Elevator Linkage

2006 Nov 21

Table of Contents:

Caution: Disconnect all linkages from the servos. Failure to do so will result in mechanical binding which can damage your servos.

Introduction:

This a Step by Step guide to setting up the Elevator Linkage. The steps are outlined in a chronological order. Use the Table of Contents to get a visual perspective of the setup.

The instruction manual on page 14 directs you to install a set of balls on the servo control horn; approximately 10.5mm from the center of the servo. This is the ideal setup for the beginner.

If using the Futaba predrilled servo control horn, select the appropriate hole out from the center.

As your flying skills develop, you will begin to notice that the cyclic control / response rate is sluggish.

To increase your cyclic rate, refer to the Cyclic Rate Tip page.

Repositioning the servo ball on the aileron control horn will change the angle of the linkage geometry. Therefore, you must redo the Linkage Rod Alignment and
Servo Mechanical Binding Verification steps.

Servo & Swash Plate Direction Verification :

Note: Any servo that is reversed after completion of the linkage alignment will be off centered and will require a realignment. This is primarily due to the internal workings of the radio's software program when switched from normal to reverse or vice versa.

Turn on the radio transmitter and receiver. Extend the radio's antenna to dissipate the RF energy.

I would advise on disconnecting the elevator linkage from the servo to avoid mechanical binding when the transmitter stick is fully deflected.

Move the transmitter's right stick forward (towards the antenna) and observe the elevator servo's control horn.

A forward input stick command will yield a counter clockwise servo rotation as viewed from the right side (header tank). See photo above.

If the linkage are connected, the swash plate should deflect towards the nose of the model when viewed from the right side (header tank), photo at left.

Access the radio's servo reversing program menu and change the corresponding channel to reflect the correct stick input command as required.

Linkage Dimensions:

Refer to page 22 of the manual.

Set all linkage rods according to the manual.

The length of the linkage rods connected to the servo control horn are approximate and will be adjusted accordingly. This is primarily due to the different manufacturer's servo dimensions.

I highly recommend purchasing a ball link duplicator. See photo at right.

If a ball link duplicator tool is used, use only "one set of balls" and the "same set" to obtain repeatable measurements. I have found variances in the distance between both sets of balls yielding unequal measurements.

Superimposed the linkage rod's ball link over the ball link duplicator. Do not snap the linkage rod's ball link on to the ball link duplicator as this will force the measurements.

Do not be alarm if a half turn of the ball link is needed to obtain the proper length. The manual shows that the TT Tiger name should face outwards for correct installation. I have had no issues with a ball link popping out in flight due to a ball link orientation.

Servo Control Horn Alignment:

Turn on the radio and receiver and extend the radio's antenna to dissipate the RF energy.

Verify the radio's programming menu parameters are set as follows:

Elevator Front Panel Trims = CENTERED

Elevator Sub Trim Menu = 0%

Elevator End Points (ATVs) = 100% / 100%

Rotate the servo control horn on the servo output shaft's spline for the BEST control horn arm that will be @ 90 degrees to the elevator linkage.

To simplify this setup, a special home made tool (linkage alignment tool) can easily be fabricated.

Click HERE for the linkage alignment tool fabrication page.

The swash plate must be leveled so that the elevator lever (PV0014) will be at it's initial position.

Level the swash plate using a swash plate leveling tool and disconnect the Aileron, Elevator, and Collective Linkages to ensure a pure mechanical leveled swash plate.

It would be a good idea to review the information on the Swash Plate Level Tip page.

Ensure that the swash plate remains level during the adjustments of the elevator control surface.

Note: When checking the servo control horn for perpendicularity, move the radio's control stick in one direction and then back to center. Repeat the process in the opposite direction. This technique will reveal any mechanical hysteresis in the linkage sytem. The linkage system should return to the same spot or have an equal amount of hysteresis error in both direection.

Place the linkage alignment tool so that the short arm is resting against the servo horn's ball. Use care when performing this step as excessive force on the servo control horn will change the alignment due to the servo's mechanical gears backlash. This is also known as hysteresis.

An additional ball placed on the opposite end of the selected servo control horn arm will aid in the alignment. Or, use two screws without the balls. The objective is to provide a means for the alignment tool to rest on.

Align the alignment tool's intersecting point on the selected mounting hole on the servo control horn's arm. The mounting hole from the center of the servo should be @ 10.5 mm (beginners) or @ 13.5 mm (advance).

The long arm of the alignment tool should be directly over the elevator lever (PV0014) ball's center. If this is not the case, rotate the elevator servo control horn selecting the best servo control horn arm that will yield a center alignment.

If neither of the servo control horn's arms meet the alignment requirements, and mechanical hysteresis (see above notation) has been eliminated, then select the servo control horn arm that requires the least percentage of sub trims adjustment to obtain a center alignment with the elevator lever ball's center.

Adjust the Radio's Elevator Sub Trim as required to obtain a center alignment.

The use of excessive sub trims to establish perpendicularity will adversely affect the symmetry of the servo travel.

It would be recommended to use a blank servo wheel and custom drill the holes required using a servo wheel drill gage as a template.

Move the radio's elevator stick in one direction then release. Use the linkage alignment tool and check that the servo's control horn remains perpendicular to the linkage.

Repeat this process in the opposite direction. The objective of this process is to rule out any mechanical hysteresis.

If hysteresis is present, the error should be "equal" on both sides of center. If the error is "not equal", adjust the radio's sub trims and repeat the alignment process.

Linkage Rod Alignment:

With the Elevator, Aileron and Collective linkage remove, use a swash plate leveling tool and level the swash plate. For more information see the Swash Plate Level Tip page.

