Using A Seperate RX Pack In Electric Models

[GaryW]

This one has probably been asked and covered sometime in the past on the forum But I thought I would put it out there....

 

About 8 - 10 years ago myself aswell as a few fellow fliers I know had issue where the ESC in electric models totally failed also cutting power to the RX

causing the models to pile them selves into the ground totally obliterating themselves into many pieces.... Since then I have always powered the radio gear in all my electric models ( RX &  Servos ) with a separate RX pack ( red wire from ESC Servo lead to the Rx removed ) so as to prevent such an occurrence from ever happening again..  So the Lipo whether its 3s or 4S supplies power only to the motor via the ESC & the on board radio being supplied by usually a 4.8v

around 2600 mah rx pack.. 

 

Now recently while visiting a couple of model shops having a model with me , It was noticed by people looking at my model that I'm running a separate Rx

pack to the main lipo flight battery, & when asked why I explained what I and a few others have had happen in the past & why i run a separate RX pack,

they looked at me as if I'm totally crazy,,, One even commenting " There's no way I would ever run a separate receiver battery, That's just asking for trouble ""

 

So my question I guess would be Dou you agree/disagree with running a separate Rx pack in an electric model, Would you run a separate Rx battery or does anyone else think like me and also run a separate Rx battery..?????

Edited July 31, 2023 by GaryWebb

[Tim Kearsley]

I've used a separate Rx battery in several electric-powered models.  I run a Hangar 9 82 inch span Spitfire on 12S and use separate LiFe batteries (2) for the Rxs (2 FrSky X8Rs).  I can't see a disadvantage other than the weight penalty.  Having said that, my smaller electric models all run on the BEC built in to the ESC.  As a kind of middle ground between those two options I have also used a separate BEC in some cases, usually where the servo load is likely to be too great for the ESC BEC.

[GaryW]

Adding extra weight is ofcoarse a valid point on average a 4.8v rx pack is around 90g/3-4oz

[PeterF]

For smaller models up to 6S I use the BEC in the ESC after making sure that the BEC rating is adequate. I have had one ESC failure doing extreme arobatics with full power spinning where I believe that the extra gyroscopic loading on the motor from the spin overloaded the ESC but it did not blow the BEC so landed dead stick OK. For larger models up to 6S I use the ESC BEC subject to a high current rating coupled with a back up battery through high current Schottky diodes to provide higher reliability. For larger models above 6S with opto ESCs I use either 2 battery packs or a separate BEC and back up battery, again with Schottky diodes.I

 

Your choice of a separate battery pack with basic RC switch is in my view no more reliable than the inbuilt BEC in an ESC as long as the BEC has enough current rating. In the early days of electric flight a lot of ESCs had BECs that had too low a current rating or were of the type that generated a lot of heat (linear BEC) on anything above 3S packs. The mechanical switch is probably less reliable than a quality inbuilt BEC that has an appropriate current rating. Both habe single points of failure. The only RX power related crash I have had is black wire corrosion on an IC powered model, something that should not occur on a BEC powered model.

[Martin McIntosh]

I would second that TK. If I am using an electric model with high capacity Lipos then for the small extra weight of a couple of LiFe 700 packs via an electronic switch it is not worth the risk of flying without them.

[kc]

A slight disadvantage is you would have to remember to switch off after each flight  and charge the Rx battery after the session, unlike  an ESC/BEC setup.   

[GaryW]

6 minutes ago, kc said:

A slight disadvantage is you would have to remember to switch off after each flight  and charge the Rx battery after the session, unlike  an ESC/BEC setup.   

