Yes, agreed, at this current level they are *very* interesting. I wonder how many cycles they will work.

I picked this up on another list. . .


The lithium poly technology may be just what we need.

This one refers to a 230mah cell that puts out 1 amp and weighs 6gms!

http://uttam.freeservers.com/goodies.htm

Larry

clicked on the link and then on the "click here for more info" but could not find where to order them or a price. all I could find was some diposable lithiums for the blimps on the site.

nevermind, after reading a little closer I saw the part about this being the company that is GOING to carry these cells.

Aeronutz Mark has some LiPoly's that are around 200 mAh. I spoke with Kevin at Skyborne and he hasn't been able to find the manufacturer of the ~200's, but is still looking. The important thing is that they exist, so someone will have them for sale at some point. Kokam doesn't make their cells in that size. Pretty soon we will probably have 135's, approx 200's, and the 570's that are already available. Then we will be set. I seriously doubt that a company the size of Plantraco is having LiPoly's custom made for them. The key differentiating factor in LiPoly's right now are vendors that HAVE them as opposed to those that are GOING to be getting them. We are still at the early stages of LiPoly in the Micro area. But, we've been reading that these were on the horizon for more than a year, and now they are here, but in somewhat limited quantities and sizes. All that will change, but we don't know when.

I flew an arf pennyplane made by IKARA "Bulldog". I used the Rffs 100 ,a pager motor from DIDEL with two stage gearing (16:1) with an 8 inch rubber prop from IKARA and a 140 mah POLYLI cell That a friend of Matt at AeroEnivornment gave me.Total weight with rudder and throttle was 14 grams. Flew great but only for a minute or so as one of my glue joints let go.The crash broke the vertical stab but repairs are under way.This happened last Wed.Next indoor is 3 weeks away.Motor current is 160 ma with 8in prop and 250 ma with 10 in prop. Have not flown with 10 in prop due to crash.Looked like it was climbing fine on the small prop at less than full throttle.

Gordon,

I take my hat off to you. Excellent work!

Roy

Mark got his lithium poly from plantraco but I don't think there a regular item yet.



Graham

Graham,
Thanks for the source for Mark's LiPoly. Maybe they will have them soon available for the general public.

Charlie,
Great work. Your plane shows what can be done with these cells and the Didel gears and motors. I'm going to use one of these cells on my Stechmücke at the next indoor fly in about two weeks. With rudder and elevator control and geared M20 it will weigh 18.7g. If I have time to rig up a geared pager motor it will weigh even less, probably about 16-17g.

Jochen,
Here's a link that Bob Selman found to the manufacturer's site. It lists the life at 500 cycles at 1.0C. I'm guessing that even if we abuse them we would get sufficient cycles that we would still be happy with our investment.

Here's an updated graph of my static tests. All tests are 6:1 gearing with a Micro-ARC 5x2.7 prop. I'm deleting the graph at the tops of this thread. This graph has a LiPoly test for the M20-LV (E-Charger). I need to at some point redo the LiPoly test for the M20-HV as that was the first one I did, and I now know I can charge these cells to about 4.3V. I'll have these graphs and the tables with the data behind them on my site in the M20 static test page tonight.

Right now I'm working on planes to take advantage of these cells. Hint, if the right planes have round engines and two wings, what's even better?

Charley,

Just wondering how slow did it fly? Do you think it would be able to fly in a large living room? Maybe 20x20. Did you happen to take pictures before hand?

Philip

Gordon,

I ordered two of the 135 cells from Kevin today. I think this is the right direction to head. I don't know if it is possible but, if we can pull enough current, say 5 or 6 hundred mah, at this weight the small semi-scale planes become more practical. Might have to go to a double gear reduction and a larger than normal CF prop. Even if the useful cycles dropped from 500 to 100, thats only 20 cents a flight...I could live with that.

Dave W.

Dave,
What size semi-scale planes were you thinking of? My sense is that if we are talking somewhere in the neighborhood of 75-100 square inches (depending on the plane and construction) and RFFS-100 based planes you can probably use a single stage gearbox and an M20. I won't know till I fly one, but I think there will be enough thrust. One of the reasons these tests are with a 5x2.7 prop is I wanted something that wouldn't be too big for a semi-scale plane. I also want to be able to ROG, so with a small plane, a large CF prop might be a problem. It ended up being a tradeoff and for now, and after a bunch of tests, I've settled on 6:1 gearing and 5x2.7 prop. I'll let you know after I fly with this setup.

For slightly larger planes I'm thinking about using two of these cells, or two of the ~200mAh cells since flight time will go down with two cells, and a Astro Firefly with the new metal gearbox or the DC5-2.4 with planetary gearbox from MTM Intl. I haven't made a two-cell pack yet, but intend to and do some tests when I have time.

What are you going to use to charge your cells? You might call Dan Krieg. His site specifically says not to charge anything other than his two-cell pack. But, if you could find out who makes his charger you could contact them directly and may find that it will work with one of these after all.

It's great you took the LiPoly plunge.

" What are you going to use to charge your cells? You might call Dan Krieg. His site specifically says not to charge anything other than his two-cell pack."

Actually, I was trying to figure out where we said that. Our webmaster (wife) might have written that in somewhere but I can't find it.

Our charger ($27) will work on any 1 or 2 cell lithium ion pack. The charge rate is switchable between 20, 40, 60, 100, and 200mA. So it looks like for your 135mAh cells, 100mA charge rate looks good. It needs a 12 volt car battery type source.

Lithium ion polymers are the future. That is all I will fly untill fuel cells or something else more advanced is available. Prices are going to continue to fall. We are getting rid of ALL our NiCD and NiMH batteries.

The 950mAh 2-cell pack we sell is perfect for the GWS A drive IPS.

I predict that the lithium packs are going to make even more radical model designs practical.

Dan Kreigh
WildRC.com

I can see these cells being great where two cells might previously have been used. 12" biplanes, 16" highwings, 15" low wings and the like. The extra voltage can only help. A kpoo (low voltage n20) geared with a fairly low ratio could be used on the scale models where a smaller prope looks better and then use a high ratio gearbox for your "floaters". It's a bit of a dream come true really

A note on the price, obviously the prices paid for the cells above reflect the fact that they have been bought in small quantitys. But to give you an idea of how the price reduces with quantity, I received a quote from Kokam for 100 at $4 each. That sounds pretty good. Hopefully if people show enough interest someone will buy them in this sort of quantity and we'll be looking at a very economical cell. Take two for an evenings flying.

Graham

Gordon,

I have an old Se5a Howard McEntee (sp) plan that was stick & tissue. 15 3/4" span, about 90 sq in. I would love to build it from sheet like the Pixel but I thought it would be a bit heavy/draggy for an M20. By shedding 8 grams of battery weight that might just do it. As Gram said in a later post, if the cells are cheap enough ($4) even 10 cycles are only 40 cents a flight, looks like pretty decent duration too. There was a charger schematic in a recent RC Microflight that might be adaptable, but at $27 for Dan's, it would be tough to justify putting any time in making your own.

Dave W.