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  • Writer's pictureMarcos T Rubino

To servo or not to servo - the grand finale!

And the shade motor is finally complete.

After addressing the existential conundrum of whether to actuate the window shade drive with a boring servo motor/disconnect coupling arrangement or go through the thrill and excitement of developing a new bi-directional overrunning clutch, I reluctantly went with the servo/coupling concept, and the shade motor is now complete.

While a very simple concept, this was a fun project, with plenty of setbacks and learning.

The most important takeaway is that I suck at soldering: I used a standard prototype board and soldered jumpers for the connections, resulting in a circuit board that, while perfectly functional, could very well be one of the contraptions built by The Little Rascals.

My next step, therefore, is to learn KiCAD so I can design and order decent printed circuit boards for my next mechatronics projects.

The shade itself came in with a defect, and after a few dozen phone calls, e-mails and chat in their website, the manufacturer sent me a replacement ... with two defects. Maybe due to COVID they didn’t want the first one back when they sent me the replacement, so I just fixed both myself and now I have 2 shades. It’s just as well, since I have 2 windows to cover anyway!

Now, instead of a voice activated remote control that only works when I’m around (“Honey, please go and tape a sheet of paper to the window, the sun is blinding me”), my wife has a motorized shade controlled by an infra-red remote.

In order to minimize clutter at her workstation I used the same remote that she’s already using for the space heater. Since it’s infra-red and the heater and shade are at opposite ends of the room it works just fine.

The design parameters were met and are as follows:

  • Smaller than 230 x 150 x 150 mm which is the largest envelope for my 3D printers.

  • Actuated by a low voltage DC motor.

  • Moves while the remote’s buttons are being pressed, stops when the buttons are released.

  • The shade can be moved manually without back driving the motor.

  • When the shade reaches the top or bottom limit of travel the motor automatically stops, a blue LED flashes and a buzzer beeps 3 times.

  • No need to reset the end of travel sensors after moving the shade manually or after power failures.

  • Maintenance free.

  • Low cost (who would have guessed?).

As Tom Sawyer found out when getting the other kids to whitewash Aunt Polly’s fence, doing something that can otherwise be a predicament turns out to be a lot of fun when you do it because you want to!

And here are the pre-installation test and of the final result.

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