first into the wall. Taking the time and
learning how to use the full range of
travel (either using linear or
exponential settings) will result in
being able to drive much more
smoothly. Smooth driving is controlled
driving, and controlled driving gives
you an advantage.
I prefer fast bots. The bots I run
at events are usually some of the
fastest machines in the class. Most of
the time, I’m not using nearly all of
that speed. I spend most of my time
in matches below 50% throttle, only
going to the limits of the travel when
I’m lined up for or trying to avoid an
attack. That being said, when fights
I’m in go to the judges, I tend to
score highly on aggression.
So, why would the bot that’s
driving slower and in a more
controlled manner score high on
aggression? It’s simple: Aggression
isn’t the fastest bot. It’s not the bot
that’s constantly charging in the
general direction of their opponent.
Aggression is the bot making
successful attacks on their opponent.
Blasting past your opponent and into
the wall just gives them a free shot.
Speed is great. Accuracy is better.
SERVO 06.2015 21
Quality Versus Quantity —
Or, Why One Axle is
Sometimes Better Than Two
● by Pete Smith
The drums on my Saifu kits have worked pretty well, but when they lose it’s usually been the
same problem: bent axles. The drum
uses a shoulder screw as a live axle at
one end and the shaft of the
Outrunner itself at the other (Figure
1). Initially, I used a 3/16” shoulder
screw and that would be the failure
point. I fixed that by moving to a 1/4”
shoulder screw, but then the weak
point was the 1/8” diameter axle in
the Outrunner. A big hit would bend
that small shaft and the motor would
then seize up.
The existing design was simple to
build as the entire motor would be
glued into the drum, but it was clear
that a tougher solution was required.
First thoughts were to replace the
motor shaft with a tougher one. A
customer tried a titanium shaft, but
that did no better; my next thought
was to use a custom hardened steel
one. This may have worked, but
hardening steel is a complex subject
and getting the right blend of
hardness and toughness could have
been tricky. I had also been
considering another solution for some
This would have been to take the
motor apart and use a much bigger