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Radio Control Bully Servo Amplifier

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  • 21 KHz Pulse Width Modulation RATE




  • NOT SIMPLY A  " boosted"  R/C servo IC


BullyBoyColor2.JPG (8418 bytes)Pushes Anything Around!
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 mechanics.

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 radios.

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 BULLY provides 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.

FEEDBACK: 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.

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Part Voltage Con't TypLoss Approximate Wgt Min. Wiring Comments
Number Range Amps  LegOhms  Size Oz. Size    AWG

RBSA13 9-15 24 .006 6.25 X 2.2 X 4"  25 16   Versatile 12V BULLY

RBSA16E 9-15 40 .004 6.25 X 2.3 X 4.5" 39 12  Extruded Aluminum Case

RBSA23 18-30 24 .006 6.25 X 2.2 X 4"    25 16  Drives SKF actuators.

RBSA26E 18-30 40 .004 6.25 X 2.3 X 4.5" 39 12  Biggest 24 VDC BULLY !


Measure your motor's continuous running current under actual normal mechanical load. Or determine your DC PM motors armature terminal resistance by consulting specifications or measurement. Take the measurement by mechanically locking the motor shaft, and reading the current drawn while briefly powered from a fresh alkaline 1.5 volt "D" cell. The SELECTOR CHART shows armature resistance in "D" cell amps or ohms. At your operating voltage the model choosen should list lower Ohms or higher Amps than your motor. For actuators packaged with pre-calibrated RBSA amplifiers ask about our complete BULLDOZER systems.


V Ohm "D"Amp Part#

12 0.13 7.6 RBSA13

12 0.09 NA RBSA16E

24 0.26 4.4 RBSA23

24 0.18 5.7 RBSA26E

WARRANTY & REPAIR: Our one year limited warranty covers parts and repair labor for a nominal charge for units not abused, tampered with, or immersed. Details available on our Warranty page.
Note: Our products are not safety devices nor for use in life-critical or life support systems. Specifications and price subject to change without notice. Patented. Some trade names, trademarks & content owned by others.

Sales: (800) 882-6832

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