had its price cut in half. Gens Ace Tattu specializes in
batteries for RC airplanes and drones, so we had a
suspicion this specific pack was being cleared out because it
was too big for a drone that wasn’t meant to be flown into
The last major electronic components were the speed
controllers. In both Troublemaker and Protobot, we ran
Victor 884s and 885s, but those would not be nearly
enough to handle our Ampflows. The stall current on the
Ampflows was 390A, and we had no interest in burning
out our speed controllers. We really liked the current-limiting feature on the Ragebridge 2.0 that we run in
Troublemaker, but we were concerned it wouldn’t be able
to supply the continuous current we needed for our long
Fortunately, there was another option that would give
us both the continuous current and current limiting that we
were looking for. The Pro Victor BB speed controllers from
VEX are new versions designed specifically for combat. The
BB can supply up to 300A continuous; can operate at input
voltages up to 50V; and has current-limiting capabilities.
These impressive features come encased in an aluminum
body with a forest of fins for heat dissipation.
Four beefy (but delightfully floppy) eight gauge wires
extend from the body, and the controller connects to the
receiver with a standard PWM cable. A simple feature that
we really appreciate is the plastic covering from the PWM
connection on the BB that forces the PWM cable to make a
90 degree turn when connecting to the BB, and ensures
that the cable won’t pop out during the rough and tumble
of a match.
One of the simple things that seemed strangely missing
from the BB documentation was an identification of the
four wires (red, black, white, and green) coming out of the
controller. We felt fairly comfortable that the controller
would not defy convention and that red would correspond
to power, black to ground, and white and green to the
motor leads. It was still strange that we saw nothing in the
documentation actually saying so. Maybe we missed it and
it really is in there somewhere, but it still made for some
trepidation when we powered up the drive train for the first
time. However, we had miles to go before we got there.
More than a Feeling, but Less
than a CAD Render
One of our goals with this project was to put together
the drive train without the aid of a fancy CAD program to
show that low-tech classic design techniques can still get
the job done (especially since we don’t have any fancy CAD
programs). Since our design was pretty open-ended to
begin with (carry the cannon, make it cool), we needed to
identify some design constraints to give us some focus.
Twin brothers hack whatever’s put in front of them, then tell you about it.
SERVO 08.2017 55
A28-400 AMPFLOWS WITH SPEED REDUCERS.
THE 26,000 MAH LIPOS FROM GENS ACE TATTU.
VICTOR BB SPEED CONTROLLERS FROM VEX.