Are we at the limit? - RC Groups
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Oct 28, 2001, 05:25 PM
AMA 697691 / FAA 13675

Are we at the limit?

That is, are we at the limit of sport plane e-duration with RC3000 NiMH cells?

My favorite planes are rapidly becoming my heaviest planes. You know, the .40 and .60 size sport planes converted to e-flight. They fly so true and simply don't care about reasonable winds.

When using an Astro Flight Cobalt motor on xx cells, are we limited in duration to the RC3000 cell?

Does a MaxCim brushless provide better efficency therefor better power or duration?
Latest blog entry: Greg's Web Hangar
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Oct 28, 2001, 06:56 PM
Visitor from Reality
If you mean the size and weight of cells available to us right now, yes, we are.

Once the CP1700 ratchets up to 3000, the goalpost truck will have driven on some more

Right now, I have my indoor / parky models - 7 x 350mA cells, my 10 x 2400 ships and the 20 x 2400 ships. The rest of the 'standards' proved to be uninteresting and got peddled off. I think next year, I may have a tinker with something a tad bigger than S400, which I personally found very limiting, but unless a good ferrite comes along in that area, it will be brushless.

The indoor/parkies have their own special niche, my ten cell ships are handy for filling in between flights with the heavy metal, but the first time I lifted off my MaxCim/20 cell 4*40, everything else went very pale ...

Where the MaxCim wins hands down is the total drivetrain weight and flexibility - lighter than an Astro, its gearbox is about the same, but has easily swappable ratios and does away with the receiver nicad. Having flown my 4*40 on both with 20 cells, the MaxCim won hands down, with around a half pound less in model weight.

It probably wouldn't bother a Cub-type envelope, but it sure bugged me in aerobatics. There probably is an efficiency gain with the MaxCim also, though I'd not be able to quantify that.

The only way I could extend the CAP's duration is by not flying it like I do. That ain't going to happen, anyway, it would never thermal
Oct 28, 2001, 09:16 PM
ὅπερ ἔδει δεῖξαι
Gerald's Avatar
Greg, it may be possible to use cells in parallel for greater AH capacity if that's your question.

Dereck, speaking of thermalling, I had my longest flight yet with the Aveox powered Senior Kadet couple weekends ago. Flew for over 26 minutes on a 16 cell 2400 pack. There must have been widespread thermals because I flew most of the time with the throttle cut off and even with the big 16" prop draggily windmilling.

Started getting heckled by the glo-flyer crowd "hey, how many batteries ya got in that thing?" Most of the flight was just floating around in the pattern but there was still enough aerobatics included to impress. Landed with enough power left to still do one more touch-n-go and a "victory loop" before calling it quits.

What I like about this big plane is that it happily flies on a few cells or as many as I care to load it up with. If the flights keep getting longer I'm gonna hafta start bringing out a recliner chair to keep from getting tired. Average flight time on this bird is about 15 minutes now. There always seems to be a lot of wet powered Seniors flying so it's easy to compare it to them for performance. On 16 cells it outperforms most of them and on 20 it blows them away.

Nothing flies like a Senior!
Oct 28, 2001, 11:52 PM
Registered User
Originally posted by Gerald
On 16 cells it outperforms most of them and on 20 it blows them away.

I wouldnt say that, I have seen that one that crashed out there stay up for 45 minute- an hour, we dont have quite the vertical yet either, but getting close.
Oct 29, 2001, 09:03 AM
AMA 697691 / FAA 13675
Ok, thanks guys. I just wanted to make sure I wasn't missing anything.

When I fly my sport planes, the throttle is on full and stays there! It is a great speed fix that keeps on feeling good even after landing.

Looking at it from another perspective, if you assume that my 7.5lb, 18-cell, Arrow 3D is underpowered with my AF625G motor unless I run full throttle, would installing a more powerful motor simply draw even more current to deliver the power or could I throttle back a bit to achieve basic aerobatic performance with longer duration?

