Page 172 - Build Your Own Combat Robot

Controlling Your Motors
Chapter 7:
4QD controllers ship as open printed circuit board assemblies, so the end user 153
will have to make his own housing and mounting arrangement to keep the 4QD
board isolated from impact shocks and protected from debris. The 4QD controller
is physically much larger than the Victor and the smaller Vantec controllers, and is
generally used in weight classes of 100 pounds and greater. It does offer great reli-
ability, built-in automatic current limiting, and a better power-to-cost ratio than
other variable speed controllers.
The downside of the 4QD boards is that they are not compatible with hobby
radio gear. The 4QD board has a purely analog input logic, and it is designed to
directly connect to analog throttle and direction control signals. Getting a 4QD
board to talk to traditional R/C units is the biggest challenge in successfully im-
plementing this design. One method to generate an analog signal is to connect a
potentiometer to the output shaft of an R/C servo. Feed 5 volts through the poten-
tiometer to the 4QD controller, and then drive the servo with the regular R/C
transmitter set. Although this works, it is not recommended because it adds more
parts that can become damaged during a combat match.
The ideal way to generate the analog voltage is to use a microcontroller to read
in the transmitter’s signals and convert them into an analog signal to drive the
4QD controllers. Getting the signal conversion just right is a challenging task if
the builder wants consistent and reliable control out of his 4QD board. The 4QD
boards offer a lot of power for the price, but the difference between smooth con-
trol and spastic twitching can take a lot of control-system troubleshooting.

The OSMC Motor Controller

The Open Source Motor Controller (OSMC) was developed by robot builders for
robot builders (www.robot-power.com). The OSMC is a modular control system
that offers the high current capacity of the 4QD with the plug-and-play interface
of the Vantec and Victor controllers. The OSMC was developed as a collaborative
effort between robot builders to develop a high-powered, low-cost speed controller
alternative to the then-limited supply of commercial controllers.
The OSMC is a modular system, available fully assembled in kit form or as bare
boards. The controllers can be assembled with several different FET configura-
tions to give current capacity of up to 160 amps continuous and voltage capacity
to 50 volts. The controller is made up of two separate circuit boards the logic
board and the power board. The logic board is the interface to the radio receiver
and handles channel mixing. The power board contains the FETS and associated
driver circuitry. One logic board can drive two separate power boards, allowing
for complete drive-train control over a tank-steered robot.
The open source nature of this controller means that the full development de-
tails—schematics, parts list, and control code—are freely available to developers.
The hobbyist nature of the controller means that a lot of rapid changes have oc-
curred in the development of the software and documentation of the controller
logic, and different versions of the control board with different features are available.