Locking the box

Robotics and electronics discussion Mechanical design and actuators
1

Hi there!

I’m quite new to the field, but do have a question I couldn’t find answered anywhere else.

I’m trying to find a reliable way to lock a box from the inside. Now I’ve come as far as thinking of a locking mechanism, but am having trouble selecting the right equipment. My idea was, that the lid of the box will have a metal pin attached that slides on the inside of the box when closing. This metal pin will have a hole in it, in which another pin will slide, locking the box shut. The latter pin will need to be operated by a motor/stepper/servo or something similar.

Inside the box I’ll have some logic deciding wether or not the box will need to be locked, and I was thinking about using a servo to actually lock the box. My biggest concern here is people trying to open this box without proper access, while the logic in the box is powered down. I know that when using a digital servo, my servo will stay in position when no power is applied to it, but this is limited to the gears used in the servo.

Has anyone ever made a lock like this, or does anyone have info about which servo-torque to choose so that people cannot accidentally (or purposely with magnets, etc) open the box when they are not supposed to?

Any hints, including completely different locking mechanisms are appreciated!

2

Generally, when a servo is not powered, its pretty easy to turn it by hand. So you should make your design so that when someone tries to open the box, the force gets transferred to something other than the servo.

Here’s an article about someone who made a box that locks and unlocks itself using a servo:
arduiniana.org/projects/the-reve … he-puzzle/

From this picture, you can see how his mechanism works:
arduiniana.org/wp-content/upload … 0-6501.jpg

–David

3

If your servo is not accessible when the box is locked, and there is not rotating force on it when trying to open the box, your solution should work. This can be seen in the project David linked to (there is a sheer force of the locking pin when trying to open it, but this will not cause a rotating force on the servo).

Just ensure the force is on the locking pin and not on the servo when trying to open the box. The servo will not turn while it is powered off unless it is forced.

Kroony