Two channels on one servo

[Wingin' Wayne]

I'm teaching my son to fly a Slo Stick. I remember the trouble I had going to a four channel and haveing the rudder on the right stick, ailerons are not for ground handeling. My question is, can I connect channel one and channel four to the same servo? Then it would ground handle on the left stick and fly on the right stick like a four channel plane. Logic tells me the signal would loop back into the receiver or something like that. Could someone please give me an answer or an idea of how to do this, other than starting with the rudder on the left stick.

Thanks,
Wingin' Wayne

[Bruce Abbott]

You can't do it with a Y cable, as each channel would short the other one out.

A vtail mixer should work (eg. GWS V-TAIL MIXER-II (http://www.gws.com.tw/english/product/aux%20circuit/010.htm)). Plug the mixer's input cables into the aileron and rudder channels on your RX, and connect the rudder servo to one output.

If you have a computer radio then it may have built-in aileron to rudder mixing available.

[Sparky Paul]

I'm teaching my son to fly a Slo Stick. I remember the trouble I had going to a four channel and haveing the rudder on the right stick, ailerons are not for ground handeling. My question is, can I connect channel one and channel four to the same servo? Then it would ground handle on the left stick and fly on the right stick like a four channel plane. Logic tells me the signal would loop back into the receiver or something like that. Could someone please give me an answer or an idea of how to do this, other than starting with the rudder on the left stick.

Thanks,
Wingin' Wayne
With a computer radio, you can put the rudder servo on the rudder, and on the left stick, and mix the right stick to the rudder channel... 1->4 MIX..
This gives both rudder steering with the left stick, important when taxiing, and turning with the right stick in the air.
It's simple to add ailerons to the right stick when that time comes.
Otherwise, don't taxi, and fly from handlaunch, with the rudder on the right stick for turning.

[BMatthews]

..... Logic tells me the signal would loop back into the receiver or something like that....

You've already gotten the how but no one mentioned the why.

The signal to the servo is a very short pulse that changes it's width as the Tx stick moves. The servo looks at that pulse width and uses it to figure out where to put the output arm. That's the simple explanation.

But if you connect two channels to the servo it'll see two pulses that are not the same width and it won't know which one to pay attention to. The result will be it'll constantly jitter back and forth in response to each one that comes in trying to move to the spot the most recent one requested. It's sort of like if you took the stick and moved it back and forth extremely fast so the servo doesnt have time to reach the one spot before it sees a command to move back the other way. It'll also be drawing a LOT of power from the flight battery as it fights to obey these two bosses.... and we all know how poorly that works and the stress on the guy in the middle.... :D