FIGURE 1. Micro Power Data Logger.
FIGURE 3. Power panel.
was difficult. It would move too fast,
so most of my measurements were
done with the wheels up or against a
wall, wheels spinning. Wheels-up
testing detected gearbox problems
effectively. Bad mechanical
conditions showed higher that
This worked okay for most of my
needs. But as my lifter got more
powerful, I found the need for faster
measurement. Some events, like the
1/2 second of the lift, were not
visible in the display of the watt
meter. A data collection device with
sufficient samples per second was
needed. The Micro data logger from
Eagle Tree Systems fit the bill.
The Micro Power E-Logger from
Eagle Tree Systems (www.eagle
treesystems.com) can measure
±100 amps and 4. 5– 45 volts. It
calculates amp hours and watts. All
FIGURE 4. Installation
in a robot. This is small!
this is recorded in memory for
later retrieval. Sampling rate is
10 per second. Data retrieval is
via a supplied USB cable. The
PC software is also provided
(see Figures 1 and 2).
Real-time amps, volts, watts, and
amp hours can be displayed with the
optional Power Panel LCD. Think of it
as a dashboard for the robot (see
The entire combination is half
the size of the Astro watt
meter. Figure 4 shows installation in
a 12 lb robot.
Preliminary setup prior to first
use is required. The data logger has
many add-on devices. What is
installed — like the LCD display —
must be declared for them to work.
For my tests, the LCD was the only
extra device. The current and voltage
detectors on the data logger are
The instructions for what data to
collect is also required. I displayed
volts, current, amp hours, and
wattage. Volts and amps are direct
from the on-board sensors. Wattage
is calculated from volts and amps.
Amp hours are calculated
from amps and time.
With the LCD panel,
you may conduct real
time monitoring such as a
wheels-up test. You do
not have to retrieve the
collected data. If the
buffer gets full data,
collection simply stops.
The real-time display of
displayed volts, current,
amp hours, and wattage
will continue. (Just this is
pretty cool.) The unit is small and will
fit anywhere. I usually use masking
tape to hold everything in place.
A new recording session is started each time the logger is turned on.
Plug it in to the battery circuit after
the power switch. I find it helpful to
script the sequence of events ahead
of time. Once the data is extracted,
current draw will be your only indication to tie the section of the trace to
the test event. A wheels-up test at
full power may be indistinguishable
from full speed reversals on the
ground or from wheel spin against
the wall. So noting which test was
done first allows you to link the first
peak in current draw with that test.
After the tests are done, turn off
the power. Remove the data logger
from the robot and bring it to
your computer. Start the software.
Connect to your PC with the provided
USB cable. The connection will power-up the data logger and connection
will be established. We now have to
explicitly request data from the device.
Until the memory is full, you may
plug the logger again and again to
collect more data. Each power-on is
easily distinguished as a new session
in the graph. For example, I could
save five separate test sessions in the
data logger before I had to clear data
and start over. I saved the data to the
same file name and each time I did
another test, all of the data from the
previous test was still in there. No
problem! The saved file just got larger each time I saved to the hard drive
(see the sample graph in Figure 5).
I encountered one problem after
clearing data memory and running a
few more data collections. I retrieved
28 SERVO 01.2008