OVERVIEW: The RBSA BULLYsBULLYs are closed-loopPulse Width Modulation servo amplifiers with aselection of output ratings big enough to pushhundreds of pounds around! They are commandedby a single channel from a conventionalRadio/Control receiver. The optically isolated inputplugs into your Futaba J, Hitec, JR, or Airtronicsreceiver like any other servo. Use these stand-aloneunits to build your own custom battery poweredposition servos with potentiometer FeedBack orvelocity servos with DC tachometer FB. The sturdyoutput circuitry drives DC Permanent Magnet brushcommutated motors. Powerful proportional positionservos may be constructed quickly by using SKF,Warner, or similar linear actuators with built in FBpotentiometers.

They are not simply "boosted" hobby servoelectronics but instead employ 10 bit digitaltechniques to convert the Servo Command Pulse to astable command voltage for classic analog processing.The analog circuitry compares the command voltagewith the FeedBack element voltage to generate anerror signal. Servo systems require electroniccompensation for mechanical attributes like inertia.Unlike hobby servos the BULLYBULLY features a fullcompliment of adjustments to facilitate stable servosystems up to the limits of the mechanics.

The error signal is then converted to 21KHz PWMto drive a modern MOSFET H-bridge outputamplifier. No special heatsinks are required.Provision for low current limit switches that close to shunt

the PWM drive are provided Finally, a microprocessorperforms house keeping functions for a well behavedsystem under fault conditions. See Block Diagram.

Velocity applications are briefly covered in the back ofthe manual.

POSITION SERVO INSTRUCTIONS: The BULLYBULLYmust be set up by you for your actuator and system.This includes feedback calibration, lag/leadcomponents, TrimPots, and Logic Jumpers. Afterestablishing proper operation plug-in parts should besecured with silicone or solder to prevent them fromfalling out under vibration.

The factory default setting for the Logic Jumpersand TrimPot adjustments are for the Position Servomode, with a specified failsafe position, and theSTanDard transfer curve. Providing you areconstructing a position servo we recommendmodifying the jumpers and adjustments ONLYAFTER you have the system operational.

HOWEVER, every installation has differentfeedback requirements so calibration resistors R44and R49 must be installed by you BEFORE thesystem can be tried. The RBSA requires your FBelement to be between 2.5K and 25K ohms. It mustbe designed for servo service with suitable bearings,be monotomic, and driven by low backlash gears.Actuators are available with built in FB pots.Ideally your feedback element supplies a DC voltagerange over its desired mechanical range that matchesor tracks the ServoCommandPulse's resultantanalog voltage which nominally is a +-0.939 mV

vantec.com Phone:(541)471-7135 FAX:(541)474-3987 460 Honeycutt Dr., Grants Pass, OR 97526

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R/C AUTONOMOUS BULLYBULLY POWERCLASSIC PWM SERVO AMPLIFIER

q MODELS RBSA13 - RBSA26E

q BUILD MONSTER POSITION SERVOS

q POSITION or VELOCITY

q CLOSED LOOP CONTROL

q 21 KHz PWM RATE

q SMOOTH & QUIET

q LAG/LEAD ADJUSTABLE

q CLASSIC DESIGN USED

Help: (800)882-6832

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change from 2.5 V for each +-1 microsecondchange from 1.533 ms; OR:

While 1-2ms is the nominal pulse span commonlymentioned actual radios may vary. For example: theFutaba FP-8UAP swings between 1.12 ms and 1.94ms with 100% ATV, 100% Dual Rate, no trim, andfactory settings, on the aileron channel.

The RBSA excites the FB potentiometer by 5Vthrough calibration resistors from the -Exc and +Excterminals. The -Exc terminal plug-in calibrationresistor is R49 to ground. The +Exc plug-incalibration resistor is R44 to +5V. These resistorsplus the FB potentiometer form a three resistorvoltage divider so the proper excitation voltage onthe FB element may be set. More voltage on the FBpot yields less servo travel. The mechanical center ofyour mechanical system should yield a FB potvoltage of 2.50V. Note that this may be or not bethe FB pots actual center, use the excitation resistorsR44 and R49 handle the offset. The load on your FBpot wiper is 235K at 2.5 V. Trimpot R2 Center

provides some adjustment for SCP and excitationtolerances.

