A Line-us Clone 2.0: The Arms and 3d Printing Misfortunes

I spent the weekend starting on designing the robot. A few things have changed since I started the project. I’ve been trying to figure out how to feed the robot the images and finally decided on an idea. I’m going to write a python program that works as paint whilst remembering how the paths/drawing is drawn by logging the x-y coordinates of the lines. It’ll be a simple program that will output the x-y coordinates to an output file of some sort that will then be loaded onto the MCU.

I then went back and deliberated whether I needed the PSOC to be the MCU as it is probably overkill. I think I may switch to a teensy, but I haven’t quite decided yet.

I also started designing the physical robot itself. I started with the arms as it was one of the more crucial parts of the project. I started by trying to print the gearheads of the servo into the arm with poor success. My 3D printer has a 0.4mm nozzle so getting the definition of the micro servo’s gears were difficult. I then decided to switch back to my original idea of using the servo arms and incorporating them as part of the robot arms. That worked out much better. I had real struggles with the tolerance on my 3d printer as I wanted the bearings to all have a press fit. I managed to get some and not on others. It was a real hit-or-miss for a while until I managed to calibrate my printer. Just shows that I need to be using that printer more often.

I had particular issues trying to get the pin for the middle of the bearing made. Because the bearing I’m using was so small (3mm x 3mm x 7mm – requiring a 3mm pin), the printer tended to overheat the print causing it to melt sadly as it grew. 

You can see the deformation at the base. This caused the bearings not to sit well on the arms. I tried reducing the size of the pin to compensate for that. Finally, by a stroke of luck, when I printed one of the prints at ulti-quality (printing it slower) it came out perfectly. I then figured that the nozzle was probably applying too much heat on that small surface area. I then decided to print a smaller test print of the same height a little away from that print so that the pin had time to cool after each layer.

Prior to figuring that out, I decided to heat one of the pieces with a lighter and smoosh a bearing on top in hopes that it would form to the bearing. It didn’t. I would not recommend this. Lessons were learnt

I also tried using glues and toothpicks to adhere the bearings to the plastic. Turns out hot glue does not stick to metal bearings well and elmer’s glue… well doesn’t work. It probably would have been easier to just screw everything together, but I was really aiming for that sleek look.

I finally figured out how to get the perfect prints after many many iterations. Here are some of the scraps with the 2 arms on the right actually being useable. There were more scraps that were lost during the prototyping process that aren’t in these pictures.

3D printing lessons were learnt this weekend, but overall I managed to get the arms all designed and mostly printed. I’m still tweaking the dimensions slightly to get an oh so much better fit. Unfortunately 3D printing is not like machining. I think I need to build more often as this tweaking took longer than it usually would have took me.