Frankenplotter - pen up/down

Where we last left our Frankenplotterhero: X-Y axis movements appeared to be working well, and data was getting to the system via a Java-TTY-Arduino call-and-response mechanism.  I let that run through the entirety of the vector file, and this is what I got:

First significant plot output with test star and "circle" drawings, and first drawing of ship to completion

Another plot without the star/circle test drawings, but with no pen up/down control

The inability to raise the pen was making for a lot of scribbles on the page.  I figured the best explanation was that this was a depiction of the ship traveling at warp speed.

The next step, clearly, was that I needed to find a way to raise and lower the pen.  While doing that, I'd also find a way to get more rigidity at the bottom of the pen so there would be less curvy lines.

Mike and I discussed different ways to get this done, and ended up choosing a solenoid-based approach.  I'd never used one, but went at it with the brash confidence.  I found three solenoids and reasonable slugs at Halted.  I was fortunate in that I had a range of voltage choices -- 5V, 12V, 24V -- since I could get any of those from the various power sources available (either the Seasonic ATX motherboard power supply, or 24V from a salvaged Canon printer power supply).  I ended up selecting a 24VDC solenoid that had a slug where the end of the slug had a funny clip attached.  That gave me different connection options that the other slugs didn't.

To run the solenoid, I simply wired it to through the SainSmart 4-channel relay.  It was loud, but convenient, and could easily handle 24VDC and the amperage required by the solenoid.

Mounting the solenoid and pen was a total hack job.  I chopped up a ball-point pen and used pliers to weaken the top so that I could shove it into the clip at the end of the solenoid slug.  Then, I used whatever wood and metal pieces I could to make it the right height.  The original piece of wood that I'd used for the earlier pen holder turned out to be just the right width to fit in-between some plastic prongs on the printer ink carriage.

Solenoid up-down pen assembly clamped to printer carriage

In this design, the solenoid would activate, raising the pen.  Gravity would let the pen down, and a hole in the metal bracket would help align the pen to a particular location.  It took a bit of fudging things to that the lift and drop wouldn't run into things.

After some tests, though, I wasn't getting much ink on the page, partly because it was a less friendly ball-point pen than I'd used before, and partly because there wasn't much downward pressure on the pen.  Fortunately, I could add a rubber band and clip it to another piece of metal on the mounting bracket so that the pen would be pulled down towards the paper, rather than just relying on gravity.  There was sufficient force in the solenoid and the assembly left the slug close enough to the solenoid hole so that the pen could be lifted, despite the rubber band's downward force.  In the pictures below, the tan-colored rubber band is the one pulling the solenoid slug and pen down.

Merit badge:
- Use a solenoid!