Page 109 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

90 Making Things Move

• Flexiforce pressure sensors are more accurate —about ±2.5%—but are about
twice as expensive as FSRs. However, at around $20, they’re still on the low
end of the price scale for force measurement options. An example is the
SparkFun sensor SEN-08685.
• Luggage/fish scales also come in digital versions. A company called Balanzza
makes popular versions that start at around $15. MakerBot Industries used a
digital fish scale to measure the pull force of its plastruder motor for the
CupCake CNC machine, as shown in Figure 4-13. See Project 4-2 for how it
works and to learn how to make your own version.

The next step up on the price scale is a big one. FIGURE 4-13 MakerBot Industries
Higher-end force measurement tools use fancy used The Rack to measure the pull
force of its plastruder motor.
electronics for precise measurements. They
generally come in two varieties: handheld and
button types that can be integrated into projects.

• Digital force gauges, like McMaster’s
1903T51, start at around $370. You
can attach a hook or a plate to the
measurement end to measure force
when pulling or pushing.

• Load cells, like the MLP-100 from
Transducer Techniques (www
.transducertechniques.com/), start at
around $300. Unless you’re a whiz at
electrical engineering, you’ll also need the
$400 display to read the force. However,
if you need accuracy and a sensor you
can integrate into a project, these are
ideal.

Measuring Torque
Measuring an unknown torque directly can get expensive. You can set a torque
wrench to a certain number and tighten a bolt just the right amount, but torque
wrenches are not really made for measuring an unknown torque. Torque wrenches
start at around $100 and climb up steeply from there.