 

Personally I've not forgot to turn rx off after each flight yet to date and i charge all my models ( Rx packs ) the night before flying using a standard overnight trickle charger in the same way i wud with glow powered models regardless of how many flights they have each flying day

Edited July 31, 2023 by GaryWebb

[GaryW]

9 minutes ago, PeterF said:

For smaller models up to 6S I use the BEC in the ESC after making sure that the BEC rating is adequate. I have had one ESC failure doing extreme arobatics with full power spinning where I believe that the extra gyroscopic loading on the motor from the spin overloaded the ESC but it did not blow the BEC so landed dead stick OK. For larger models up to 6S I use the ESC BEC subject to a high current rating coupled with a back up battery through high current Schottky diodes to provide higher reliability. For larger models above 6S with opto ESCs I use either 2 battery packs or a separate BEC and back up battery, again with Schottky diodes.I

 

Your choice of a separate battery pack with basic RC switch is in my view no more reliable than the inbuilt BEC in an ESC as long as the BEC has enough current rating. In the early days of electric flight a lot of ESCs had BECs that had too low a current rating or were of the type that generated a lot of heat (linear BEC) on anything above 3S packs. The mechanical switch is probably less reliable than a quality inbuilt BEC that has an appropriate current rating. Both habe single points of failure. The only RX power related crash I have had is black wire corrosion on an IC powered model, something that should not occur on a BEC powered model.

 

In the one incident I had myself as well as others ive seen My model loss was due to total power loss to the rx from the esc which i swore from that day i wud never rely on just the lipo and esc again and ive been running a rx pack ever since

[leccyflyer]

As pointed out, years ago the linear BECs on some speed controllers were rather suspect and you had to take care, especially with the number of servos that they were expected to service. Issues of electrical noise also made it desirable in some cases to abandon the onboard BEC, opt for an OPTO esc and make provision for a separate power supply, either via a receiver pack or via a separate UBEC or SBEC. These days ESCs are more sophisticated, with well specified switching BECs onboard which should be more reliable.

 

On that basis I did used to carry a  4 cell RX pack in some models, but IIRC I've since replaced all of those with 5A UBECS and mostly done away with the radio switches, as they are quite a likely point of failure. 

[john stones 1 - Moderator]

Over the years I've seen many an I.C model lost through battery/switch failure, seen relatively few on lecky models, I put that down to using regimes on lipos, more attention paid because they can go mental if not looked after. KISS for me.

[Graham Bowers]

I'm hoping to maiden a new model in a few days. 6S battery for propulsion with a small 2S LiPo through a powerbox digiswitch / reg for Rx and servos. And a redundant backup battery. If it goes in, it's going to be my fault ;-) Sebart Mythos 50e.

[Adrian Smith 1]

All my large scale aircraft (30cc and above equivalent) run on OPTO ESCs using a separate RX pack. I also ensure the the RX pack is returned to "storage" voltage after each flying session. If the power packs fail along with the ESC at least you have control of the working surfaces and not lose all control. Also, Gary be wary of ill informed comments by people in model shops. Check & check again on being told things by so called field experts. I agree that for smaller models using an ESC with BEC built in is the way to go, but it's really a matter of personal judgement. By the way, and I may have been lucky here, but I have never had a 2S RX battery or RX (futaba) fail in  since flying electrics for about 6-7 years. Just my opinion. 

[GaryW]

25 minutes ago, Adrian Smith 1 said:

All my large scale aircraft (30cc and above equivalent) run on OPTO ESCs using a separate RX pack. I also ensure the the RX pack is returned to "storage" voltage after each flying session. If the power packs fail along with the ESC at least you have control of the working surfaces and not lose all control. Also, Gary be wary of ill informed comments by people in model shops. Check & check again on being told things by so called field experts. I agree that for smaller models using an ESC with BEC built in is the way to go, but it's really a matter of personal judgement. By the way, and I may have been lucky here, but I have never had a 2S RX battery or RX (futaba) fail in  since flying electrics for about 6-7 years. Just my opinion. 

 

I have also had a few people cringing at the thought of me using 4.8v Rx packs with Spektrum receivers even one or two insist I change them for 6v rx packs or a 7.4 2s lipo via a 5v BEC,,, to be 100% honest as spektrum Rx's have an operating voltage of 3.5 - 9.6v ive never had an issue with 4.8v rx packs & as I've ben in the hobby for some 30+ years now I do like to think I at least know a little of what I'm doing with my models...lol.... I do also have my group of trusted people i can turn to anytime I need that little extra guidance

Edited July 31, 2023 by GaryWebb

[leccyflyer]

Do those who are using a separate lipo for the radio side take that RX pack out of the model when not actually flying, or are they leaving that pack in the model between flying sessions?

