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Dual Receiver Questions

Old 05-11-2005, 12:14 AM
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Default RE: Dual Receiver Questions

Attached is picture of my airplane, it is a 40 pound twin with two G-62's. I still have this airplane thanks to having two complete radio systems installed, two recievers, two batteries, two switches, etc.. One system is connected to the right side elevator, aileron, and engine, and the other system is connected to the left side surfaces. I was flying one day when one of my batteries failed [X(] I noticed that control of the plane was sluggish and knew immidiately what happened, but instead of watching my plane crash I just flew with the equivelent of slow rates. The engines were at half power when the battery died, so the dead side was stuck at half throttle and there was no landing the plane until that engine ran out of gas. After over a half hour of circling the gas finally ran out on the bad side and I brought the good side out of idle and made a normal landing . I would recommend running two seperate systems whenever you have a lot invested in an airplane, it saved my butt, works well, and gives me a lot of confidence in my model. I can enjoy flying more not having to worry if the radio is going to quit and destroy my plane .
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Old 05-11-2005, 12:31 AM
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Default RE: Dual Receiver Questions


ORIGINAL: splais

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.

Fail-safes are stored parameters within the RX. The TX transmits the failsafe parameters to the RX during set-up; the RX subsequently stores them and recalls them when needed.
Old 05-11-2005, 12:37 AM
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Default RE: Dual Receiver Questions

ORIGINAL: JettPilot
I was flying one day when one of my batteries failed
Of course dual receivers had NOTHING to do with this. If you had TWO batteries in parallel into a single receiver you would have had an even better result by not having to fly around waiting for the other side to come back.

You did NOT have a receiver failure, so dual receivers had NOTHING to do with this "success". In fact your dual receiver and single battery per receiver caused a bigger potential problem.
Old 05-11-2005, 05:16 AM
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Default RE: Dual Receiver Questions

This is why I stated this is what I do for the mear fact the discussion always brings about arguments. If you want to use dual receivers use them if not don't. Don't talk people out of them. I have witnessed a 40 percent saved by a dual setup for a receiver failure. Half control is better than none. The failsafe is a crap match. 3d rates for a failsafe is a horrible idea. The purpose of failsafe is safty not plane recovery. The aircrft is most dangerous on take off and landing. Just imagine 3d elevator on a failsafe takeoff, snap in to someone . There are to many what if it was here when it goes into failsafe. It is a crap match. As far as flying around and waiting for the fuel to run out. a choke servo on 1 receiver and the throttle on the other. ALWAYS SAFETY. I have NO and I mean no range problems with this setup. I can walk with engine idling, antenna down, away from the plane to the point I cannot see it and still have control . That is with someone watching it to verify. This system has alot of benefits as does Anyones other choice. Try it maybe you'll like it maybe you won't.
Old 05-11-2005, 05:22 AM
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Default RE: Dual Receiver Questions

Aresti,

I have had receiver failure with dual rxs and the second receiver saved the airplane. Dual rxs allow you to "plan for failure" for most of the components in the plane.

Interference is another issue. Interference will affect both rxs and if they are PCM, both will lockout and the plane is history. Please re-read my previous post because I think I have a system which gives you a "back door" to receiver lockout from interference.

Elson
Old 05-11-2005, 08:58 AM
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Default RE: Dual Receiver Questions

This has been a pretty good discussion. the one thing that is clear is that there are oh-so-many things that can happen. Everyone has to decide for themswelves what level of redundancy/protection they want. But you all have been very helpful here so far.
Old 05-11-2005, 09:15 AM
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Default RE: Dual Receiver Questions

Aresti,

You are way off base. In my situation, it was the battery. But if I were to use just dual batteries like you say, I would still depend on just one receiver, ONE battery connection plugged into to that reciever[X(], one battery splitter circuit, etc. etc. Failure of any ONE of those things failing would cause my airplane to crash. With my current setup of two complete radio systems, NO one failure would ever cause me to lose control of the airplane.
Old 05-11-2005, 09:18 AM
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Default RE: Dual Receiver Questions

ORIGINAL: aresti2004


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.

