<div dir="ltr"><div><div>Run the cord through rosin<br><br></div>That helps it grip.<br><br></div>Have you considered that cord with little beads on it? See <a href="http://www.goelst.com/uploads/images/Gallery/7400-7800/7800.jpg">http://www.goelst.com/uploads/images/Gallery/7400-7800/7800.jpg</a> tht will engage and drive even if it is not tight.<br><br><br></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Sep 25, 2017 at 6:04 PM, Andrew Errington <span dir="ltr"><<a href="mailto:erringtona@gmail.com" target="_blank">erringtona@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><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<div><div class="h5"><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" target="_blank">helmut.walle@gmail.com</a>> wrote:<br type="attribution"><blockquote class="m_-6942810363844663184quote" 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="m_-6942810363844663184elided-text">
    <br>
    <div class="m_-6942810363844663184m_-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_-6942810363844663184m_-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_-6942810363844663184m_-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_-6942810363844663184m_-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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