Twin Power Management Mark 2

Definitions:  For the purpose of this discussion, the term inboard is used to reference the engine(s) on the inner side of the turning circle.  That is, the wing that travels the least arc when turning.  For example, in a right turn, the right wing travels the least and is deemed to be the inboard wing.  The wing that travels the greater arc is defined as the outboard wing.

Building on the original Twin Power , this improved version incorporates the Loss of Signal safeguard suggested by Mr. RC-CAM and auto-throttle stick calibration that can be attributed to Michele Schieppati, CatsEyes and TugBoat. 

Additionally, CatsEyes suggested that the rudder channel be moved to GP3 (which is an input only pin) and that the signal be passed straight through to an output pickup for the rudder.  In doing so, the need for a Y harness on the rudder is eliminated and, no matter what happens to the PIC, the rudder signal will be passed to this primary control surface.

Caution:  This application has not been field tested.  It is offered as an academic example only.

Note:  This rig can be used to control multiple engines on each wing.  Just put a Y harness on the RIGHT and LEFT ouputs.

The auto-calibration routine picks up the low stick and then the high stick positions.  The two are averaged and that value is used as the mid-stick.  The three values are written to EEDATA where they are subsequently read in and used to interpret stick commands.  In this manner, the differences between individual transmitter and receivers are overcome.

With the trims at maximum, we normally associate 100 as 1.0 msecs = absolute low stick, 150 as 1.5 msecs mid-stick and 200 as 2.0 msecs as absolute high stick.  With the trim in centre, the values are reasonable.

The user enters the calibration routine by removing the gear servo lead and plugging in the jumper.  The transmitter throttle stick is moved to the low position.  Then the transmitter and receiver are powered up, the PIC senses a zero input on GP4 and enters the configuration routine.  The LED flashes 5 times and reads in 5 values for the low stick position.  The 5 values are then averaged.  The LED then goes solid for 5 seconds to tell the user to move the throttle stick to the high position.  The LED then flashes five times as it reads 5 values of the high position.  These high five ;-) are then averaged.  The PIC code then adds the low to the high value and divides it in half to compute the mid-stick.  Low, high and mid-stick values are then written to EEDATA on the PIC.  The LED goes solid and stays on to tell the user the routine is ended and to switch off the receiver.

The user then removes the jumper and plugs the gear servo lead onto the input pin and the receiver is powered on again.  Now the PMW on GP4 will read as a non-zero value and normal operations will occur.

When on the water, the user selects GEAR DOWN to engage steering using both water rudders and the engines.  The throttle will follow the power setting on both engines until the rudder stick is moved away from centre.  Then the inboard engine will freeze at the power setting and the outboard engine will follow any subsequent throttle movement.  When the rudder is brought back to centre, the inboard engine will match the outboard engine.  If the outboard is higher than the inboard, then the inboard recovers slowly so that engine problems do not occur.

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Last modified: March 18, 2004