I was planning on using a solenoid lock, but then found out that I can't have it "active" for more than 10 seconds or so. So if I need to have it activated (unlocked) for any considerable period of time, then the solenoid lock is not the right device for the job.
SO, I was researching other options and now considering using a servo motor or a stepper motor. The question is which one would you recommend to use? I just need 2 positions, "lock" and "unlock" . Would either motor hold their position after they are activated and then power cut off? I don't need to maintain electrical signal to the motor if I don't need to.
I know the difference between the two 'theoretically', but I don't have either motor to play around with yet, so I'm looking your recommendations. Is one more reliable than the other? would they hold with any force or would you be able to rotate it back easily (which is counter productive for a lock). Which do you think is more suitable for my application? Any other options to consider?
Find web-sites for companies offering security products and door entry systems and see what is available. There are things called 'suction cups', which a are large electro-magnets that are designed to be permanently energised. They can be used both hold a door open or hold it closed.
If this is for a house door you can look for a "smart lock". I assume most of these use a regular geared-down DC motor. DC motors are reversible. But I assume they also have some kind of non-geared mechanism so it can be operated manually.
If it's for something simpler you might be able to find a "bi-stable" solenoid which hold either position without power.
You can consider the solenoid ‘reversed’, so it defaults to LOCKED, then energised is unlocked...
Servos are an easy one to use, with a cam to push against a spring loaded plunger, or a stepper/DC motor driving a gear, or threaded rod.
From what I've seen so far, the suction cup or the electromagnets are interesting but I think they demand constant current.
For the linear actuator, once it is activated and current removed, would it maintain its position?
Is the bistable Solenoid the same as the Latching solenoid? This might work!
I think the automotive actuator would work but its too big from what I've seen, and it's a version of the linear actuator
A question regarding Servos and Steppers though, would either one maintain position after you remove power? for a simple application of 2 required positions with no 'reset' to default position, which would be better? I'm narrowing down my options and want to eliminate one of the servo or stepper.
Railroader:
Is it a lock rated for Fort Knox OP is asking for? I don't think such big artillery is needed.
LOL, no, just a small mechanism that performs a locking function, and will not change positions after power is cut off. I've narrowed down my options to Linear screw actuator (as long as it holds position with no power), servo or bistable/latching solenoid
I'm not sure I know what you mean by spring, but with the regular solenoid lock, I can't keep it active for more than 10 seconds but, I might want to keep the door unlocked/open for 30 minutes or a couple of hours. So I want something that maintains either position (lock or unlock) with no power and for any length of time.
I think you will find groundFungus' suggestion the most practical. These kits are ready-made for exactly the purpose you describe. You have to provide the mechanical details of a bolt that engages with whatever part it is you need to lock, but you needed to do that anyway and are responsible for ensuring it fits accurately. A common bolt assembly will probably be suitable.
Thank you Paul__B, and groundfungas for the suggestion. Do these pre-made kits have a name to search for? the setup of the motor with worm gear sounds like a linear actuator. Is this the kit you are referring to or is there something else?
notacreativeusername:
Do these pre-made kits have a name to search for? the setup of the motor with worm gear sounds like a linear actuator. Is this the kit you are referring to or is there something else?
Well, Groundfungus gave you a reference to start with.
Some of these car door lock actuators - which are all "linear" actuators - do in fact use a worm gear (as I know, having to replace a broken one on my car), others I think use a "rack and pinion". In either case however, they allow for manual operation as well, so do not impede movement of the locking arm. They may drive in one direction and then return to a neutral position and have a loose link with the locking arm to facilitate this.
Note that in order to operate a fairly stiff mechanism and quickly they draw a considerable current - possibly several Amps - which also means they must be strictly prevented from being powered for more than one second or so!