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Zach Allen
Nov 28, 2018
In Robot Builds
I purchased the CAD (SolidWorks) files from Chris’s website so I could make some design modifications and then 3D print. I wanted to be able to export high-res STLs, so curved surfaces were curved rather than triangulated. I printed everything on my Prusa i3 MK3 (8” square build surface) with IC3D Red PET-G. All in, not considering reprinting any parts, it was just north of 70 hours of print time and under 2kg of filament. Maybe the most visible design modification is at the base. I integrated the base and the J1 Turret, as well as the support ribs. This took the longest to print, at around 15 hours. Due to the build surface constraint, I had to cut the J2 arm in half. For increased rigidity, I made the walls taller, similar to the supports Chris recommends when printing. I made some overlaps and printed a separate, bolt-on stringer to tie them together. It’s still a little wobbly, so I may revisit the design. The modification with maybe the most design work is with the J5 actuation. I changed from the lead-screw-driven system to a bevel-gear-driven system. Initial (no load) testing shows pretty good prospect. By tensioning the belt, the J5 extended arm is slightly bent (it’s plastic...), so I may revisit this and go to a more direct-drive system. But for now I’m happy with how it’s working. By changing to the bevel gear drive, I used a geared stepper, which sticks out the back of the J4 arm further. To utilize this space, I incorporated the J4 hub into the J5 motor mount. For the J5 drive pivot on the J6 assembly, I had a hard time getting enough torque on the J5 drive pulley set screw without cracking the plastic. I modified the whole J6 design for ease of printing (modular instead of all-in-one) and used the leftover 8mm keyed shaft from J3 to fix the pulley. So far so good! As for the electronics...that’s the next part of the fun. I plan to make a custom PCB that acts like a shield for the Arduino Mega. It will have screw terminals for the motor driver control wires, as well as for external IO. I’ll also include 2 DC-DC step-down converters to take the 24V from the power supply and output 12V for the Arduino and 5V for the RPi (see next paragraph). That way I can eliminate the 5V power supply. This concept needs validation, so I’ll update this post once I get it sorted out. For actual control, I’ve modified the AR2 software to work on the RaspberryPi. I’m planning to use an RPi Zero W. I have it set up as a wireless access point, so I can access the GUI with a tablet via the free VNC Viewer app (android and iOS). Initial testing shows good prospect, but I need to validate that the RPi can handle the processing. If it works, I’ve got a headless unit - no Windows computer required! That’s all for now, I’ll continue to update this post as I make more progress. Let me know if you have any questions! -Zach
3D Printed AR2+α content media
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Zach Allen

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