Servo - August 2015

• Button A = Open and close all fingers and thumb together • Set slow speed • Close the four fingers at the same time • Swivel thumb up and close it • Open thumb and swivel down • Open the four fingers at the same time • Button B = Move each finger then thumb independently, slow then fast • Set slow speed • Close and open finger one • Close and open finger two • Close and open finger three • Close and open finger four • Swivel thumb up, close and open, swivel down • Set fast speed • Close and open finger one • Close and open finger two • Close and open finger three • Close and open finger four • Swivel thumb up, close and open, swivel down • Button C = Finger and thumb pinch — “precision” grip of something • Set slow speed • Swivel thumb up • Close finger one and thumb at the same time • Open finger one and thumb at the same time • Swivel thumb down • Button D = Close and open fingers and thumb alternately and fast • Set fast speed • Close and open finger one and finger four at the same time • Close and open finger two and finger three at the same time • Close and open finger one and finger three at the same time • Close and open finger two and finger four at the same time After attaching the tendon string to the first finger and threading it through all the eyelets, I would pull the other end of the string — which closed the finger — across a piece of paper and would mark the position of the end of the string. Then, after releasing the string with the finger returning to open, again I marked the end of the string on the paper.

This allowed me to measure the distance the string travelled, and therefore how far the servo needed to travel to open and close each finger.

This measurement would be used to fine-tune the servo travel angle in the code for each finger.

Using the example Arduino ‘sweep’ sketch, I connected a single servo to the Arduino, secured it to the table alongside the above measurements, and ran the program.

Watching the tip of the servo horn as it moved back and forth, I could clearly see that the travel angle I needed was a full 180 degree sweep. However, the length of the servo horn was too short as it didn’t travel the full horizontal distance needed. So, I made a small wood extension for each servo horn and made sure the distance they travelled once attached to the servo matched the horizontal measurements (Figure 16)

With those key measurements done, it was time to write some code. I started with the basics of attaching the buttons to digital pins: • buttonPinA = digital pin 13