Page 207 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 6 Options for Creating and Controlling Motion 185

Using hydraulics is a bit like working with AC power. You want to make sure you
know what you’re doing before you try, or the consequences could be lethal. The
equipment also tends to be very expensive. The high pressures and forces that
hydraulic systems can create aren’t usually necessary for the kinds of projects this
book encourages.

Pneumatics
The field of pneumatics deals with gas-driven mechanisms. Gases are compressible,
and they can store the energy it takes to compress them for later use. Pneumatics are
normally used at much lower pressures (around 100 psi) than hydraulics, which makes
them much safer. Pneumatic actuators are used where electric motors are dangerous
(as in underground mines) or impractical (as in common dentistry tools). Pneumatic
drills and nail guns are commonly used for DIY construction projects.

Cheap resources for compressed air include air brush kits, bike tire pumps, car tire
pumps, and portable tabletop compressors. Compressors need electricity to squish the
air before you can use it as a source of power. Black & Decker (among others) sells a
small, portable inflator (Model ASI300) you might find useful for projects in this area.

Air muscles are another technology that uses compressed air. Think of them as a
sealed version of those mesh-woven Chinese finger traps you played with as a kid.
They work by inflating the mesh-woven tube so the overall result is contraction. The
ones from Images (www.imagesco.com/catalog/airmuscle/AirMuscle.html) can
contract to 75% of their relaxed length. You will need an air pump that can reach at
least 50 psi, so a small compressor or even a bike tire pump would work fine.

Artificial Muscles
There are two flavors of materials emerging that contract when you feed them
electrical energy: electroactive polymer actuators and nitinol. Since they mimic human
muscle motion, both technologies are commonly referred to as artificial muscles or
muscle wire. They are attractive options for engineers and designers because they
could potentially take up much less space and be lighter than motors, leading to
mechanisms with more human-like actuators and motion. However, the technologies
are immature, require high current, and can be hard to apply.

Shape Memory Alloy
Wire made of nitinol (a nickel-titanium mix) is one example of a material that will
shrink when heated past a certain point, and then return to its original length at