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Forums > CSDb Entries > Release id #160665 : Stepper Test 1.0
2017-11-30 15:02
ChristopherJam

Registered: Aug 2004
Posts: 707
Release id #160665 : Stepper Test 1.0

Copying the production notes below, but I'd really like to see some results from other people's drives for this one.
 
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2017-12-01 09:11
Krill

Registered: Apr 2002
Posts: 919
Quoting soci
More seriously the sectors could be realigned with a small program on the demo disk once it was written out.
I'm thinking of a custom format routine that would align the tracks and have the same size for all block gaps (so no big tailgap) and then simply disk-copying or transferring stuff onto that disk.

Quoting soci
Unfortunately this will likely trip on a "gapped" disk fault on a custom formatted disk unless the headers are kept in the same place which is difficult.
Not sure what you mean, but if you were reformatting disks on the fly, you should read a track, format it, then write back its contents.

Quoting soci
Is it really worth it over out of order loading (with prefetch)?
This isn't mutually exclusive. You can have out-of-order loading on top of a perfectly-formatted disk, or plain sequential loading on a perfectly-formatted disk with meticulously hand-crafted file layout. :) But the point is also getting rid of the big tailgap (which is bad for KERNAL format and worse for fast formatters), such that you get the same, maximum time between reading arbitrary blocks, thus missing fewer blocks after transferring a previous block.
2017-12-01 09:12
Krill

Registered: Apr 2002
Posts: 919
But let's not hijack this thread and move the UniFormAt (R)(TM) discussion somewhere else. :)
2017-12-01 11:20
Tom-Cat

Registered: Apr 2003
Posts: 14
Here is my 1541-II that I currently have attached to my c64c:



Looks ok ? :)
2017-12-01 11:22
Oswald

Registered: Apr 2002
Posts: 4137
you win the graph niceness compo so far :)
2017-12-01 11:41
icon

Registered: Apr 2002
Posts: 72
Here is two of my drives (more to come):

1541 (grey and cold)


1570 (white and cold)
2017-12-01 15:56
Groepaz

Registered: Dec 2001
Posts: 8317
Quote:
that drive is *fast*! Did you install a turbo?? Code would have to have a bit of a redesign to zoom any more tightly on that top edge.

random old drive, i only ever cleaned the head and rails and made sure its 300rpm :) (it would be nice of your program had a few maintenance features... like rpm check, motor on/off switch, step to track 1/18/35)
2017-12-01 17:41
Impetigo

Registered: Jun 2004
Posts: 11
My Oceanic:
Stock JiffyDos kernel, high current power supply.
Doesn't work properly with the original power supply.

2017-12-01 19:12
Dr.Science

Registered: Oct 2011
Posts: 24
1541-II (cold)
2017-12-03 09:54
ChristopherJam

Registered: Aug 2004
Posts: 707
Thanks everyone, those are all really useful.

Spending too long on the half track is looking pretty costly on a lot of drives, especially if you catch that spike somewhere around 20-24 bycles. Entertaining given that 25 bycles is the default stepping time before acceleration kicks in..

I suspect what's happening there is the head is oscillating a bit, and that far in it's swung almost back to its starting point. I've tried running a simple physics sim with acceleration proportional to sin((phase-desiredphase)), and friction proportional to velocity. My friction model clearly needs work, as it keeps ringing for far too long, but even with the model as it stands I can already see shapes that loosely approximate some of the readings.



Some sets of parameters indeed result in a spike if the head has almost returned to the starting track at the end of T1, supporting my hypothesis above:


        def iter(x0,x1):
            a=np.sin((target-x1)*np.pi)
            v0=(x1-x0)/dt
            dv=v0*dt/Td
            v0=v0+a*dt*Ta**-2
            v0=v0-dv
            return x1+v0*dt

(iter calculates the new head position as a function of the previous two, assuming a constant timestep of dt. Head position in tracks.)
2017-12-07 17:23
ChristopherJam

Registered: Aug 2004
Posts: 707
…and some more measurements, these from j0x (thanks again!)

Two from an old 1541 push-down mech drive:




and two from an (almost as) old 1541-II:


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