Great and simple write-up. Vaguely remembered nycresistor from other articles I've read, so I'm glad this was posted here.
I think HN would be well served to have more front page retro hardware hacking articles. They may not be useful in the same way as other posts, but they sure as heck are delicious brain food and a relaxing diversion.
Plotters are just one small step removed from a 2D mill. This particular kind of plotter, where the paper is fed through to obtain one axis of movement suffers from bad registration, any kind of slippage on the paper (and there always will be some) will lead to registration errors. Try different kinds of paper to determine which kind gives you the least slippage by repeatedly drawing very large patterns in different colors and then studying the horizontal edges near the limits.
I can't tell from the pictures, but around that time period diamond grit drive wheels came into use. Either the top or bottom drive wheels would have a diamond grit on their surface which would make an indentation pattern in the paper which acted to key the paper in place. The registration was even better than drilled paper which could develop a little slop around the pins and the holes.
I have a cutting machine that’s pretty much a plotter with a blade (though it can also take pens) which uses a similar design. It doesn’t take paper directly, it has an adhesive plastic sheet you stick the paper to. I assume that’s to provide a higher friction substance.
It seems pretty accurate, to within a couple of millimeters.
The brown rubber wheels seem to be the only things in contact with the paper.
There were also some plotters with spiky steel wheels at the paper edges to feed the paper, those would work a bit better when new but the spikes would wear off fairly quickly.
Since OP mentioned the nice big HP x,y plotters, that reminds me I once wrote an emacs lisp HPGL driver to hit the serial port and run one in grad school. I'll have to dig it up sometime.
Edit, just remembered: it was probably to output one of the VLSI CAD layer formats, like GDS or EDIF.
I really should find mine. I got it for free off of a local computer store's junk table about 12 years ago. My understanding is that it's fairly uncommon, at least compared to the Imagewriter I/II. Would be cool to take the roms and try to write an emulator for it, though I think emulating the Laserwriter would be more valuable from a historical perspective, since it was so influential in desktop publishing (and one of those odd cases were the peripheral had a faster CPU than the computer it was connected to, much like the Commodore 1541 disk drive).
Edit: And on second glance it's quite possible that 410's Z80 is clocked faster than the 6502 in the Apple II.
However, I spot a 4.9152 MHz crystal on the photo of the PCB (a quarter from the left, halfway down)
So, I guess it either is overclocked or (IMHO more likely) that that clock is divided into a 2.5MHz clock.
Either way, I agree with you that it likely had a faster clock than the 1MHz of an Apple II.
However (certainly if you can get around with 8 bit registers; it shifts a bit if you can use the 16 bit parts of a Z80) a Z80 has to be clocked faster (some people claim by a factor of about 2:1) than a 6502 to be faster (extreme example: a NOP takes 4 cycles on a Z80, 1 on a 6502)
In summary, I guess this _is_ faster than the Apple II it was designed to connect to, but not by much.
The simple plotters of the past were really great pieces of kit; and fun as the day is long.
Even the little Commodore 1520 was a very capable machine in a toy form factor. Four independent color pens, and a great tool for learning geometry and programming at the same time.
Yes I remember using one to print the results from an experiment at my first job we had a rig that used a high speed cini camera to record the movement of an "object" when subjected to high flow regimes underwater.
To digitize it I covered the wall of a spare office with graph paper and projected the film onto the graph paper and manually using pencil marked up the graph paper then transcribed the x,y coordinates which I than plotted on a HP A3 plotter.
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I think HN would be well served to have more front page retro hardware hacking articles. They may not be useful in the same way as other posts, but they sure as heck are delicious brain food and a relaxing diversion.