RUDDER MIXER

This PICAXE based project was designed to improve the manoeuvrability of twin motored boats and this is achieved by mixing in the rudder (steering) demand in equal and opposite amounts to each ESC (Electronic Speed Controller). Thus, for example, when turning to port the starboard motor speeds up and the port motor slows down to assist the turning action. If the boat is stationary, rudder application will drive one motor forwards and the other in reverse allowing the boat to literally turn on the spot. A major difference from the commercial rudder mixers I have so far encountered is that the proportion of rudder mixed into the throttle signals can be adjusted by the user - I found that the usual 100% mix resulted in the boat accelerating whilst turning, and I now use about a 60% mix for a decent balance between low speed manoeuvrability and good steering behaviour when under way.

Transistor buffers are used to condition the rudder and throttle signals from the receiver. The output voltage swing of some receivers (especially 2.4Ghz types) has been found to be insufficient to trigger the PICAXE 08M (Schmitt Trigger type) input. The potentiometer is used to set the proportion of rudder mixed into the two throttle outputs.

As can be seen from the picture, the unit is easily constructed on stripboard and has been designed to utilise a small flanged ABS box (Technobots #2800-225) which will afford protection against accidental shorting and/or moisture. The rudder demand is passed directly through to a 3 pin header for the rudder servo to be connected to, thereby obviating the requirement for a Y lead. The two ESCs are plugged into the remaining two 3 pin headers.

Those of you wishing to build one for yourselves should follow the link http://www.technobotsonline.com/rudder-mixer-by-alan-bond.html where you will find additional technical detail, a stripboard layout diagram and parts list (all parts are available from Technobots).