I received a few notes on and off gopher for more information about the 
gravity-battery raspberry pi described in my previous post.  Here's a 
bit more detail along with a status update.

The most general summary is that I am trying to build an alternative- 
power raspberry pi that will serve rawtext.club itself, or at least some 
service(s) for rawtext.club.  The method for powering it is to tie a 
weight to a rope and, using a pulley attached to the ceiling, hoist the 
weight in the air.  As the weight descends, the spinning pulley will 
turn a generator that will power the raspberry pi.  But rather than 
power the pi directly, it will power a battery which will maintain the 
pi even when the generator is not spinning (like when I am re-hoisting 
the weight).

Here are the components of the system:

1.  Weight, tied to a rope
2.  Bicycle wheel - serving as the pulley
3.  Freewheel on the bike wheel (note: the rope may actually be a bike chain)
4.  Transmission - transfer power from bike wheel to generator
5.  Crank generator
6.  Voltage regulator - don't blow up the battery
7.  Battery management system - seriously, don't blow up the battery
8.  Rechargeable battery (currently a 10000 mAh power bank)
9.  Raspberry Pi (Zero W, for now)
10. A frame to hold it all together

I am slowly accumulating all the components described above and testing 
as I go.  I documented the first test in my previous post [1], which was 
simply to measure how long the pi could run when starting with a full 
battery.  (It ran for a little over two days.)

Since then, I received the generator in the mail. The generator is a 
cheapo Chinese product, but it contains a built-in voltage regulator and 
USB output.  Since the battery's input is USB, this is perfect.

Generator in hand, my next test was to see if I could power the pi 
directly from the generator (no battery this first time).  Because the 
generator has a USB port, I was able to plug the pi right in and start 
cranking.  The pi's green LED light flickered to life!

But to really test it, I had to try connecting to the server.  I have a 
web server running on the pi, so I just needed to hit the webpage to 
confirm that it is online.  Unfortunately I was using both hands to hold 
and crank the generator, so I couldn't type https://pi.rawtext.club into 
my keyboard.  I ended up pre-typing the URL into my browser address bar 
and then, while cranking the generator, hit the enter key with my nose.  
Success! The page loaded! The pi was online, powered by nothing more 
than what I had eaten for breakfast.

EDIT: A very rough estimate is that it took 200+ RPMs to power the pi. A 
serious consideration in the future will be about the lifespan of the 
generator at this rate.  Let me again emphasize the word "cheapo" above.

Next test: use the generator to charge the battery while simultaneously 
powering the raspberry pi.  And here is where I hit my first setback.  I 
plugged the pi into the battery and it started up as expected.  Then I 
started cranking the pi and everything continued flawlessly.  But when I 
stopped cranking, the battery evidently let out a power surge and the pi 
reset itself.

To investigate this further, I tested with a second battery and by 
plugging the battery into a wall outlet.  In both cases, a power surge 
reset the pi.

So it looks like I need some kind of surge protector between the battery 
and the raspberry pi.  I doubt I'll be able to find an off-the-shelf 
product so I am now thinking about what it would take to build my own.  

Next steps:
* handle the power surge coming out of the battery
* rig up the frame (thanks to sloum at colorfield.space for a great 
  video example! [2])
* calibrate the weight so that it turns the generator at the necessary 
  RPMs to maintain the battery
* decide which services to host on the pi (gopher, pleroma, other?)

This gravity battery pi is just one of a number of projects underway on 
rawtext.club.  I've been really pleased that some very smart, creative 
and interesting people have joined.  If you like collaborative tinkering 
on projects like this (although more often on coding projects) feel free 
to ask me for an account.

I don't currently have any leads on a spare bike wheel with a freewheel, 
so I am keeping my eyes open for those.  But the main hurdle to overcome 
right now is handling the power surge.  If you have ideas about this, I 
would love to hear from you.

Onward!

--
[1] gopher://zaibatsu.circumlunar.space/0/~cmccabe/18-off-grid-pubnix-test-01.txt
[2] https://www.youtube.com/watch?v=foqqxqW8aBg