Servo - August 2015

and ended up attaching the completed thumb assembly at a 45 degree angle to the bottom corner of the palm. I drilled a hole in this point of the palm and also through the last thumb segment, then screwed them together with a small amount of play so the thumb assembly could swivel smoothly.

Elastic for the thumb was two-fold; where the thumb assembly itself has strips of elastic for each segment of the thumb, a single separate piece of elastic is also required to return the entire thumb assembly back to the open palm position.

I attached this piece of elastic to the thumb segment closest to the palm, then anchored it to the forearm. Two small pieces of metal were then screwed to the back of the palm to stop the thumb assembly from continuing to rotate (Figure 10).

Next in line were the tendon guide eyelets. For these, I basically just drilled small holes at the lower end of each finger segment, then cut an eyelet in half and glued the Figure 13. Tendons all threaded and ready. The anchor point to swivel the thumb assembly can be seen at the bottom of the thumb.

Figure 10. The mechanics are complete. The final step was applying the thumb assembly return elastic.

Figure 12. The complete mechatronic assembly. The servo at the bottom of the picture controls the thumb assembly swivel, with the tendon running underneath the servos on the right.