I also realize that if I drop 1lb from my 7.5lbs, it will improve things also.
Latest blog entry: Greg's Web Hangar
Oct 29, 2001, 09:28 AM
Product Manager at Hobbico
GWRIGHT's Avatar
Greg, why don't you get a higher ratio gearbox and put a "real prop" on the front? My old large E3D (the 64" span one) first flew with a 16X10 geared for 40 amps (400+ watts ) and it flew well. Geared higher and spinning the 18X10, at a touch less current (40~50 watts less going in) it flew much much better. With less current, the flight times were better too. In the short time I've been playing with e-flight, I've kept reading everywhere about watts per pound this and watts per pound that. I don't think watts is always watts so to speak. If you put a big enough prop on front, you can get really good performance on much lower "wattage" than some people think. This assumes that you don't mind going a few mph slower. Take for instance the big yellow plane, was last flying at 4.5 lbs, 10 cells and about 350 watts. Yes, it was basically a huge, aerobatic slowflyer,.. but power was NOT a problem. The kit version E3D flies at 400 watts on 3.5 lbs. The thrust to weight is roughly the same, but the pitch speed is up from 40mph to the low 50's. It's taking well above 100 watts/lb for this extra 10mph or so of speed, whereas the larger one was well below 100watts/lb. You can easily got gobs of thrust on low wattage by just using high gear ratios and bigger props. If you absolutely must have more speed,.. it's gonna take a lot more energy however. Model helicopters hover at around 50atts/lb. There's no magic here, it's just a high ratio and REALLY BIG "prop" I've got a 25Gthat I picked up cheap,.. but I haven't found a good use for it due to the low ratio.
By the way,.. I think you're running a 12X8 on that plane, which is the "optimum" prop on the E3D. I'd be interested in what kind of rpms you're turning the prop at. The 10-cell/endo setup gives in the mid 7K range,.. around 7500 rpms. Probably much lower than your 25G on 16 cells,.. but it's a 2lb power system (cells/motor/gearbox) whereas you're probably at 3lbs plus with the 25G and 16 cells.
Latest blog entry: blog
Oct 29, 2001, 09:39 AM
Visitor from Reality
Hi Greg
Weight, if not everything, is pretty close. My CAP now weighs 6.5lb, only needs full power for big rounds and vertical legs. Longer aerobatic flights come from matching the power applied to the model's need and speed, and taking any help from Mr. Gravity you can arrange for. You might want to try flying like that instead of 'throttle switch to on" - no-one's ever told me my CAP is boring to watch

She's getting a bit porky now, having been through the scenery once or twice too many times. Her replacement will be essentially "model aircraft" as opposed to semiscale, the plans are underway and it will be close to a scale down of an FAI pattern ship.

I reckon I can get to 6lb with 20 cells and a MaxCim, which should allow me to prop down to 'only' 80 -90 watts/lb and get even longer flights. Another possibility is 20 x 2000nimh, unless Sanyo up the CP1700 to 2K first That would be nice.
Oct 29, 2001, 11:00 AM
AMA 697691 / FAA 13675
Both suggestions are good ones.


You are already aware that I like to fly my ships faster with lower gear ratios but your suggestion of sacrificing speed for power and duration is a valid one.

After flying so many 28"- 40" ships, the bigger 60" sport planes already look like they are going slower but I know it is merely perspective. This ease of keeping up with the larger higher powered ship combined with the fact that wind has little effect on it may be why I am enjoying it so much!

I think I will start by a simple weight reduction pass on my Arrow 3D. I built the ARF stock with little reguard to adding weight. I currently use 18-cells of 1900SCR and RC3000. I use the big rubber wheels and a seperate Rx. battery pack. She flies beautifully and I can even dead stick landings.

Since I have my E3D kit now, I will use that design for my slower more aerobatic 3D fix. I realized when I received the box that I'm still a laser kit "virgin", so it will make a fun Winter project for me. My Extra 3.25 is almost complete and I made the expensive ESC, Futaba receiver, and battery packs swappable for the E3D.

By the way, did you ever test the C-50 BEC out yet?


I think that I may be getting the MaxCim bug? Will this R/C frenzy ever subside?!?

On your last post, you entered a new phrase that is not in my decoder book. Does "having been through the scenery once or twice too many times" mean crashing and this is why the ship is "getting porky" or gaining weight?

What would be a good MaxCim motor for a 7lb Sport plane? It seems like I'm a virgin here too.
Latest blog entry: Greg's Web Hangar
Oct 29, 2001, 11:04 AM
Product Manager at Hobbico
GWRIGHT's Avatar
Yes Greg,.. flying the C-50's on BEC now with 4 HS-81 servos and 10 cells. HAve not had a single problem. It is above their specs, do it at your own risk,..but I haven't had the slightest problem. I think Mike Zellars is doing the same,.. using BEC, no RX pack.
Latest blog entry: blog
Oct 29, 2001, 11:59 AM
Balsa Flies Better!
Has anybody tried the SR Max 3000 cells? I've got an 8 cell pack looking for a home- it was in my P-38 but I'm going to separate battery packs for that plane.

Some specs-
wt. 24 oz.
amp draw- probably about 50 or so - I saw over 400 watts on the P-38 before I yanked it. This thing does supply more watts than RC 2400 cells- however, it's a third heavier. (Note- I don't have a tach, but by ear in my setup, it was clearly turning the props faster.)
Total capacity- not real sure- first time I charged it up from flat it took 4014 milliamps on a 110D charger.

I suspect I may have to go add some cells, but I'm thinking with 10 cells and some of the Aveox motors I should be looking at 36 ounces of drive weight at 500 watts with about 4 minutes of WOT.

Sam Brauer
Stamford, CT
Oct 29, 2001, 12:48 PM
AMA 697691 / FAA 13675
Sweet! Thanks, Gary. Those BECs are typically rated for standard size servos anyway.

I wonder if those SR 3000 MAX cells are NiCd or NiMH? If they were NiCD and they didn't cost an arm and a leg, it would be an interesting alternative...

