really weren’t many major problems or challenges.
The first problem I encountered was the servos I’d
harvested from an old four-channel RC helicopter. They
were basic unbranded micro servos, and although they’re
not bad to begin with — especially considering the low cost
involved — they’re designed to be harnessed to the
helicopter frame, so the servo housing base plate is not
secured to the rest of the housing with four screws like you
would usually see.
This meant the plate kept popping off, grease inside
was leaking out, and they really weren’t secure like regular
servos. Initially, I put a rubber band around the whole
housing which stopped the insides from popping out.
However, despite this, in the end they just weren’t up to the
task — a few stripped gears and a failed motor appearing
as time went by.
As I have been flying e-Flite Blade RC helicopters for
several years, I knew their micro servos were reliable,
strong, and relatively cheap. So, I went ahead and bought
six servos to replace the others at a reasonable $17 each.
The next hurdle was the Arduino. My coding
experience with C and VB was many years ago and totally
removed from microcontrollers. The ultimate end result of
this project was multiple servos doing multiple things at the
press of a single button (four buttons/functions in total), so
it was a steep learning curve.
However, after discovering the online community,
downloading a few sample sketches, and blowing away the
coding cobwebs in my head, I wrote my first basic sketch to
move a servo using PWM (pulse width modulation).
It was really easy, and the code is simple to
understand. So, all in all, the challenges were fun, relatively
easy to work through, and not daunting “can’t sleep at
night” problems. The beauty of the Arduino is the massive
community online with help just a search away, along with
great write-ups on various websites such as Arduino.cc,
Adafruit, and SparkFun. Plus, there’s the articles available in
issues of SERVO and also Nuts & Volts
Fast forward one year and I built an all metal version of
a similar hand. This time, I used spring wall anchors/toggles
for knuckles and 10 pound braided fishing line for tendons.
Once again, I used parts that could be easily found at a
hardware shop along with the same Arduino Uno and e-Flite micro servos.
The metallic hand looks a bit cooler — in a Terminator
way — like an exoskeleton. It has full wrist rotation and
wrist flexion/extension movement, along with finger
splaying/adduction (although I never finished that function).
I am now working on version 3, made mostly of 3D
printed parts, and using linear actuators I designed myself
and am currently configuring. It is much more efficient,
precise, and compliant, and the pipe dream is to make an
inexpensive, capable, and modular mechatronics kit for kids
If that works out, and as the design improves, my
ultimate vision is to make affordable, easily customized
prosthetics for lower limb amputees. SV
Arduino.cc; Adafruit.com; Sparkfun.com
SERVO 08.2015 35