[GaryW]

7 minutes ago, leccyflyer said:

Do those who are using a separate lipo for the radio side take that RX pack out of the model when not actually flying, or are they leaving that pack in the model between flying sessions?

 

If i was to use a 2s lipo for an rx battery i wud certainly take it out when not flying i know that much as i wud never leave any lipo in a model.. in fact i am planning on getting an Hirobo Shuttle again soon which the rx pack for that will be a 2s lipo via an align 2 in one regulator for rx & on board glow power like the one shown below... except in the pictures below that guy mounted the gyro in the wrong place as it should be inside the main frame between the servo tray and the engine

 

 

Edited July 31, 2023 by GaryWebb

[GaryW]

Correct position for a gyro in an Hirobo shuttle unlike in the photos i used  above 

 

Edited July 31, 2023 by GaryWebb

[Martin Harris - Moderator]

Does it actually matter where it's mounted?  Doesn't a gyro sense angular rotation which is the same wherever it's mounted?

[GaryW]

2 minutes ago, Martin Harris - Moderator said:

Does it actually matter where it's mounted?  Doesn't a gyro sense angular rotation which is the same wherever it's mounted?

 

Best position is as close to the main pivot/ rotation axis/point of the main head  to get maximum effect stability of the gyro to place it away from that pivot/rotation axis cud cause tail gyro to over compensate 

 

[GaryW]

11 minutes ago, Martin Harris - Moderator said:

Does it actually matter where it's mounted?  Doesn't a gyro sense angular rotation which is the same wherever it's mounted?

 

[Martin Harris - Moderator]

I could understand that if it utilised accelerometers but I think the GY401 is a simple gyro instrument.  If the fuselage yaws by n degrees, the same rotation would be measured at any part of the airframe.

[GaryW]

2 minutes ago, Martin Harris - Moderator said:

I could understand that if it utilised accelerometers but I think the GY401 is a simple gyro instrument.  If the fuselage yaws by n degrees, the same rotation would be measured at any part of the airframe.

 

Im only guessing from my own experience by I guess its in a similar context that auto stabilisation units like fms relex units and as3x rx's need to be situated/orientated correctly to function properly where if say a fms reflex unit isnt correctly level then the auto stablisation auto levelling wont work correctly... However I cud be wrong

[Dickw]

49 minutes ago, leccyflyer said:

Do those who are using a separate lipo for the radio side take that RX pack out of the model when not actually flying, or are they leaving that pack in the model between flying sessions?

My F5B gliders use 2s 350mAh Rx packs and I leave those in the model all the time including when recharging before flying sessions and between flights. Some have been in there for a couple of years.

With bigger and more accessible packs I would probably take them out. Not really sure why as the small packs have been no problem at all.

 

Dick

[Philip Lewis 3]

47 minutes ago, leccyflyer said:

Do those who are using a separate lipo for the radio side take that RX pack out of the model when not actually flying, or are they leaving that pack in the model between flying sessions?

I use separate RX LiPo packs in all my planes, OK I also have no choice as they are all 10 cell and the ESC has no BEC but I would anyway, I've had a few ESC failures over the years and they some were spectacular, one in particular (started by the motor going dead short and burning up at the same time) melted every lead off the ESC and what was remaining was just char so even if it had a BEC it wouldn't have worked even if it hadn't melted the battery connector wires off.

 

Yes I always but always take the two LiPo batteries out, (two batteries using isolated supplies) and I also set them to storage charge after flying, I only use two 500 mah LiPo's in a 2 M plane and they are good for six flights. Surprising how long LiPo's last when only being used in a low power situation.

 

I would also never dream of charging them in a plane either, I don't use a switch, just unplug after every flight and use sprung XT30 connectors, I'm using HV servo's so run unregulated.

 

Might seem a bit much but these are expensive airframes.