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From: AMuzi <am@yellowjersey.org>
Newsgroups: rec.bicycles.tech
Subject: Re: Suspension losses
Date: Sun, 5 Jan 2025 09:57:46 -0600
Organization: Yellow Jersey, Ltd.
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On 1/4/2025 5:20 PM, Jeff Liebermann wrote:
> On Sat, 4 Jan 2025 16:28:21 -0500, Frank Krygowski
> <frkrygow@sbcglobal.net> wrote:
> 
>> On 1/4/2025 2:52 PM, AMuzi wrote:
>>> On 1/4/2025 1:36 PM, Jeff Liebermann wrote:
>>>> On Sat, 4 Jan 2025 12:35:20 -0600, AMuzi <am@yellowjersey.org> wrote:
>>>>
>>>> User manual on an early analog computer including a few useful
>>>> examples.  Try to visualize what those problems might look like on a
>>>> slide rule or today's personal computers:
>>>> <https://www.analogmuseum.org/english/collection/eai/tr10/>
>>>> <https://www.analogmuseum.org/library/eai_tr-10.pdf>
>>>
>>> Ah, such as a slide rule. Got it, thanks.
>>
>> The device I was talking about was nothing like a slide rule.
> 
> I called the analog computer that I build in a briefcase an
> "electronic slide rule".  I didn't want to, but that made it more
> acceptable to the college bureaucracy.
> 
>> It looked
>> vaguely like the one in Jeff's last link above, but the classroom
>> demonstrator was much larger - maybe 3' x 4' IIRC - with much bigger
>> knobs (4" diameter?) and meters.
> 
> I couldn't find anything with such huge knobs.  Maybe something like
> these from Edmund Scientific?
> <https://www.google.com/search?q=edmund+scientific+analog+computer&udm=2>
> 
> Would you believe a Heathkit EC-1 analog computer?
> <https://www.google.com/search?q=heathkit+ec-1&udm=2>
> <https://www.nutsvolts.com/magazine/article/may2016_heathkit_restoration>
> Fig 7 is a bouncing ball simulation, which is similar to the bouncing
> bicycle simulation.
> 
>> We were talking about electrical analogies for vibrating masses, and
>> that's one of the things the analog computer could simulate. One would
>> have to calculate the values of voltage, inductance and resistance to
>> correctly simulate the damped spring-mass system, set initial
>> conditions, then let the circuit run. The system's meters would then
>> swing back and forth in a manner analogous to the position of the mass.
>> All this was before digital computers were desktop devices.
> 
> Meters?  Too crude.  We used an oscilloscope or X-Y pen plotter.
> 
>> (In those days, the programs I wrote for vaguely similar problems were
>> room sized and run by full time technicians, and I'd turn in a program
>> stored as a thick deck of punched cards, hoping output would be ready
>> the next day.)
>>
>> As I recall, we students never did any actual work with that analog
>> computer.
> 
> We did.  My guess(tm) that would 1969.  We had groups of 5 or 6
> students sharing one machine.  I got some extra experience because I
> worked for the "calibration department" repairing them.  The problem
> was we had a large number of foreign exchange students from Iraq. Most
> had never done any manual labor or learned to use tools.  When faced
> with a knob that had reached its end of rotation, they simply applied
> more force to help it rotate.  That usually broke the expensive 10
> turn potentiometer (Helipot).
> <https://www.google.com/search?q=helipot&udm=2>
> 
> I was the idiot who found a solution to the broken potentiometer
> problem.  Between the knob/turn_counter and the pot was a short shaft
> extension.  I machined a few of these and added a plastic shear pin.
> If they hit the end of rotation and break the pin, all they had to do
> was rotate everything full counter clockwise, push the pin out of the
> hole, and replace it with a new pin (or toothpick).  The reason I was
> an idiot was because I had found the solution, I sentence to working
> overtime retrofitting all the analog computers with shear pins.
> 

Thank you, especially for the Heath Kit page (although much 
of that went beyond my understanding). The reader comments 
were great, especially the last one!

-- 
Andrew Muzi
am@yellowjersey.org
Open every day since 1 April, 1971