[chbot] Home Automation - Curtains

[Andrew Errington]

Thanks Helmut.

I can't attach the cord to the pulley as it is a continuous loop from one
side of the window to the other.  So it must be free to wind "on" on one
side and "off" on the other.

I have made several turns around the drive pulley, but sometimes the
incoming cord winds on top of the other coils instead of next to them, so
it snarls up.  I think I need fatter cord and fewer turns to avoid this.

I need grippy, stretch-free cord, and grippy pulleys with only one turn
around them.  A spring would work for tension, or a rubber band cut from a
bicycle inner tube.  I might try that too.

Thanks,

Andrew

On Sep 25, 2017 5:44 PM, "Helmut Walle" <helmut.walle at gmail.com> wrote:

There are two ways to get traction: rather than just winding it around the
drive pulley, clamp or attach it to a point on the circumference there, so
that it must follow when the wheels are turning... Or wind it around the
drive pulley a number of times - "rope" friction around a pulley is
proportional to the number of turns, everything else being equal. Also, for
keeping it taut, you can use a steel spring; this is quite common in
string-based transmissions.

On 25/09/17 17:38, Andrew Errington wrote:

There's also "fishing line I happen to have to hand", which is clearly
unsuitable in this case.

I'm going to try the builder's line again.  This time with a cable tie that
I can crank down on to get the tension.

Thanks,

Andrew


On Sep 25, 2017 5:01 PM, "Charles Manning" <cdhmanning at gmail.com> wrote:

There's fishing line... and fishing line.

Nylon stretches like anything. Braid (eg. https://www.completeangler.co.
nz/line-95/braid-97/) has practically no stretch and is available in many
colours and strengths.


On Mon, Sep 25, 2017 at 3:51 PM, Andrew Errington <erringtona at gmail.com>
wrote:

> Hi everyone,
>
> I thought I'd start a new thread, as we got away from the relative merits
> of Banggood vs DealExtreme.
>
> I am trying to motorise my curtains, particularly as there are six windows
> in one room, plus home automation is cool.
>
> So far I have identified a suitable motor and gearbox, 12Vdc supply, 60rpm
> output, with good torque and fairly quiet.
>
> At one end the motor, with a 16-tooth GT2 pulley, is attached to the wall
> using a purlin bracket (purlin brackets are cool).  At the other, I am
> using a sewing-machine bobbin on an M6 bolt as a pulley.
>
> It's early days, but I have tried builder's line, which doesn't stretch,
> but does slip.  I have tried fishing line, which does stretch, and slips.
>
> I think GT2 toothed belt would work well, but I haven't tried it yet.
>
> The motor is temporarily connected to a 12V battery for testing.  Later I
> will use an ESP8266 with microPython to control the motor.
>
> Finally, I'll link it to home automation software and relax in my chair as
> the sun goes down and the curtains gently and quietly close.
>
> That's my plan, but there is plenty of room for alternatives or failure.
>
> The attached link is for a belt clamp and tensioner made from zip-ties,
> which I think I will adopt!
>
> Best wishes,
>
> Andrew
>
> http://diyprojects.eu/wp-content/uploads/2017/01/belt-connec
> tion-zip-ties.jpg
>
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