This is absolutely the truth. This truly is the only way to provide true redundancy... you're going to pay though.. with RX, the setup is close to $800 and it still won't protect against a servo failure.

The MTBF of the receiver (mean time between failure) is the highest of any component of our systems (i.e. meaning the least likely to fail) - servos, wiring, connections, battery, switches, ignition, your transmitter! and even the airframe itself ALL have far lower MTBF numbers than the RX.

I agree with Arresti... the only benefit I see of using 2 RX is psychological. If it makes a person feel more confident in their bird... use two.


Elson - to clarify, the JR 945 is a dual conversion RX. There is an "unofficial" bulletin floating around the JR team camp advising against the use of 2 JR Dual Conversion RX's due to heterodyning when they are in close proximity to one another (i.e. less than 24"). My guess is the 945 may have the same issue.. its the same RX, less the secondary conversion (IF) section.

DP




Old 05-11-2005, 09:23 AM
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Default RE: Dual Receiver Questions

ORIGINAL: JettPilot

Aresti,

You are way off base. In my situation, it was the battery. But if I were to use just dual batteries like you say, I would still depend on just one receiver, ONE battery connection plugged into to that reciever[X(], one battery splitter circuit, etc. etc. Failure of any ONE of those things failing would cause my airplane to crash. With my current setup of two complete radio systems, NO one failure would ever cause me to lose control of the airplane.

Batteries and switches fail far more than any other component. As a result, nearly all of us use 2 switches going to 2 batteries into 2 regulators plugged into 2 separate ports on your RX.

On my more exotic setups, I use a powerbox, just because I hate all the wiring mess the two circuits create + the box provides true load sharing.

The basic setup however provides two fully redundant paths and will back up and failure of a regulator, switch or battery.
Never use Y-harnesses or multiple batteries on a single connection - it completely defeats the purpose of having two batteries.


DP

Old 05-11-2005, 03:44 PM
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Default RE: Dual Receiver Questions

As desertplug hinted at, a viable alternative to a dual RX setup is real simple.

1) If it is a large aircraft with numerous servos a power distribution system to separate the servos from RX is a preferred setup -- I certainly would use one on a 40%'r but maybe not on a 30%'r. As a matter of fact I don't even have a dual battery setup on my 28% Christen Eagle II but will probably do so in the near future.

2) If all your really looking for is to enhanced your reliability I think the best configuration for that is a dual battery/switch setup. Use 2 high quality DP switches and connected each to a separate channel in the RX. RXs rarely fail, you are more likely to loose a battery or a switch. Your batteries have to be the same voltage but they don't have to be the same amperage. I ran 6volt batteries, a 1500mah NIMH and a 2100mah NIMH on my Hanger 9 Cap 232 with two heavy-duty MPI switches, one of which is the MPI Miracle switch which has both a regulator and a failure prevention circuit.

Old 05-18-2005, 01:27 PM
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Default RE: Dual Receiver Questions

ORIGINAL: desertpig


The MTBF of the receiver (mean time between failure) is the highest of any component of our systems (i.e. meaning the least likely to fail) - servos, wiring, connections, battery, switches, ignition, your transmitter! and even the airframe itself ALL have far lower MTBF numbers than the RX.

Except the quality of the UPLINK itself....if the two recievers are on 2 different channels than you will increase the MTBF of the system (when including UPLINK performance) many fold.
Old 05-18-2005, 03:48 PM
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Default RE: Dual Receiver Questions


ORIGINAL: desertpig


I agree with Arresti... the only benefit I see of using 2 RX is psychological. If it makes a person feel more confident in their bird... use two.


DP

So you two just ignore all the reports here on RCU where using 2 RX's have saved many planes?????
I'm not talking about battery failures, but RX failures. Many people have saved their planes when one RX failed and they landed using the other RX and 1/2 the planes control surfaces.
I don't understand how you can say there is no benefit to using 2 RX's when it has been proven over and over again.
Stick your heads in the sand if you want, but don't try and confuse the rest of us.

