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[Tugger]

could anyone out there tell me how to modify an optic 6 so that i can have a switch which will have a centre off and a function on each throw. I want to operate a towing winch on a tug. I have two spare channels one on a slider and one on a two way switch which is normally used for the undercarriage on an aircraft.

[Model Boats Website]

Tugger,

You will have to use the channel with the slider since it will work with variable resistance. Disconnect the three wires going to the variable resistor and find out what the full resistance across the pins. Also take note of whether the full swing is being used on the variable resistor (some controllers only use about 45 degrees swing on the pots).

Then, get hold of a two-way spring return switch (I think this will do the job) and wire up the pins as below:

The resistors shown in RED will need to be added if the full swing of the old potentiometer was not being used.

Now the calculations:
If full swing was being used

Each resistor = half the old potentiometers full resitance.

If full swing was not being used

Find the reistance shown, this is the resistance of the resistors shown in RED.
Subtract that resistance from the full resistance and divide by two to get the resistance value of R1 and R2.

Hope this helps, if you get stuck send me an email, I might stick a page on my site that will explain a little better.

[Tugger]

Thanks for the info I will give it a go. If I get stuck I will email you at modelfireboats.

[OMK]

Tugger, what Fireboat has said is pretty much spot on. Further to what he's saying, you might want to know that the majority of transmitters use a value of around 5000-Ohms for each gimbal pot. If this is the case with your Tx, then it's possible you might hit a few problems with the resistance values that Fireboat has shown. Nothing wrong with his schematics - merely a possible hiccup with the calculations, is all. You might find that your servos will glitch. It's probably because the timing sequence of the encoder pulses will be out of sync.  But eyeballing the actual pulse on a 'scope shows that the majority of Tx gimbal pots have been pre-set to a value of approximately one-third total pot resistance. This puts the channel pulse at 1.5mS of the encoder's frame rate and corresponds with the servo being at neutral (centre) position. Fireboats' suggestion of halving the total pot resistance means you'd likely experience those out-of-sync glitches. If I'm not stepping on Fireboat's toes, might I suggest the values shown in the attachment. Being that a 2-position switch is used, it means the servo can be switched either fully CW or fully CCW.
You also mentioned that you need a switch with 'center-off' action. This can be done. It would result in, say, a servo being fully CCW with the switch in the 'up' position; servo neutral at 'center' position, and servo fully CW at switch 'down' position. But it needs a slight change to the way the resistors (and their values) are connected. You'll need a SPST 'center-off' toggle switch.

Fireboat, I'm still using dial-up. Well worth the wait to see them vids, though.
Nice work!