SERVO 07.2015 23
Building Better Bots:
The Power of the Watt Meter
● by Russ Barrow
So, you’ve mastered the calipers (even if you can’t quite seem to keep it
turned off), figured out how to
use the voltage and continuity
dials on the digital multimeter,
and are pretty sure you have the
scale figured out (except for that
awkward triple beam balance
thing). So, what about that watt
meter that all the cool builders
are using? Should you spend the
money and energy into this black
box that fits between your
batteries and the robot?
The short answer: Yes, you
should. Watt meters have
dramatically reduced in price over
the years, and include all kinds of
features that not only can be used to
observe operational conditions of
your robot, but can help you design
a machine that will work more
efficiently and eliminate many
headaches that will cost you time
and money later.
Let’s see “whatt” all we can do
with this new tool.
What is a
Watt Meter?
A watt meter is an instrument
used to measure the power a system
consumes as a factor of time. They
typically consist of an insulated
sensor with a display, with source
and load wiring on each end. The
meter is placed between your power
supply or battery, and the system or
robot that is consuming the power.
Ohm’s Law tells us power is
equal to voltage (potential energy)
multiplied by current (flow of
electrons), represented by P = I x R.
So, a watt meter will provide a
summary of current draw and
voltage as consumed by the load
over time, measured in watts.
So, at a minimum, a watt meter
will provide a real time measurement
of voltage and current. However,
most also include peak rating
capture, amps or watts per hour,
and perhaps even logging
functions. Figure 1 is an
example of a simple high current
watt meter.
Baseline and
Inspection
Some of the new online
hobby stores and web products
have revolutionized robot
building. The perfect motor or
battery is merely a click away
and as far as pricing, bargains
are to be had everywhere. As far
as quality, well, there is always room
for improvement. Whether a product
is going to work as advertised often
depends on the first test.
Unfortunately, too many of us
are confirming successful operation
by listening to a sound it makes,
how hot it gets, or if smoke comes
pouring out.
Figure 1.
Personal CNC Mills
www.tormach.com/servo
PCNC 1100 Series 3
$8480
(plus shipping)
starting at:
Shown here with
optional stand
and accessories.
Shown below is an articulated humanoid
robot leg, built by researchers at the
Drexel Autonomous System Lab (DASL)
with a Tormach PCNC 1100 milling
machine. DASL researcher Roy Gross
estimates that somewhere between 300
and 400 components for “HUBO+” has
been machined on their PCNC 1100.
