Equal Throw Method

2007 Jan 19

Table of Contents:

Introduction

The term "Equal Throw" is defined has having an equal amount of mechanical throw from either side of the servo control horn ball's center. The servo control horn must be first set at 90 degrees to the control linkage.

In any mathematical equation, to solve for "X", we must have at least two known values. In the case of our model helicopter, we know the maximum and minimum mechanical travel limits.

What we need to find is the center position of the total mechanical travel. But to locate the center position, we must establish three electronic reference points.

These reference points will be when the servo control horn is at full minimum stick deflection, half stick position, and at full maximum stick deflection. The servo control horn must be at 90 degrees to the linkage rod at the half stick position.

A simple tool can be fabricated out of piano wire to simplify this procedure.

You could even use an "L'' ruler or the sides of a note card.

Click on the images to view the technique and its application.

The radio's end point values must be initially set at 100% / 100% and must be set so that both sides are equal in percentage values. If you cannot obtain the same values, then your setup is not equal.

The sub trim values must have the least percentage value obtainable.

Understanding the "Equal Throw Method"

In Figure A, the red, blue, and green arrow represents the linkage control rod traveling throughout the range of the servo control horns arc.

As the servo rotates throughout its full range, the linkage control rod corresponds to a position on the mechanical linkage as shown by the numerical graph.

From the above example in Figure A, the control rod points to the minimum value of 4 in the numerical graph when the servo is at minimum stick deflection.

As the servo rotates to its full maximum stick deflection, the control rod points to the maximum value of 4 in the numerical graph.

Hence the term "Equal Throw". The control linkage is aligned at equal points at both ends of the mechanical limits.

The mechanical center is known when the servo is at its electronic center, aka, half stick position, provided the servo control horn was set 90 degrees to the control linkage at half stick position.

Mechanical Binding

Figure B shows the control linkage binding at full stick deflection. Due to the control linkage being short, the servo will not be able to rotate to its full end point travel limit.

The result of this type of setup will cause servo damage, battery drain, and mechanical failure.

To determine if there are any binding in the mechanical system, one end of the control linkage ball link must be removed. Give full stick deflection and verify that the control linkage does not exceed the mechanical limits.

Figure C shows another instance of mechanical binding at full stick deflection due to the control linkage being too long.

Control Linkage Adjustment

A method used to set the control linkage to the proper length is to find the total error then adjust the control linkage to 1/2 the total error.

Set the radio's end point to 100% / 100% and sub trims close to 0%.

Align the servo control horn 90 degrees to the control linkage. Refer to the Introduction section.

Disconnect one end of the control linkage from the system.

Set the radio to full stick deflection in one direction.

Super impose and adjust the linkage control rod's ball link until the ball link aligns up to the center of the ball on the mechanical control arm at full mechanical throw. Obtain full mechanical throw by manually moving the mechanical control arm to its mechanical limit.

Set the radio to full stick deflection in the opposite direction.

Super impose the control rod's ball link on the center of the ball of the mechanical control arm at full mechanical throw in the opposite direction.

Estimate the total error that the control rod's ball link is offset from its target point. The target point will be the center of the ball on the mechanical control arm at its mechanical limit.

Adjust the control rod's ball link to 1/2 the error.

Increase or decrease the radio's end points "Equally" until the control rod's ball link aligns on the center of the ball on the mechanical control arm.

Continue to repeat the process from full stick deflection in one direction, then the other and remove 1/2 the error until no further adjustments are necessary.

Because of the arc of the servo control horn, adjustment of the end point values will cause an interaction in the total error. Repeat the above steps and continue to remove 1/2 the error until there are no further adjustment.

Reconnect the ball link to the mechanical control arm's ball.

The end results will have the end points adjusted Equally with no mechanical binding.

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