recent availability of
much cheaper units
have made them
attractive for use in the
smaller 1-12 lb weight
classes.
The ESC I used in
our beetleweight was
the Turnigy TR35A-V2
from www.hobby
king.com and it cost
less than $40. As
delivered (Figure 3), it has a small
fitted fan, long cables, and a
separate on/off switch; it weighs a
total of 2. 5 oz. The fan is too fragile
for use in a combat robot; the
switch is another failure point; and
the wires are too bulky and heavy. I
removed the fan (it’s held on by only
two small screws) and clipped off its
power cables close to the ESC’s
circuit board. The wires for the
switch were cut about an inch from
the board, stripped, soldered
together, then protected by some
heatshrink.
The other wires were shortened
and new connectors added to match
the type I use in my other
beetleweights (so we can use the
same batteries). There was also a
large capacitor that was held in
place by the fan, and that was
secured using a dab of Shoe Goo®.
The result (Figure 4) is much neater
and almost one ounce lighter.
The ESC is best programmed
using the optional programming
card (Figure 5). The various options
are explained in the manual that
comes with the ESC. I initially tried
out the brake function but found
it stopped the drum very abruptly
FIGURE 4
FIGURE 3
and applied too much stress to the
pulley on the weapon motor. I
reduced the braking settings to zero
and found that the drum still stops
and reverses quickly enough for it
not to be a problem. I used the
rudder function on my TX to operate
the forward, stop, and reverse of the
motor. After a few problems with
calibration (the lights did not come
on as per the instructions), I had it
running well. The rudder stick is
spring loaded so it always
returns to the center “off”
position if released — a useful
safety feature. The ESC also fail-safes correctly if it loses the
signal from the TX.
Weta had its first
competition at Motorama in
February and the reversibility
of the drum really proved very
useful and allowed us to win
at least two fights we would
have otherwise lost. Removing
the fan did not create
overheating problems since the
“cruising” amps to drive the
drum were well below the rating
of the ESC.
We went on to take 2nd
place in the 3 lb class. Weta’s
fights can be seen on You Tube by
searching for “Weta” and
“Motorama.”
Hobby King also has 60A and
18A versions which could work in
hobby and antweights. The 35A we
used and the 60A version both run
on 3S LiPo (with the 18A one only
for 2S). Some reports say that the
60A will run on 4S, but that has not
been confirmed. SV
FIGURE 5
MAN UFACTUR IN G:
DIY CNC f r CAD/CAM
● by J. Miles
When I get ready to start building a new fighting robot,
the first thing that I do (besides
daydream at work about what I
want it to look like!) is sit myself
down in front of a computer and
SERVO 05.2010 27
