Author Topic: Is an AXI 2820/8 man enough? (Read 2288 times)

John Hammonds · « **on:** May 01, 2009, 10:39:40 AM »

Hi All,
I'm thinking of building a P40 class model as the next step in my flying education. Still plenty to learn with the electro streak but just thinking ahead.

I'm keen to stay with the A123's for a while as I'm very happy with them overall and if it ain't broke dont't fix it.

.

I quite like the look of the Cardinal and people seem to have nothing but good things to say about it. But the P40 or even the Pathfinder are alternatives as well.

Would my AXI2820/8 be enough motor for these? I'm thinking of a 3s2p setup (So 4600mAHr, 9.9v) or should I perhaps go 6s1p and go for a lower rpm/v motor such as an AXI 2826/10 or Scorpion 3020/16

If anyone has any ideas please shout up.

Thanks in advance

TTFN
John.

I'm out of town until Monday so if I don't reply until then that's why.

Mark Scarborough · « **Reply #1 on:** May 01, 2009, 11:19:04 AM »

I cant really speak to the specifics as they relate to your battery selection, however using the theoretical formula for PA performance as I have read in other threads....

volts X KV X .75( headroom allowance for govenor control) = theoretical rpm range

I came up with
9.9 X 1100 X .75 = 8167
To me this appears pretty low, but then I run Lipo's I dont know how the voltage fall off works for the A123 cells. My guess is that at this rpm you would need somewhere around an 8 pitch prop to get a workable flying speed.
Just my thoughts, take them for what they are worth?

Alan Hahn · « **Reply #2 on:** May 01, 2009, 11:45:41 AM »

I agree with Mark--from what I have seen posted here on this site, a Brodak P40 seems to require something in the 9000 rpm range with the "standard" APC 12-6 electric prop. It should be noted that the APC 12-6 seems to actually be in the upper pitch range of "6" inch pitched props, so I don't think another brand 12-6 prop will get you there (at 8000 rpm anyway). To get all the way down to the 8k rpm range would require more pitch (12-8 --maybe), or more diameter (13-6 maybe--but clearance may be an issue), or more blades (two 12-6's on the same shaft??). If I had a setup like yours, ready to fly, I would certainly try out those 3 prop options before buying a new motor or battery.

I fly a Nobler at 8000 rpm using the APC 12-6 and get good lap speeds (5.1 on 60"lines), but I think the larger planes with the thicker airfoils need more thrust to pull them.

So the issue is the kV of your motor is a little too low for the pack voltage. The motor can handle enough power (a 4s configuration for example would work), but its "gearing" (=kV) is too low. I was planning on trying a 3s2p2100 mAHr Lipo on a P40 with a 1080kV motor to see how it will work--assuming I will need to be in the 9000 rpm range with the 12-6. Need some good weather around here first.

Dean Pappas · « **Reply #3 on:** May 01, 2009, 01:03:48 PM »

Hello John,
I think I would duplicate Igor's Vice-World Championship setup: 2826/12 and 6S1P A123s.
Dean

Cheers ...

Dennis Toth · « **Reply #4 on:** May 01, 2009, 01:51:13 PM »

John,

When I started into ECL about a year ago I decided to go with the exact setup you are describing. I used an old 1950's ship with over 600sq in and weight of 55oz. I tried several props starting with the APCE 11x5.5 and going up to the APCE 12x6. I would generally pull around 3800mah out of the A123 1S2P pack. The AXI 2820/8 with this pack seemed happy on a cut down and repitched APCE12x6 to 11 1/5 x 5.5. I later moved to the lipo packs and went up to the AXI 2826/10 and the 1S1P 3850mah pack, this saved 4 oz and the ship was happier. The A123 had one advantage in that you could charge it at 10C and get a full charge at the field (about 18min).

Best, Dennis

Alan Hahn · « **Reply #5 on:** May 01, 2009, 01:51:29 PM »

Quote from: Dean Pappas on May 01, 2009, 01:03:48 PM

Hello John,
I think I would duplicate Igor's Vice-World Championship setup: 2826/12 and 6S1P A123s.
Dean

Cheers ...

Come to think about it, I wonder if 5s1p A123 would have enough juice to get through a pattern with the 2820/8 motor. I don't recall your ESC, but the standard Castle Creation Phoenix 35 and 45 can handle a 5s lipo (according to my spec sheet).

