Log inRegister an accountBrowse CSDbHelp & documentationFacts & StatisticsThe forumsAvailable RSS-feeds on CSDbSupport CSDb Commodore 64 Scene Database
You are not logged in - nap
CSDb User Forums


Forums > CSDb Entries > Release id #160665 : Stepper Test 1.0
2017-11-30 14:02
ChristopherJam

Registered: Aug 2004
Posts: 1359
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.
 
... 25 posts hidden. Click here to view all posts....
 
2017-12-01 18:12
Dr.Science

Registered: Oct 2011
Posts: 39
1541-II (cold)
2017-12-03 08:54
ChristopherJam

Registered: Aug 2004
Posts: 1359
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 16:23
ChristopherJam

Registered: Aug 2004
Posts: 1359
…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:


2017-12-29 19:15
soci

Registered: Sep 2003
Posts: 472
A bit late, but anyway.

1541-II with refurbished mechanic:


1571:


Another 1571:


Old 1541:


1571CR:


Unfortunately I couldn't do my oceanic this time as it's not here. That'll be interesting as it has an unusual stepper motor and mechanic.
2018-01-01 23:55
ChristopherJam

Registered: Aug 2004
Posts: 1359
Thanks Soci.

Those 1571s are particularly slow; well worth knowing about.
2018-01-02 12:16
Frantic

Registered: Mar 2003
Posts: 1626
The drive in my SX64



I haven't really read this thread very carefully, so a brief comment on what this graph tells about my SX64 drive would be much appreciated.
2018-01-02 21:03
ChristopherJam

Registered: Aug 2004
Posts: 1359
Frantic, the large black area at upper left means the optimal stepping time for your drive is a little higher than some of the others (you're looking at around 40 bycles/10ms), but it's well within the margins that current loaders rely on (12ms per track). More importantly the lack of a large black spike in the middle says your drive is much less likely than many other to stall for a bit when the normal stepping routine is being used.

So your drive's a little more consistently behaved than many, and is probably saving you a full disk rotation about one seek in twenty.

These results are mostly useful in the aggregate; they'll help tune the timing for improved stepper motor control in the next generation of loaders.
2018-01-02 21:33
Frantic

Registered: Mar 2003
Posts: 1626
Excellent commentary there, sir! :D
2018-01-21 21:38
Krill

Registered: Apr 2002
Posts: 2804
Quoting ChristopherJam
These results are mostly useful in the aggregate; they'll help tune the timing for improved stepper motor control in the next generation of loaders.
"Next generation of loaders" \:D/

I've just added Shrydar Stepping®™ to the massively overhauled next version of my loader, which is now seriously scratching on the 7 KB/s mark for uncompressed files.

I'm now looking at all these graphs, trying to find the optimal T1 value with a given T2 ≥ 72 bycles (the block transfer takes 72 cycles per byte plus random IRQ/DMA delays).

What would be a good value that's also guaranteed to work across all drives? Want to avoid that Chasm of Death many of them exhibit. :)
2018-01-21 21:55
ChristopherJam

Registered: Aug 2004
Posts: 1359
Quoting Krill
I've just added Shrydar Stepping®™ to the massively overhauled next version of my loader, which is now seriously scratching on the 7 KB/s mark for uncompressed files.

\O/

Quote:
What would be a good (T1) value that's also guaranteed to work across all drives? Want to avoid that Chasm of Death many of them exhibit. :)

Given the significant spike at 20-24 bycles exhibited by hedning's Oceanic, and the even heaver one further to the right on THCM's SX-64, I'd probably lean towards going as low as 12-16. For almost all of the drives, that's going to intersect the upper left diagonal edge (minimal total step time) too; most of them will be good to go another dozen bycles later, ages before the block transmission time is over :)
Previous - 1 | 2 | 3 | 4 - Next
RefreshSubscribe to this thread:

You need to be logged in to post in the forum.

Search the forum:
Search   for   in  
All times are CET.
Search CSDb
Advanced
Users Online
iAN CooG/HVSC
Rock/Finnish Gold
Nova
Airwolf/F4CG
Mason/Unicess
Freeze/Blazon
radius75
Dr. Doom/RAD
Nordischsound/Hokuto..
Guests online: 1131
Top Demos
1 Next Level  (9.8)
2 Mojo  (9.7)
3 Coma Light 13  (9.7)
4 Edge of Disgrace  (9.6)
5 No Bounds  (9.6)
6 Comaland 100%  (9.6)
7 Uncensored  (9.6)
8 The Ghost  (9.6)
9 Wonderland XIV  (9.6)
10 Bromance  (9.6)
Top onefile Demos
1 Party Elk 2  (9.7)
2 Cubic Dream  (9.6)
3 Copper Booze  (9.5)
4 Rainbow Connection  (9.5)
5 TRSAC, Gabber & Pebe..  (9.5)
6 Onscreen 5k  (9.5)
7 Dawnfall V1.1  (9.5)
8 Quadrants  (9.5)
9 Daah, Those Acid Pil..  (9.5)
10 Birth of a Flower  (9.5)
Top Groups
1 Booze Design  (9.3)
2 Nostalgia  (9.3)
3 Oxyron  (9.3)
4 Censor Design  (9.3)
5 Crest  (9.3)
Top Diskmag Editors
1 Jazzcat  (9.4)
2 Magic  (9.4)
3 hedning  (9.2)
4 Newscopy  (9.1)
5 Elwix  (9.1)

Home - Disclaimer
Copyright © No Name 2001-2024
Page generated in: 0.051 sec.