same.
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Re: Adjusting the spindle motor speed.

Postby Paleorama » Sun Oct 14, 2012 6:53 pm

I figured out how to fix the sudden speed change to a nice and smooth speed change. I sent out a PWM pulse from my dear arduino and changed it into a analog out with an RC-circuit. Video will be up soon!
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Re: Adjusting the spindle motor speed.

Postby guest » Mon Oct 15, 2012 2:32 pm

what value R and C did you use?
what is the PWM frequency? a higher PWM frequency may not require the filter.
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Re: Adjusting the spindle motor speed.

Postby Paleorama » Tue Oct 16, 2012 8:47 am

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Re: Adjusting the spindle motor speed.

Postby Bendu » Sat Jan 18, 2014 11:13 am

EDIT:
I just realized my oversight … this would only apply to old-school belt drive floppy drives.


http://m.youtube.com/watch?v=vi_oE3ayn0 ... i_oE3ayn0M

Extrapolating from Dr. Breen:

I get the appeal of an electrical solution for its possible more finite control but...
How about an inelegant but simple mechanical solution to control motor speed?
A larger spindle on the motor.

You could also place an tension arm with a roller on it and vary its distance from the spindle to vary the speed.

A smaller spindle would increase the speed like it shows in Dr. Breen's video when the belt snaps down below the upper spindle.

Personally I also like the idea of an exposed spindle to enable scratching.

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