Issue with print cooling fan on Hemera tool

Discussion in 'Tool heads & ToolChanger' started by dc42, Jan 25, 2021.

  1. dc42

    dc42 Well-Known Member

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    I have two Hemera tools on my TC, design is based on Greg's but using two Duet 3 Tool Boards as described at https://miscsolutions.wordpress.com...l-changer-to-duet-3-with-hemera-tools-part-1/ and subsequent entries on that blog. The print cooling fans are 12V versions of the Winsinn centrifugal fans used in the original Bowden tools.

    I noticed that the print cooling fan on one of my Hemera tools didn't always start, so I removed the fan duct assembly to investigate it. What I found was that the Winsinn fan doesn't work when its back is mounted right against the Hemera stepper motor. It needs at least a 1mm gap to run well. A 2mm gap is sufficient for it to run at full speed.

    This issue isn't unique to the Hemera stepper motor, the fan also stops if I hold the back if a different stepper motor against the back of the fan. So I need to modify the fan duct to hold the fan slightly away from the motor.
     
  2. ByteSized

    ByteSized Member

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    That's an interesting observation David. I'm in the process of switching my Titans for Hemeras so happen to have a Hemera tool sitting on my bench, and some spare 24v fans, so I did some testing.

    This tool is built using Greg's default printed parts, the fan is a 24v Winsin, the gap between fan and motor is 0.9mm, the fan runs at or close to full speed and I couldn't make it stall even when I dismounted it to remove the gap. I also have 2 other, apparently identical, 24v Chinese fans (not Winsin) which I tested against the motor in the picture: 20210126_153510.jpg
    One fan slows appreciably when close (<1mm) to the motor, but doesn't stop, the other fan stalls completely at <1mm and doesn't restart until >5mm. Slightly offsetting the fan from centre actually makes it slightly worse, but against the side of the motor causes no problems. All these fans look identical, I doubt there is anything intrinsically different about the Winsin fans, it is more likely going to be pot luck whether a given fan works close to the motor back.

    Gregs tool mounts don't have enough gap between tools to move the fan without first redesigning the tool mount, however a bit of experimentation shows that a thin ferrous metal plate between fan and motor seems to solve the problem (even just a 0.5mm feeler gauge is enough if positioned behind the centre of the fan). I'm going to hunt on Ebay for thin metal sheets and retrofit all my tools with a metal backplate.

    Now if only I could think of a snappy name for it...


    "ByteSized backplate" anyone?
     
  3. dc42

    dc42 Well-Known Member

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    It's nice to see that I am not the only one who sees this issue. My guess is that the Hall sensor that senses rotor position is close to the back of the fan, and when it is close to a metal surface, the eddy currents in the metal surface weaken and delay the changes in the magnetic field.

    Thanks for the info about a ferrous metal plate fixing it, I may try that. Perhaps a piece of tin can well suffice. For now I just filed the three mounting holes in the printed fan duct parts to an oval so that I could move the fan away form the motor a little, however the fan still isn't running at full speed.
     

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