Chuck and Ryan's Build Tips

[ceslaw]

Auto pilot, Part I

Auto pilot in a Carbon Cub? Purists would say ‘that’s just wrong.’ But in the broad scheme of things the additional cost is not that great and the G3X has the means of controlling it without any external controls, so no one need know our plane is so equipped. Unless they read this post.

Pitch. The bracket and hardware for the pitch control is straightforward. The positioning is pretty well defined by the bracket. Here are some tips:

1. Temporarily set the drive pulley in place when installing the bracket. The pulley should be centered below, and the bracket parallel to, the torque tube.

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2. Five of the AN960-416 washers provide about the right spacing between the bracket and the support clamps. Friction tape was used under each of the clamps.

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3. Use AN3-7 bolts to fasten the servo motors to the brackets.

4. A bit of filing was needed to fit the short perpendicular support that bolts to the servo.

5. The cable that goes around the pulley and connects to the control cable was not installed. It will not be added until after the plane is complete and all control surfaces adjusted.

Roll. The bracket and the hardware for the roll servo is from Tru Trak. Here are more tips:

1. There is a diagram on Drop Box under the Tru Track caption that references the location. We deviated slightly from those measurements so that the control arms on the servo and the torque tube would be on the same plane. (No pun intended). Note that the servo shaft will be parallel to the adjacent cockpit floor in this location. The backing plate on the outside of the seat base looks better positioned this way, in my humble opinion.

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2. The Garmin stop that came with the servo was used rather than the Tru Trak stop. A tiny corner of the Garmin stop was trimmed to fit. The arm does not reach the stop, but it will prevent the servo from going beyond its intended arc and locking the stick in a full left or right position. (This issue is detailed in the G3X manual).

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3. The control arm that bolts to the torque tube is secured with a single rivet on the bottom. We will not rivet it until the plane is complete and all adjustments are made.

4. The wire harness for the two servos was carefully routed and tied in place. Note that there are two extra green wires; GSA03A22 and GSA04B22. The former is grounded and the other connects to the Normally Open (NO) kill switch that needs to be mounted on the control stick. The second wire from that switch is also grounded with a builder supplied wire. All the wiring was routed to assure no interference with the control cable below the torque tube.

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5. Careful attention needs to be paid to possible mechanical interference between the battery cables and the servos. The roll servo linkage was very close to the positive lead, so an Adel clamp was added to an existing bolt on the front of the seat support. Another clamp was added to the side to neatly secure the wire harness.