Jim
Old 05-18-2005, 04:40 PM
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Default RE: Dual Receiver Questions

Hammbone - if you dig and dig deep, I think you will only find one bona-fide RX failure - i.e. where the electronics or crystal within the RX failed. All the rest are battery, wiring, or servo stalls that took the second RX out. One failure the guy lost his antenna because the RX was not vibration isolated. I believe in all but the case of the servo stall, the failure would probably not have happened due to the abundance of extra wiring and complexity of the system. In the case of the servo stall, the plane still crashed but was not a total loss... I guess a controlled crash would be the best way to describe it.

I won't argue there are times where 2 RX's actually make some sense - mainly on very large A/C when spreading the load across many servos, multiple batteries and very long runs where servo extensions could be 6' or more in length. The second receiver becomes less costly than powerboxes and load sharing units and obviously the less wire in an install, the better. I guess anyone will have a hard time convincing me that the 2nd RX does anything beyond spreading the load or optimizing the wiring. I would also argue that in more cases than not, it simply adds complexity and another point of failure where it is not needed.

My analogy on 2 RX is like the guy who puts up a brick house because his old house was destroyed by wind, only to have a flood come and ruin this one as well. We can't plan for everything. Some times ya just got to fly and not worry.

One thing I can say - there is no wrong way here. We use what we are comfortable with. If I was flying a 42% Comp-Arf Yak, I would have the dual receiver setup on the Emcotec master / slave box. Great idea, but not worth $600 for a small plane.

DP




Old 05-18-2005, 05:29 PM
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Default RE: Dual Receiver Questions

On a typical duel receiver setup, how is the throttle servo run and how is the battery power typically supplied to the receivers. Is it most common to have the throttle servo run to only one of the two receivers and to have one battery/switch powering each reciever?

Thanks,
Old 05-18-2005, 05:37 PM
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Default RE: Dual Receiver Questions

That is correct. One battery / power source per RX, separate switches and throttle on one RX, Choke or Cut-Off switch on the other RX. Basically you want to be able to still kill your engine if either RX quits.

You cannot share servos across receivers, at least not yet!

DP


Old 05-18-2005, 06:22 PM
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Default RE: Dual Receiver Questions

desertpig,
We must not be reading the same posts because I've seen several stories of 2 RX's saving a plane. Rx failures are more common than you seem to think.
I agree that you can't plan for everything. We all just have to decide how we each want to set up our own planes.

To say that the only benefit of using 2 RX's is psychological though, is completely wrong and I wasn't going to let that slide.
If you have 2 seperate systems (RX's), each controlling 1/2 of your plane, the chance of 2 different things failing at the same time is very small. You would probably never have both systems fail at the same time. In the case of one thing failing; whether it be a battery, regulator, switch, or RX (yes, RX's do fail!); you would still have control over 1/2 of your plane and would probably be able to land safely.
This is a proven fact and as I said, there are several stories of it happening here on RCU.

A second RX is only $100 to $150, you don't have to use the Emcotec master / slave box or any other unit with the 2nd RX to benefit from the 2nd RX. I'll gladly pay this much to help protect a plane worth several thousand dollars.

Maybe you don't feel it's worth the extra money, but don't say a 2nd RX won't benefit us, because it definitely will. It has been proven to.

Jim
Old 05-18-2005, 06:24 PM
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Default RE: Dual Receiver Questions

Lets assume we have two planes. One setup with dual receivers and one setup with a single receiver with dual batteries/switches.

Each plane flies 1000 times.

Now I will make some very crude assumptions about failure rates.
Out of 1000 flights I would assume a battery would fail maybe 10 times.
Out of 1000 flights I would assume a switch would fail maybe 10 times.
Out of 1000 flights I would assume the receiver would fail maybe 2 times.
I will assume you can't have multiple part failures on the same flight.

Single receiver setup over the 1000 flights you would have lost the plane 2 times due to receiver failure. You would not loose the plane due to battery or switch failure due to the redundancy of using dual batteries/switches into the signle receiver.

