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Dual Receiver Questions

Old 05-05-2005, 09:06 PM
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Default Dual Receiver Questions

I have read that when using a dual receiver setup in your plane you hook one side to one receiver and the other side to the other receiver. I have a few elementary questions on this setup:

1. Does it matter if you run right side to #1 and left side to #2 or should you cross the surfaces, i.e., L elevator, R aileron, etc.

2. A typical setup would be L aileron, L elevator & rudder on one receiver with a battery and switch; and R elevator, R aileron & throttle on the other receiver with another battery and switch?

3. Does it matter how you run the two receiver antennas in relation to each other? Could you run them down the same antenna tube?

4. Are you likely to have any trim issues between the two receivers and your radio?

5. Is there anything special to watch out for if you do loose one receiver.

6. What would happen if you ran something like the choke (engine kill switch), or even the throttle off a Y into both receivers.

Any other comments on this system are appreciated.
Old 05-05-2005, 09:25 PM
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Default RE: Dual Receiver Questions

ORIGINAL: splais
1. Does it matter if you run right side to #1 and left side to #2 or should you cross the surfaces, i.e., L elevator, R aileron, etc.
I like to cross the surfaces. I feel it makes it easier to control by helping to eliminate some of the asymmetry.

ORIGINAL: splais
2. A typical setup would be L aileron, L elevator & rudder on one receiver with a battery and switch; and R elevator, R aileron & throttle on the other receiver with another battery and switch?
Yes, or if you cross them, L aileron, R elevator on one receiver, etc... It would be best to split the throttle on one side, and a kill switch or choke on the other. That way you will have some control over the engine no matter which receiver quits.

ORIGINAL: splais
3. Does it matter how you run the two receiver antennas in relation to each other? Could you run them down the same antenna tube?
It does. You want to run them as far apart as possible. Most will run one down the upper left side of the fuse, and the other down the lower right side of the fuselage. You can also run one down the wing, and the other down the fuse. You never want to put them in the same antenna tube. Also, its best to keep separation between the receiver mounting points as well. I find 4-6" adequate.

ORIGINAL: splais
4. Are you likely to have any trim issues between the two receivers and your radio?
No, they receive the exact same instructions from the transmitter, and will react accordingly. If you setup the linkages properly, there won't be an issue.

ORIGINAL: splais
5. Is there anything special to watch out for if you do loose one receiver.
Yes, controlling the airplane

ORIGINAL: splais
6. What would happen if you ran something like the choke (engine kill switch), or even the throttle off a Y into both receivers.
You don't want to do this since the receivers are not in sync with each other. Basically, the instructions to the servo will not be in perfect sync, and thus will confuse the servo. You also don't want to run servos separately to each receiver, then connect the servos via control linkages to the same control surface.

Hope this helps.
Old 05-05-2005, 09:34 PM
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Default RE: Dual Receiver Questions

Stephen,

Nice post...well put and easy to understand, even for me
Old 05-05-2005, 10:38 PM
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Default RE: Dual Receiver Questions

A question about failsafe with dual recievers. I would think it would be better to have them all set for a neutral failsafe postion. This way if one reciever locks out it would send the affected servos to the preset neutral positon. If they were set for Hold you might have the affected servos at an extreme postion, which might make the model uncontrolable.
I would think the best way would have all set for neutral in failsafe and this would give you the abilty to control the model with the other reciever. Whats everyone elses thought on this.
Old 05-05-2005, 10:48 PM
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Default RE: Dual Receiver Questions

thanks Stephen, well written.
Old 05-05-2005, 11:03 PM
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Default RE: Dual Receiver Questions

Mark,

Agreed, for the reasons you mentioned. Its also another reason why you don't tie a servo for RX1 and another servo from RX2 to the same control surface with linkages. If one receiver goes into failsafe, or tries to hold the control surface steady, the other working receiver will be commanding the other servo to drive the control surface. You will have two servos fighting each other on the same control surface which will cause a high current drain and receiver power clipping.
Old 05-06-2005, 04:37 AM
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Default RE: Dual Receiver Questions

Antenna routing:

The two antennas need to be run in a non-parallel manner. I run one antenna along the bottom of the fuse and the second antenna to the tip of the vert stab.

Hook the choke to the rx without the throttle. Then if you loose the rx with throttle control, you can still kill the engine to land the plane.

Elson
Old 05-06-2005, 11:42 AM
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Default RE: Dual Receiver Questions

Elson,
I think you have hit on somehting I never gave much thought to. I am a big advocate of dual receievers. Only downside I can see other than expense (insugnificant in my opinion) is the reduced range. I never considered running antenna's non parrallel. Is this enough to recover some of the range? Can you elaborate on it any?

