Author Topic: Motor Specs (Read 2335 times)

Crist Rigotti · « **on:** August 11, 2008, 09:41:31 PM »

Looking at Scorpion motor specs it usually lists continuous max amps as xxx. What voltage is this usually? What I'm looking at is how big a motor can I run with my CC 35A esc. It is rated at 35 amps and they say that an esc should be as large as the max amp rating of a motor. I know we don't run the motors at full power. Yes I know the way a brushlees motor is run at full amps but very shortly for each pulse. If I go to a higher voltage battery lets say from a 3S to a 4S, the current will go down for a expected motor run. Does this mean I can go to a larger amp rated motor? Am i making any sense?

walterbro · « **Reply #1 on:** August 12, 2008, 08:45:57 AM »

Hi Crist

Most of the max. continous amps are given for the recommended number of cells.
This is usually 3cells- 11.1volts. Another factor is the continous Watts the motor is rated for.Do not use the Max watts as this is for only 30sec. Do you have a motor that you could bench test with your 35 esc? If so that would be the safest way to
see how many amps/watts you can draw in static conditions without cutoff. Then
you could use a factor to determine the continous amps @ 11volts or 14 volts.
For example My axi2826/10 pulls 32amps static with 14volts.The in- flight average
is 22amps with same prop and battery based on MAH used.
Dont forget the Kv of the motor. Dean's formula is Kv*Volts*.7= target RPM this is very useful. Steer clear of any motor if the Kv,Io & internal Resistance is not given.
Usually, the lowest internal resistance at the desired Kv will be the most efficient motor.

Walt

Alan Hahn · « **Reply #2 on:** August 12, 2008, 08:59:59 AM »

Crist,
As far as the motor is concerned, volts don't matter, only amps. This is a heating issue which of course goes as I^2*R, R being the motor resistance (for motor specs of course). The rating is more or less set by the size of the outer shell as that is where most of the heat can escape (it is hard to get a lot of flow between the windings as it is a pretty confined space).

As regards to punishing the ESC, it is true that the measured current from our watt-meters is the average current and not the instantaneous. So if we are flying at 1/2 throttle and measuring 20A for example, the instantaneous current is actually 40A during the 1/2 of the pulse that the FETs in the ESC are turned on, (and 0 during the off half). So the ESC heating at flying at 1/2 throttle and 20 Amps is (due to the I^2 term) is twice as much (40^2 x 1/2) as it would be if the ESC was pulling 20A continuous. However this is still less (65%) than 35A continuous. Fortunately Castle Creations builds their ESC with conservative specs.

What is tricky is understanding how much throttle you are actually running (% wise) since it isn't an easy thing to measure the way we run these things (in governor mode). So far I haven't had a problem with my setup--but it doesn't mean I am not worried about it. The best thing to do is to try and put on a motor with a kV which would insure you are running a throttle setting in the "upper" range (>70%??) during level flight. That's why I went from a 12 turn Scorpion 3020 (kV=1088) to a 16 turn Scorpion 3020 (my own winding which gave kV=880--higher than I had calculated) when I changed to a 4s2100 Lipo pack from a 3s4200 pack. Basically kV~1000 is great for a 3s system (and rpm in the 8k range) while ~750 is a better kV for a 4s pack (and same rpm range).

Forgot to add that it is also kinder on the battery pack to match kV---for the same reason, the heating will be less, even though you appear to be pulling the same average number of amps.

One final comment or addition----the motor is actually drawing current through its coils 100% of the time. When the ESC turns off the supply amps from the battery (what I was referring to above), another FET actually shorts out the motor coil and allows the current to keep flowing (the energy to do this is in the magnetic field of the coil wires). If you would be able to look at the motor current, it is more than you are supplying from the battery (but the power total is slightly less than what you are getting from the battery--related to ESC efficiency).

Mark Scarborough · « **Reply #3 on:** September 08, 2008, 11:27:54 PM »

***Dean's formula is Kv*Volts*.7= target RPM this is very useful. Steer clear of any motor if the Kv,Io & internal Resistance is not given.***

Ok I read this, then I look at my moter, Axi 28-26-10, It lists the kv as 920 I am using a 4 cell pack, so 14.8 volts right? sorry Li Poly batteries
so if I do the math,

920 * 14.8 * .7 = 9531
so should I be targeting a lower pitch prop say a 4 inch pitch or 4.5 to run this at its happiest range? I would anticipate the 12 x 6 apc e prop reccomended by some for this motor to be running around 8500 rpm to get 5 sec lap times. My wet motors running 4 inch pitch props generally turn around 97 or 9800 to see the lap times I want.
Thanks guys, my bird is sitting there waiting to be programmed so I can fly it.

I should add, same basic setup as Rudy, Profile P-40, axi motor, Cc speed control. I have both ztron and JMP timers.

Alan Hahn · « **Reply #4 on:** September 09, 2008, 07:18:01 AM »

Mark,
More or less your battery and ESC will be happier with the higher rpm, that's for sure, but it isn't clear you will be happy too! I think you get better tension with the larger diameter prop, and at least for APC electric props, the 12-6 is the lowest pitch they do. Of course you can always try re-pitching it to a lower value like Dennis T. (aka Stuntman) does.

