# Not sure how to design this servo push/pull mechanism

I have a wooden pencil box with a sliding lid, like this:

What I want to do is use my servo to power some mechanism (probably using 2 arms linked together?) to open and close the drawer. It seems like it would be really simple but 1) I've never done anything like this before and 2) I can't picture it in my head at all.

What should I be doing to come up with a working design before I build something? Does anyone know how this problem has been solved easily before?

I was thinking of maybe building something with Popsicle sticks.

Thanks.

You could use a motor to drive a string around pullies to move the cover. Drive the motor forward to open and backwards to close.

Weedpharma

What are the dimensions of this box? What is the range of travel you expect of the top?
I question if a servo is the right choice of drive since you must devise a method to convert radial motion to linear which may be cumbersome in mechanics and space. Perhaps something like this would be a better choice.

• Scotty

What about something simple like a piece of stiff wire connected to the servo arm.

…R

Would be easier to convert the box from a sliding top to a flip top if you want to use a servo.

scottyjr:
What are the dimensions of this box? What is the range of travel you expect of the top?
I question if a servo is the right choice of drive since you must devise a method to convert radial motion to linear which may be cumbersome in mechanics and space. Perhaps something like this would be a better choice.

• Scotty

+1 to the question Scotty asked.

You need the servo arm to be at least half as long as the distance you want the lid to lid.

If you look at Robin2's diagram, you can get an idea of the limitations of a simple servo design. The lid can only slide twice the distance from the center of the servo horn to where the wire connects to the servo.

So you're pretty much limited by the width (or depth) of the box.

If you need to move a string back and fourth to slide a lid, then a servo might be used. I've got a plastic jar lid that has a 2.25" radius which gives a ~14" circumference. If a servo can rotate 180 deg., then it has the capability to move a sting ~7" that is attached to the jar lid which has the sting wrapped around its circumference and attached to the servo horn. Clunky, but an option.

Where will the mechanism be mounted? Outside, hidden inside, side, end, top?

A gearmotor like this:

With a pinion gear, mounted inside on the end with the pinion engaging a rack gear under the lid then hidden by a partition.

These things are very frustrating when there is no interaction from the OP.

...R

Sorry.

The mechanism would be placed at the front of the box.

Also, I'm going to modify it by cutting out a gap in the front of the box and adding rails to the inside walls. The "lid" would actually slide along the rails and go in and out of the gap rather than sliding along the top. Like this.

The range of travel needs to be the entire length of the box.

The box is 15cm and the lid is 18cm (I made a new longer one).

If the servo doesn't need to be in the box then a arm like the one Robin posted should work fine. Just make the arm a bit longer than half the length the lid needs to move.