Page 165 - Build Your Own Combat Robot

Build Your Own Combat Robot
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You may hear about number of cells, maybe number of windings on your motor,
and raves about how tiny the ESC is to fit in a small model. But, as a robot builder,
you don’t really care about these specs—you need an ESC that can handle extreme
current loads without frying.
The hobby ESCs that have been proven to be usable in small combat robots are
the Tekin Titan and Rebel models and the larger Novak speed controllers. Larger
robots need more current than hobby grade controllers can deliver.
When selecting a hobby ESC, you need to select one with a voltage rating that is
higher than the voltage your robot’s motors need. Since these speed controllers are
rated in terms of cells, you can divide your actual motor voltage by 1.2 to give you
an equivalent cell rating. Choose a controller that has a higher cell rating.
Next, find a controller that has a current rating that is higher than what your
robot’s normal current draw will be. This is the hard part of the selection process.
You will have to obtain detailed specifications of the ESC—most likely, direct
from the manufacturer, since their current ratings are usually theoretical instanta-
neous ratings. Most hobby ESC’s reverse current rating is lower than the forward
current rating, so the selection process should be based on the reverse current rat-
ing. Although this may be a challenge, the hobby ESCs work well when used
within their designed operating ranges.
Table 7-1 shows a short list of several electronic speed controllers. The maximum
current rating is generally the advertised current rating. In practice, the continuous
current rating for these types of controllers is approximately one-fourth the maxi-
mum current rating.

Manufacturer Model Number Voltage Max Current
Associated F1 Reverse 4.8–8.4 100
Associated F1 Power 4.8–8.4 170
Associated F1 Pro 4.8–8.4 270
Duratrax Blast 6.0–8.4 140
Futaba MC230CR 7.2–8.4 90
Futaba MC330CR 7.2–8.4 200
HiTec RCD SP 520+ 6.0–8.4 560
Novak Reactor 7.2–8.4 160
Novak Rooster 7.2–8.4 100
Novak Super Rooster 7.2–12.0 320
Tekin Rebel 4.8–12.0 160
Traxxas XL-1 4.8–8.4 100

TABLE 7-1 Hobby Electronic Speed Controllers