Page 167 - Build Your Own Combat Robot

Build Your Own Combat Robot
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is difficult without testing it—simply buying the booster cable and using it is prob-
ably the best idea.
Like a hobby-speed controller with a battery eliminator circuit, the Victor 883
controller uses a voltage regulator to produce a 5-volt power source for its control
logic. But, unlike the hobby-grade controllers, the Victor 883 does not feed power
back to the radio receiver, and uses an opto-isolator for full electrical isolation be-
tween the controller and the radio to prevent electrical noise generated by the motors
from getting into the receiver power circuit. Figure 7-14 shows a block diagram of the
Victor 883 electronic speed controller.
The electronics on the Victor 883 are contained on a single small circuit board,
which is encapsulated inside a sealed plastic housing. The controller is highly impact
resistant and does not need special mounting to be safe from impact shocks, al-
though it’s still a good idea to protect all onboard electronics from large shocks.
Take care to ensure that the cooling fan has access to ambient air; the 60 amps
continuos rating assumes that the fan has a constant source of external room-tem-
perature air to blow over the FETs. Sealing a Victor 883 inside a box will have it
circulating the same air over the cooling surfaces again and again, which will reduce
the effective current capacity.
As a final safety measure, Victor 883 controllers ship with auto-resetting
30-amp thermal breakers. Intended to be wired in series with the motor, these heat
up and disconnect the power at a current rating well under what the controller it-
self can handle. After a few seconds, the breaker will cool off and reconnect the
motor. While these will ensure that the controller will not be damaged by over cur-
rents or shorts, they effectively cut in half the maximum current that the controller
can source. While most motors used by robots in weight classes under 60 pounds
usually don’t draw more that 30 amps continuous, many motors in the larger

FIGURE 7-14
Block diagram of
the Victor 883
electronic speed
controller.