Arrakis 2.0 recently developed a minor problem- the ball started shifting while it was drawing patterns and it started making unusual noises. When I opened it up I found that the pulley on the left side motor had come loose, but wasn't completely rotating on the motor shaft. It would rotate a little with some reversals of direction, galling the motor shaft in the process.
I had used some locktite on the set screws for the pulley and couldn't get them to tighten, and could barely get them loose enough to get the pulley off the motor shaft. I installed a new pulley which quieted the mechanism back down and I decided to address a couple things I had been thinking about for a while.
The homing sensors were mounted high on the motor mounts and were easy to break if I was taking the table apart to transport it. I wanted to redesign that part of the mechanism so they sensors and flags could be positioned where they would be less likely to get broken.
There were three parts that needed redesign/print. The magnet carriage, the left side Y axis bearing/pulley block, and right motor mount.
Magnet carriage
The original magnet carriage design had a flag on the top piece which is why the X axis home position sensor was mounted in a precarious position on the right side motor mount. I wanted the sensor to be mounted lower, so I had to redesign the magnet carriage to put the flag on the bottom piece instead of the top piece. I also wanted to make the X home position somewhat adjustable and decided it would be easier to adjust the flag than to adjust the sensor position, so the flag is now a piece of plastic that attaches to the magnet carriage with a screw. The new magnet carriage consists of the old bottom piece that has become the top piece, and a newly designed and printed bottom piece that includes a tab to mount the homing flag.
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| Original magnet carriage. The projection to the left is the flag for the X axis homing sensor. |
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| The new magnet carriage design. The old bottom piece has become the top piece and the flag (black) mounts with a screw so it can be repositioned if needed. |
Right side motor mount
Now that the flag was moved lower, the sensor could be mounted lower, so the newly designed motor mount includes an extra wall to mount the X axis homing sensor. I mounted the sensor using some industrial double-sided tape. If the adhesive lets go, I'll drill some holes and screw the sensor to its mount.
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| The original right side motor and mount with the dangerously positioned X axis homing sensor. |
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| The new right side motor mount with the X axis homing sensor moved to a much safer position. |
Left side Y axis bearing/pulley block
The original design had the Y homing flag glued to the top of the pulley block and the sensor on the top of the left side motor mount, both in easily bumped positions. The new design has the flag printed as part of the bottom piece of the pulley block, and the sensor mounts on the side of the motor using the same tape I used for the X axis sensor.
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| The original left side Y axis bearing/pulley block with the Y axis homing flag glued to the top of the block. |
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| The new left side Y axis bearing/pulley block with the homing flag printed as part of the bottom piece. |
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| The original left side motor with the Y axis homing sensor mounted on top of the motor mount where it could be easily broken. |
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| The new position for the Y axis homing sensor on the left side motor. It is taped to the motor using some double sided adhesive tape. |
Now everything is secure and in positions that are not likely to get bumped when taking the table apart or putting it back together.