Alan Hahn · « **Reply #6 on:** May 01, 2009, 02:49:03 PM »

I can't find the AXI2820/8 specs but the AXI 2820/10 is listed as 1110. So I wonder if Mark's initial response is off about 25%-the kV should be 1.25*1110 rpm/volt or 1400 rpm/volt. If so, then John's original idea of 9.9V may be ok after all for an rpm in the 9k range.

Mark Scarborough · « **Reply #7 on:** May 01, 2009, 03:25:47 PM »

FWIW specs comparing the two,,, the /8 an /10,
the -8 is an 1130 KV and the -10 is 920 Kv

specs for the 2826/8
Kv (rpm/V)    1130
Max Power (W)    600W
Max Amp (15sec)    55A
Max Efficiency    83%
Io (No load A)    2.9A
Rm (Resistance)    0.030Ohm
Shaft Diameter    5mm
Gearbox    N/A
Motor Diameter    35mm
Motor Length    54mm
Motor Weight    181g
Built in Fan    N/A

for the 2826/10
No. of cells 10 - 16 Nicd/Nimh, 3 - 5 Li-Poly
RPM/V   920 RMP/V
Max. efficiency   84%
Max. efficiency current   20 - 30 A (>78%)
No load current / 10 V   1.7 A
Current capacity   42 A/60 s
Internal Resistance   42 mohm
Dimensions (diameter. x length)   35x48 mm
Shaft diameter   5 mm
Weight with cables   181 g
Max Rpm    15,000
Poles    12
Case    Outrunner
ESC Timing    22 deg
ESC Switching Freq.    8-16KHz

Alan Hahn · « **Reply #8 on:** May 01, 2009, 03:54:27 PM »

Ahhh, but he has the 2820, not 2826 (unless John's original was a typo). If I'm correct, then the kV of the 20 mm length magnet will be higher than the 26mm length magnet motor.

FWIW, my Scorpion motors are also 20mm length magnet motors.

Mark Scarborough · « **Reply #9 on:** May 01, 2009, 05:24:14 PM »

Ok fine, so go and get all technical on me why dont ya!

I guess I am so programmed to see the 2826, that the 0 looked like a 6,, or uh,,, I know, I am overdue for a prescription check on my glasses,,

Ok, so now that I have excavated my foot from deep within my mouth,, lol,, thanks for catching that Alan,, sigh, thats what I get for responding while I am at work,, trying to be sorta sneaky,, lol

Dennis Toth · « **Reply #10 on:** May 03, 2009, 08:42:30 AM »

Looking at my prior post I incorrectly listed the A123 pack as a 1s2p, the pack was a 3s2p, 9.9V 4600mah. With the AXI 2820/8 it will get through the pattern but you need to control the prop load to a static load of 52amps. For my ship this was an 11 3/4"x 4 3/4" APCE (cut /repitched 12x6) at 8600rpm, 62' 0.015 lines.

Best, Dennis

John Hammonds · « **Reply #11 on:** May 05, 2009, 06:20:11 PM »

Cheers all, Replies are very much appreciated, Yes the motor is an AXI 2820/8 The specs on the AXI site read as follows...

No. of cells 6 - 8 (2 - 3 Li-Poly) RPM/V 1500 RMP/V Max. efficiency 82% Max. efficiency current 25 - 37 A (>75%) No load current / 10 V 3,3 A Current capacity 55 A/60 s Internal Resistance 26 mohm Dimensions (diameter. x length) 35x48 mm Shaft diameter 5 mm Weight with cables 151 g

It's the motor I currently have in my Flightstreak running from a 3S1P A123 pack via a CC PH45, I'm currently running it at 9600 on an APC TE 10*5 and get a good solid 5 minutes putting between 1850 and 1950 back into the pack, I've also tried a 10*7 and 10*10 but hit the LVC early. It was the RPM/v and decent current handling which 1st attracted me to it, delving back through the old posts I found Dennis's threads on his excitation ship and I now feel even happier.

One of the the nice things I've found about ECL is I can make packs 3S2P or 6S1P simply by making some different leads and different Alloy mounts to suit different motors. So basically all of the options above are viable without major airframe surgery.

The specs above don't indicate "Power". Is it correct to take the "Max. efficiency current" and multiply by the Max pack voltage listed (i.e 11.1v * 37a = 410w) or should I use the "Current Capacity" which gives 610w? (I know my figures will be lower with a 3S A123 pack). Or am I way off base

Also if I go down the 6S1P route with one of the lower RPM/v motors suggested I have to disable the bec to the timer. Does that mean I need a separate bec in circuit between the flight pack and the timer. Do I just disconnect the power leads and leave the signal lead connected from the ESC? Sorry if this is a basic question but I have to ask.

