Physics of bumping and possible mitigation

[unjust]

a manufacturer a few years back did a high speed MRI of a lock being bumped for their anti-bum R&D. sadly i've not been able to track it down again since i watched it ages ago. my understanding of it from this is that:

it's apparently exactly not like a newtons cradle, but more like the cue ball following a ball to the rail and the cue ball bouncing off while the ball stops at the rail.

the force of the hit drives the entire stack up, over compressing the spring, which allows the key pin to bounce off the driver pin at the top of the stack.

if you ponder things, that makes sense, as the spring applies much more force back than the mass of the driver pin, and explains why different springs *kinda* works to prevent bumping as it slightly alters the timing of the overall stack rebound (as the rate of compression changes across stacks), where if it was a newtons cradle situation, the spring alone as the last element in the series would be what would bounce up, and bumping wouldn't work.

[gumptrick]

IMHO there are two major issues between the Newton's cradle example and lock bumping:

1) A newton's cradle lacks spring pressure
2) A newton's cradle lacks the friction that would exist between a pin and the pin chamber

One might argue that a newton's cradle has some kind of "spring force" equivalent via gravity and the rotating arc of the balls, or that it has "friction" via air resistance. But those are very small forces compared to the mass of the balls. The pins in a lock are extremely lightweight compared to the force of the spring. The effects of that spring would be very significant here.

This sort of thing would be easy to mathematically model, though. We need to find ourselves an engineer who has this fresh in their mind (I haven't done it since College).

[unjust]

when i teach bumping, i only use newtons cradle to get people thinking about the impact and the visible gap moving, then clarify that it's really NOT like that, but that something similar is happening.

[WilsonTrucking]

In reading all your posts i had a thought no one seems to have considered doing. I dont have any bump keys myself or id try this, so ill explain it as best i can. My idea is to have something akin to a non newtonian fluid replace or inhance the spring. What comes to mind is memory foam. The trick would be to somehow have a small piece of the foam sandwiched between the coils of the spring as a dampener, or even the full length of the spring erunning lengthwise top to bottom. This would still allow the spring to compress and expand, but limit the speed at which it will do so, thereby rendering the lock un bumbable but still allowing normal operation.

[WilsonTrucking]

Another idea that just came to me is to have the driver pin be double the mass of the keypin, or more than double. That would then make the amount of kinetic energy required to get it moving to be that much greater... Just some random thoughts as in laying here trying to fall asleep hah!

[gumptrick]

Or one could mechanically key the keypins and driver pins together like the Corbin Emhart! Nobody is going to bump that....

[GWiens2001]

Or one could mechanically key the keypins and driver pins together like the Corbin Emhart! Nobody is going to bump that....

Or like the driverless pin systems like the Medeco cam locks or BiLock.

Gordon

[gumptrick]

One thing which came to mind would be making the keypins and driver pins stick together via magnetism. It could be as simple as using magnets for drivers and then magnetic keypins. Or both could be magnetic and set up so there are opposing poles at the shear line.

[Ralph_Goodman]

One thing which came to mind would be making the keypins and driver pins stick together via magnetism. It could be as simple as using magnets for drivers and then magnetic keypins. Or both could be magnetic and set up so there are opposing poles at the shear line.

I haven't experimented too much with building magnetic systems, but that sounds like a great idea. Adding magnetic components to locks almost always complicates manipulation.

Looking forward to knowing what the mechanical issues would be with such a system. Especially because there seem to be a lot of people with a good grasp of physics on the forum.

[gumptrick]

The only concern that I can think of would be that magnets might end up attracting small metal bits that could gunk up the workings of the lock. However, I would think that would be a minor concern. Most locks and keys are made mainly of brass (or nickel silver), both of which are non-magnetic and therefore any debris that wore off the lock itself or its key wouldn't be a problem. But I could see it might be a problem in environments with little bits of ferrous metal floating around, like a shop that does welding/grinding/machining, etc. I can't imagine it is a significant issue, after all the EVVA MCS has been around for years and it contains magnets as part of its inner workings.

[demux]

I can't imagine it is a significant issue, after all the EVVA MCS has been around for years and it contains magnets as part of its inner workings.

I don't personally own a MCS, but as I understand it the magnets are only in the key. The elements in the cylinder are basically just rotors that are aligned by the magnets in the key. So I don't think there would be any concern with getting small metal bits stuck in it.

[demux]

Or one could mechanically key the keypins and driver pins together like the Corbin Emhart! Nobody is going to bump that....

Yeah, I like the Emhart approach, not only for bump resistance but also because it adds a rotation component to picking. Only downside is the mods required to the plug and key...

[gumptrick]

I can't imagine it is a significant issue, after all the EVVA MCS has been around for years and it contains magnets as part of its inner workings.

I don't personally own a MCS, but as I understand it the magnets are only in the key. The elements in the cylinder are basically just rotors that are aligned by the magnets in the key. So I don't think there would be any concern with getting small metal bits stuck in it.

I don't own an MCS either, but I can't help but think that the lock itself must contain magnets otherwise the "rotors" wouldn't rotate to the positions indicated by the key. If the rotors simply contained pieces of magnetic material rather than actual working magnets then the key would simply attract those parts "blindly" rather than being able to rotate them. I can't see how the MCS could function unless the rotors inside the lock had N and S poles so that the magnets in the key could rotate them properly.

[demux]

I can't help but think that the lock itself must contain magnets otherwise the "rotors" wouldn't rotate to the positions indicated by the key. If the rotors simply contained pieces of magnetic material rather than actual working magnets then the key would simply attract those parts "blindly" rather than being able to rotate them. I can't see how the MCS could function unless the rotors inside the lock had N and S poles so that the magnets in the key could rotate them properly.

Yeah, I'm not sure how that would work either. Got me curious though, so I went and did a bit more digging. Best description I could find is from Security Snobs:
https://securitysnobs.com/EVVA-Brand-Info.html

Reading that, it looks like the important point is that "the locking rotors never come in direct contact with the key". Reading between the lines a bit, I'm guessing that the rotors are behind some sort of shield, and are only magnetized just enough to interact with the key through that shield, but not attract/retain metal bits.

An alternative explanation would be that the rotors are made up of regions of both ferrous and non-ferrous material, and there is some algorithm involved in what sections of the rotor are allowed to be which and what sections of the key are allowed to be magnetized or not, so that they align in predictable ways. Something analogous to the MACS specification or step progression in a pin tumbler lock...

[gumptrick]

Reading that, it looks like the important point is that "the locking rotors never come in direct contact with the key". Reading between the lines a bit, I'm guessing that the rotors are behind some sort of shield, and are only magnetized just enough to interact with the key through that shield, but not attract/retain metal bits.

There is a link to a breakdown/gutting of the MCS on this board. Check it out here: http://www.lockpicking101.com/viewtopic.php?f=9&t=63856

It seems like the lock has a series of plastic rotors that have magnetic inserts put in them, and this is separated from the key with a thin shield. Thus there is no direct contact to the rotors. If that shield wasn't in place then you could simply rotate the rotors directly using a thin hooked tool.