Assistance needed - Nezuko Box opening door mechanism?

[Boneman]

Hello RPF,

I need some advice and suggestions on what electro-mechanical device(s) I could use to have the door on a box (worn like a back pack), auto open and close by the push of a button. This is for a Tanjiro / Demon Slayer cosplay build I'm helping my 16yr daughter with. Here are some examples of the box for context. We've already built a study 14"W x 24"H wood box using cedar 1x1 as an internal frame and then skinned with 1/8" Mahogany plywood - very light yet strong.

The Concept:

We thought it would be really cool to have the ability to push a button (hidden) and have the door be able to open (not all the way) and then be able to close. We would have some LED lighting and a plushy "Nezuko" doll inside.

I was thinking along the lines of a linear actuator like this, hooked up to a small battery pack and remote system. I would hinge the linear actuator at the bottom, hinge side of the door, so if was a shorter stroke one, it would pop the door open 45 degrees. Would want the door opening and closing to be somewhat slow - definitely not super fast.

Obviously weight is a concern as we are wanting the box to be as light as possible as it will be worn for hours at Comic Con conventions. An actuator or servo that could run off a USB Battery Bank (3-5vdc) would be optimal.

Anyone with any thoughts or input on how we could simply achieve this action would be much appreciated!! Thanks!

 

[laellee]

With that size of the door and the relative weight, a linear actuator is a good choice for the force you need. Most actuators I have worked with were 12v so I had to put together a rechargeable battery pack to mate with it; you can find all kinds that will work on Amazon/aliexpress/etc.. Mate that with a 12 volt remote system (aliexpress/etc again) and you should be good.

 

[Boneman]

Ordered everything off Amazon and tested it out today. Everything seems to work very well and all for $130CAD.

The next step is figuring out the correct location and position to mount the linear actuator.....

 

[laellee]

Nice!

Just my two cents, but I would put the actuator at the inner bottom perpendicular to the closed door, a lot like a screen-door cylinder location; out of sight for the most part. That's awesome that you're actuator has that much 'throw' on the arm, I've had ones that were a 1/4th of that

If your actuator has enough strength to handle it, I sometimes add a couple of slots for neodymium magnets on the opening-edge of the door to secure the door when it's closed. The actuator will hold the door closed fine, but between the linkages can have enough play to let the door jiggle a bit with movement; especially on a backpack that is swinging around/etc.... Anyways, my OCD always hated the wiggle room, so I would cheat and let a couple of magnets help

 

[Boneman]

Nice!

Just my two cents, but I would put the actuator at the inner bottom perpendicular to the closed door, a lot like a screen-door cylinder location; out of sight for the most part. That's awesome that you're actuator has that much 'throw' on the arm, I've had ones that were a 1/4th of that

If your actuator has enough strength to handle it, I sometimes add a couple of slots for neodymium magnets on the opening-edge of the door to secure the door when it's closed. The actuator will hold the door closed fine, but between the linkages can have enough play to let the door jiggle a bit with movement; especially on a backpack that is swinging around/etc.... Anyways, my OCD always hated the wiggle room, so I would cheat and let a couple of magnets help

Now I left with trying to figure out where/how to mount the actuator......lol.....

 

[laellee]

Just take off the buckle ends, drill a hole in them, and screw/bolt them to your door and box. You'll have to test the extension of course to get the right spot, but that's to be expected. The whole unit can be installed with two bolts

Check out my AWESOME paint skills

 

[Boneman]

Thank you laellee for your drawing (and superior MS Paint skillz!!) and pointing us in the right direction! Big help!

Well through some trial and error, not to mention some dumb luck, found the mounting locations for the actuator so the door half opens and closes. We only want it half opening so worked out well. This would have been a LOT easier if we did this process BEFORE we enclosed the box - would have been much easier with the back, or even the top, removed.....

Happy with how it functions and really nice to have built in limit switches in the actuator to auto stop the piston travel.

Daughter is super happy with it (so am I)! Still had a lot more work and have a roll of 12vdc pink LEDs to go inside as well and then doing our best to 'hide' as much as possible with a false bottom and black cloth.

I'll post up completed pics and video when fully done.

 

[Boneman]

We pretty much have it all sorted and finished. Now with LEDs and a false bottom to hide all the electronics. Very happy with the results and thanks to everyone for their input!

 

[laellee]

That came out beautifully! Thanks for posting the pics and video as well, it helps to visualize what can work for other projects too.

Which power pack did you use? I have bought the cheap Chinese 12v packs before with mostly good luck, but some features were a little finicky. One example, the pack would charge ONLY if I had the pack switched to the on position while charging; otherwise, no charging, and there wasn't an indicator light either way. Not a huge deal, but took me a day and a multimeter to figure it out lol

 

[Boneman]

That came out beautifully! Thanks for posting the pics and video as well, it helps to visualize what can work for other projects too.

Which power pack did you use? I have bought the cheap Chinese 12v packs before with mostly good luck, but some features were a little finicky. One example, the pack would charge ONLY if I had the pack switched to the on position while charging; otherwise, no charging, and there wasn't an indicator light either way. Not a huge deal, but took me a day and a multimeter to figure it out lol

The power pack was a 'cheap' one from Amazon and yes it also has to be switched ON to charge.

Amazon.ca

 

[laellee]

The power pack was a 'cheap' one from Amazon and yes it also has to be switched ON to charge.

Amazon.ca

Well I know my problem lol. I want to say my last one was about 1/2 the price, 2000Mah, had one green-to-red indicator, and didn't come with a wall charger It was a personal project so I went super cheap, but I also (obviously) got what I paid for. I'll give this one a shot next time, thanks!

 

[Boneman]

Well I know my problem lol. I want to say my last one was about 1/2 the price, 2000Mah, had one green-to-red indicator, and didn't come with a wall charger It was a personal project so I went super cheap, but I also (obviously) got what I paid for. I'll give this one a shot next time, thanks!

So far testing this power supply seems to work ok and has held a solid charge for over a month now. We'll put it through it's paces early next year, but going to run some more tests at home like leaving the LEDs on all night and see what happens.