Multiplex Heron – Build Report – RC-Equipment

Last Change: 21.05.2017   

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Choosing The Receiver

Four flaps, rudder, elevator and motor. That means 7 channels if each servo is to be controlled individually. Selecting an appropriate receiver for our Heron turns out to become a classic example of the trial-and-error method. There are two limiting factors:

  1. The cross section of the receiver tunnel in the fuselage
  2. Position of the receiver

The receiver simply needs to be where the servo wires end. It can be positioned a few centimetres fore or aft in the tunnel. But there is not much of a choice here. We do not want the receiver or the servo wires to protrude into the cockpit area, where they would obstruct battery change, cg tuning or other maintenance work.

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Heat 1: An AR7350 (including AS3X and telemetry) we purchased earlier for testing was to be reused for our Heron. It fit the Heron’s fuselage and promised a compact solution. Then there came a steep learning curve about programming the AS3X. Soon, we found ourselves programming against the AS3X, rather than profiting from it. We failed completely to have it make a butterfly configuration. In addition, the programming software and documentation available seemed to tell us, that Spektrum does not want us to use AS3X like this. – Next try.

Heat 2: To stick with Spektrum’s state-of-the-art receivers we ordered a new AR8010T (without AS3X but with telemetry). Just by comparing size of the receiver to the room in the fuselage, it would have fit, however, with only a few millimetres left in height. But considering all the wires in there and the limited access to the cavity, the solution was judged to be too crammed after the first dress rehearsal. Off went the AR8010T to the spares box. – Next try.

Heat 3: If it had not been for the AR7350 already at hand, we would have chosen the used AR8000 from our spares box right from the start. Now we resorted back to it, adding telemetry capability using a TM1000 transmitter which came from the spares box as well. Only the small AR8000 needs be installed in the receiver tunnel of the fuselage, whereas the TM1000 will find its place under the canopy in the cockpit area.

Installing The Remote Receiver

The AR8000 requires a remote receiver (and so did the AR7350 and AR8010T we tried before). It would not operate correctly without it. The remote receiver is installed before the main receiver.

Room is sparse in the receiver tunnel. So the remote receiver (SPM9645) has to go somewhere else. We choose to place it in the wing mounting area, between the wings just unter the locking mechanism. Some foam material needs to be cut away to avoid obstructing the locking pin. The antenna are bent slightly downward into the fuselage to keep them out of the way of the wings, and a little bit to the front to enhance antenna diversity.

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The connecting cable to the main receiver in the tunnel is laid through the same opening as the flap servo cables. The original 6-inch (15.2 centimetres) remote receiver extension turns out to be too short for this. It is replaced by a 9-inch extension (JRPA182).

Installing The Receiver

This is what we call the Hydra: Lots of wires driving you haywire. It is a good idea to test everything now, before it goes out of sight into the fuselage. We double-check the port allocation. Since we will be using airplane type glider on our DX9, the standard channel usage will not match the descriptions on the receiver.

Port # Port Label Function Used Remarks
1 BIND/DAT
  • bind
  • data to telemetry
We use a Y-cable here. One end is connected to the telemetry module.
The other end remains open for the bind plug.
2 THRO left aileron
3 AILE right aileron
4 ELEV elevator
5 RUDD rudder
6 GEAR right flap
7 AUX 1 left flap
8 AUX 2 motor
9 AUX 3 (not used)

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Please note the “armoured” antenna of the receiver. A piece of yellow straw encasing the vulnerable antenna is fastened to the receiver’s box with a generous dab of hot glue. This will allow us to push the receiver – the antenna facing backwards – into the tunnel as far aft as possible without bending or breaking the antenna. It will also keep the antenna’s direction strictly within the longitudinal axis, which makes it perpendicular to the antenna of the remote receiver for maximum antenna diversity.

Now we push the receiver into the tunnel. How can you prevent the velcro strip on the receiver’s back from getting caught too early by its counterpart in the tunnel? We make it slide on a cake spatula guided by a pair of giant tweezers. Both tools came in handy from the kitchen drawer.

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Once the receiver reached its final position at the rear end of the tunnel, the hydra is gone. The cockpit area looks tidy now, more or less. Only the telemetry cables and the bind cable are visible.

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Installing The Telemetry

Our initial telemetry setup consists of three components, whick will all go under the canopy:

  1. TM1000 telemetry transmitter for receiver and battery voltage data
  2. GPS sensor
  3. Variometer sensor

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Telemetry is not mandatory. We purchased an additional canopy for the telemetry components. So we can fly with or without the telemetry stuff by simply replacing to canopy.

We use strong Pattex double tape to fasten the telemetry components to the base plate and some white insulation tape to keep the wires and antenna where they are supposed to be. Two wires will connect the canopy unit to the rest of the Heron, one for power and data from the receiver (black plug) and one for battery voltage data (red plug).

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We sand the interior surface of the canopy with wet 400 grain to create a semi-opaque look. This retains some of the glass cupola appearance for scale flights but does not reveal all the technical secrets inside. The base plate is glued to the canopy with UHU Por to keep it easily removable for maintenance.

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