A Calculator program for Windows95/MS-DOS isavailable from our www.vantec.com website.Resistor R47 is 1k and is in series with the FB potwiper and a capacitor forms a "wiper noise" filter.

UNDERSTANDING THE ADJUSTMENTS: Noservo amplifier and motor, no matter how powerful,can stop instantaneously because of inertial lag. Soit is necessary to anticipate closure to the targetposition. When the servo is moved slowly it stopseasily but at full speed it takes longer to stop. Thetime necessary is proportional to the speed. The rate-of-change in FB voltage yields this needed speedinformation. VANTEC introduces Leadcompensation in the FB amplifier before the errorcomparison circuitry. The FB amplifier has a fixedgain DC section to accurately know position and anAC delta-rate section to derive the Leadcompensation. This AC gain momentarily modifiesthe position output to anticipate closure to the targetposition.

The RBSA BULLYBULLY provides adjustable compensationthat includes Lead Gain, Lead Time, ErrorComparison Gain, Centering, and FailSafeTrimPots plus plug-in components for otherparameters. Vantec has set these for your initial

SCPmilliseconds

Equivalent FBvoltage

Comments

.896 3.1 absolute limit1.533 2.5 CENTER2.175 1.895 absolute limit

vantec.com Phone: (541)471-7135 FAX: (541)474-3987 460 Honeycutt Dr., Grants Pass, OR 97526

operation so it is only necessary to have arudimentary understanding of them.

See the Block Diagram. The AC gain and frequencyresponse are adjustable by R4 Ld Gain and R5 LdTime trimpots. VANTEC expresses the frequencyresponse as time; think of it as braking time.Because mechanics size and inertia vary widelyamong applications a plug-in compensationcapacitor C35 is provided. It is the courseadjustment and R5 Ld Time is the fine adjustment.Clockwise on this and all 25 turn trimpots increasestheir function. R5 Ld Time adjusts over a 20:1range. Begin by using the default C35 value alreadyinstalled. Typcial C5 values range from 1ufd to22ufd tantalum; observe polarity. The greater thesystem inertia the larger C5 needed.

Too much lead time yields an over damped positionservo which slows prematurely. To little lead timeyields overshoot of the target position. Begin by

using the overdamped default setting.

ERROR COMPARISON AMPLIFIER: It featuresadjustable trimpot R3 EC Gain and plug-inintegration components R40 and C28. Start by usingthe default reduced gain TrimPot setting and 220ohms and .056ufd respectively.

WIRING: Follow the layout schematic. Do notpower the RBSA from batteries under charge,battery eliminators or chargers without consultingfactory.

POWER & MOTOR: Observe battery polarity. ThePart Number chart shows the minimum size wire forbattery power and motor wiring; wire with theminimum length wire practical and keep this wiringseparated from the R/C receiver and SCPulse cables.Ground your chassis at a single point but don't usethe chassis to conduct current. Include the smallestregular-blow fuse in the +1 lead that will support

normal operation.

Install a .001 ufd "102" ceramicdisc capacitor and/or AC typeMOV directly across the servomotor brushes for RFI protection.Two additional .001 ufd ceramicdisc capacitors may be necessary,one between each brush and themotor case.

FB ELEMENT: To wire the FBelement use a single shieldedcable with the shield connected tothe Terminal Block Shld only.Do not bundle with any otherwiring.

LIMIT SWITCHES: Optionallow current limit switches may beconnected on F.Lt and R.Lt.Connect their common directly toG1 and combine with no otherwires. The switches must close toshunt PWM drive for thepertinent direction.

