My timer release system.

Ideas and instructions how you can make your own bondage toys.
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BlindMike
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My timer release system.

Post by BlindMike »

I designed my own timer release using a 12 volt solenoid to hold the keys up out of reach, and a infinitely adjustable timer to supply the power to the solenoid. When the timer clicks off, the keys are dropped to within reach, and I can uncuff myself. it's effectively foolproof. If there is a power cut, the timer cuts out and the keys drop. I have the timer in a drawer that I can open [with a bit of a struggle] and turn it off, thus releasing the key. If I have tied myself to my chair, I have to shuffle it around a bit to get to the drawer, if I have tied myself in bed, I have to hop to where the keys are when I hear them fall, or, to the drawer to unset the timer if necessary. Here is the solenoid,hanging from the ceiling. I'll post the timer when I can resize it to fit the size requirements. ok, it looks as though I cannot post a photo of the actual timer, the file is too large, and I have absolutely no idea how to reduce it to the required size.
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ruru67
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Re: My timer release system.

Post by ruru67 »

Just make sure there's a decent amount of weight on the keys. Solenoids often have a bit of residual magnetism, so you could cut power and not drop the keys. Make the weight (including keys) just a little lighter than what the solenoid can hold, so it's sure to drop when the power goes away. Extra weight will resist jamming as well.

Also check the duty cycle of your solenoid. Most solenoids are intended for short bursts of operation, e.g. to unlatch a door or throw a bolt, and could overheat if kept powered for long periods. Failure due to overheating will probably drop your keys, but you don't want to destroy your kit.

I've seen timer switches fail (even industrial grade ones), so it might be a good idea to plug the main timer into a secondary timer, set longer so that you won't be stuck forever if the timer sticks. I've used that as a backup for magnetic locks with a computer controlled relay control, in case of computer failure or software error. Your "shuffle to the switch" release is probably OK, but if you do a scene where that won't be possible or could fail, then definitely have a Plan B.

Finally, make sure the solenoid is vertical, so it falls cleanly and doesn't jam in place. For that reason, or the key bouncing somewhere unreachable, consider having an independent Plan C.
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GeneralError
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Re: My timer release system.

Post by GeneralError »

this looke like a proven and reliable setup.
Regarding the residual magnetism that remains even after the electric power is switched off: It can be surprisingly strong. I often use a thin layer of material between the electro magnet and the key, like a piece of paper or a thin plastic. If there is no direct contact between metal and magnet, the residual magnetism is going down close to zero.
Regarding this question
... cannot post a photo .... no idea how to reduce it to the required size
Just open the image in MSPaint (assuming you are running windows) and use the resize function.
OrgasmAlley
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Re: My timer release system.

Post by OrgasmAlley »

You can vastly reduce the issue of residual magnetization (such that it doesn't matter here) with a capacitor wired parallel to the coil. May have to play with rating, obviously should have Vmax greater than the charging voltage. This causes a reducing oscillation between coil and capacitor after power-off... cap charges coil, coil discharges into cap, repeat.
Sergio
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Re: My timer release system.

Post by Sergio »

This is where fire door retainers are safer as they're specifically designed to have little or no residual magnetism - you don't want the door staying open as the stairwell fills with smoke.
BlindMike
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Re: My timer release system.

Post by BlindMike »

The solenoid does point down, and it has a small spring to ensure it pops the magnet out when the power goes off. I have used it for up to 3 hours, and it does get a bit warm, but is set off the wall a bit so as not to conduct heat into the wall. Has never failed yet. When it lets go, the key falls to a few inches off the floor, so it's in reach whatever my position at the time. Unfortunately, I cannot figure how to resize the picture of the timer so cannot show it here..but it is a simple domestic style of timer which can be set to any duration up to 24 hours.
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ZipMeUp
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Re: My timer release system.

Post by ZipMeUp »

@OrgasmAlley What happens if the capacitor fails or the solder joint goes bad? You wouldn't know until the timer clicked off and... the keys didn't fall.
An easy, semi-permanent way to prevent residual magnetism would be to take a layer or two of duck tape, cut a circle out of it, and stick it on the magnet.
Also, if the timer decides to stop ticking, you're stuck as well. A good solution for this would be to use a rechargeable battery to power the circuit. Given that you are just holding keys, a pair of AA size NiMh batteries would be plenty strong enough, yet guaranteed to eventually die should the timer fail.
An added plus of using a pair of AA batteries is that you're running the solenoid at several times less than it's design voltage and overheating is a non-issue.

I hate to be the safety police but you don't want to end up like "the force of nature" story. A lot of selfbondage accidents happen because the release didn't trigger.
It it ain't inescapable... It ain't my kind of bondage.
OrgasmAlley
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Re: My timer release system.

Post by OrgasmAlley »

Everyone has to pick their own level of safety, to be sure. Reliance on any one thing will always present some amount more risk than a redundancy. However, I'm not really sure why you addressed your post to me. I provided a simple factual explanation of defeating residual magnetization with a capacitor, for those who didn't know it... I didn't say a capacitor was the only safety consideration anyone should employ. But let's look at these two concerns.

