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

Yeah, it's definately just what I was looking for! Very thorough explanation of how to control the motor.

Looks like it's not possible to speed up the rpm more than the 360 rpm, but possible to slow it down to the roughly 120 rpm (according to the experiments from the guy with the drawbot)

This guy, with the guide just provided, says the following:
The CLK signal I arbitrarily decided to generate a 300kHz 50% duty cycle square wave (since this frequency was used by one of the reference Motor Control ICs I found earlier). For the CLK signal, I used a 555 timer circuit. When interfacing the 555 output to the CLK signal line, I used a BC547 NPN transistor.

A CLK of 300kHz resulted in a pretty jerky spin motion. Reducing the frequency worsened the performance. Increasing the frequency helped a lot, with a smooth continuous rotation discovered around 1MHz. Further increases in frequency heated the motor driver IC up quite a bit, without any noticeable gain in spin performance.

Using a 1MHz CLK signal, I was able to get this motor to spin at near 360RPM (measured with light strobe).


But it could still be very interesting to record audio at a lower rpm, and playing with the clock frequency as a pitch knob - and have different rpm's during recording. Could be very interesting for audio-collage. I hope I can get this pulled - will try tomorrow night when the wife is off to town. ;)
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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!
Image
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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

guest wrote:what value R and C did you use?
what is the PWM frequency? a higher PWM frequency may not require the filter.


Acutally a filter may not be required at all but then there will be no need for PWM either. The SPD pin on the spindle PCB takes float voltage, the CLK can be sent a ~1MHZ signal to drive the spindle motor.
The thing is, I tried with just taking a pot and scaling a current between 0 and 5V, directly to the SPD pin and there was this (as before mentioned) very steep transition between the highest and lowest speed on the middle position of the pot. I tried converting the PWM signal to "analog out" with the RC filter and now it works smoothly.

(I used the values 4,7K res. and a capacitor of 1uF.)

Oh yeah and the pulse freq is determined by a potentiometer to Analog In on the AVR. Just scaling between 0 and 1023.
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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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