Author Topic: Advice on new model (Read 1321 times)

Jason Greer · « **on:** September 15, 2009, 01:47:43 PM »

Guys,

I'm in the planning stages for my next stunter. I've decided to build a full size Geo-xl. This is a pretty large model at about 730 sq in and a 62" wing span. According to Bill Werwage the original weighed 53 ounces with a PA 51 and pipe. The Geo does have a fairly thin wing at only 2" thick at the root, so drag will not be as high as most larger models. I'd like to try and keep the weight at 55 or so ounces. I've been tossing around battery and motor configurations and I really think the Adamisin's are onto something with the 6s power system. So far I've come up with the following power system:
Motor: Scorpion 3026 710 (7 ounces)
Battery: Thunder Power 6s 2600 prolite v2 (12.5 ounces)
ESC: Ice 50 (2 ounces)
Prop: 13x6.5 or 13x5

Total power system weight with these components is around 22 ounces. That would leave me 33 ounces for the airframe. My 580 sq in omega airframe came in at 27 ounces with no power system, so I think 33 should be feasible. Monokote will help save on finish weight. I'm a little concerned that the 6s 2600 might not have enough capacity, but I feel the higher voltage should allow a reduction in capacity. Any thoughts? Also, is the 3026 710 to high of an rpm motor for 6s?

Like I said i'm in the very early planning stages and nothing has been ordered(except plans) so if I'm way off track please let me know. Would anyone be interested in a build thread as I get further into the construction? I'm by no means a professional builder, but it might be of some help to someone who's new to the electric side of things.

Thanks,
Jason

Alan Hahn · « **Reply #1 on:** September 15, 2009, 07:03:54 PM »

Jason,
As I think I have mentioned many times, energy is basically equal to weight. As long as you adjust the kV of the motor to match, you can use any combo of cells and capacity to fly the plane. A 6s requires a low kV motor, a 4s a kV ~6/4 (1.5) of the 6s system.

The 4s will use higher capacity cells than the 6s (6/4 times more, or 150% larger), but the result, in the end the capacity and weight are exactly the same. Even the battery "C" capacity will scale ok.

So the main question is how much capacity will you need. Capacity is basically the # of cells times the mAHr of the cell. If you know the total you need, you can divvy it up any way you want. In this case, it may be determined by the kV of the motor you want to buy.

It is natural that as the motor gets physically larger (diameter or length), it's kV tends to get smaller, so yes, so the higher cell count packs also become a no-brainer choice.

I also think the new ICE ESC's which can handle higher voltage packs with ease, also will drive people to use the 6s and larger packs.

If you want to save weight, you ought to look at the Thunderpower Lites. They certainly cost more than the cheaper packs, but they generally are significantly lighter.

Hmmm, if I had bought the Ice 50 with the heat sink, then I might consider 2 4s 2100's in parallel. AFAIK, the 2100's still represent the lightest weight/mAHr of all the cells. I am not too sure why this is the case.

Dennis Adamisin · « **Reply #2 on:** September 15, 2009, 08:09:49 PM »

Hi Jason
Thanks for the shout out!

I agree with Alan, the Scorpion you hae picked out would be great except I think the kv is too high for 6s. It needs to be in the 550 to 650 range to work with a 4 to 4.5 pitch prop. If you want to use the 6.5" pitch prop then the kv better be closer to about 450.
PLAN B use 5S or even a 4S pack.

BTW one of the reasons I wanted to try 6S was that it was LIGHTER than 5S or 4S. That is not the case all the time but when cell count goes up you can use smaller capacity packs - there is some madness to the method!

I used 2800 packs, but the Strega has flown with 2650's too. Remember that is at 79 oz, if you can hit your 55 oz target, your power usage should be much lower. Heck, even at 63 oz that would be ONE POUND lighter than the Strega! The thinner wing will also draw a lot less power...

BTW I went to the Scorpion site and did a quick check on the motor you called out - if I read it right that version has been discontinued!

As for the build thread DO IT! I always like to pick on other people's stuff!

All seriousness aside, build threads are fun to follow, Crist's profile build and flight test thread ended up 4 pages long. LOTS of , uhhh, "assistance" from the peanut gallery.

Alan Hahn · « **Reply #3 on:** September 15, 2009, 08:31:29 PM »

I agree with Dennis.

In actual fact, the cell capacity isn't a continuous distribution---they occur in fixed values. So it might be you can find a 6s pack with enough capacity, while a 4s pack ends up being bigger simply because the cell size you need to choose is larger than necessary.

Also like I mentioned, and maybe what Dennis means, for some reason certain cell capacities just seem to be lighter per mAHr than others. I am not sure if this is due to different chemistries or manufacturing processes.