SERVO COMMAND PULSE:The input plugs into yourreceiver like a servo. Only thereceiver common and ServoCommand Pulse signal wire arerequired to drive the opticalisolator inside the RBSA. Theunit neither takes power from norsupplies power to the R/Creceiver; thus the plus (red) wire

vantec.com Phone: (541)471-7135 FAX: (541)474-3987 460 Honeycutt Dr., Grants Pass, OR 97526

is not used. If supplied with universal connectorsand used with some Futaba receivers observeconnector orientation since polarizing lip is absent.No harm will come from incorrect servo plug in.The RBSA works only with FM and PCM receivers.

Use the full length supplied R/C antenna and locateit away from other wires and metal structures.

MOUNTING: Don't mount the unit directly adjacentto the R/C receiver. Operation near maximumratings may require cooling air or mounting theRBSA side-opposite-the-terminal-block to additionalheat dissipating surfaces such as your metal robotframe. No special heatsinks are required. Whilemounting remove the cover to monitor mountingscrew length; screws should not thread into the casemore than 1/8".

INITIAL OPERATION: Recognize the likelihoodthat the FB will be backwards, the limit switchesreversed, the compensation all wrong and the motorwill go wild. Take precautions to limit the damage.Disconnect from mechanical load and remove hardstops. Initially leave the motor disconnected.

POWER FOR THE FIRST TIME: If at any timethe RBSA gets too hot to hold, cease operation andinvestigate. Leave the motor disconnected. Powerup cautiously at the lower end of the RBSA voltagerange with no SCPulse input. Verify excitation andFB values by manually turning the motor andobserving that the voltage swing at the TerminalBLock FB over the intended mechanical travel is 2to 3 Volts.

POWER FOR THE SECOND TIME: With poweroff connect the motor to the RBSA but with asubstantial series resistor selected to limit speedand torque. Power up cautiously at the lower end ofthe RBSA voltage range with no SCPulse input. Themotor should not run.

Apply a 1.5 ms SCPulse and observe servooperation. If the servo jams in one direction themotor polarity is probably wired backwards relativeto the feedback.

Provided the servo responds to slow movement ofthe joystick cautiously check the position extremesto validate R44 & R49. If the servo jitters or huntsslightly reduce the EC gain by turning EC gainCCW.

With a 1.5ms SCPulse adjust R2 Centering +-3turns to mechanically center or stop the servo. Ifgreater adjustment seems required the FB excitationresistors R44 & R49 are not quite correct. (Clue forresetting the default Centering: Vantec has set theCentering trimpot by disconnecting the FB pot andadjusting to null as indicated when the motor stops.)

If basic position servo operation is achieved by theservo following your joystick and it does not jamthen advance to the third power up.

POWER FOR THE THIRD TIME: With thepower off connect the motor directly to the RBSAby eliminating the motor series resistor. Power upcautiously at the lower end of the RBSA voltagerange with no SCPulse input. The motor should notrun. Apply a 1.5ms SCPulse and observe the servogo to center position and stop. The dynamiccharacteristics will change dramatically; expect re-adjustment. Adjust R3 EC gain CW so the servojust oscillates, then back off CCW till it stopsoscillating. In the majority of cases with the initialcomponents and settings the RBSA will have over-damped compensation. If overdamped turn R5 LdTime CCW. With proper compensation it should bepossible to increase EC, try it. Repeatcompensation adjustment. If the system is stilloverdamped with R5 fully CCW then reduce thevalue of C35. Repeat adjustments.