Dual receiver setup over 1000 flights gets:
10 battery failures resulting in loss of one reciever
10 switch failures resulting in loass of one reciever
2 receiver failures resulting in loss of half controls of the aircraft.
Therefore:
You will loose the receiver powering the throttle on average 11 times our of 1000 flights.
You will loose the receiver NOT powering the throttle on average 11 times out of 1000 flights.
Now comes some additional failure assumptions. Out of 11 flights with only half the flight controls, how many times will we loose the plane? I would think that we have worse odds of loosing the plane when the receiver fails powering the throttle than if the non throttle receiver fails/looses power.

What does the above information show? There are obvious advantages/disadvantages to both configuration but I personally feel neither configuration is clearly better than the other.

Fly whichever one makes you feel most comfortable. The best system out there for redundancy is the Emcotec box for dual recivers. Even then you have a potential single point failure with the Emcotec iteself, but I would guess those odds are like 1 in 1000
Old 05-18-2005, 06:30 PM
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Default RE: Dual Receiver Questions

I can simplify that a lot.

The point still remains that EVERY time you have a RX failure with one RX you will loose your plane. If you have 2 RX's and one fails, you have a very good chance of keeping your plane in one piece.

Do you want to have more risk or spend more money? The choice is yours.


Jim
Old 05-18-2005, 06:33 PM
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Default RE: Dual Receiver Questions

I personally have had two receivers fail in the past year. Both did not crash the plane. One was discovered on landing when everything just quit working while on the runway. The other was during a preflight check here at the house. Both were mounted on 1/2 inch foam with Velcro straps. So I do know they fail. Both receivers had the same type failure. You could push on the wires where they plug in and make the airplane controls work and quit working by simply applying a small amount of pressure to the connectors. I fly two it makes me feel better.
Old 05-18-2005, 06:34 PM
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Default RE: Dual Receiver Questions

ORIGINAL: Hammbone

If you have 2 RX's and one fails, you have a very good chance of keeping your plane in one piece.

Jim
Jim,

What would you consider the statistical odds of saving a plane that only has half the controls available? 50%? 70%? 80%? 100%?
Old 05-18-2005, 06:36 PM
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Default RE: Dual Receiver Questions

I would say 90 to 100%, unless you are hovering when the RX that the throttle servo is on fails (or something similar).

Jim
Old 05-18-2005, 06:44 PM
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Default RE: Dual Receiver Questions

hehe, now we are getting somewhere.

So if you are mainly a 3D pilot (do alot of hovering), you are probably better off statistically with a single reciever setup.

If you don't do alot of hovering (we will say you have a 95% chance of saving the plane)
You will save the plane 95% of the time with 22 flights with only one of your two receivers in operation; therefore, you will plant a balsa tree approximately 1.1 times for 1000 flights using two receiver setup.

With the crude assumptions made, I don't see any clear statistical advantage of one configuration over the other, unless you are a 3D kind of guy
Old 05-18-2005, 08:18 PM
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Default RE: Dual Receiver Questions

I don't understand why you would ever be better off with a single RX.
You always have less risk of loosing your plane with 2 RX's no matter how or what you fly.

The only advantage I see to having just one RX is it costs a little less and it is a simpler installation. There is more risk with a single RX though. It's a trade off.
It's also a personal decision. I'm not saying one way or the other is wrong. It's just a matter of choice how we each want to set up our own planes.

Jim
Old 05-18-2005, 08:21 PM
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Default RE: Dual Receiver Questions

Oooh I really opened the can o worms didn't I.. Again, not faulting the concept. As one mentioned, there are pros and cons of both setups and it really is a matter of personal preference. The money thing never really was an issue, you are right $150 - $200 is a small part of a $4000 plane.

DP
Old 05-18-2005, 09:40 PM
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Default RE: Dual Receiver Questions

Did a Futaba receiver poll and out of 124 votes. 72 ran single and 52 dual.

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