PARTS IS PARTS:
Fine-Tuning a Brushless Electronic Speed Controller
● by Pete Smith
My 12 lb Hobbyweight bar spinner Surgical Strike had a
problem at the last couple of
events. If I tried to spin up quickly,
the blade would seem to “stall” at
about half speed and stay there
unless I backed the throttle off and
then backed up again to full speed.
It would then run up to its full
speed.
In most fights, this wasn’t
really a problem since there was
time to get it spun back up
between hits. However, if the
opponent was a good driver they
could be attacking when the
blade was stalled and perhaps even
stop the blade completely, getting
me jammed against the
arena bumpers. Surgical
Strike’s only defense is
its spinning blade and
if an opponent could
get — and keep — it
stopped, they would
usually win.
I had noticed this
problem first at Franklin in
I had three main suspects.
The first and second were
purely mechanical. First, a loose
pulley on the motor or the
drive shaft could be slipping
under the heavy load at
start-up but then stop slipping
as the blade got up to speed
and the load decreased. The
second possibility was the
motor’s bell housing slipping on
the motor’s shaft. This is a
known problem and can usually
be fixed by tightening and
using Loctite on the screw that
secures the bellhousing to
the shaft.
The third possibility was that
the settings of the Electronic
Speed Controller (ESC) were
incorrect. I had used a variety of
controllers over the last few
years but had mostly used the
Turnigy Plush 80A. It had
worked with few issues. The
speed controllers are
programmed using a simple
FIGURE 1
FIGURE 2
FIGURE 3
programming card, and you can
adjust a variety of settings. I
suspected that perhaps I was not
using the right settings and it was
this that was causing the stalling
problem.
The ESCs we use are designed
for use in model aircraft or cars, so
there are no recommended settings
from the manufacturer for quickly
and smoothly spinning up heavy
metal blades. I decided to
methodically try all the options and
see which worked best. First, I
needed a safe setup so that I could
spin the blade up without risking an
accident if a tooth or even the
whole blade came loose.
I used three sections of my
Antweight arena with its 3/8”
Polycarbonate (PC) walls as an
enclosure, and used another old
section of PC and some zip ties to
secure the bot in a stationary
position (Figure 1). I screwed a
square of thin UHMW under the
weapon’s axle to reduce friction and
to stop the axle from wearing a hole
in the PC sheet.
To allow me to check for
mechanical slippage, I used a black
sharpie to draw lines (Figure 2)
across the joints of the various
30 SERVO 11.2011