Adjust the compensation for Critical Damping bycommanding the servo with abrupt step commands.Incrementally increase R3 EC Gain and repeatcompensation pot adjustments. Maximum R4 LdGain should not be required. Excessive R4 Ld Gainis manifest by the servo hesitating rather thanslowing as it approaches the target position inresponse to an abrupt step command. There is some

SPECIFICATION CHARTPart Voltage Con't TypLoss Approximate Wgt Min. Wiring CommentsNumber Range Amps LegOhms Size Oz. Size AWGRBSA13 9-15 24 .006 6.25 X 2.2 X 4" 25 16 Versatile 12V BULLYRBSA16E 9-15 40 .004 6.25 X 2.3 X 4.5" 39 12 Extruded Aluminum CaseRBSA23 18-30 24 .006 6.25 X 2.2 X 4" 25 16 Drives SKF linear actuators.RBSA26E 18-30 40 .004 6.25 X 2.3 X 4.5" 39 12 Biggest 24 VDC BULLY !

vantec.com Phone: (541)471-7135 FAX: (541)474-3987 460 Honeycutt Dr., Grants Pass, OR 97526

trade-off between Lead gain and Lead time but lessgain/more time is preferred. Finally fine tune forsmooth slow operation.

Backlash in geartrains, FB element drive and evenrocking of the FB pot wiper will limit the resolutionthat can be achieved. Stable maximum R3 EC Gainis seldom realized, we suggest going 1/2 turn CCWfrom oscillation stop point to assure stability.

OTHER ADJUSTMENTS: When calibration andcompensation is satisfactory the FAILSAFE jumpermay be implemented. When the R/C ServoCommand Pulse fails the servo can do one of severalthings. It can continue the last known command orassume a failsafe position or speed (velocitysystems) which you set with trimpot R1Failsafe. AnSCPulse less than .87 ms and greater than 2.2 ms, orpulses not repeating between 9.5ms and 200ms willinitiate a FailSafe. Some PCM radio systems havefunctions that may override this feature. Test thisfeature by un-plugging the Servo Connector.

FailSafe operator POT WideDeadBand

Hold OFF Don't CareR1FailSafeposition

ON OFF

ShutDown/stop ON ON

CURVES: Four jumper selectable transfer curvesdetermine the servo response to the joystick:STanDard, and optional LINEARized, EXPOnential,and unusued CUSTOM. STanDard provides a 1:1response and is the only response curve factorysupported.

JP1 JP2STD OFF OFFLINEARize ON OFFEXPO-nential

OFF ON

CUSTOM ON ON

The SAVER and STUCK jumpers options are NOTavailable. SAVER & STUCK jumper = open

VELOCITY SERVOS: The RBSA Velocityapplications require a DC tachometer that generatesa positive voltage for one direction of rotation and anegative voltage for the other. The tach commonterminal needs to be connected to 2.5V so zero RPMnets "stopped". By plugging in 4.7K for both R44

and R49 and then connecting the +Exc and -Excterminals together a 2.5V node is developed for thetach connection. Like the position FB, the tachshould supply a voltage output over its intendedRPM range that tracks the SCP voltage. An externalvoltage divider may be required to satisfy the tachmanufacturer's load resistance requirements inconcert with FB voltage requirements. To aid incalculating voltage division R47 feeds a 235Kimpedance.

For Velocity Servo applications a certain and wide"stopped" joystick position is desired. This isopposite the smooth and contiguous responsedesired for a position servo. Install the Wide DeadBjumper for velocity applications. This jumper alsoshuts down the servo during FailSafe when the POTjumper is installed.

JMP1-2, WDB = as required

SAVER & STUCK jumper = open

An alternative FB path for velocity FB is providedthrough optional IR compensation. It is implementedby installing resistor R58 and adjusting R6 IRComp. This FB works by monitoring the motorcurrent. When "stopped" there is no FB. As themotor torque load is increased it draws more currentand the positive IR FB increases the PWM driveduty cycle to maintain speed, albeit crudely.Excessive positive FB will cause the motor to runaway. Experiment.

WARRANTY & REPAIR: Our one year limitedwarranty covers parts and repair labor for a nominalcharge for units not abused, tampered with, or immersed.These products are not safety devices nor for use in life-critical or life-support systems. Specifications and pricesubject to change without notice. Patented. Some tradenames & trademarks owned by others.

vantec.com Phone: (541)471-7135 FAX: (541)474-3987 460 Honeycutt Dr., Grants Pass, OR 97526