Arm Calibration at 4x Speed

This video shows a sped up version of how the tattoo machine is calibrated and the results that are subsequently sent to the 3d modeling software. The workflow starts with values going from the TouchOSC app on my Android phone wirelessly to the gHowl plugin for Grasshopper, which is a plugin for Rhino 3d. The data is then sent to Processing using both the gHowl and Firefly plugins, which then splits the strings and sends them to the Arduino. There is no feedback loop whatsoever which means that any flaws in the physical machine wont impact the 3d model. From this calibration test I have discovered five problems that I will need to rework later in the project:

1) At regular speed the threaded rod ‘wiggle’ is not very noticeable, however at 4x speed there is clearly a problem. After some trial and error I found that forcing the pen piece back towards the gears made it run a little smoother, but I hope to find a way to fix this so I am not always pushing it with my finger.

2) Four reference points across the arm is fine, but there should be more points down the arm to achieve a more accurate 3d model. This lack of resolution is really apparent around the wrist and the elbow areas as the transitions are too smooth. I am considering implementing non-uniform sections around those areas that need higher resolution.

3) To obtain all 16 reference points it takes just over 7 minutes which is about twice as long as I had wanted. Some time could be saved by getting reference points in both directions rather than sending the pen piece all the way to the end and collecting the points on the way back. However, because the calibration only needs to be done once per arm, this is not that big of an issue.

4) Things move that shouldn’t. My arm shifted quite a bit during the calibration, the pen piece moves up and down a lot, and the supporting arch moves back and forth a few centimeters. These are my biggest concern right now. I haven’t tried applying a tattoo yet as I haven’t done the coding for it, but I assume any problems with the application of the tattoo will be largely due to these factors.

5) Things don’t move that should. The wires to the pen piece and the third servo (that I still haven’t put in yet) have to switch sides so they don’t interfere with the gears. This can probably be fixed by putting an arch over the gears to keep the wires from getting tangled, but a print of that size will probably be too large for my 3d printer. The first two times I tried recording this video I had to stop the camera because the wires kept getting caught in the gears.


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  1. A robotic tattoo artist - July 15, 2013

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