Throttle Linkage

2006 Apr 2

Table of Contents:

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

Radio Requirements:

Verify that your radio meets the following parameters prior to beginning the throttle linkage setup.

Sub Trims = 0%

ATVs, End Points, EPAs, Travel Adj = 100% /100%

Front Panel Throttle Trim - Full Low Position.
Note: JR 9303, throttle trim at center equals 0% on throttle curve menu. If trim is at full low position, throttle curve goes to -15%. Mechanical binding will result if you bring your throttle trim to below center and have a mechanical setup set at half throttle trim.

Throttle curve menu - Normal Mode (default) 0%, 25%, 50%, 75%, 100%

Throttle Hover Pitch menu - INHIBITED
(This function in some radios cannot be inhibited. Set the throttle stick to half stick, 50% point and rotate all knobs and slider switches. Verify that the throttle servo does not move.

If this function cannot be inhibited, ensure that the knob or slider switches are at center position. Be careful not to move this knob or slider switch at anytime during the alignment process as this will adversely affect your mechanical alignment.)

Servo Direction = Throttle / Collective stick moved towards the antenna, throttle barrel arm rotates counter clockwise as viewed facing the throttle barrel arm.

Governor = Set your governor's A / B limits to 100% / 100%.

Mechanical Requirements:

Study figure A and ensure that your setup meets the following initial requirements.

Adjust linkage "A" & "B" per dimension "C". "Do Not Readjust". This is the key to the mechanical setup.

The servo control horn and throttle arm must be at 90 degrees to the linkage at half stick position when the throttle curve is linear (50% point).

Place the balls on the servo control horn and throttle arm at equal distance. Note: This is the initial settings and will vary.

It is not necessary to use two sets of linkages. The advantage of having two sets is of linkages is to have a redundant system, in the event of a worn linkage or minimized the "dying chicken" dance as a result of a crash.

Servo Direction:

Its is very important that the throttle servo moves in the correct direction. Failure to do so can result in personnel injuries as a result of the model starting up at full throttle position.

To avoid mechanical binding, remove one end of the throttle linkage.

Move the throttle / collective stick to the full throttle open position. This will be towards the radio's antennae.

Take note of the direction that the throttle servo control horn moves in relation to the throttle arm.

The throttle arm should rotate in a counter clockwise direction, full throttle, as viewed facing the muffler side of the engine.

If this is not the case, access the radio's reverse programming menu and change the corresponding channel to reflect the correct stick command as required.

Another technique in locating the open or close throttle position is to start the engine without the glow plug igniter. A fully open throttle barrel will make the sound of air rushing through the engine and out the exhaust port as the engine is being crank over.

Any servo that is reversed after completion of the linkage alignment will constitute a realignment due to the internal workings of the radio's software.

Servo Control Horn Alignment :

To select the optimum servo control horn position, your radio settings must be set per the Radio Requirements.

Position the throttle / collective stick to half stick. Use your radio's digital throttle curve menu and target the stick position to the 50% set point.

To ensure repeatable readings and avoid mechanical hysterisis, always move the stick in the same setting direction. If you exceed the 50% set point, move the stick back to the initial starting position.

If you do not have a digital menu, use the analog markings on the Throttle / Collective gimbals.

Locate the best position on the servo control horn that will have the control rod linkage at 90 degrees to the servo control horn.

Figure B shows the technique in finding the best position.

A great tool that can easily be fabricated, will simplify this alignment procedure.

Mount two servo balls or screws to the servo control horn to aid as a back stop when aligning the alignment tool to the center of the throttle arm.

A piece of piano wire or a spare tail rotor control rod can easily be bent to the shape of a T-pin.

Click on the photo to see this technique in use.

Verify that the X and Y axis of the alignment tool are perpendicular to each other using the corners of a piece of paper.

Select the best servo control horn by rotating the servo horn on the servo's spline shaft, that will yield an alignment of the T-pin's arm on the center of the servo spline's shaft and the center of the throttle arm.

If alignment of the T-pin's arm does not align on the both the servo horn and the throttle barrel center, adjust the radio's Sub Trim menu to obtain a center on center alignment.

Excessive amounts of Sub Trims will effect the outcome of the mechanical setup, so select the best servo control horn that will yield a Sub Trim value closer to 0%.

Servo Ball Placement:

The ball placement per the manual is approximately 10.5 mm from the center of the servo. Due to a variety of different engines and throttle arms, this distance will vary significantly.

The initial placement of the servo control horn's ball should be approximately the same distance as the throttle arm's ball when measured from the center of the throttle arm's axis of rotation.