18 cells x $14.50 = $261 *gasp*

That's digging into my MaxCim money.
Latest blog entry: Greg's Web Hangar
Oct 29, 2001, 01:00 PM
Visitor from Reality
Hi Greg
Sorry, yes, "going through the scenery" amounts to slight impromptu changes in aircraft shape (a crash results in a pile of matchsticks around a hole where the pack pushed the motor underground. It ain't really a crash unless the rudder is broken )

MaxCim 13Y, geared around 3.75:1 - very easy to tweak to suit your model - 20 x 2400 cells, 14 x 10 APC-E. Whatever, the part number is - MaxCim only make two motors and two controllers, you need the 21 cell capable ESC, with BEC.

In my CAP, that lot amounts to around 32A-ish and very satisfying performance . MaxCim pinions go pretty much in one tooth steps, and can be swapped using two hex wrenches / allen keys (see - I am bilingual too ) without a lot of fuss. 20 cells might not have the pit-posing potential of 36, but can power a decent little sports aerobatic ship in decent fashion.

If you wanted to stay a tad lower, MaxCim's 13D wind is rated for up to 14 - 16 cells, but can take 50A. I've even sniffed around the new H9 "Aresti" 46 sized BARF - nice looker, has aerobatic potential - for a D wind MaxCim.

If you are hesistant about the alphabet soup, do what I do - call Tom Cimato at MaxCim, tell him what model you fancy and see what he comes up with. He really knows the sports flying game, as opposed to electrical rocketry, but patience may be needed in getting to him as he is MaxCim, total, from CEO to HCBW (Head Cook & Bottle Washer ) and has a full time day job too.

Sam - my Aveox 1409/3Y on ten cells / Aeronaut 8.5 x 7 fixed and 33A has been a great combo in my now somewhat aged Embat. It's replacement was to have been a "Fierce Arrow" RC version, but you beat me to it - rotter! Direct drive gives very quiet model which has been handy for hand-tossing over a lumpy grass patch, but that little prop limits performance once the speed bleeds off.

Your FA is slated for my January EFI column, BTW ...
Oct 29, 2001, 01:32 PM
Registered User
Greg, if you strap a Maxcim on it you will never go back to cobalts I have one on my sig senior and it fly's 5 times better than it did with a astro 40 geared, plus flight time are alot longer. I get exactly 10 minutes of 3/4-full throttle flying on a 20 cell pack of cp-2400's and it will almost prop hang for a second or 2.
There are only 2 maxcim motors, the D wind and the Y wind, like Derek said the D wind is for fewer cell count and the Y will go up to 25 cells with the right controller.
I also have another y wind on the bench to be installed in my cloud dancer.
Oct 29, 2001, 01:38 PM
AMA 697691 / FAA 13675
Thanks, Dereck.

I found the MaxCim site and absorbed a good deal of imformation. I also e-mailed Tom C. about a recommendation.

Looking at the graphs of comparison between the MaxCim and Astro Flight (AF) motors, the main difference I see is that the MaxCim motors are about 10% more efficient and 3-4oz lighter (with controller) than the AF Cobalts.

The price difference is roughly $340 for a MaxCim 3Y w/controller and about $225 for an AF625G w/Jeti controller.

It is interesting stuff, indeed! For now, I think i'll continue my research and start a weight-reduction effort on my Arrow 3D. The first pass may prove easy to find things. I use components like 4 Airtronics 94102 Precision Heavy Duty Standard Servos that weigh 1.6oz each and stock 3" rubber wheels. The ARF was meant for a .60-.90 size IC engine.
Latest blog entry: Greg's Web Hangar
Oct 29, 2001, 02:48 PM
Visitor from Reality
Yo Greg
Hitec HS 225 MG servos - 1oz weight, 40+ oz torque, pretty durn fast enough.

Can't remember the wheels, but you want the "Lite" ones with rounded tyres / tires and tread cut into them. Use the smallest wheels that will work for your patch. APC-E props are the best around for turning electricity into something useful, but are a tad light if there's rough ground around.

MaxCim also means no hauling a receiver pack around - add that to the saving. Funnily enough, I acquired a AF25SB this year - wonder what to do with it?

Ancient saying (from an ancient ukie aerobatic driver) - "It is easier to take 1gm (he wasn't so ancient he'd not heard of metric ) off 100 pieces of a model than it is to try and take 100gm off a finished model".

Folk who go around saying weight doesn't matter on big models probably fly different to wot I try to fly like

I'd say that an "Ultimate" electric sports aerobatic ship only starts with a top line motor (there is only one that seriously matches what a sports flier needs IMO ). This has to be followed by matching RC components fitted into a very optimised airframe. To give you a break, I'd reckon the most you need to go to are matched RC2400s from B & T batteries (check his prices for why ) or even CP2400s.

I'd rather have 2 packs of CP2400s than one Zapped!, Whapped!! and Slapped pack at several times the cost any day, for sports flying. You gonna measure loop size to quantify battery performance ?

For the first time since starting in sports electrics, I am contemplating going backwards to a 14 - 16 cell model. Or maybe I will use my MaxCim D wind in my E3D and stay with 20 cells for serious donkey kicking sports aerobatics

One of my bigger Astros is destined for a big, 1920's looking parasol sports ship for ambling around on nice days - they are great motors and about everlasting, and there are models around that aren't too fussed about the odd RX pack, after all.