Thanks in advence, great idea. I think I'll get into the wave propagation books today and see if I can come up with supporting data.
Thanks,
Kev
Old 05-06-2005, 12:17 PM
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Default RE: Dual Receiver Questions


ORIGINAL: rc bugman
Antenna routing:

The two antennas need to be run in a non-parallel manner.
Well, I disagree that they NEED to be run in non-parallel, Ive flown, seen and owned planes with them in the same direction and zero range issues.
Old 05-06-2005, 12:48 PM
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Default RE: Dual Receiver Questions

John, they don't NEED to be run non-parallel, but they should be for the best range. There is indeed a loss of range running the antennas in parallel, and most RF engineers will confirm that. I think it comes down to how much of a loss is it, and what pilots will accept. I've run them parallel, and did notice a loss, but it wasn't that much for me to worry about. There are some pilots that any loss would be unacceptable, and I bet there are others that would accept a much greater loss and say, "well, lets take her up and see what happens!" Gasp! On top of that, in some airframes, running them parallel could be a disaster with greatly reduced range, while in others they may only loose a few percent. RF is a funny animal, and each installation is different.

I typically run them in parallel, but with good separation. If I see a loss in range over my other installations that concern me, I rearrange the antennas. Only once did I have to rearrange them, and all I had to do is run them down the fuse slightly skewed from each other, and my range was back.
Old 05-06-2005, 01:56 PM
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Default RE: Dual Receiver Questions

Can you mix receivers? PCM / FM
Old 05-06-2005, 02:46 PM
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Default RE: Dual Receiver Questions

PCM and FM can not be mixed. The radio will only send out one signal at a time either FM or PCM.
Old 05-06-2005, 02:58 PM
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Default RE: Dual Receiver Questions

Your right, I forget about that.
Old 05-06-2005, 07:19 PM
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Default RE: Dual Receiver Questions

Maintaining as much physical separation between the antennas within the fuselage as possible is best, same with the RX's themselves (some believe this is more important).

Ideally you’d route one antenna 90 degrees from the other (such as within a wing panel). They are then (sorta) out of phase.

Every install is physically (and electrically - on all levels) different, the bottom line (once again) is (and will always be) the rigorous range testing you will perform pre-first flight to look for anomalies...
Old 05-07-2005, 08:07 AM
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Default RE: Dual Receiver Questions

Mark,
I run duals in my wildhare extra. In regards to your failsafe I set all of my servos to neutral EXCEPT the throttle I set the throttle to failsafe to idle. So if on take off or maybe downline more so takeoff and landing the plane slows and is a MAjor safety BENEFIT.

Don't overlook making a jumper to run from one receiver to the other. This will allow power to one if say a switch or battery open failure. Make the jumper available to disconnect for charging
Old 05-09-2005, 08:48 AM
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Default RE: Dual Receiver Questions

Being new to the duel rx system. Can someone explain how the hook-up is made?
Old 05-09-2005, 05:49 PM
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Default RE: Dual Receiver Questions

What I do is my choice and differs by any person. I use 2 receivers each having its own switch and battery. One receiver powers one half aileron and elevator. Rudder is put on either one. One receiver has throttle while the other uses the choke servo. I keep one channel on each open which I use for a positive and negitive wire jumper to attach. no signal. I remove this wire connection when I charge the batterys so there is no question of charging system problems. I use mpi switches so with the jumper removed you can easily test individual battery power. Hope this helps.
Old 05-09-2005, 06:11 PM
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Default RE: Dual Receiver Questions

You can also use Y connectors on either the battery connection or any of the servo ports if you have a situation where all available servo ports are required.
I have done one jumper where I changed the female end to a mail so that it could be plugged and unplugged from the other Y rather than plugging and unplugging from the second receiver.
ORIGINAL: b-mccor8

What I do is my choice and differs by any person. I use 2 receivers each having its own switch and battery. One receiver powers one half aileron and elevator. Rudder is put on either one. One receiver has throttle while the other uses the choke servo. I keep one channel on each open which I use for a positive and negitive wire jumper to attach. no signal. I remove this wire connection when I charge the batterys so there is no question of charging system problems. I use mpi switches so with the jumper removed you can easily test individual battery power. Hope this helps.
Old 05-10-2005, 08:54 AM
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Default RE: Dual Receiver Questions

Thank you for all the input. But can he two rx's be used in tandem? That is, so if one fails the other will take over the control of the aircraft. That also is not hooking the rx's on thier half of the system, but both will control the system equily and if one does fail the other will take over. Hope this makes some sense. Or am I barking up some tail feathers?
Old 05-10-2005, 09:06 AM
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Default RE: Dual Receiver Questions

padoni wrote:
Being new to the duel rx system. Can someone explain how the hook-up is made?
I don't know if similar systems are available in the U.S. but this is how its done in the old world nowadays:
[link=http://www.acteurope.de/html/body_diversity-empfang.html]http://www.acteurope.de/html/body_diversity-empfang.html[/link] (sorry about the german link).

