Hi forum!
I want to find the best way to lock and unlock a 3d printed box (Arduino controlled).
I am currently using a solenoid and a latch (SEE PHOTO) which works ok but has some limitations, like high current usage and locks whenever the lid is shut - requires power to unlock.
Is there a better way out there? like a worm gear (without too many mechanical parts?).
Any suggestions appreciated!
A small servo to push or pull the locking pin would be my choice.
...R
Thanks for the suggestion
Could you send my a drawing of some sort? How do you convert the rotational movement to a longitudinal one?
The servos come with an arm that attaches to the output shaft. Just put a suitable link (perhaps made from piece of a paper clip) between the servo arm and the locking pin.
...R
I notice the lid is spring-loaded. That may introduce some resistance to the action of a latch.
Note that a servo must be powered to operate - it will have a standby current so to operate from batteries you will need a FET to disable it until needed. Not quite as much current as the solenoid, but quite significant (generally up to an Amp).
Obviously you require power both to engage the latch and to release it if you use a servo, unless you manufacture a spring-loaded latch - like the solenoid - which is temporarily displaced as you close the lid.
Other possibilities might be a small "gearmotor" which will have a much higher torque than the servo but could have lower current consumption.
Paul__B:
Note that a servo must be powered to operate - it will have a standby current so to operate from batteries you will need a FET to disable it until needed. Not quite as much current as the solenoid, but quite significant (generally up to an Amp).
Small servos such as the SG90 draw very little current (milliamps) when they are stationary and not holding a load.
...R
Paul__B:
I notice the lid is spring-loaded. That may introduce some resistance to the action of a latch.
It does sadly :(. Can't think of a way round that using solenoid.
Paul__B:
Other possibilities might be a small "gearmotor" which will have a much higher torque than the servo but could have lower current consumption.
Yes good idea that could work and so could a servo. How reliable would the rotational to linear, mechanical mechanism be? Is the photo below what you were thinking of? Not sure if there's a simpler/ more reliable way? Any photos/diagrams of how to implement it into lid would be amazing.
willpowell:
I. How reliable would the rotational to linear, mechanical mechanism be?
Very
Is the photo below what you were thinking of?
Yes
I think the time has come for you to do some experiments. Arduinos are great for learning-by-doing
...R
Servo could actually be powered down when not required.
Checkout around 1:30 into the video below....... crude but workable.
Hi wil.
How about sound an alarm if there is any attempt to open the lid?
John.
Im not sure if you want the box to lock without a explicit lock-command, but if so; you could use a magnet to pull/push the lockpin into its locking slot.
If you cut the lockpin at an angle, the angle should help to press the lockpin in when you close the box and the magnet (or spring if you prefer) could push the lockpin back to lock the box.
Observe the lockpin in your average door to get an idea of what im trying to say. 
The door closes without the use of the door handle, but requires the door handle to be turned in order to "unlock"/open the door.
You could use a electromagnet to overcome the strength of the permanent magnet / spring, in order to unlock the box.
You could of course use a servo to pull the lockpin back to unlock the box, but i would use a wire/string between the servo & lockpin so the pin can retract independently of the servo.
..unless of course you DONT want the box to lock without a command, then the only way that i can see is to use a servo as explained by others in this topic.
But in that case you dont have to use a linear motion connected to the servo, you can use the servo arm itself to rotate into a groove to lock the box.
xarvox:
You could use a electromagnet to overcome the strength of the permanent magnet / spring, in order to unlock the box.
Don't suppose you happened to look at the original picture and read the original explanation? 
Paul__B:
Don't suppose you happened to look at the original picture and read the original explanation?
Hehe now that you mention it, a solenoid is actually a electromagnet.. well, i cant be perfect all the time you know.. 
I was thinking of a actual electromagnet to pull back the lockpin, pretty much a solenoid without the moving parts, that pulls on the ferrite lockpin.
But i do agree, i was a bit to quick to throw in my solution without considering the facts..
Ive been thinking of a similar concept myself, a self-locking cigarette case that only feeds out a new cigarette after a preset amount of time has elapsed (to prevent me from chain smoking), and that magnet idea was the best i could come up with to create a sturdy and unpickable lock in a tiny package.
Get the (full dose) patches, use a nicotine inhaler or chewing tabs when you still feel the urge. Combination therapy; that's our current advice.
There's presently some flak on vaping, but we still advise it to be substantially less harmful than smoking between quits.
Interesting anecdote: The suggestion is not to throw out all the cigs, lighters and ashtrays but to keep them on the top of the fridge (or similar). The psychology is that you are not, not smoking because you don't have them - which would just lead you to nip out to the shops - but because you have decided not to. 
regarding solenoid operated locks: Opening a safe with a solenoid
just skip ahead to 3:40
xarvox:
But in that case you dont have to use a linear motion connected to the servo, you can use the servo arm itself to rotate into a groove to lock the box.
Yeah I think servo or motor of some sort is probably required. I will experiment with mechanisms and yes maybe plausible with arm, however i needed it to be completely unlockable.
bluejets:
Checkout around 1:30 into the video below....... crude but workable.
something like this could work nicely, although more secure.
HillmanImplink=msg=4624018:
How about sound an alarm if there is any attempt to open the lid?
Hahaha that isn't bad at all!
