Well - it is the last day of this marathon design challenge and everything pretty much needs to go flawlessly to produce actual graffiti. But of course a lot of things are not going right. All the subsystems have been tested and are working well, but the bot is just making puddles. I thought the nozzles would be problematic, but the main drive is not running properly, so put on the troubleshooting hat and dive in. It looked like the batteries were dying, so take some time and charge them up. Still no joy. Meanwhile I'm using up all my resources for printing - the "road" I am printing on is blue shop towel - it gets darker when wet. It is handy for absorbing the lakes I am creating, but there is a finite amount of towel. Once it is wet, there is no contrast until it dries out.
Next I'm wondering if the cables can handle the motor current for 10 motors. So - make up some heavy gage cables. Still no joy.
It turns out the battery I am using can only very briefly supply enough current for a full motor load - because the batteries use an internal circuit to generate 5 volts. So I dug out an old (slightly larger) battery I happened to have, and stuck it on. But this battery only had a partial charge and there was no time left to charge it.
So I have enough juice for one run (I think), I have only enough roadway (paper towel) for one run, and I have not gotten it working well enough to sort out the pixel timing or flow rates or steering stability etc. I don't even know how far it will travel, so I don't know how to set up the camera. It all comes down to one last ditch attempt to get something printed ..... no pressure ... only four months of work all riding on 10 seconds of suspense with a boatload of unknowns. Who said there was no drama in engineering?
It is too late to build the suspense any more, so here is the video of that final attempt:
Here is a picture of the full print as it tailed off the road:
It looks a little cleaner immediately after printing ("E"), but the clogged pump is more apparent...you can even see where a drill bit is stuck in a nozzle...
After all the hours of meticulously designing this machine to draw graffiti, it actually works, but GraffitiBot takes a great deal of artistic license in how it presents its work.
I just stood there and looked at it for quite a while.
It was one of those moments you just have to lock in.
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