Alexa Enable Bar

How to build an ‘Alexa Enabled Secret Bar!’ Part 1: Mechanics

Last updated on 9th April, 2021

We all had our projects during one of the many lockdowns and an ‘Alexa Enabled Secret Bar’ was mine! This project started out with building two industrial sideboards for the corner of my dining room. The question: what to do with dead space in the corner? The answer: a pop up unit that made full use of that space. And hence, the idea for an Alexa Enabled Secret Bar was born.

In this 3 part series of posts, I’m going to give you a good idea on how to build your own version of an Alexa enabled secret bar. But, at the end of the day, this is just a stepper motor hooked up to a WIFI enabled controller. So I am sure there are many other projects you could do with this method. Automated blinds, window/door openers, extending shelve….you get the idea! I’d be really interested to hear about any project to get up to.

If you haven’t already, check out the video of the finished project. I started writing this post but it has quickly grown! So I have split this into 3 separate posts:

  1. The Mechanics
  2. The Electronics
  3. The Firmware & Software

Part 1: The Mechanics

I spent a lot of time over thinking this one. Initially I was inspired by This Old Tony and his amazing Scissor Lift. I started out on this path but soon discovered that the initial torque required to start the lift was way more than any of my little motors (and my little arms!) could turn.

Next I thought about using electric actuators – this would have been perfect but I struggled to find any with a reasonable extension to body ratio. I didn’t want a stubby little shelf popping out – I wanted to use as much of the space as possible.

Finally I decided to use a method I used in the past on CNC machines and 3D printers. A stepper motor and lead screw. This allows me to use parts I already have lying around, it means I can make full use of the space and the torque required is constant throughout the lift. There are a few downsides though, namely speed. For example, with a 2mm pitch leadscrew and a 200step motor: I would need 60,000 steps to open my bar!

The Frame

For the design of the frame itself, I decided to use the same steel tube construction as I did on the industrial sideboard post. The big difference with this unit is that, since it is in the corner, it doesn’t need any wooden sides. This also means you don’t need all those corner tags! There is one important tag you do need though: for the stepper motor. I was planning to use a Nema23. For this, I didn’t quite have anything wide enough so I mounted the stepper on a 45degree angle to the frame. I’m sure I’ll come to regret this decision at some point in the future but for now, it’s all good!

The Drive Mechanism

The next challenge was how to support the shelf and all the contents of the bar whilst going up and down. I needed to incorporate a linear bearing. I’ve already gone into quite a bit of detail on liner bearings so I won’t rattle on here. After a lot of thinking and chatting to my good engineering buddies (thanks Ben!) I decided to go for a set of roller bearings directly on the steel frame. This design had two major bonus’. First – beautiful simplicity! And the second is the fact that the weight of the shelf results in a bending moment about the frame which then helps to steady the cantilever. Hence, the more alcohol in the bar, the smoother the ride!

The downside to this linear bearing set is that the entire weight of the shelf and bar contents was now being transferred through my leadscrew! If I’d just hook everything up to my stepper motor as is, I’d sure the bearings in my stepper would have went bang pretty quickly. So instead I mounted a thrust bearing under the leadscrew coupling. When I did the final installation, I followed the below procedure to apply some preload on the bearing:

  1. Secure the leadscrew nut to the shelf
  2. Position the thrust bearing on the stepper motor housing
  3. Install the coupling onto the leadscrew and tighten the grub screw
  4. Load the leadscrew into the leadscrew nut
  5. Position the coupling on the stepper motor but do not tighten the grub screw
  6. Next, loaded up the shelf with weight. This, in turn, loads up the thrust bearing.
  7. Finally, tighten the grub screw onto the stepper motor.

Effectively following this procedure preloads the thrust bearing and make sure that the stepper motor doesn’t take the weight.

The keen eyed among you might have noticed that I have not support the leadscrew at the top. This was fairly deliberate. I wanted to leave everything as flexible as possible to all for the low precision of my linear bearing mechanism. Leaving the leadscrew does lead to a little bit of leadscrew whip which would be unacceptable for a CNC application. But for a pop up bar…I’m fine with it 🙂

Finishing Touches

The final part on the mechanical side was to build a wooden box complete with mini shelf, LED strip recess and touch button recess. The overall box was made so it could be dropped into place and rested on the shelves when the bar unit was installed in the corner of the room. This also means that if there is any slight misalignment, the top of the bar can actually move slightly. A little bit of vanish and some jazzy wallpaper and the bar section was done!

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