Homebrew Drum Computer

Tony Duell ard at p850ug1.demon.co.uk
Fri Dec 14 18:43:53 CST 2007

> Robert Nansel wrote:
> > I'm looking at what it would take to make a barebones "museum piece" 
> > bit-serial computer along the lines of an LGP-30 or maybe a Bendix G-1
> So I am not the only madman araound here !

Is anyone here sane? I would hope not! I know I'm insane...

> >   And the keep the project within budget (i.e. none to speak  of),
> That is, I believe, a recipy for disaster. Your really need to budget 
> for having PCB's made if you want some reliable operation of whole cpu.

Why do you need PCBs? This thing sounds slow enough that almost any 
construction technique would work (stripboard, for example). And if you 
do ened PCBs, they'd only have to be double sided, and those you can make 
at home.


>   What I haven't been able to get a
> > handle on is how to make a serviceable magnetic drum. 
> A major mechanical challenge, I believe outside most people's 
> capabilities. Tony is bound to comment on it though !

The comment 'bl**dy difficult' springs to mind...

If you have the heads in contact with the media -- E.g. wrapping 
recodinng take round a drup and hainv heads rubbing on it -- you;ll get 
wear. Lots of it. It'll work fine for some minuts/hours and then fail. 
Rememebr thati n a tape recorder the head doesn't (normally) keep on 
going over the same bit of tape). 

If you have heads spaced away from the media, then rememebr that the air 
gap is critical -- the larger the gap the lower the density of recoridng 
yoyu can use. But the gap, in turn, is detemriend by the mechanical 
tolerances of the drum and bearings -- and you're going to have problems 
from that. I would think any form of ball/roller bearing is going to have 
too mich run out -- even an adjustable tapered toller bearing. I would 
think tapered bush bearings (and used in a good lathe headstock) would 
do, but making them -- and adjusting them -- would be 'interesting'.


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