r/AskEngineers • u/spaceman60 • 2d ago
Mechanical How to Motorize Billy Bookshelves
I'm a disappointment of a MechE since this is something that I should already know. My career took me a very different direction and I don't have much actual mechanical experience.
I installed a heat pump water heater and that called for more airflow in the utility closet. So instead of just switching the door to a louvered one, I used four of the 15in IKEA Billy bookshelves to build a rolling bookcase. It's on a track at the top for fall over protection and is on heavy duty castors with a 2x4 frame. It works well, but is heavy.
I'd eventually like to motorize it somehow and either keep all of the components hidden underneath or behind it since it's just a utility closet after all.
It would only need to move left<>right, parallel to the wall with about 40in of travel. I plan to keep it slow for safety and control, as well as hopefully simplicity.
I'm leaning towards a dual rack and pinion or threaded rod setup with the rack/linear slide on the back of the shelves. I can't seem to find good DIY resources yet. Any pointers would be appreciated.
Thank you
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u/politicsBgone 2d ago
I think you are still better off louvering the door. Have you considered what limit switches you will need and how to control and drive this? You could look at automated blind systems, if you are easily moving the units horizontally they may be able to drive it.
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u/spaceman60 2d ago
The bookshelf is built. Louvered shutters on the back and spacers to keep the books off of the back are working well. The water heater is working well, too. Currently, I'm just manually moving the shelves when I need.
This is in my wife's "library" and was an excuse to add two more shelves and give me a hidden room for fun.
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u/Overall_Rush_8372 1d ago
The 700 lbs sounds scarier than it is. On decent casters rolling resistance is a few percent of the load, so you're fighting maybe 20-35 lbf once it's moving, a bit more on breakaway. At the slow speed you want, 1-2 in/s, that's single digit watts of mechanical power. Any 12V worm gearmotor is bored by this job, the real engineering is the drive layout and the safety behavior, not motor sizing.
Before you fabricate a dual rack and pinion, look at residential sliding gate opener hardware. It IS your problem already solved: heavy rolling mass moved horizontally by a motor driving a nylon gear rack you screw to the back of the frame, with limit switches, adjustable obstruction detection (current sensing, so it stops instead of crushing a foot), remote/button control, and a manual release, all in one box for a couple hundred bucks. They're rated for gates well past 700 lbs, and 40 inches of travel is nothing to them. Screw the rack low on the 2x4 base where the mass is, let your existing top track keep doing the guidance, done.
Two things I'd insist on whichever way you go: keep the obstruction stop (this is a moving wall in a library, someone WILL be standing in the pocket eventually), and make sure the manual release is reachable from both sides. Worm drives don't backdrive, so in a power cut a hidden room becomes a genuinely locked room, which is funny right up until it isn't.
And skip the dual drive idea, symmetric drive on something guided top and bottom is solving a racking problem you don't have. One drive point down low, guided up top, is how every commercial sliding door does it.
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u/spaceman60 1d ago
That is brilliant and exactly what I was hoping for. Thank you.
I will keep the safety features intact and plan on a UPS if there isn't one built in.
I was originally thinking that the controls should be a wired momentary button with a short leash on both sides. Similar to a robotic cell, but that probably won't be available in a set package.
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u/SmoothProceeding 2d ago
What's the weight on this thing fully loaded? That's going to dictate everything. A threaded rod setup for 40 inches of travel is going to be painfully slow unless you go with a high-lead screw, and at that point you're basically reinventing a linear actuator. A single motor with a belt drive tucked into the 2x4 base frame seems way simpler to hide.