Dual elevator servos?
01-03-2015, 03:31 AM
#1
Thread Starter
Dual elevator servos?
I've never had a model with a servo for each elevator half (in the tail). So how do I do the radio setup for this? In my hazy thinking I imagined I could just connect the two with a Y-harness and then a long lead to the Rx. But the Y-harness reverses one servo. Or is there some other type of Y-harness needed? Or is the additional elevator servo also connected to the Rx, and if so how?
I'm using an 8-ch Airtronics RDS8000.
I'm using an 8-ch Airtronics RDS8000.
01-03-2015, 07:11 AM
#3
Thread Starter
This 30% ARF is designed for two (mounted externally in the tail as on aerobatic models). I don't want to mess with that. There must be a standard way of doing this since it's very common with large aerobatic models.
01-03-2015, 07:52 AM
#4
You can use a reversing Y cable which will reverse one side of the Y. Available from MPI - Max products. The problem with this set up is that each servo may not move at the exact same speed or the exact same degree of throw on one side or the other. Sometimes you can adjust the programming of digital servos to even things up. Another problem is that long wire runs sometimes cause problems, ether because of voltage drop or the introduction of interference.
If you have a computer radio that supports dual elevator mixing then the problem is much easier and depending on the radio you can adjust throw and speed directly from the transmitter so the servos operate exactly the same.
Hopefully some of the giant scale guys will jump in and offer more specific help.
If you have a computer radio that supports dual elevator mixing then the problem is much easier and depending on the radio you can adjust throw and speed directly from the transmitter so the servos operate exactly the same.
Hopefully some of the giant scale guys will jump in and offer more specific help.
01-03-2015, 01:32 PM
#7
Thread Starter
Art, I always read the manual...right after I try everything else and come to my wit's end. 
Seriously, I just didn't even think about this since the dual setup seems so common. When I was ordering the long (twisted) servo leads, almost without thinking I order enough for both servos. It was only much later that it occurred to me to wonder where I would plug in TWO elevator leads.
Anyhoo, looks like it's RTFM time. (My worst fear is that I'll discover that "you can't get there from here" i.e. that I can't do this with my current Tx.)
Seriously, I just didn't even think about this since the dual setup seems so common. When I was ordering the long (twisted) servo leads, almost without thinking I order enough for both servos. It was only much later that it occurred to me to wonder where I would plug in TWO elevator leads.Anyhoo, looks like it's RTFM time. (My worst fear is that I'll discover that "you can't get there from here" i.e. that I can't do this with my current Tx.)
01-03-2015, 01:41 PM
#9
If your TX does not support dual elevator servos you can look into a Smart Fly Equalizer. This little device will plug into your elevator channel, and then you plug your elevator servos into it. The device allows you to reverse either one of the servos, adjust their center and end points independently so you can match up the elevator travels perfectly. Something you just can't get with a reversing Y.
01-03-2015, 02:13 PM
#11
Thread Starter
That Smart Fly Equalizer looks like I clever bit of electronics...and at a reasonable price. And I'll reconsider my assumptions about the aileron connections as well. This large model is challenging a lot of my "standard" knowledge about RC.
01-03-2015, 02:33 PM
#12
JR Matchbox, Smart Fly equalizer are both viable options but really, why spend the money when your radio will do it for free?
Also, when you get into larger aerobatic designs most of us go to metal servo arms like Seacraft or SWB. Unlike a standard 4 prong plastic arm where you can center the servo and rotate the servo arm around until you find the place on the spline where it lines up 90 degrees, you're pretty much stuck with as close as you can get with a metal arm. This is where you get into needing sub trim for each servo get your linkage geometry correct. Your radio already does all this, just take the time to figure out how
Ahh twisted extensions...... yes there is no reason not to use them but for RC they don't provide any benefit, other than looks, they do look pretty
I know that places like Tail Dragger that sell heavy duty extensions made of 20g silicon wire, they twist them because they have no choice because that wire gauge isn't available in ribbon strips like 22g servo wire. But hey, if it makes you feel better, then it is better.
