Solenoid

[Dominic B]

I'm looking for a solenoid to use in order to secure a safe door - so will need to remain in the extended position until activated, and then return to the extended position.
All I've found is a PCB solenoid, (here/here) but I don't think that the armature will be long enough to work, or strong enough.

Thanks

 

[alband]

Why not use a normal one that can be returned by hand but will stay without interference and have a small magnet in the hole that the armature will extend into. This would keep it in the whole but can be overcome but the solenoid's elctromanget.

How strong is this safe going to be. Is it an elaborate piggy-bank or are you going to keep your life's saving in it.

If it is the later, can I advise you use some of those savings to buy a professional one.

 

[Dominic B]

The problem with using a normal solenoid is that I cannot think how the armature can be returned to the extended position, without needing the safe door open... kinda defeating the purpose

It's for my GCSE coursework, so providing it secures the door I'm not really bothered!

 

[BeanieBots]

Does it HAVE to be a solenoid? (normally returned by a spring or gravity).
For a GCSE project, I'd use a hobby servo.

 

[alband]

Sorry I must be misunderstanding your project.

You have a safe with a door. In the door you are going to have a PICAXE controlled solenoid. The arm from the solenoid will extend into a hole in the safe to keep it closed. So the door is shut then the arm of the solenoid extends into the hole stopping the safe being opened unless the PICAXE is made to retract the arm.
Is this right?

 

[Dominic B]

Could be a servo, but a solenoid strikes me as being a lot easier to use and to mount onto the door, I can't really see how to mount a servo so it will lock the door

Yes, that's right, but the problem with the solenoids I've got at the moment (these) is that the armature will not return to the extended point whatever I try

 

[alband]

I would say a servo is much easier. A PICAXE can directly control one easily and it would stay where put. How thick is the door.

 

[Dominic B]

Ok, well, I'll try, but the problem of mounting it still applies. I'm not quite sure what thickness I'll use, at a guess 5mm MDF?

 

[Andrew Cowan]

My experience with servos is that you really need seperate power supplies, as servos draw more power than batteries can provide. A 6V power supply, large reservoir cap and low drop out regulator can be used, but that starts to complicate things. Plus, depending what else you want to run, the capacitor may have to be a large size.

My GCSE project had an LCD and a servo. They were both connected to a 9V 600mA power supply with a 1000uF capacitor. They each had a 7805 ro step the voltage down. Even so, when the (micro) servo was used, the LCD stopped showing its text, and the picaxe occasionally reset due to the low voltage spikes. Maybe it just needed a bigger capacitor?

Andrew

 

[alband]

That thickness could be tricky. Correction; would be tricky.

Might have to settle for a solenoid. You'll have to use a relay but that's no biggy.

Have you tried looking for point motors. This is one I have: http://www.hornby.com/track-91/point-motor-r8014/product.html

It is just a solenoid and it stays in place. It is a bit bigger that 5mm (something like 10x10x40 from memory) so would extend inside the safe a bit. Other than that I can't think of any problems. (oh, and it gives a nice "click").

 

[Artie2]

You could always use one solenoid to latch the plunger, and another to unlatch it:

 

[wapo54001]

If you can spend the money, this is an option:

http://www.firgelliauto.com/product_info.php?cPath=110&products_id=127

 

[BeanieBots]

@Andrew,
Your problem was trying to power the servo from a 7805.
If you have a supply capable of giving the required current, (which a 7805 can't) then it works well from the same supply with a little decoupling.
If the 9v was a silly little PP3 type battery, then your 9v would collapse almost instantly.
Try 4XNiMh as a single supply. The LCD might dim a little but there should be no resets.

 

[boriz]

Maybe I misunderstood, but surely all you need is a spring?

 

[smurf384]

Central Door Locking Actuators

Try car remote locking unit, they have a small motor with a pinion on a rack with a travel of 15mm L293 will give you forward and reverse. Here in Oz can be sourced from

www.oatleyelectronics.com

 

[pssmith]

MUTR do a linear actuator for under a tenner Here. Another device that would show the concept (but might not have enough throw by itself) are point switches used in model railways. They do need 12V and a bit of power to actuate though.

 

[Andrew Cowan]

I agree those linear actuators do the job - I have seen a safe that uses one. The only problem is their size - the project that used one had to be big, with a door about 4cm thick (with the actuator in the middle).

Andrew

 

[Dominic B]

Ok, well I've taken the latching solenoid apart, and now just have the coil/plunger which I'm going to experiment with, but I'll also try and get hold of a linear actuator.