Twin receivers

[IAN TURNEY-WHITE]

Peter , I fit diodes after the switches on each battery then join the positive wire to form a positive "rail" and ditto for the negative battery wires.
From these two rails, i then fit four supply leads which plug into the receivers , ie. two into each receiver .
This means that both receivers will carry on working if you loose a battery , or a switch or a power lead to one of the rx , or an open circuit diode fault.
If you get a battery fault the diodes prevent the good battery draining into the faulty battery .
On my large models I may have four batteries and six rx power input leads to share the power loads from several large servo,s
I also have a servo operating the choke so that I don't have to reach around a large prop , rather simply operate the choke from a three position switch on the tx , along with a micro switch operated by a servo which cuts the separate battery supply to the ignition.
These two controls are wired so it works on the say rx2 and the throttle on rx1.
Hope the above makes sense , we are after "true redundancy"
Best regards Ian Turney-White

[John Greenfield]

Hi Ian
I have to disagree that you have "true redundancy" With all 4 batteries connected to just one positive and 1 negative "rail" if you have a servo go short (see previous comments) it will pull the power from all 4 batteries and you will still have a problem.
It would be better if you used 2 rails for positive and 2 for negative and only had 2 batteries on each rail with one pair of rails supplying each receiver.

John

[IAN TURNEY-WHITE]

John , I can see your logic with two sets of "rails" , I tend to think in terms of probability , the most common faults being a battery failure ,switch failure or battery lead/connector failure .
Thankfully servo or rx failure is less common , I have only had two servo failures and one rx failure over the last four decades (now showing my age ! )
The servo failures sorted them self,s out , ie. they drew enough current to create enough heat to cause an open circuit in the servo , effectively disconnecting the faulty servo .
For a ground based system fuses could be fitted for say each servo but this is not a practical option for our air borne systems
I suppose its a matter of choice , another recommendation would be to use the excellent LiFe batteries , they have a low internal resistance , for their weight a high capacity and safe to recharge inside the model , also the charging process is much more reliable than nickel metal hydride batteries.
For a 2 cell LiFe ( 2S ) the voltage is around 6.6/6.7 volts which is similar to a nimh 5 cell battery
Ian Turney-White

[sean smith]

On the subject of dual receivers. Would you still need two rx's if you were using one of the new FrSky dual band TD R18 rx with twin battery inputs?

[IAN TURNEY-WHITE]

I don,t really know the details of your receiver but doubt that it would be suitable on its own for an over 20kg model .
The idea behind two separate receivers is that if one fails there is enough control on the remaining receiver and its servos to direct the model away from the public and throttle back or stop the motor .

[Rob Buckley]

Looking at the receiver, it appears to meet the current minimum requirements for an over 25kg model. It's got two receivers, three antennas and two power supplies all built into one box, so at a top level looks to be functionally no different to two discrete receivers plugged into one power management box.

The limiting factor will be the power handling ability of the PCB traces if several high powered servos are used. The rated power handling spec of the receiver should be compared to the spec. current draw of the servos used, with some margin for the wife & kids.

[IAN TURNEY-WHITE]

Sean , I had a look at the online manual for your rx , which seems a bit limited in detail , the real question is , are there any common components , that if they failed would prevent the rx working ?? and you loosing control of the model .
Still favour two totally separate receivers which have no common connections , maybe a bit more expensive , bit more effort to install but in my mind , total redundancy , ie if one fails the other rx can still provide enough control to stop or throttle back the motor and the model can be turned away from the public
Regards Ian Turney-White

[Cary Bailey]

Sean, in support of Rob & Ian’s comments, of which both are valid, I am in favour of 2 totally separate receivers whereby the opportunity of a single point of failure is alleviated. My resin for this is evident whereby should an incident occur that causes a legal case be brought upon an individual due to a failure of a model aircraft, when faced with a question “ did you make every effort to alleviate any failures, should they occur, to enable you to attempt to bring your aircraft either to land or directed away from any potential injury to person(s), with 2 independent receivers, you can confidently say that you have. Anything that has a “common” point, power supply, bus-bar, encoder/decoder, even if the item says it has 2 receivers, has that potential to have a single point of failure that in aviation is generally not accepted. This is just my opinion but for me and the size of models I fly, I want redundancy should my primary system faulter or fail to allow me to make a safe option.
Cary

[sean smith]

Hi All, Thanks for the comments regarding the FrSKY RX. I'm not currently flying any models large enough to require 2 rx's but will use 2 in the Mosquito when i get that finished.

Happy New Year.
Sean.