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Trasmitter hack, replace var knob with 3 pos switch HELP im a noob!! LOL

#1
So I want to hack my cheapo Hobby king 6ch Transmitter to have 3 pos switches for ch 5 and 6 instead of the var knob. So my understanding is that the knob is obviously just a variable resistor, and im thinking that a 3 pos switch has 3 or resistors or maybe just 2. i was wondering if anyone has done this before and knows what the value of the resistors I would
 

PHugger

Church Meal Expert
#2
I'm not sure this post is in the right sub-forum. Perhaps on of the admins can move it to a more appropriate location where people will see it and respond.

This should be easy enough to figure out if it will work, providing you have a few basic tools like a multi-meter that can measure resistance. Power up your model and use the variable knob to set what ever it is you are trying to set to it's various configurations. If it works, note the positions of the knob you are interested in. Power everything down. Carefully un-solder the leads to the potentiometer. Measure the resistance at the various positions. Before removing the potentiometer or modifying the case, temporarily wire up your 3 position switch with the appropriate resistors in the circuit. Test it out. If it works - great! If not, you can still put it back together as it was with any permanent damage.

I'm pretty sure one of our resident EEs like Dan can tell you the straight poop......



Best regards,
PCH
 

Epitaph

Ebil Filleh Pega-Bat ^.^
Mentor
#6
Basically, what people are recommending is a small switch somewhere that you can change from one position to another and thus decide if the channel will be controlled by a pot or a switch at that moment

Switch+Pot mod.jpg

This is the basic diagram to do it. I put down a slider as the selector because they are smaller and you wouldn't knock it easily in flight by mistake.

There is no need to add resistors as when the pot is in full throw on one side or the other, the signal wire is in direct contact with the positive or negative depending on which way you have turned it. You won't be burning anything out as there is a resistor already in line with the signal wire due to the fact that it started out life as a pot. On that diagram they are adding it for centring reasons, but there is no need as when there is no signal going into the pot signal it is centred. If you want to test out the theory, put a switch in line with the signal wire you have on the pot... when the switch is on, the servo will be positioned depending on where the pot is, but if you turn the switch off, the servo will centre (unless you have some weird setup in your radio, which I have never seen). I have done this tupe of mod on several transmitters and it works fine without resistors or a 1P3T switch.
 
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pressalltheknobs

Posted a thousand or more times
#7
There is no need to add resistors as when the pot is in full throw on one side or the other, the signal wire is in direct contact with the positive or negative depending on which way you have turned it. You won't be burning anything out as there is a resistor already in line with the signal wire due to the fact that it started out life as a pot. On that diagram they are adding it for centring reasons, but there is no need as when there is no signal going into the pot signal it is centred.
That's nifty.