On 2012-10-09, Ecnerwal wrote:
In article ,
"DoN. Nichols" wrote:
[ ... ]
That requires memory, which requires a reliable power source,
especially to energize the solenoid to lock it against other rotation.
(You might as well make it a numeric keypad to enter the combination,
but again the need for a reliable power source comes into the game. And
what do you make it do if the power fails? Does it lock forever? Does
to fail unlocked? Do you have provisions for connecting an external
power source if the battery dies? What if someone applies too much
power to those connections, frying the circuit? All questions which
apply to a lock with memory. :-)
Well, obviously the folks that will use electronic locks do go there,
but I was thinking (somewhat vaguely) more of something mechanical like
a "wax or grease clutch" that would heat up with excessive repeated dial
spinning and disengage the dial and the rotors, as I was contemplating a
servo motor spinning the dials for hours on end. But it's really not
needed or particularly useful, since there have been other solutions for
decades that work fine for the purpose.
O.K. You were thinking of powered attempts, not hand attempts,
that does make a difference.
The typical small-firesafe (not much of a safe) type electronic lock
seems to be battery powered, locked forever if not powered, remembers
combination in non-volatile memory if the batteries die or are removed,
and the batteries can be replaced from outside.
O.K. That works. I've avoided those because I was not sure
that the batteries could be replaced from outside -- or that the safe
could be opened after the internal batteries died. :-)
Presumably they fry and
stay locked if overvolted. If it's got power to take a combination, it
has power to note that it's had 3 wrong attempts in the past 5 minutes,
or whatever time limit you pick.
And then start ignoring any more input until the required
quiescent period had elapsed.
As with any, if they can pick it up and take it with them, it doesn't
matter how it's locked, it will be opened. If they can't pick it up and
want what's in it badly enough, they'll have means to cut it open or
they'll make you open it for them... And if it's yours and it fails
locked, you'll cut it open or get it cut open. I think the last time
safes came up in the group there was a shaggy dog story of someone who
whimsically built a vault door (surplus, perhaps) into the basement,
which became known, which lead to him unlocking it (rather shakily) at
gunpoint one night (nothing to speak of in it per the shaggy dog) which
lead to the door being removed from the hinges for the remainder of his
tenancy in the house.
:-)
I had an opportunity to bid on a used government surplus vault
door, but just getting it home would be difficult enough. :-)
I do think that the dial-spinner would be a good robot project - buy the
cheap safes with lost combinations, park them in the corner until the
robot non-destructively unlocks them, remove goodies if any (possible
but unlikely, since goodies in lost combination safes tend to lead to
the owner of said goodies having the door cut off) and sell the
unlocked, undamaged safe for a better price. But it would require at
least enough information to know that "this lock has to be spun 4 times
to the right before the first number", etc.
And typically, the government security file cabinet locks (three
setable numbers) jstart off to the left, not to the right (required, if
the final motion to withdraw the bolt is to be in the proper direction.
Enjoy,
DoN.
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