What sort of flying weight would be acceptable bearing in mind a 6 cell A123 pack weighs in at around 16oz. As I've said I really like A123's so far but I do have to admit the weight scares me a little... If a 5S1P pack would do the job that would save me a few oz so something else to ponder... Of course moving to Lipos as Dennis did would save me another 3-4 oz. $:-\$ Nope I've decided A123's it is, the decision is maybe and that's final....

TTFN
John.

Igor Burger · « **Reply #12 on:** May 06, 2009, 02:03:21 AM »

John, the "current capacity" on axi speciffications means maximal current for short time interval (I would better call it "thermal capacity" of motor frame

). so you should certainly count with the suggested current for good efficiency, and even more, we are using them in PWM mode, so you should keep somewhat less than max.

If you want stronger power train, you can use 6s1p pack with combination of AXI 2826/12 and APCE 12x6 or even better newer custom F2B version AXI 2826/13d (not listet on axi home page) ... it has better copper filling and little lower KV (compared to Axi 2826/12)

if you use ESC for higher voltage, without BEC, then you will need separet BEC, or just simply something like 7805 integrated circuit making 5V from main battery, our timers use very small current. But it is always better to use ESC with switching BEC, they are rated for higher voltage.

John Hammonds · « **Reply #13 on:** May 12, 2009, 05:53:59 PM »

Hi Igor,
That 2826/13d sounds very tempting indeed, Every time I read through these threads I find something new and more questions to ask. I've never seen it mentioned as an ECL conversion but I've done an about turn on the airframe front. Another few flights on the streak and despite taking it home in one piece (Twice in a row).

A few hairy moments reminded me I still have a lot to learn. Sweaty palms and an increased heart rate have tempered my enthusiasm for a full blown P40 pattern ship just yet so I've gone and bought a Gotcha Streak They seem a really good deal at the moment only working out at $20 more than an UK supplied ARF Flightstreak including shipping from the US to the UK. It's got the Psycho wing and includes the optional tip extensions (So 48" and 500SQ or 54" and 550sq). It's light at (Apparently) 16oz minus power train, in reality I'll be over the moon if it comes out under 40oz. I'll take patterns off anything I can but if the worse happens replacement foam cores are available. It seems to accept a wide range of engines so my 2820/8 should be a starting point but I can go for the bigger motor as confidence increases (Someone tell me it will increase eventually)...

As I'm going to need to play around with pack configurations I've been looking at purchasing loose Life cells to save a bit of cash and also to allow me to make packs to fit the airframe rather than butchering the airframe to fit the packs like I did with the Flightstreak. Where do people get loose cells from? Are these any good? http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=370193563656&ssPageName=ADME:B:SS:GB:1123 As a comparison 1 * 6S1P in the UK retail at around $117 (Scary

) These are $100 (Shipped) for 12. (OK I need balancer cables etc but still too good to be true)? Should I run a mile or bite their hand off? What's the minimum wattage iron I should use and what should I use to make the connections? ECL in the UK ain't cheap.

I came across this site last night, It's an Electric car site but it has some nice diagrams showing wiring configurations for packs and power systems. Probably elementary stuff to you guys but I found it worth a look. http://scriptasylum.com/rc_speed/index.html

TTFN
John.

jjorgensen · « **Reply #14 on:** May 20, 2009, 11:14:24 AM »

The more I look at this subject the more confused I get. I gave up on my electric ringmaster and converted it back to glo when I could not get it do much more than a weak loop on a scorpion 3014-16 and a 3 cell A123 pack. Increasing to a 4 cell pack got me more power but the added weight made it want to sink at the bottom of the loop. An even bigger concern to me was I could not get more than 2 and 1/2 minutes of flight time before the voltage started to drop off a lot. How does Igor get enough time to fly the pattern on a six cell, 2400 mah pack? If I understand the concept (and I probably don't!) a 3 cell, 4 cell, 6 cell, whatever all have the same mah. So even if I go to a 6 cell pack won't my rather puny flight time remain the same? I would really like to convert my .35 and .40 size stuff to electric and want to stay with A123 for the cost and ease of charging but can't see it if I can't get enough time to fly the pattern. Any suggestions for a novice?

Alan Hahn · « **Reply #15 on:** May 20, 2009, 01:43:16 PM »

Jim,
I will try!

#1 the A123 aren't the lightest things to begin with, so that's a small issue I think, but not probably the biggest one.