/Red B.
Old 05-10-2005, 09:33 AM
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Default RE: Dual Receiver Questions

Sounds like more work and worry that its worth....

We tested a Dual JR 945 RX setup in a Carden recently. With two receivers, engine off range was 90 feet. Engine on range - 75 feet. We disconnected one receiver and engine off range was 150 feet and engine on range was 145 feet. These were measured with a distance measuring tool, not "paces". On the dual receiver setup the RX went into lockout several times at 60 feet.

Antennas were not routed near each other and RX's were 10" apart.

There are plenty of people who run dual JR's.... I wont though.

The plane is being flown on a single 945... flies great!
DP
Old 05-10-2005, 09:05 PM
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Default RE: Dual Receiver Questions

DP

Were the antennas parallel? That type of range loss is typical of parallel antennas. JRs are known for poor interference resisitance since they are single conversion.

The most selective receivers I have tested (I have tested a lot of them because I carry 1.5 watt txs on board) are FMA. I currently use a FS-8, a PPM with fail safe or last frame hold on one side and a Quantum (PPM without last frame hold) on the other side of the airplane. I believe this setup is the best of both worlds. It allows you access to the airplane regardless of the lockout type of interference.

Dual PCM or PPM with last frame hold or failsafe can lock you completely out of the airplane with no chance of recovery. Been there, done that. Plane with 40 minutes of fuel went deaf and the plane was recovered 65 miles away. Scary incidence but no harm.

Elson
Old 05-10-2005, 11:08 PM
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Default RE: Dual Receiver Questions

I'd like to raise the question about best failsafe when running two RXs. I have lost two planes to lockouts, running single RX. I had failsafe set to all surfaces neutral, and engine to idle. Well, when a plane goes into failsafe during 3D at high altitude, guess what, it points its nose to the ground, and a few seconds later it's RIP. I had failsafe set as I did, because I always expected lockouts to only last a very short time, (fraction of a second - 2 seconds), and you could fly on from there. Now, I have my failsafe set to full up elevator (3D style), since plane will most likely hit ground at least airspeed this way, and the least amount of internals (engine, engine parts, headers, pipes, servos, ignition, batteries, etc.) will have the best chance of surviving. I hold no hopes for saving a 40% plane in lockout, but the airframe is only part of the whole package.
Now, my question. I understand how, with dual Rxs, setting failsafe to all surfaces neutral and engine to idle, will make the plane most controlable, if one RX goes into failsafe. BUT, ask yourself this, why does an RX go into failsafe? If one RX loses signal, do you think the other RX gets any? If the crystal goes bad or shakes lose, does a PCM RX go into failsafe? If an RX craps out internally, does it go into failsafe? If the answer is, that only when a PCM RX loses signal does it go into failsafe, then you have to ask yourself, what are the chances that the other RX gets a good signal, and are chances that both RXs go into failsafe. And if so, is the neutral failsafe position really the best?
DKjens
Old 05-10-2005, 11:22 PM
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Default RE: Dual Receiver Questions

I might be missing something here. Admit I've never read about it or used it intentionally. But isn't failsafe "in" the transmitter. If one receiver craps out and is not receiving a signal then the transmitter can sand all the failsafe signals it wants but nothing will happen. Is this not true. Or it will send a failsafe signal to both receiver and you still loose the plane. So I'm thinking the failsafe issue is not relevant to this 2 receiver discussion. Were am I going wrong.
Old 05-10-2005, 11:59 PM
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Default RE: Dual Receiver Questions

You go into lockout it does not matter HOW many receivers you have. 1, 2, or 10. Lockout is lockout. You are hosed.

Lockout is caused by INTERFERENCE. If you have INTERFERENCE it will effect BOTH (or all 10) receivers. Matters not.

2 receivers are nifty if they make you fell all warm and fuzzy. If you INSIST on running them the ONLY way that makes any sense is to use the Emcotec DPSI-Twin unit. Give TOTAL redundancy.

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