It pays to look around and see what is available. I might also mention that the high "C" cells (like 30C, 40C) tend to be heavier (and bigger) than the same cell in a 20C. We tend to discharge at an average ~8C level (a little higher if you look at the instantaneous current that we get due to running at partial throttle). So 20C cells are probably fine for us, but if the weight would be the same, I would choose higher "C" cells, simply because they typically have less internal resistance, which means they heat up less, or waste less energy in the pack itself.

But I am moving onto esoteric topics!

Jason Greer · « **Reply #4 on:** September 15, 2009, 08:59:45 PM »

Thanks guys. The main reason I decided to go with the 6s setup was indeed to save weight. The thunder power 6s 2600 prolite v2 claims to only weigh slightly over 12 ounces while a 5s 3700 is closer to 17 or 18 ounces depending on the manufacturer. 6 ounces is a huge weight reduction when the target weight is 55 ounces. I have been doing some research on scorpion motors and I think I am going to get a custom wound 3026 with a kv of 600. If my math is correct then that should put me very close to my goal of 8400 rpm with a 14x7 apc e at 70% throttle. My smaller omega with a 3020 890 is running at 8400 on 4s. So I basically took 890 multiplied by 4(4s) and got 3560. I then divided 3560 by 6(6s) and got 593 as my target kv. I dont know if that is good logic, but its the best I could come up with. What makes it seem logical to me is that my target rpm on the 6s system is going to be same as the 4s system. I hope that makes sense. I suppose its really all a good(hopefully) guess.

Alan Hahn · « **Reply #5 on:** September 15, 2009, 09:27:12 PM »

Jason,
You are using good logic!

I will mention is that if you intend to buy the kit 3026, I don't believe the parts are from the newer V2 motor. However that is only a 10% less efficient setup (I think), and you will get some of that back by matching the kV better. So for the same # of winds, the old motor components will give you a higher kV than the new components.

One detail, is that I wound my own 3020 motor, calculating the kV from other stock 3020 motors (the original stock V1 motors). However my kV seemed off by the equivalent of one wind. Not too sure how that happened, except my definition of # winds and Scorpions is off by one wind.

If you are winding yourself, I would recommend first doing it with some "easy" small gauge wire. Then measure the no-load rpm and calculate the kV. That will tell you if you are where you want to be. If you are happy, remove the test wire and then wind with the largest gauge you can stuff into the motor to get the # of winds you want.

Dennis Adamisin · « **Reply #6 on:** September 16, 2009, 06:21:14 AM »

Jason & Alan:

I have no direct experience on this but heard it from Will DeMauro; perhaps he will check in and clarify.

Will was flying a version 1 Scorpion (3026 I think) and it was working well - until he installed a LH (Pusher) prop, then he burned up the motor in 1 flight. According to Will, the culprit was that V.1 apparently had the cooling openings oriented to help scoop and pump air into the motor. When rotation was reversed these holes no longer could pump air. Apparently Version 2 motors use non-oriented cooling openings, and the new motor is working well with the pusher prop.

Alan, you indicated that the BYI version of the Scorpion was a Version 1 motor? If so it may run afoul of this concern...

Crist Rigotti · « **Reply #7 on:** September 16, 2009, 07:21:57 AM »

Jason,
I have a spreadsheet that should help with calculating an ECL set up. Check you email. Here is what it looks like:

The unshaded areas are the inputs the program needs to return the values in the shaded areas. I put in your expected weights and the Kv for your 8400 rpm target. You could put in the actual Kv of the motor and see what rpm you should be running at. Hope this helps.

Alan Hahn · « **Reply #8 on:** September 16, 2009, 07:24:13 AM »

Dennis,
There really isn't much of an issue with how you rotate the motor. Most cooling is actually through the outer shell of the motor (the part where the magnets are attached. If you look inside the motor, you don't see much light---not if it is wound correctly, so there isn't much airflow through the motor--there is some of course. I think the most important thing is to make sure air can flow around the outside of the can.

Jason Greer · « **Reply #9 on:** September 16, 2009, 07:48:34 AM »

Wow, thanks so much for all the input guys. I have been corresponding with Lucien at Scorpion motors and he can get custom winds in the 3026 vII motors from Scorpion. According to him the 710 has 9 winds, 10 winds would be 640 kv, and 11 winds would be 580 kv. I think I am going to give the 11 wind 580 kv a try and see how that works out. This would give me some ability to experiment with some different props. I'd really like to run a 14" diameter to maximize the disc area, but I dont know if thats going to be possible or not.

Crist,

Thats a great spreadsheet that you came up with. Thank you very much. I will spend some time plugging numbers into it. It will take a lot of guesswork out of this.

Thanks,
Jason

Dennis Adamisin · « **Reply #10 on:** September 16, 2009, 08:23:40 AM »

Crist:
That is a great work-out on the spreadsheet, the battery capacity line really shows the cause/effect well.

On the Strega we dialed back to 7900 RPM, Jason's project should be lighter and less draggy, so he might be able to dial down a little more yet - maybe 7700 to 7800?