I fly a Brodak Electric Clown Arf on a 3s2100mAHr Lipo pack (5.5 oz) and it has plenty of power. I have also used a 3014-16 Scorpion motor which in my case (since I wound it myself) had a kV of ~1250 (stock is 1187). I used an APC 10-7 Electric prop turning at about 8500 rpm. This gave me ~4.9 to 5.0 s laps. The flying weight is 28oz charged up and ready for takeoff!

I am guessing in your case that you are using a lower pitch prop and therefore need more rpm to make the needed thrust to fly the pattern. However the A123 batteries have a lower output voltage than the lipo, and as a result, you probably don't have a high enough kV to get the rpm you need (or conversely, with that motor, you don't have enough voltage in the A123 pack). I believe you have enough stored energy, but it is coming out too slowly! At least you have enough for longer than 2 minutes I think. You didn't say how much your charger is putting back into the pack after a flight.

So what to do---the easiest is to change props--go either to a higher pitch prop--like I did---an APC 10-5 might be marginal for me I think--I can't turn it at a high enough rpm with a 3s pack after 4 minutes of flying---or go to a larger diameter prop-- like the APC 11-5.5 prop. Either one will give you the thrust at the lower rpm that I "think" you can't get with your current prop. The idea is to have an rpm that the battery/motor combo can provide for the entire duration of the flight.

About your flight time, going up a cell will give you a longer flight, because you will draw fewer amps (Power=volts *amps and for a given airplane setup, the power needed will have a fixed maximum and minimum). The 'conversion' occurs in the ESC (high voltage-low amps from the battery to lower voltage-higher amps in the motor.

Most of us fly with an governor which allows the ESC to raise the throttle setting during the flight to compensate for the dropping battery voltage. That means of course that we are not flying at the start with wide open throttle, probably more like ~70% throttle. Even without the governor, most timers allow you to ramp up the throttle as the battery winds down. You have to play a bit with the initial and final throttle settings to get a reasonable ramp-up rate.

Igor Burger · « **Reply #16 on:** May 20, 2009, 02:31:12 PM »

Quote from: John Hammonds on May 12, 2009, 05:53:59 PM

What's the minimum wattage iron I should use

looks like 100W is minimum ... you must heat it up to accumulate lot of heat and the to do very quickly drom of solder od that nickel circle, it goes easy ... then you can connect copper cables easily

Igor Burger · « **Reply #17 on:** May 20, 2009, 02:45:35 PM »

Quote from: jjorgensen on May 20, 2009, 11:14:24 AM

The more I look at this subject the more confused I get. I gave up on my electric ringmaster and converted it back to glo when I could not get it do much more than a weak loop on a scorpion 3014-16 and a 3 cell A123 pack. Increasing to a 4 cell pack got me more power but the added weight made it want to sink at the bottom of the loop. An even bigger concern to me was I could not get more than 2 and 1/2 minutes of flight time before the voltage started to drop off a lot. How does Igor get enough time to fly the pattern on a six cell, 2400 mah pack? If I understand the concept (and I probably don't!) a 3 cell, 4 cell, 6 cell, whatever all have the same mah. So even if I go to a 6 cell pack won't my rather puny flight time remain the same? I would really like to convert my .35 and .40 size stuff to electric and want to stay with A123 for the cost and ease of charging but can't see it if I can't get enough time to fly the pattern. Any suggestions for a novice?

I think Allan got it well. I think 3 cels need kv~=1500. And for that energy and 5 minutes of fligt time you need 10" prop. I did not do such a small model yet, and I also do not know ringmaster. But I expect that weight approximately 800-900g and span up to 1200mm will be OK. Does it match your ringmaster?

Just for info, I have two similar models, The weight is 1800g and 1740g, span is 1500mm, orriginally done for piped OS Max LA .46. Both converted to 6sA123, Jeti 66A ESC, AXI 2826/12 or 13 (both tested). One of them was used on WC in Sebnitz and placed 10th (glow) and now used on WC in Landres and placed 2nd. so probably that electric works better that glow LA

Flight time is 5minutes on my new timer, on governor 9000rpm with APCE 12x6. After flight I charge back approximately 2100mAh. Lap time 5.1s on 19.5m long lines.

We have now in Czech and Slovak actualy 5 such models as far as I know - I posted a video from our local contest in another thread where you can see 3 of them - all use the same setup, all works for firts try.

