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Oct 13, 2021, 02:44 PM
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Glider power systems - lipo vs lion vs ??


Hey everyone, my kid has sort of gotten into flying rc helios/quads and I used to build/fly gliders as a girl with my dad and uncle (which lead to a career in aerospace, wee!) and because of his interest into things I've had a bit of an interest take root in building and flying again. As it is, I have a few kits on their way plus some experiments started in scratch building DLG's... but there have been some pretty huge advances in radio tech, specifically battery tech vs the last time I flew, were we just shoved 4 AA nicads in the front of a Gentle Lady and flew it.

So, my questions are more geared to the smaller airframes and I don't have a ton of lipo battery knowledge so pointers on care and feeding of the stupid things would beneficial. I thought about sticking this in the general battery forum, but this seemed like enough of an application specific use case that it should be posted here.
SO, here we go!

I see people using BEC's with higher voltage lipo pacs, is this just to function as a voltage regulator for the receiver/servos?
Most of the modern radios I've been looking at have had receivers that have a fairly wide voltage input range, can these be used with smaller 1s lipo packs that run at lower voltage? I'd be curious if anyone has torque data on the sub-micro servos operating at the different input voltage ranges. Ie, 1s packs vs 2s packs.
How are yall managing battery voltage on the airframe to keep from running under the "minimum" voltage threshold? Remote voltage sensors?
Do the 1s packs need something to step the supply voltage up to 5v for the receiver/servos?

The next challenge I have is to find a controller I like, lol.
I've found most of the traditional style controllers too big for comfort for me, so I'm leaning towards one of the smaller video game style ones. The Frsky X-lite controllers look interesting to say the least.
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Oct 13, 2021, 04:22 PM
Registered User
Welcome back to the hobby. I too took a long break. The technology is better than ever and super exciting. In addition to the new battery chemistries (not invented yet back in the day) we have two way transmission for real-time telemetry (ditto), carbon fiber (ditto), amazingly efficient airfoils and live hinges (ditto, and not drawn around a shoe anymore lol), fully digital and high tech spread spectrum 2.4gHz radios (ditto) and rare earth magnets which allow super powerful and light servos and motors (again, ditto).

As for batteries, the general trend is towards higher voltage than the old 4.8v, not lower. The following are generalities: Lipos are the battery of choice for power systems, which is where ESCs with BECs come in to power the receiver from the motor battery and eliminate a separate receiver pack. For unpowered gliders, you can still run 1s or 2s lipos directly (ensure that your receiver and servos are rated for the appropriate voltage as not all are). Also consider LiFe batteries (safer and arguably better suited for pure receiver packs) or even 4- or 5-cell NiMh. Yes, onboard sensors can measure and transmit voltage and capacity consumed, so it’s possible to know exactly when you should land.

For all batteries with a balancing plug (all the lithium types at least) you’ll need a special charger, not the old wall charger.

Also, voltage regulation is a possibility (from say 2s lipo to a constant 6V), but it’s optional and not needed on most gliders. You'll also find that many servos are rated for speed and torque at multiple voltages.

There are a ton of “care and feeding” type threads, so you may want to do a little research.

There are plenty of choices and you can really tailor your system, but that does make the initial learning curve a bit steeper.

On radios, although I'm not familiar with the system you mention, you can get SO much more for the radio buck than ever before. Most systems will have servo reversing, endpoint adjustments, and centering trim. More advanced radios will offer advanced and pre-made mixing functions, such as the ability to handle 4- or 6-servo wings and a plethora of mixing options. Touch screens are becoming more common, and there are many other features that are starting to blur the line with smartphones (if only a little). Do your research.

Feel free to give a little more specific info on the application and I’m sure you’ll get some good advice here. You mention DLG… that is definitely a specialized application (and one I know next to nothing about) so you may want to post in that forum too.
Last edited by rjtw; Oct 13, 2021 at 04:50 PM.
Oct 13, 2021, 04:34 PM
a.k.a. Bob Parks
bbbp's Avatar
A DLG will fly for a long time on a 1S LiPo and it is a weight saving using smaller cells and no BEC.

I use an 800 round cell and can fly it for a couple of hours.

Look for threads for whatever DLG you are considering and see what's the popular vote on cells.

BP
Oct 13, 2021, 05:49 PM
Registered User
I've got a 1 meter glider on 1S, 150 mAh. The servos are slightly slower at low voltages, and obviously there's less of a safety margin on voltage, but it's been working fine. Don't let lipos go below the minimum voltage, and don't store them fully charged or discharged. I think 3.8 volts per cell is supposed to be good for storage.

For a 1.5 meter dlg that needs a light battery, my preference is 2S lithium iron phosphate, if you can find the right size. Also good for bigger gliders. I even have a 3 meter electric launched glider that climbs ok on 2S A123 cells. (I forget the exact capacity, maybe 2800 mAh?) You need a special charger or charger setting. You can charge some lithium iron phosphate batteries very fast, like 15 or 20 minutes. Lithium iron phosphate batteries are supposed to be safer. I charge them while still in the model, which I wouldn't to with a lipo.