Select a predrilled hole on the servo control horn that are approximately the same distance as the holes on the throttle arm when measured from the center. Refer to Fig. A.

Do not secure the balls with the backing nut until completion of the setup. The balls will be shifted in or out on the arm to achieve an End Point value close to 100% / 100%.

Linkage Rod Length:

The objective in this setup is to make the throttle linkage control rod the same distance from the center of the servo control horn to the center of the throttle arm.

Super imposed the throttle linkage rod's ball links over the center of the servo shaft's spline and the center of the throttle arm, (see photo).

Adjust the throttle linkage rod's ball links so that the centers ball links are aligned directly over the center of the servo spline and the center of the throttle arm.

Do NOT readjust the throttle linkage control rod during the course of this mechanical setup. This is the key for a symmetrical setup.

Linkage Control Rod Alignment

Before we begin this setup, it will be to your benefit in understanding the "Equal Throw Method".

On the "Equal Throw Method" page, it refers to removing 1/2 of the error by adjusting the ball links on the control rod linkage. In the case of the throttle linkage, we will be removing 1/2 the error by adjusting the throttle arm.

As stated in the previous section, DO NOT readjust the throttle control linkage.

Verify that you have met the Radio Requirements and Mechanical Requirements prior to begriming the Linkage Alignment.

Slightly loosen the retaining screw / nut securing the throttle arm to the throttle barrel. The trick will be to make the throttle arm snug to facilitate a rotational adjustment of the throttle arm to its intended target. If the throttle arm is too loose or too tight, adjustments will be cumbersome.

Connect one end of the throttle control linkage rod's ball link on the throttle arm's ball. Do not connect the other end as it will be superimposed on the servo control horn's ball during the alignment process.

Move the radio's throttle / collective stick to full low stick position.

Set the throttle trim to full low position.

Rotate the throttle arm so that the throttle control linkage rod's ball link is superimposed directly on the center of the servo control horn's ball.

Set the radio's throttle / collective stick to full high stick position.

Superimposed the throttle control linkage rod's ball link over the servo control horn's ball and note the error from the intended target.

The error is the distance from the center of the control linkage rod's ball link center to the center of the servo control horn's ball.

Rotate the throttle arm by 1/2 the error.

Increase or decrease the radio's End Point value EQUALLY until the servo control horn's ball is directly centered on the control linkage rod's ball links center.

Repeat the process from full low stick position to full high stick position and continue to remove 1/2 the error. Adjust the radio's End Point values until no further adjustment are necessary.

The final setting should have the servo control horn's ball directly centered on the control linkage rod's ball link center and the radio End Points with equal percent values.

It is important that you maintain an End Point percentage value that is EQUAL on both sides and within +/- 10%. A minus 10% value will be mechanically faster than a plus 10%. 

Your End Points greatly affect the calibration / operation of a Governor / Limiter. I have had instances in setups where I found the end points not equal on both sides and at 80% which caused the governor to not function properly.

If your End Points are not close to 100%, move the balls on either the servo control horn or throttle arm in or out from the center of its axis to achieve the desired End Point values.

Repeat the entire Linkage Alignment if the balls have been relocated.

Securely tighten the throttle arm retaining screw / nut. This is the difficult part of the setup because the throttle's retaining screw / nut must be tightened and it is during this process that the throttle arm will rotate out of alignment.

The throttle arm must be properly tightening to prevent the throttle arm from loosening during flight operations.

If the throttle arm does rotate, you will have to redo the alignment process. A trick for this process is to note how much the throttle arm rotates and offset the throttle arm by that amount.

As you tighten the throttle arm's retaining screw / nut, the throttle arm will rotate to the amount of offset you dialed in. Be patient as it will require several attempts to dial it in.

Servo Binding Verification:

Mechanical binding can be defined when the control linkage rod is electronically control beyond the mechanical limits.

The results of a mechanical binding can cause severe servo damage or premature wear to the servo, battery drain, or control linkage rod failure.

To verify for mechanical binding, remove one end of the control linkage rod's ball link from the servo control horn's ball.

Set the throttle trim to full low position.

Move the throttle / collective stick to full low position.

Superimpose the control linkage rod's ball link over the servo control horn's ball and verify that the servo control horn's ball is directly centered on the control linkage rod's ball link. Refer to figure D and F.

Repeat the above process at full stick position and ensure that the servo control horn's ball is directly centered on the control linkage rod's ball link.

If all parameters are met, reconnect the control linkage rod.

If not, DO NOT readjust the linkage control rod. Redo or verify the requirements per the following sections:

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