If you want to know anything else, just ask.

jjorgensen · « **Reply #18 on:** May 20, 2009, 04:23:33 PM »

Thank you for the info. Actually, I tried everything from a 9-4 to an 11-7 prop, and I was flying on 44 foot lines. So I thought it should have pulled much better than it did. Weight is a definite issue on that small a model. I think my next attempt will be on a 46 size with Igor's suggested setup.

John Hammonds · « **Reply #19 on:** May 20, 2009, 07:34:28 PM »

Hi Igor,
Thanks, I had heard Soldering A123's was a definite no no, so I started looking around for "Solderless Battery tubes" as I had heard good things about them but unfortunately Mec have ceased trading so they are no longer available.

I'll get myself a decent Iron and chance buying some of the cells and see how I go.

Jim,
My original incarnation of the Flightstreak was powered exactly as you describe with a 3S1P A123 set up and a Scorpion 3014-16. I had some very scary flights on 60' lines where lap times could be measured with a Calender and loops were only just possible if I ran backwards at the same time. (Model weight 32oz). I upped prop sizes until I was running an 11*10 and it was only a little better. I almost abandoned ECL and dusted off my few ageing engines. The advice I got here put me back on the straight and narrow. I now have the same powerpack but run an AXI 2820-8 (KV 1500). The transformation was amazing to say the least. and I'm sure any other motor around the same KV/v that can push out the watts would be just as good. A good solid 5 minutes flying time and more manouvres than I'm capable of at the moment. The other big improvement came when I got a CC ESC and learned how to program the governer. It now turns a 10*5 APE TE and runs like a train right up until the end (Putting 1850 - 1950MAHr back in).

The 3014-16 is going in my almost completed Buster but with a Lipo setup which will hopefully give me the extra rpm's I need.

Don't give up, ECL is great and you will save a fortune on paper towels.

I'm still waiting for the delivery of the Gotcha Streak and beginning to get a little impatient.

TTFN
John.

pete beddows · « **Reply #20 on:** May 21, 2009, 02:41:13 AM »

Hi John
regarding soldering the cells take them to model power they are not far from you and will weld the packs for you and put leads on for about £5 if you need directions email or phone
they are in Mancetter uk. see you soon weather permitting.
pete beddows

Alan Hahn · « **Reply #21 on:** May 21, 2009, 07:36:51 AM »

Quote from: jjorgensen on May 20, 2009, 04:23:33 PM

Thank you for the info. Actually, I tried everything from a 9-4 to an 11-7 prop, and I was flying on 44 foot lines. So I thought it should have pulled much better than it did. Weight is a definite issue on that small a model. I think my next attempt will be on a 46 size with Igor's suggested setup.

Well it certainly looks like you tried! What rpm are you actually getting? I wonder if there is something else going on.

I am not an expert on A123 cells (never used them), but from what I understood from the proponents was that you can get back some of the voltage disadvantage (vs a LiPo) by being able to "abuse" them more--running them to just before the voltage falls off the wall. A lipo wants to always have about 20% left at the end of a flight if you want it to have a lifetime at all.

So I would have thought that there should be enough power to at least do loops at the 1 minute mark for example. Maybe you have a bad cell in the group???

jjorgensen · « **Reply #22 on:** May 21, 2009, 03:32:34 PM »

It's possible I had a bad cell, although I had 3 different packs that I tried. 2 - 3cell and 1 4cell. When I made up the 4 cell from one 3cell pack I had I made sure to charge the new cell before I added it to the pack so all cells were at the same level. Like I said, I did get a power increase and was able to do loops for about 1 and 1/2 minutes before the voltage dropped significantly but it was only good for one loop at a time. You could hear the motor sag when the nose came up and it would not pull it through two consecutive loops. I was only getting around 7600 rpm on the 3cell packs with a 10-7.5 electric prop after an initial burst at around 8000. By comparison, with a OS max .30 on a 9-6 I'm getting over 9000 and it pulls like a truck on 55 foot lines.

Alan Hahn · « **Reply #23 on:** May 22, 2009, 08:01:08 AM »

ok, I guess the output voltage of a 3sABC is just too low for the 3014-16 and a prop that both fits on the plane (ground clearance) and flies it at a reasonable speed.

With a 3s2100mAHr FMA Lipo, I can easily spin the 10-7.5 at 8500 rpm, for the full 5 minutes of the pattern (58 foot 0.012 lines). The lighter weight of the lipo helps too.

Author Topic: Is an AXI 2820/8 man enough? (Read 2288 times)

Alan Hahn

Alan Hahn

Alan Hahn

Alan Hahn

Alan Hahn

Alan Hahn

Alan Hahn