There's nothing wrong with 4 or 5 nicad or nimh cells, if you can afford the weight and space. With nimh, batteries that are rated high for their size sometimes have a lot of internal resistance. I seem to recall some 2600 mAh AA's that had a lot of voltage drop at relatively modest discharge rates, so perhaps those are not suitable for a big glider with a bunch of servos. OTOH, you can get nimh that have less internal resistance.

If you still have a 72mHz radio in good working condition, with a dual conversion receiver, I see no reason not to use it. I use 72 mHz more often than 2.4 gHz, even now. There are, or have been, some 2.4 gHz systems with inadequate range, so a bit of investigation may be justified. I've had poor luck with the Dx5e and the Dxe transmitters. But those aren't available any more. I gather that you have to be careful with carbon fiber and 2.4 gHz receivers, though, to a lesser extent, that's been true for 72 mHz as well. But I haven't had any trouble yet with the latter.
Oct 13, 2021, 06:12 PM
Registered User
The A123's are either 2300 or 2500 mah depending on when you bought them.
Oct 13, 2021, 08:15 PM
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Gotcha, I'll ask those guys. I want to say a lot of them are running 1s packs already but it never hurts to ask. Both the kits I have coming in have smaller forward bays so I'll definitely look at what I can do in order shove the biggest batteries in there.

On my smaller planes, they'll be running the super tiny sub-micro servos which, from what I've researched, aren't happy when run with higher voltage packs. For the larger kit, I'm going to throw some money at higher end servos that hopefully will work better with a 2s pack i hope.

Regarding radios, I haven't used a 72mhz radio in over 20 years and I don't have one anymore... I'll be pretty much collecting a bunch of gear and equipment for these builds. About the only thing I've decided on is that I want a radio with openTX because OPTIONS are awesome and I don't mind having to program it. The lua scripting options are nice on them too. The kits I have coming (micro Bird of Time and a Yellow Jacket) don't need the complexity, but the programing options and mixes are nice QOL things.
Oct 13, 2021, 11:24 PM
Registered User
If the servos are rated for 6 volts, i.e. 5 nicads, they can probably handle 2S lithium iron phosphate. Two of those, fully charged, have only about 0.2 additional volts, if I remember correctly.

Of course, if space is really tight, and you don't need nose weight, lipos will do the job.
Oct 14, 2021, 07:56 AM
Mark LSF # 3792
Quote:
Originally Posted by Al M
The A123's are either 2300 or 2500 mah depending on when you bought them.
The 18650 size cells are 1100 mah.

https://www.radicalrc.com/item/A123L...50-Cell-102056

Where as the 26650 size cells are 2500 mah.

https://www.radicalrc.com/item/A123L...B-Cell--106918

First welcome back to the hobby. I too have taken some time off in the past.

The 26650 cells would definitely not fit in the either a DLG or the Yellow Jacket, even the 3.5 meter. Not being familiar with the 3.5 F5J YJ the 18650 cells might fit, but would not be my first battery choice for that application. My Geronimo , 2.5 m. F5J, has a set up that powers the motor system and HV (high voltage) servos from a single 2S 950 mah. LiPo pack that works quite well. I usually get four motor runs before charging and that equates to enough air time that I need a drink before the battery needs some electrons.

For servos I tend to put the highest quality servos I can in all of my builds now. I hate servo failures and one gets what they pay for most of the time with servos. Besides ask yourself, "do I want to trust the airplane I spent hours to build to a $5 servo?" It bogles my mind why somebody would cheap out on a couple of servos in a prized airframe, they are the muscles of the system. Also, HV servos don't cost much more than std. voltage ones and they can be run without a regulator or BEC, additional failure points, on 2S LiPo packs.

As long as a person is careful and uses a reasonably good charger designed for the battery chemistry being charged the chance of a catastrophic failure during charging is very low now, unlike the early days of LiPo batteries in the hobby. LiPo batteries have very high energy densities and are readily available in many sizes and voltages too. They do require special handling for longevity and safety though. My battery chemistry of choice for larger non-motorized gliders now is LiIon, because they are much more benign than LiPo and handle the storage/handling issues better than them. All this being said you may want to look for a 2S LiFe receiver battery if your YJ is non-motorized.
Last edited by Soarmark; Oct 14, 2021 at 09:00 AM.
Oct 14, 2021, 08:21 AM
Space!
ruhrho's Avatar
Thread OP
Quote:
Originally Posted by Soarmark
The 18650 size cells are 1100 mah.

https://www.radicalrc.com/item/A123L...50-Cell-102056

Where as the 26650 size cells are 2500 mah.

https://www.radicalrc.com/item/A123L...B-Cell--106918

First welcome back to the hobby. I too have taken some time off in the past.

