8 SERVO 02.2016
Last month, I said that using a sophisticated motor
controller is far more effective than having your primary
brain handle the low level work of PWM and motor
direction. Well, I must admit that I have traditionally done
what I advised against, and worked out the speed and
direction from my main robot controller. I decided that I
needed to put my robot where my mouth is, er, I don’t
think that I like that metaphor. Moving on ...
This month, I picked a motor controller to work with to
see just how simple it can be. I chose the Pololu
( www.pololu.com) TReX Jr motor controller (Figure 1). I
chose this controller because it was capable of handling my
16V LiPo battery packs at the 2. 5 amps per channel that I
required without having to spend a lot of money on it. The
TReX Jr costs about $60 and can control three motors using
logic level serial (a robot), RS-232, RC pulse control, and
even analog settings. Without going
into great detail, it has a ton of useful
commands and abilities including
current limiting and trapezoidal
acceleration profiles. All that, and it is
less than 5 cm square.
It’s starting to look like this answer
may turn into a multi-part robot
makeover series ...
The Pololu site has a nifty program
called the TReX Configurator (sadly,
only available on the Windows OS) that
can be used to handle the fine-tuning
of the controller, allowing a simple
program to actually control the motors
(Figure 2). You can also test your
motors out with the graphical motor
control page (Figure 3).
Configuring the TReX
Jr to the PC
Being somewhat of a creature of
impulse with attention deficit leanings, I
decided not to delve into the world of
tuning acceleration curves or setting
current limits or any of the other fancy
by Dennis Clark
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hrough the magic of publishing, I am speaking to you from the past. It is nearly
Christmas as I write this and I assume that my readers — like me — are out
frantically finding those perfect Christmas gifts for friends and family. I can only do
that for so long before holiday overload kicks in, then I must go hide in my robot
cave to experiment and dust off brain cells. The Robot Cave now exists as a series of crates
and an old desk with a broken chair hidden in the basement. Soon it will emerge from its
chrysalis and fly into a nicer part of the house ... but I digress.
Photo courtesy of Virtuabotix.