New electric lock for self-bondage

[Sergio]

I've used magnetic door locks for self-bondage for several years and they work well although having that great chunk of metal and bolts on the end of a chain is clumsy to say the least.

I think I've just found the perfect electric lock for self-bondage: http://www.aliexpress.com/item/DC-10-18 ... 68664.html and not too expensive at about £25 delivered to the UK (€30/$35). I've just received one (delivered in just a week with no customs hassle) and testing on the bench it seems to work as expected, but note that there's a magnet in the striker part so they have to be within about 12mm of each other for the lock to engage (probably as these are designed for glass doors where if the bolt was extended before the door was closed it could damage the glass). The plan is to attach both parts about 8-10mm apart to a small piece of wood that will tuck under one leg of the head of the bed, but could be attached to all sorts of immoveable objects (I'll probably drill a selection of holes to enable this). To the end of a length of chain I'll attach a metal ring like a curtain ring about 30mm diameter either using a chain link or by looping the chain through and back on itself. With the ring positioned so the bolt traps it when power is applied to the lock, the chain will be retained for as long as power is maintained. The advantage of this arrangement over simple magnetic locks is that once open there's just the ring on the end of the chain rather than a large chunk of aluminium with bolts sticking out, so much less danger of it snagging on something, or in overhead situations, hitting you.

You can probably work out various scenarios for yourself but my main intention is for overnight spreadeagle bondage for which I've used conventional magnetic locks before. To the other leg at the head of the bed I attach a 1.5litre bottle with the end of a chain coiled and frozen, which will take 8-15 hours to melt depending on weather (I generally avoid bed bondage in hot weather) and to the other ends of the chains are comfortable but secure lockable wrist cuffs. Once in place I take up most of the slack in each chain and use two small padlocks in my hands to secure it. I'm now spread-eagled for the night until either the time expires or the ice melts when I have a free hand with which to reach keys to the cuffs, several sets of which are secured around the bed just out of reach while bound.

Note that like the conventional magnetic locks this lock is fail-safe, in that it requires power to keep it locked, so if the power fails I'm free, and that's why it's been hard to find as most solenoid-type locks are fail-closed. For safety I also have the ice backup and use a good quality power supply with both a mechanical timer set for about 12 hours plugged into a digital timer set to the actual release time I want. The wiring is done carefully to avoid risk of fire, and the low voltage side goes through a junction box that loops in both a smoke detector and a movement detector placed in the hall outside my bedroom so I'll be released if either of those are triggered. As a final backup I also have mobile and cordless phones attached to the head end of the bed within reach, and an ex that I'm on good terms with and knows my kinks.

[Gregovic]

Looks very interesting. One thing I would test thoroughly though is the ability for the lock to disengage under load. Does the bolt still retract when the ring is being pulled? How well can it handle this side load before something bends and it becomes stuck. Wouldn't want to get stuck because you struggled a bit too hard.

[FatherOfFour]

Good catch!

...
Wouldn't want to get stuck because you struggled a bit too hard.

Most electric door locks I've seen got stuck under load. Also, worked with special plungers, they had bronze inner sheet, and a "tail" to help momentum load...

I hardly trust drone load release systems: unless copies of naval tug hook, they are flimsy...

Have fun, overengineer Your kink,
f4

[Sergio]

Those thoughts had crossed my mind so although not yet quantitative test I did try pinching the plunger when disconnecting power and it had a very strong pull back, plenty to overcome my grip, but I'll be testing further once I've got a way of mounting them. I'd certainly be careful to ensure that the ring and chain couldn't become entangled and although other arrangements like looping two chains (one for each arm) would be possible it would exponentially increase the potential for failure. Possibly setting the timer to re-engage and disengage a few times after the initial release time might be a worthwhile safety measure.

But that's why I've got the ice release, telephones and someone expecting to hear from me.

The nearest I've come to getting it wrong was setting the timer for a slightly later release, forgetting to adjust the clock radio accordingly. I'd take 45 firm strokes of a riding crop over 45 minutes of listening to politicians justifying themselves on the Today programme on Radio 4 any day.

[davisev5225]

It may be possible to use such a lock to hold a relatively light weight, just enough to swing a line to within reach (think fishing weight). Then you could use a panic snap as your primary anchor, and use the electric lock as your primary release. Line swings down, you pull the cord, panic snap comes free.

[Stoneybridge]

Thinking something that big could magnatise whatever its holding, i've used one of these beforehttp://www.ebay.co.uk/itm/12V-DC-Sucked ... SwPCVX64hX it's 9 volts but works with a lower voltage transformer so only a little bit magnetic + a time switch.

[OrgasmAlley]

The little Chinese disc electromagnets such as the one linked directly above have a very strong caveat... they product a LOT of heat. I've done some experimenting with several different sizes. The one that's roughly the diameter of a US quarter and has a claimed holding force of something like 2kg @ 12VDC (they're all seriously over-rated) will heat four times its weight in aluminum to which it is thermally connected to around 130-degrees F in an hour. Run in free air, mine exceeded 170 in that same time. Just be aware!

[Gregovic]

Sort of depends on just how crappy they were made. As an example I have one of those magnets lying right here, and I measured it's resistance (47 ohms). If I were to run it at 12v it would take roughly 250mA. Meaning it generates roughly 3 watts of power. Not a massive amount, but enough to give off a bit of heat. If this is a problem it's quite easy to drop the voltage a bit (to say, 9 volts) which will drop the heat output to 1.9 watts. It will reduce the holding power of the magnet a bit though. You could also add a bit of extra cable to achieve this drop by series resistance. I use a rather longish cable on the magnet I use as my release (also one of these cheap chinese magnets) and this adds a bit of extra resistance as well (that one reads a tad over 60 ohms at the plug, meaning it generates about 2.5 watts over the cable and magnet. About .5 of which is generated in the cable. The magnet does get quite warm to the touch but I wouldn't go so far as to call it hot. Due to the added resistance of the cable the magnet is actually running at around 10 volts if the supply voltage is 12 volts. With a decent contact plate it's still plenty to hold a decently bundle of keys or a pair of scissors.

Heat does require taking into account. The magnets are really intended to be used built into a metal structure which acts like a heatsink.

[AlexIsBound]

How would I wire those and connect them to a power source?

[occorics]

Sort of depends on just how crappy they were made. As an example I have one of those magnets lying right here, and I measured it's resistance (47 ohms). If I were to run it at 12v it would take roughly 250mA. Meaning it generates roughly 3 watts of power. Not a massive amount, but enough to give off a bit of heat. If this is a problem it's quite easy to drop the voltage a bit (to say, 9 volts) which will drop the heat output to 1.9 watts. It will reduce the holding power of the magnet a bit though. You could also add a bit of extra cable to achieve this drop by series resistance. I use a rather longish cable on the magnet I use as my release (also one of these cheap chinese magnets) and this adds a bit of extra resistance as well (that one reads a tad over 60 ohms at the plug, meaning it generates about 2.5 watts over the cable and magnet. About .5 of which is generated in the cable. The magnet does get quite warm to the touch but I wouldn't go so far as to call it hot. Due to the added resistance of the cable the magnet is actually running at around 10 volts if the supply voltage is 12 volts. With a decent contact plate it's still plenty to hold a decently bundle of keys or a pair of scissors.

Heat does require taking into account. The magnets are really intended to be used built into a metal structure which acts like a heatsink.

Electromagnet have a duty-cycle that they are rated for. Not all are made for continuous operation. If lowering the voltage reduces the holding power too much, an option could be to drive it with short pulses (PWM signal). This should have less effect on the holding power while reducing the duty cycle.