Hello!
I’m starting to assemble the upgrade kit to version 4.1.
While assembling the control arm, the spool keeps getting stuck in the new arm part.
I’ve attached two explanatory videos.
I tried sanding the inside of the spool to reduce the friction, but even after several minutes of sanding, the spool still fits quite tightly in several sections of the arm.
Does anyone have a trick to make this easier, or would applying some lubricant be recommended?
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With the drill I polished the head of the arm screws a little too
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I ran into this also (4.1 Arms & Spools Are Tight - #2 by stuart_powles) and did some light sanding on them. While still not free spinning once assembled, the motors do not have any issue with a lower force setting to extend or retract the belts.
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Nice trick ! Will try and get back with result.
Was just using sand paper inside the spool..
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I only sand the part of the arm that doesn’t have a belt, the part opposite the one that carries the motor. After several work cycles, the toothed reel that holds the belt tightens a little due to the tension the belt accumulates, so I don’t want to sand this part to avoid weakening it.
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Awesome technique with the sand paper!
I am also happy to send you some new parts 
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