OVERVIEW: The RBSA BULLYs are closed-loop Pulse Width Modulation
servo amplifiers with a selection of output ratings big enough to push hundreds of foot
pounds around! They are commanded by a single channel from a conventional Radio/Control
receiver, such as Futaba. Use these stand-alone units to build your own custom battery
powered position servos with potentiometer FeedBack or velocity servos with
DC tachometer FB. The sturdy output circuitry drives DC Permanent Magnet brush motors.
Powerful proportional position servos may be constructed quickly by using SKF, Warner, or
similar linear actuators with built in FB potentiometers.
They are not simply "boosted" hobby servo
electronics but instead employ 10 bit digital techniques to convert the Servo Command
Pulse to a stable command voltage for classic analog processing. The analog circuity
compares the command voltage with the FeedBack element voltage to generate an error
signal. Servo systems require electronic compensation for mechanical attributes like
inertia. Unlike hobby servos the BULLY features a
full compliment of adjustments to facilitate stable servo systems up to the limits of the
The error signal is converted to 21KHz PWM to drive a modern MOSFET
H-bridge output amplifier. No special heatsinks are required.
Provision for low current limit switches that close to shunt the PWM
drive are provided Finally, a microprocessor performs house keeping functions for a well
behaved system under fault conditions. See Block Diagram.
INPUT: The optically isolated input plugs into your
receiver line any other servo. BULLYs are
available with Futaba J, JR, Airtronics, or Deans connectors and work with FM or PCM
PROGRAMMABLE FEATURES:A Wide Dead Band jumper
selects between a positive & wide "stopped" region on the joystick for
velocity servos or a smooth contiguous response for position servos. Four jumper
selectable transfer curves set the servo response to the joystick: STanDard, and optional LINEARized,EXPOnential, and CUSTOM. STanDard provides a 1:1 response. LINEARized adjusts the response to straighten the sine output from a servo arm. FailSafe jumpers select between
hold, stop, or go-to-specific position under faulty SCPulse conditions. The Servo and
Battery SAVER jumper option
reduces heat and battery drain in situations where tight deadband and precision motion are
only needed during active operation and the un-powered mechanics will provide adequate
lock on a position the rest of the time. Optional STUCK jumper stops power to a jammed servo until the
stick is moved again 25%.
ADJUSTMENTS: No servo amplifier and motor, no
matter how powerful, can stop instantaneously; there is a lag because of inertia. The RBSA
adjustable compensation for this. Adjustments include Lead Gain, Lead Time, Error Comparison Gain, Centering, and FailSafe trimpots plus a variety of plug-in components for other parameters. Complete instructions
and a Calculator program for Windows95/MS-DOS simplify the task.
Position servos require a FB potentiometer designed for servo service between 2.5K and 25K
ohms, monotomic, and driven by low backlash gears. Actuators with integral pot often are
available and are preferred. Velocity servos need a DC tachometer that generates plus
& minus voltages for opposing rotations.
An alternative FB path for velocity FB is provided through
optional IR compensation. Crude speed regulation for >8A motors can be realized.