Robotic Finger

Project Objective & Background

In my efforts to find a starter robotics project, I discovered the InMoov open source robot, and decided to start with the finger. The STL starter files are from the InMoov Website but getting the finger working was still a challenge and required some custom parts. 

Motor Mount

Though a motor mount was included with the files, it was too large for the servo motor I wanted to use, the MG90s, so I needed to redesign the part. I also had to drill out all the holes to fit screws in. 

Included Mount

V1 attempt required modification via saw

V2 included the additional space and mounting hole for a toggle switch

Videos

Though the guide recommends printer filament for the pulley wire, I started with paracord since that was what I had available. Due to fraying issues, I switched to fishing line which proved to be easier to thread through the finger pieces.

I wanted to make the finger move based on the switch position, so I added a toggle switch to the Arduino-powered circuit. While tinkering with the code, I accidentally caused the finger to slam into the table and unspool itself, and also caused the motor to burn out. Some scraping with a knife to widen the pulley track and replacing the motor fixed all the problems! 

Final assembly with the working toggle switch control

Summary

I printed and built a multi-jointed servo motor-driven finger using existing STL files but with a motor mount of my own design. I also added the toggle switch functionality to the code.

Challenges

Problem: One motor mount design did not account for the pulley wheel attachment and had material blocking the spot

Solution: I cut off the excess base using a scroll saw so I could use the mount immediately, then made a new model accounting for the space and for a toggle switch mounting hole

Problem: The paracord frayed quickly and did not maintain tension on the pulley wheel

Solution: I had to unthread the cord completely and replace it with fishing line, which proved to be stronger and much easier to manipulate

Problem: The pulley wheel was too shallow for the fishing line, causing the line to come off the track when the finger moved

Solution: The line was already threaded through the finger links and tied to the pulley wheel at the right length, so to avoid reprinting the pulley wheel and disassembly, I painstakingly scraped out the track with a knife to increase the depth and width.