Also, when you get into larger aerobatic designs most of us go to metal servo arms like Seacraft or SWB. Unlike a standard 4 prong plastic arm where you can center the servo and rotate the servo arm around until you find the place on the spline where it lines up 90 degrees, you're pretty much stuck with as close as you can get with a metal arm. This is where you get into needing sub trim for each servo get your linkage geometry correct. Your radio already does all this, just take the time to figure out how
Ahh twisted extensions...... yes there is no reason not to use them but for RC they don't provide any benefit, other than looks, they do look pretty
I know that places like Tail Dragger that sell heavy duty extensions made of 20g silicon wire, they twist them because they have no choice because that wire gauge isn't available in ribbon strips like 22g servo wire. But hey, if it makes you feel better, then it is better.
01-03-2015, 02:36 PM
#13
That's what I love about the Z-series Futaba radios. The first step in setting up a model is telling the radio how many elev. channels, how many ail. channels, etc. Once you do, the radio assigns everything to it's own channel. Then you go to the function menu to see what the channel numbers are and plug the servos in accordingly. The radio does all the mixing for you. The DX6 and DX9 that I played with worked the same way. Enough to make a guy lazy.
01-03-2015, 02:43 PM
#14
That's what I love about the Z-series Futaba radios. The first step in setting up a model is telling the radio how many elev. channels, how many ail. channels, etc. Once you do, the radio assigns everything to it's own channel. Then you go to the function menu to see what the channel numbers are and plug the servos in accordingly. The radio does all the mixing for you. The DX6 and DX9 that I played with worked the same way. Enough to make a guy lazy.
01-03-2015, 02:52 PM
#15
Thread Starter
I'll definitely be reading my RDS8000 manual today. The Equalizer would be an alternative to having to buy a new Tx/Rx system, if the RDS8000 doesn't have this feature. And, yeah, I know what you mean about that "closest gear" problem. That occurred to me as I was setting up the linkages. On this ARF, the kit includes heavy duty servo arm extensions that bolt onto the standard circular "arm" that comes with the metal gear servo.
01-03-2015, 03:04 PM
#16
Yea, about those, they work but you might want to think about something better. I have used those before but depending on your flying style you risk the plastic wheel skipping a tooth, especially on the rudder. Flying scale I wouldn't sweat it too much but you plan on cranking up the throws and hammering it, you might want to think about metal arms. If not, then dont sweat it.
01-03-2015, 03:13 PM
#17
Thread Starter
I only plan of making pretty circles around the sky with this model. Maybe eventually, after I pull the engine out to use on a truly scale WWI model, I'll replace it was a gasser and then get those metal arms.
Just checked the RDS8000 manual. No prob. Dual elevator mixing by plugging the left elevator into the normal channel 1 and the right half into channel 7. This then allows separate adjusting of EPA, REV, CENTER, and FAILSAFE positions.
Just checked the RDS8000 manual. No prob. Dual elevator mixing by plugging the left elevator into the normal channel 1 and the right half into channel 7. This then allows separate adjusting of EPA, REV, CENTER, and FAILSAFE positions.
01-03-2015, 05:09 PM
#20
There is a theory that 2 elevator servos gives you a slight safety benefit due to the redundancy. That if one elevator servo screws up, you have a chance of being able to save the airplane. Like if the ailerons go, you still have the rudder. I am NOT volunteering to test the theory.
01-03-2015, 06:39 PM
#23
Thread Starter
Guys, up to now, I've just had no need for anything fancier than a basic 4-5 servo setup. So there wasn't much need to "read the manual." But it's good to try new things. The RDS8000 is an 8-channel Tx and I've always used it with the 8-ch Rx it comes bundled with. The only time I've used anything other than E, A, R, and T channels was when I set up aileron differential on one model.
01-03-2015, 06:43 PM
#25
Thread Starter
There is a theory that 2 elevator servos gives you a slight safety benefit due to the redundancy. That if one elevator servo screws up, you have a chance of being able to save the airplane. Like if the ailerons go, you still have the rudder. I am NOT volunteering to test the theory.