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Stepper Acceleration in RWTS
- Subject: Stepper Acceleration in RWTS
- From: Sheldon Simms <wsspammy@gmail.com>
- Date: Tue, 28 Dec 2010 08:55:22 -0800 (PST)
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Hi everyone. I was looking at RWTS and I'm wondering where the values in the phase-on/phase-off tables used to accelerate the stepper motor come from. Clearly, the idea is to start stepping slowly and then accelerate. But why were these particular values chosen and why is the minimum value $1C (2.8 ms)?
I figured it must be related to some characteristics of the stepper motor used, but upon opening various floppy drives I have found that quite different stepper motors were used in different drives. The stepper motor in my oldest Disk II is a North American Philips A82709-M2, for which I have not been able to find any official documentation, but it's pretty clear from various sources, that it is a 7.5 degree per step, 12 V, 4-phase motor similar to this one: http://www.hurst-motors.com/sasdirectdrive.html
Still, nothing about that motor enlightens me as to why the phase-on/phase-off table values were chosen as they were. Was it just trial and error for a particular motor? If so, why was it ok for other motors?
Another question that comes to mind is why is the motor driven by alternating between one phase energized and two phases energized? Why not have two phases energized all the time until you've arrived at your track?