<div dir="auto"><div>Thanks Helmut.</div><div dir="auto"><br></div><div dir="auto">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.</div><div dir="auto"><br></div><div dir="auto">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.</div><div dir="auto"><br></div><div dir="auto">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.</div><div dir="auto"><br></div><div dir="auto">Thanks,</div><div dir="auto"><br></div><div dir="auto">Andrew<br><div class="gmail_extra" dir="auto"><br><div class="gmail_quote">On Sep 25, 2017 5:44 PM, "Helmut Walle" <<a href="mailto:helmut.walle@gmail.com">helmut.walle@gmail.com</a>> wrote:<br type="attribution"><blockquote class="quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>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.<br>
</p><div class="elided-text">
<br>
<div class="m_-5049689764690074579moz-cite-prefix">On 25/09/17 17:38, Andrew Errington
wrote:<br>
</div>
<blockquote type="cite">
<div dir="auto">
<div>There's also "fishing line I happen to have to hand", which
is clearly unsuitable in this case.
<div dir="auto"><br>
</div>
<div dir="auto">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.</div>
<div dir="auto"><br>
</div>
<div dir="auto">Thanks,</div>
<div dir="auto"><br>
</div>
<div dir="auto">Andrew</div>
<br>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Sep 25, 2017 5:01 PM, "Charles
Manning" <<a href="mailto:cdhmanning@gmail.com" target="_blank">cdhmanning@gmail.com</a>>
wrote:<br type="attribution">
<blockquote class="m_-5049689764690074579quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div>There's fishing line... and fishing line.<br>
<br>
</div>
Nylon stretches like anything. Braid (eg. <a href="https://www.completeangler.co.nz/line-95/braid-97/" target="_blank">https://www.completeangler.co.<wbr>nz/line-95/braid-97/</a>)
has practically no stretch and is available in many
colours and strengths.<br>
<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">
<div class="m_-5049689764690074579elided-text">On Mon, Sep 25, 2017 at
3:51 PM, Andrew Errington <span dir="ltr"><<a href="mailto:erringtona@gmail.com" target="_blank">erringtona@gmail.com</a>></span>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="m_-5049689764690074579elided-text">
<div dir="auto">Hi everyone,
<div dir="auto"><br>
</div>
<div dir="auto">I thought I'd start a new
thread, as we got away from the relative
merits of Banggood vs DealExtreme.</div>
<div dir="auto"><br>
</div>
<div dir="auto">I am trying to motorise my
curtains, particularly as there are six
windows in one room, plus home automation is
cool.</div>
<div dir="auto"><br>
</div>
<div dir="auto">So far I have identified a
suitable motor and gearbox, 12Vdc supply,
60rpm output, with good torque and fairly
quiet.</div>
<div dir="auto"><br>
</div>
<div dir="auto">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.</div>
<div dir="auto"><br>
</div>
<div dir="auto">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.</div>
<div dir="auto"><br>
</div>
<div dir="auto">I think GT2 toothed belt would
work well, but I haven't tried it yet.</div>
<div dir="auto"><br>
</div>
<div dir="auto">The motor is temporarily
connected to a 12V battery for testing.
Later I will use an ESP8266 with microPython
to control the motor.</div>
<div dir="auto"><br>
</div>
<div dir="auto">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.</div>
<div dir="auto"><br>
</div>
<div dir="auto">That's my plan, but there is
plenty of room for alternatives or failure.</div>
<div dir="auto"><br>
</div>
<div dir="auto">The attached link is for a
belt clamp and tensioner made from zip-ties,
which I think I will adopt!</div>
<div dir="auto"><br>
</div>
<div dir="auto">Best wishes,</div>
<div dir="auto"><br>
</div>
<div dir="auto">Andrew</div>
<div dir="auto"><br>
</div>
<div dir="auto"><a href="http://diyprojects.eu/wp-content/uploads/2017/01/belt-connection-zip-ties.jpg" target="_blank">http://diyprojects.eu/wp-conte<wbr>nt/uploads/2017/01/belt-connec<wbr>tion-zip-ties.jpg</a><br>
</div>
</div>
<br>
</div>
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