Replies to This Discussion

ModeratorPermalink Reply by Sgt Ric on August 30, 2010 at 11:14am

Why two channels?

Normally we use a Y cable to connect the two servos.

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Permalink Reply by palo sestak on August 30, 2010 at 11:24am

Because i usually configure ailerons as brakes and/or flaps. My aiframe is bit bigger and these are useful.

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3D RoboticsPermalink Reply by Chris Anderson on August 30, 2010 at 11:20am

That's something on the features list for a future version. The vast majority of users use a Y harness to control two aileron servos with the same channel, so we're focusing on them first. But it's a pretty simple code enhancement to do it on two channels. Just not a top priority for the dev team right now, although since the code is open source you're very welcome to add that functionality yourself.

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Permalink Reply by Ritchie on August 30, 2010 at 12:16pm

If you mean control your ailerons over two channels (but they move in same direction). Do not modify any code just use a Y-connector (like I have had to do) on the (single) aileron channel.
If you want control over either aileron (one up, one down - for spins) then you need to use aileron/elevator mixing ("elevons") which uses the aileron channel and elevator channel (like I want to do as soon as the code is implemented).

This information is based on Ardupilot Mega but the Ardupilot normal already does it as far as I believe.

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Permalink Reply by palo sestak on August 30, 2010 at 11:21pm

I use two ailerons in different directions - one up and one down. Moreover these two channels are mixed and can be used in the same direction - brakes/flaps. That's why i thing it's not good idea to use elevon mix. I need elevator completely independent from ailerons.

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DeveloperPermalink Reply by Doug Weibel on August 31, 2010 at 10:30am

Palo,

It is on the future features list and is something I will probably implement in the next couple weeks. I will probably implement a flaperon/spoileron feature as well. You are in luck, because it is something I would like to use now, so it has risen in the priority list ;)

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Permalink Reply by Curt Olson on August 31, 2010 at 12:18pm

Here's a potential problem though ...

Most RC transmitters I've seen use channels 1 + 6 for individual aileron control. This means you probably have ch1/ch6=aileron, ch2=elevator, ch3=throttle, ch4=rudder, ch5=manual override.

If you want to be able to switch between manual mode and autopilot made, this means your manual over ride system needs to be able to switch 5 channels. The current ardupilot and ardupilot mega only have circuitry to switch 4 channels.

Thus there can't be just a software fix (unless you are willing to drop one of the other channels from autopilot control.)

The ardupilot was originally designed with ultimate simplicity in mind ...

It might be possible to run two ardupilots in parallel to allow you to switch more than 4 channels between manual/autopilot, but then you would need to somehow devise a scheme to slave one ardupilot from the other, and between gps and ground station telemetry, you've run out of communication options on the ardupilot. You could connect two ardupilots to a 3rd control board that supports at least 2 serial ports (well maybe 4) and handle gps and ground station IO from this other board.

There are potential solutions if you want to get creative, but they involve diverging from the blessed path and stringing a lot more hardware together.

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ModeratorPermalink Reply by Sgt Ric on August 31, 2010 at 1:20pm

Forgive me if I am being a little dense here, but the channel to switch modes is not counted as one of the output channels.

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Permalink Reply by Curt Olson on August 31, 2010 at 3:13pm

Sgt Ric: if you are checking the math in my post, then first we really need to hear back about the specific needs of the original poster. But let me try again ...

The ardupilot and ardupilot mega can switch 4 channels.

On a typical 4 channel RC airplane, the channels are assigned like this:

ch1 = aileron
ch2 = elevator
ch3 = throttle
ch4 = rudder

This is indeed 4 channels, and the 5th channel is the selection switch which doesn't need to get switched. If you have one servo per aileron, you simply run a "Y" harness from ch1 to control both aileron servos together.

If you wish to add independent aileron control (which is a feature of many transmitters) for doing flaperons, spoilerons, differential throws, and other fancy mixing modes. you can no longer use the "Y" harness. When you configure this mode, the transmitter assigns one aileron servo to ch1 and the 2nd aileron servo to ch6 (this is the typical assignment anyway.) This adds another channel to the requirements. You now need to switch 5 channels:

ch1 = aileron1
ch2 = elevator
ch3 = throttle
ch4 = rudder
ch6 = aileron2

Note that all the fancy mixing modes are handled at the transmitter and each aileron servo is sent a separate control signal so that they can move independently.

So if you want to setup your aircraft like this (which is a very common way to do it in the RC world) *and* you want to be able to have control over all your servos in manual mode *and* you want the autopilot to be able to have control over all your servos in auto mode, then you have a problem ... you need to switch one more channel than the ardupilot/ardupilot-mega can switch.

One option would be to drop the rudder channel and wire that directly to the receiver so it is always under manual control, now you are back to 4 channels again. There may be other clever hacks/work arounds to get something useful done, but switching only 4 channels is a definite limit as you move up the RC food chain.
Regards,

Curt.

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Permalink Reply by palo sestak on September 2, 2010 at 12:05am

Sorry, perhaps my note is bit kind of lame but i'm really novice in Ardu HW - is that problem of board or something in circuits in Ardu pilot that it supports only 4 channels?
I mean if there would be another one output (the same like for present 4 out channels) then this is only problem of SW update.
Just asking - 4 output channels for servos is that ArduHW limitation?

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DeveloperPermalink Reply by jasonshort on August 31, 2010 at 3:45pm

When Doug finishes the Math in Mega I will add this to the existing Ardupilot. You will need to do some creative wiring but I have a implemented 6 channel out in software.

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Permalink Reply by Greg Fletcher on August 31, 2010 at 6:34pm

This can be easily done with an external V-tail mixer board. The flap/brake will be strictly manual. The rudder input to the mixer will be aileron (from AP) instead and elevator input will be flap channel direct from the receiver. Program your transmitter for normal(1 servo)aileron mode. Flaps will be channel 6. Get everything going the right way, set end points ect.

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