The 26650 cells would definitely not fit in the either a DLG or the Yellow Jacket, even the 3.5 meter. Not being familiar with the 3.5 F5J YJ the 18650 cells might fit, but would not be my first battery choice for that application. My Geronimo , 2.5 m. F5J, has a set up that powers the motor system and HV (high voltage) servos from a single 2S 950 mah. LiPo pack that works quite well. I usually get four motor runs before charging and that equates to enough air time that I need a drink before the battery needs some electrons.

For servos I tend to put the highest quality servos I can in all of my builds now. I hate servo failures and one gets what they pay for most of the time with servos. Besides ask yourself, "do I want to trust the airplane I spent hours to build to a $5 servo?" It bogles my mind why somebody would cheap out on a couple of servos in a prized airframe, they are the muscles of the system. Also, HV servos don't cost much more than std. voltage ones and they can be run without a regulator or BEC, additional failure points, on 2S LiPo packs.

As long as a person is careful and uses a reasonably good charger designed for the battery chemistry being charged the chance of a catastrophic failure during charging is very low now, unlike the early days of LiPo batteries in the hobby. LiPo batteries have very high energy densities and are readily available in many sizes and voltages too. They do require special handling for longevity and safety though. My battery chemistry of choice for larger non-motorized gliders now is LiIon, because they are much more benign that LiPo and handle the storage/handling issues better than them. All this being said you may want to look for a 2S LiFe receiver battery if your YJ is non-motorized.
Ah, I should have clarified, I have a 2m YJ on order. iirc the fueslage is a little smaller on that one than the HUGE ones and its the straight up glider flavor of it. Right now my thoughts are to get nicer/HV servos in that airfame and run a bigger battery if it needs it to balance.

A 2M glider is a big plane for me, lol. When I last flew I had one 2m GL and everything else was a smaller hand lunch glider in the 1m-1.5m range or small slope planes.
Oct 14, 2021, 09:00 AM
Mark LSF # 3792
In that case the area where the battery needs to go will define it's size. I would recommend you look for a LiFe battery that fits. LiFe batteries provide more head room than the older chemistries (NiXX). Also, don't be afraid of using a smaller capacity LiFe pack, they can be field charged quickly like the other lithium chemistries. You may need to do some searching to find one that fits though. By smaller I mean in the 600 mah. to 850 mah. capacity range. Just make sure your servos can handle 6 V. nominal voltage.
Oct 14, 2021, 10:38 AM
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ruhrho's Avatar
Thread OP
Quote:
Originally Posted by Soarmark
In that case the area where the battery needs to go will define it's size. I would recommend you look for a LiFe battery that fits. LiFe batteries provide more head room than the older chemistries (NiXX). Also, don't be afraid of using a smaller capacity LiFe pack, they can be field charged quickly like the other lithium chemistries. You may need to do some searching to find one that fits though. By smaller I mean in the 600 mah. to 850 mah. capacity range. Just make sure your servos can handle 6 V. nominal voltage.
Awesome, thanks for the suggestion, I'll look at those. 600-850mah should be enough for a long day of flying.
Oct 14, 2021, 11:54 AM
a.k.a. Bob Parks
bbbp's Avatar
My 2m YJ uses a 4 pack of AAA NiMh cells from Aloft Hobbies (1000 maH - easily lasts half a contest day), but I believe they are no longer carrying them. You could make a pack out of Eneloop cells or a Batteries Plus store could build one.

BP
Oct 14, 2021, 12:09 PM
That thing almost hit me
Tahoed's Avatar
If you decide on the newer wide voltage servos, you could opt for a 2S 800 mah pack. The eneloop pack weighs 110 gm, the 14500 pack weighs 43 gm.
Oct 15, 2021, 01:01 AM
Registered User
gliderguide's Avatar
I use a Taranis X lite pro. Have done now for several years. Love it. Open tx can be a little daunting to some but there’s plenty of people willing to assist…

I got the optional longer caps for the TX so I can run a pair of 18650 batteries. They last ages and can charge via USB easily.

Enjoy the return. So many good toys available now.
Oct 15, 2021, 04:13 PM
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ruhrho's Avatar
Thread OP
I picked up a Tanaris Xlite pro yesterday, a couple receivers and started playing around with everything.

I'm just diving into the radio but it looks like it has a ton of cool features and I love flexibility of it so far. I have a long way to go for figuring everything out and getting used to the interface and how OpenTX is structured for menu options and all that but it's not too bad. Both of the planes in my build queue are V tails so getting the mixer figured out for that and starting to get a handle on control differentials for the tails was the first priority.
Next up is flight modes, expo curves on the controls and the open tx companion software, lol.

It's an awesome radio though, and the ergonomics are pretty amazing on it even if it's a little big.

I've pretty much decided on a 2s pack for the YJ and smaller 1s packs for the micro BoT and the DLG experiments I'm sorta working on. Corky has been awesome for feedback and suggestions for the YJ build and what's worked on that airframe.


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