At any rate doing the math at 8400 certainly shows there is room to manuver on this, and that Jason's intended 2600 batteries ought to git-er-done.

Crist Rigotti · « **Reply #11 on:** September 16, 2009, 11:18:15 AM »

Anybody know how I can make the .xls of the spreadsheet available for download here on the forum?

Mike Anderson · « **Reply #12 on:** September 16, 2009, 11:26:26 AM »

Get in touch with Sparky and have him help you get it onto the "Downloads" page -

Crist Rigotti · « **Reply #13 on:** September 16, 2009, 01:24:03 PM »

Mike,
Thanks. It looks like I need to add the spreadsheet to my website then link to it in the download section. Or link to it right from here.

John Hammonds · « **Reply #14 on:** September 24, 2009, 04:50:00 PM »

Hi Crist,
What is the reason for the comment "(112=.7w/oz)" in the spread sheet example?

I hear figures of 140+ for a pattern plane. Is the 112 a ballpark figure as an average across the flight?

I did a similar exercise (Which gives the same answers as your example, so I guess we use the same formula).

I re-formatted mine to make it look similar to yours as your layout looked much nicer. It also includes A123 cells as a comparision and starts at 2S.

I've tried it in Excel, Star office and the online Google App and it works with them all.

Not trying to steal your limelight, but here it is until you post a link to yours.

~~It has a "txt" extension as "xls" is not allowed as an attachment, just rename it before opening.~~

[EDIT]
erm, well, that didn't work.....

Here is a link to the original sheet.

http://www.fokkit.plus.com/control_line/ECL_Battery_Sizing_Sheet.xls
[/EDIT]

TTFN
John.

Crist Rigotti · « **Reply #15 on:** September 24, 2009, 08:41:08 PM »

John,
I forgot I was going to post it for a download! The 112w=.7w/oz came from Dean Pappas as to what it seems to be taking to fly a stunter the full pattern.

Dean Pappas · « **Reply #16 on:** September 25, 2009, 02:06:01 PM »

Hi Guys,
It's 0.7 watt-hours per ounce of energy to fly the entire schedule, power.
Dean

John Hammonds · « **Reply #17 on:** September 25, 2009, 04:49:07 PM »

Hi Dean,
I presumed the figures were watt hours and just the headings were ambigious. Or am I mistaken?

I just ran my xls against the examples in the "List your set-up" thread (Where enough info was supplied). Interesting results.

It all averaged out at 108 wh? /llb with figures ranging from 86 through to 135

Crist's Barnstormer is a bit like the Bumble bee, it should not be able to even attempt the pattern.

(Of course I am in no doubt it can).

TTFN
John.

Crist Rigotti · « **Reply #18 on:** September 25, 2009, 09:09:43 PM »

Thanks Dean for the clarification.

Dean Pappas · « **Reply #19 on:** September 27, 2009, 08:08:45 AM »

Hi John,
It sounds like you were averaging 108 Watts per pound, which is a reasonable power consumption. The power summed up over time yields total energy. The total energy needed for a pattern is well correlated to both weight and line length. The 0.7 watt-hours per ounce figure is at something like 65 feet, so if you run short or long, then you subtract or add ~10%.

Take the example of a 53 ounce airplane on 67 feet of line. 53 * 0.7 = 37 W-H. Divide that by 14.4 Volts for the 4-S pack that is in that plane and you get 2.58 Amp-hours consumed. In fact the plane in question typically requires between 2500 and 2600 milli-Amp-Hours to recharge the battery. Multiply that by 4/3 to get what I would call the minimum battery capacity and you get close to 3500 milliAmp-Hours.
I hope that helps.
Dean

John Hammonds · « **Reply #20 on:** September 27, 2009, 05:42:31 PM »

Hi Dean,
Thanks, yes that helps a lot. I'm only a simple sport flyer for the time being but it really does help me to have an understanding of this. So the Mah required to recharge the battery in this example would be for a ~360s flight? I've modified the "xls" link above to use a more conservative 75% maximum discharge for Lipo's rather than the 80% I had calculated previously.

I had chance to try a pusher prop on my Flight Streak today as suggested by Dennis in another thread, I was running an APC E 10*5 on 52' lines for 4:25 and putting around 1450Mah back in (3s A123), 60 ' lines where hairy in the overheads to say the least even upping the rpm. Today I went to an APC E 9*6 pusher and settled on 9600rpm I did try a lower rpm but I think it's too heavy to cope, I'm now putting back 1950Mah but getting excellent tension all over the place (using 60' lines). Even upping the RPM on the standard 10*5 to give a similar mah draw was uncomfortable overhead on 60'. I have no idea why but these pusher props really do seem to make a big difference.

TTFN
John.

Author Topic: Advice on new model (Read 1321 times)

Alan Hahn

Alan Hahn

Alan Hahn

Alan Hahn