An average electrolytic capacitor has a rated life of around 2000 hours (some go to 5000) in use at a rated operating temperature (often 85C), and a shelf life irrespective of use in excess of 10 years... 15-20 is more typical before failing out of spec. In the absence of voltage over its rating, that capacitor will fail gradually, not suddenly, losing capacitance and thus oscillating out residual magnetization less quickly as it fails. Like an underrated capacitor. The expected life of a quality solder joint between properly mounted components is infinite. IMO, it's substantially more likely that the lock won't open to the key due to a hung pin than either of these means of potential failure when correctly sized and implemented.

You can certainly use a magnet that barely holds what you are retaining or manually render a stronger magnet to this condition, if you always hold the same thing. You can also incorporate a physical release (i.e. spring loading or similar) that the magnet can only modestly overcome. It remains the case that a capacitor in parallel with an electromagnet can quickly degrade residual magnetization.

As to timer failure, I think the easiest remediation for this possibility is to daisy chain two independent timers. Or implement a true emergency release, of course.
rmcingle
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Re: My timer release system.

Post by rmcingle »

OrgasmAlley:

I like your idea of creating what is essentially a 'degaussing' system. I submit, however, that it will require a bit more than just a cap to be safe. Your idea also only works if the timer interrupts the flow of current to the magnet. If the timer is switching the power supply AC input, then you won't get the inductive kick that will create the reversal of current.

A switch directly in the current path for the magnet coil will suffer a very significant inductive kick. This could eventually destroy a switch contact, but it would take a large number of cycles, assuming the switch had reasonable sized contacts to start with. If you put a capacitor in parallel with the coil, then it would need to be able to store all the energy in the coil (which can be a lot!) or the voltage will spike well above any reasonable capacitor rating. (thousands of volts). It won't take many cycles (one?) before the capacitor failed.

A couple of back-to-back zener diodes in parallel with the cap/coil would limit the voltage. The Zeners would need to be pretty big to handle the surge current and power dissipation.

I have no idea how big of a cap and how much energy would need to be captured in order to effectively degauss.

I can tell you, however, that residual magnetism is a very real concern. It is generally fairly consistent, so experimenting can yield a reasonably safe system. I use a large electro-magnet (holds a door closed) as part of my bondage system. If I let the metal plate directly contact the magnet, it will remain stuck after the power is turned off, although a gentle pull will suffice. If I place a single layer of Kleenex between the plate and the magnet the plate will fall off once the power is removed, yet the magnet retains enough holding force that I am unlikely to pull free.

I suspect that with a solenoid type system that the original poster is using that adding a spring to the plunger will do the trick.

R. Mc.
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ruru67
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Re: My timer release system.

Post by ruru67 »

rmcingle wrote: A switch directly in the current path for the magnet coil will suffer a very significant inductive kick.
You want a flyback diode: https://en.wikipedia.org/wiki/Flyback_diode

Doesn't need to be a zener, or need any caps or anything. Just a simple diode.

Think of a coil as being like a spring - you pull the spring back (creating a magnetic field) by applying current through the coil, and when you let it go, the force you've applied has to go somewhere. If you've mechanically opened the circuit (via a switch or relay), that means it doesn't really have anywhere to go, so the field doesn't collapse immediately, and can stick around. I've had relay-controlled solenoids stick for that reason, and a flyback diode fixes it.

If you have electronic circuits, the induced voltage can be high enough to kill components. I might have a few dead Arduinos as a result of omitting or not properly connecting the flyback diode.
rmcingle
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Re: My timer release system.

Post by rmcingle »

ruru67 wrote:
rmcingle wrote: If you've mechanically opened the circuit (via a switch or relay), that means it doesn't really have anywhere to go, so the field doesn't collapse immediately, and can stick around. I've had relay-controlled solenoids stick for that reason, and a flyback diode fixes it.
.

That's not how it works.

Two basic electrical rules: You can't change the voltage across a capacitor instantaneously, and you can't change the current across through an inductor instantaneously.

With a coil (any form of inductor) if you have current flowing and open the circuit with a switch, the voltage across the coil will increase as high as it has to in order to keep the current flowing, until the energy can be dissipated. If you are opening the circuit with a simple switch the usual result is that there will be a brief arc across the switch contacts. That arc dissipates a LOT of energy and the current will drop very quickly. As long as there isn't anything that will be hurt by having a few thousand volts arcing, no problem. If you happen to be touching it, the current may pass through you instead, which may not feel good.

By the way, this is exactly how the spark is generated for a gasoline engine.

The flyback diode give the current someplace to go, usually back to the other side of the coil. The current will continue to flow until the energy is consumed in the resistance of the coil and the voltage drop across the diode. Depending on the inductance and resistance of the coil, that could take a while. The magnetic field will remain much longer compared to not using a flyback diode. The field will also decay slowly, which wouldn't create a degaussing situation.

To degauss, you need to reverse the current.

R.Mc.
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