[time-nuts] Different Thunderbolt versions, group buy

Tom Van Baak tvb at LeapSecond.com
Sun Feb 22 02:51:38 UTC 2009

>I currently have an HP Z3801A, which seems to be running
> well.  I've been looking at the T-Bolts on Ebay for a while, but
> have been holding off buying.  This post just gave me an
> opportunity to ask some questions.
> I've seen references to the TAPR group buy in previous posts. 
> It obviously happened before I found this group, but am interested
> in the details.  
> Things like: 
> When did the buy happen?
> Which model T-Bolt was bought?
> What was the price?
> Was PSU included?
> Are any units still available?
> Is another buy planned for the near future?
> Thanks for the info.

Hi Dave,

Yes, there have been 3 or 4 large batches of TBolts sold through
TAPR over the past year or two. The price ranged from about 95
to 125. Most were sold with power supply; some without (when the
source of cheap switching supplies ran out). For more info see:

Yes, there will be another group buy or two. However, this time
I'm testing all of them first and then announcing the sale (expect
mid-March) so that no one has that long wait between ordering
and paying/receiving.

So hang on a bit longer and I'll send the details next month.

Note a number of people have asked privately (you know who
you are) and those requests will be handled first.

> Dave M
> MasonDG44 at comcast dot net  (Just substitute the appropriate characters in the address)
> Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes. 

This is an interesting T&F problem, actually. It depends what
you mean by "it". If "it goes" means the paper itself -- if you
pull at a constant linear rate then it goes neither slower nor
faster. It's constant and then suddenly ends, that's all.

If "it goes" means the rotation (frequency) of the roll -- if you
pull the paper at a constant linear rate then, yes, a predictable
drift in frequency occurs as the radius of the roll decreases.

For an interesting mental exercise (perhaps while you're sitting
down near said roll of TP) see if the frequency drift is linear or
log or exponential. For extra credit, when the roll is slightly bent
(as often happens) rather than perfectly circular see what effect
that modulation has on the short-term ADEV of the frequency.

Alternatively, if you unroll the TP by attaching a stone to the end
and letting it drop over a cliff then you have a really interesting
physics problem considering the acceleration of gravity, varying
mass, inertia, and radius of the roll, nonlinear friction in both air
and roller, etc.


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