I've got a couple of crank-open casement windows that are rather annoying to get to. I would like to motorize them. I searched for existing solutions and found them all to be ludicrously expensive. So I want to make my own. I would like some general advice on how to go about this, but I also have a specific question.

Using a luggage scale, I measured the torque necessary to turn the crank and found that it's about 18 kg cm with the window half open, and about 36 to open the window when it's been tightly shut. Shopping around on Amazon shows plenty of motors that can do that with ease. But how do I attach a motor to the crank stud? That's where I need advice.

Removing the crank shows that the crank stud is splined with 12 teeth. What sort of coupling do I use to attach to that?

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    Hello, and welcome to Home Improvement. This will probably be closed as off-topic, but let's see how others react. And, you should probably take our tour so you'll know how better to participate here. – Daniel Griscom Jun 17 '19 at 0:07
  • If you do build this and your cost is less than buying one. Get a patent on it. – user101687 Jun 17 '19 at 1:45
  • A universal joint (amazon.com/Craftsman-Drive-Universal-Joint-4280/dp/B0195UU69U) and something like (amazon.com/dp/B00B019RXY/…) or whatever, even an old handle, shaped toaccpet the 1/4" drive – noybman Jun 17 '19 at 3:01
  • the big problem, in my mind, isn't with getting enough tourque, it's with knowing when to start and stop the motor. You need a homing procedure. It should also handle power outages with the window open, where it would be easy to lose track of the position. If you operate it all manually, like an old car window, then just a slow drive should suffice, with two buttons: open, close. – dandavis Jun 17 '19 at 17:20
  • that can be done with limit switch(es), or current draw cutoff (not ideal in this application). There are options. The cost gets more, since this needs to be safe and will need AC & GFCI, and if this motor requires DC, then there is a sufficiently sized power supply – noybman Jun 19 '19 at 3:53

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