Connect the elevator linkage rod to the elevator lever (PV0014) leave the other end disconnected.

Ensure that the swash plate remains level during this alignment.

With the radio on, superimpose the elevator linkage rod over the elevator servo's ball and adjust the linkage rod's ball link so that it is centered over the elevator servo's ball.

A half turn on the ball link may be required.

From experience, I have not had any issues with a ball link coming out as a result of the Thunder Tiger name facing in due to half turn adjustments. What is important is that the link is centered over the ball.

Servo Mechanical Binding Verification:

Depending on the placement of the ball on the servo control horn, mechanical binding may not be present and the radio end point values will vary.

Understanding the Equal Throw Method is the basic key element on a symmetrical mechanical setup.

Disconnect the elevator linkage rod from the elevator servo.

Apply full elevator stick deflection with the transmitter.

Manually move the elevator linkage rod towards the servo control arm's ball moving it to its full travel, maximum mechanical deflection.

Take note of where the elevator linkage's ball link is in respect to the elevator servo's ball.

The elevator linkage rod's ball link should either be aligned on the center of the elevator servo's ball or exceed past the ball for a zero mechanical binding. Photo at left.

If the elevator linkage exceeds past the servo's ball, INCREASE the radio's end point value until the elevator linkage's ball link is centered on the servo's ball.

Do not readjust the elevator linkage rod's ball link.

If the servo's ball goes past the elevator's ball link, then there is mechanical binding. Photo at right.

DECREASE the radio's end point value until the elevator linkage's ball link is centered on the servo's ball. Or, move the ball on the servo horn closer to the center of the servo's rotational axis.

An end point value less then 80% will have a decrease in resolution. Likewise, an end point value greater then 120% will have a slower response rate.

NOTE: If the servo's ball is relocated or repositioned from its initial alignment, you must reaccomplish the Alignment Process outlined in the Servo Control Horn Alignment steps.

Repeat the above going in the opposite direction.

The objective for a beginner's setup is to obtain an End Point value of +/- 10% with both end point values equal. You may have to play with the elevator servo's ball placement so that you find the BEST percent value closer to 100%.

If you go further out on the servo horn, you gain mechanical speed and lose resolution and torque. Contrary, if you go closer in on the servo horn, you gain torque and resolution but lose mechanical speed.

Verify that the radio end point values are EQUAL.

The servo ball should be centered on the elevator's ball link at full deflection, both direction. If not, the servo horn is not perpendicular to the elevator linkage rod, radio sub trim is too excessive, the elevator trim is not centered, the linkages are not adjusted according to the linkage dimension specifications.

If all of the mechanical and electronic criteria's are met, servo horn perpendicular to the elevator linkage rod, radio sub trim value kept to a minimum percent value, elevator trim is centered, and the elevator linkage rods adjusted per the linkage dimension specification, then readjust the linkage rod from the elevator control lever to the elevator arm parallel lever approximately 1/2 turn in or out.

Repeat the Linkage Rod Alignment and Servo Binding Verification steps.

If the binding errors are equal on both sides of center at full elevator stick deflection, adjust the radio's end points EQUALLY so that the ball on the servo control horn aligns with the center of the elevator linkage rod's ball link at full mechanical travel.

Re-connect the elevator linkage rod to servo control horn's ball.

NOTE: Binding of the collective pitch arm travel will be verified upon completion of both Aileron and Elevator control surfaces. Refer to Swash Plate Binding Verification.

Swash Plate Level Verification:

This step can ONLY be accomplished after completing the Elevator and Aileron Linkage Rods setup.

Disconnect the collective pitch linkage rod and reconnect the aileron and elevator linkage rods to their respective servo control horn's ball.

Turn on the radio transmitter and receiver. This is necessary to maintain a level swash plate.

Reinsert the swash plate leveling tool and ensure that the swash plate is resting on the leveling tool.

With the left or right side of the helicopter facing you, slightly raise the swash plate with the collective pitch arm so that a small gap can be visible between the bottom of the swash plate and the swash plate leveling tool.

Sight between the bottom of the swash plate and the top of the swash plate leveling tool.

There should be an "EVEN GAP" between the two surface if the swash plate is level. See photo at right.

If an out of level condition exists, raise the swash plate with the collective pitch arm just enough to clear the swash plate leveling tool.

Move the aileron stick on the transmitter and release. Gently lower the collective pitch arm and take note of the gap for an un level condition.

Raise the swash plate again and move aileron stick in the opposite direction. Gently lower the collective pitch arm and take note of the gap for an un level condition.

The swash plate should remain level in both directions or should have an equal amount of error (hysterisis) in both direction.

If this is not the case, then check for friction or play within the control surfaces by isolating the linkages from the swash plate to the head assembly and repeating the above.

Check all bell cranks for a smooth rotation. Friction can be eliminated using ball link resizer tool.

If the swash plate remains level or there are equal amounts of error (hysterisis) the Elevator Servo Setup is complete.

End Results:

Sub Trims:

Least % value, preferably 0%.

End Points:

Both Sides Equal.

Avoid using excessive end point values if resolution is a factor.

Swash plate:

Level and 90 degrees to main mast.

Tilts according to respective stick input command (fwd / aft).

Linkages:

All linkage rod lengths are set per the manual's dimension except linkage connected to servo horn.

Zero mechanical binding at full servo deflection.

Mechanical movement is friction free with linkage rod disconnected from servo and moved manually.

Fly Bar Paddles:

Level to the Datum Reference Line.

References:

Hysteresis is a property of systems (usually physical systems) that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state. http://en.wikipedia.org/wiki/hysteresis.

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