The goal of this project was to begin to design a modular 3D printed hand that retains the same motions of a natural human hand and can at least lift an apple. Thus far, a finger with flexion and extension has been designed.

A flex sensor was inserted underneath clips fastened on each link and was used to sense the angle of flexion of the finger. A button was used to switch between the zero and ninety degree states of the finger and because this sensor was on the back of the finger, it would not matter which joint of the finger moved since the amount of stretch in the sensor would be the same, theoretically. This was in fact observed to be the case in the repeatability tests where nearly every attempt to achieve overall ninety degrees in the two primary finger joints (distal-intermediate and proximal intermediate) was able to reproduce this result. This flex sensor was placed in series with a 22 kΩ resistor and the voltage was read across the resistor through an operational amplifier buffer to the ADC of the Arduino Uno used for this test of the finger. Noise was noticeable at lower angles and may be connected to the nonlinearity in that region (it was approximated as linear for the higher values).

Initial tests show that the finger was able to have flexion and extension motions but repeatability still needs work in the extended state and may be fixable by accounting for the nonlinearity of the flex sensor.. The quick loss of function of the wheel may also require a material more capable of withstanding the rotations of the servo (perhaps it would be best to replace the direct link to the servo with a slot for a servo horn). Additionally, the finger is not yet able to perform abduction and adduction, but perhaps this could be accomplished by running the flexion / extension wires through a central rod in each finger.