For a few flights I flew my Nobler with a 1088kV motor and the 4s pack and it works ok, even if it was stressing the battery more than I like to do.

The other thing to remember is that the battery pack size (and "C" rating) matters too. I run 18C 2100mAHr cells. I calculate my internal cell resistance is ~ 20mOhms (this is consistent with the manufacturer's AC resistance values too so a 4s pack has 80mOhms resistance).

If I am drawing 18A average at 70% throttle (my estimate), then the instantaneous current is ~26A and heating in the battery is [26A²*0.08Ohms]*0.70=38 watts! This is why I am still trying to lower my kV. It is just a precaution to make my battery last longer. They are coming out of the plane at ~130 ^oF and that is at the upper limit of where I want to be. It probably is easier to play with the prop a bit to get closer to the ideal rpm rather than fool with the motor---but I guess I am a little different in that regard

!

A larger pack (>2100mAHr) or a larger "C" most likely will have a smaller cell resistance and your heat production will be less (and spread over a bigger cell volume too so the temperature rise will also be smaller.

Mark Scarborough · « **Reply #5 on:** September 09, 2008, 08:08:53 AM »

Alan,
Ok so then disregarding available prop selection. I would in fact be better off running a higher rpm. I am a wood prop junkie, I use mostly wood props on my wet setups that I have tweaked and reworked in house. Thanks to Pat Johnston for corrupting me there! I have more tied up in wood props that I do airplanes pretty close. So I am thinking that to put the engine and ESC in a happy place. I am using EVO 4200 mah 14.8 batteries. My thoughts were to get into the 9500 rpm range I will probably be looking around a 4.5 pitch. In theory as I understand it, If I were to use say a 12 x 4.5 (wood) that is cleaned up, thinner blade, sharper leading and trailing edge, I would actually reduce the load on the system even though its turning a higher rpm. Does that sound reasonable? Perhaps even look at a 12.5 x 4.5 again cleaned up.
Thanks in advance

walterbro · « **Reply #6 on:** September 09, 2008, 10:36:17 AM »

Mark
I have found that if you use Dean's formula you should use nominal volts not max volts. For example 4cell battery use 14 to 13.5 volts for your calc.
*** 14 x 920 x .7 = 9016rpm for axi2826. This rpm is approx. I use a 12x6 prop and
run 8940 Static rpm. This gives me 5.06 - 5.1 sec. laps. on 66ft 7" lines centerline to centerline. Hope this helps.

Walt

Dennis Toth · « **Reply #7 on:** September 09, 2008, 10:44:10 AM »

Mark,

One thing to remember about the wood prop vs the APCE is the effective pitch difference. The APCE is undercambered and the 12x6 seems to have a bit more then the 11" APCE prop it really pulls. It amounts to about 1" difference from the backside measured pitch. I fly my Excitation on 64.5' lines and aim for a 5.0 lap time. With the APCE 11.5x4.5 (cut down and repitched 12x6) I set the rpm at 8900 and it hits the lap time. With a wood Rev Up I need an 11.5 x6 to get the same lap time. When you compare the ECL to the IC set up, remember IC's unload or come in and pick up about 750 rpm once they get moving. Our ECL's kinda come out since as the load is reduced when the ship is released our ESC maintains rpm (you set 9500 and you get 9500, always) so it pulls back the throttle. This accounts for a bit of the difference the rest is the difference in blade design. If you go with the APCE repitching is very easy with a heat gun but you will need a pitch gauge.

Best, Dennis

Mark Scarborough · « **Reply #8 on:** September 09, 2008, 12:05:04 PM »

Great info gents,, thanks!
so If I read this right, then actually I should be targeting around 9000 rpm give or take,, As for the prop pitch gauge, I do have one, I use it religiously when reworkign my wood props.
Dennis, you mention a rev up 11.5 x 6, is that the stock blade thickness and such? I know I have seen tremendous gains by thinning the blade crossection, and sharpening the leading and trailing edge especially on zinger, and rev ups. I have managed to sand in substatial changes in pitch that way as well. I found the rev up props I have when measured actually tend to measure about an inch shallower than the listed pitch. Just my observation. I have a stack of rev up 12 x 6 props that I may play with, I can get usually from a 4..5 to a 6 inch true measured pitch from them. I will also try the APC E 12x6 for sure. I just like the lighter weight of the wood props personally, I find less issues with GP. (ok so part of it is that I get to play with plane stuff while watching movies with the girlfriend,, cause I can do it at the coffee table,,

)

Alan Hahn · « **Reply #9 on:** September 09, 2008, 01:15:25 PM »

One thing to note is not all 12-6 props will give you the same loads. I haven't really done any studies, but it isn't clear to me whether a 12-6 wood prop is a good as a 12-6 APC thin electric with respect to loading the motor down. So you may be making things harder on the battery by going to a typical "glow" style prop.

To be clear I don't really know for sure one way or the other, but you should be aware.

Mark Scarborough · « **Reply #10 on:** September 09, 2008, 01:28:18 PM »

Alan,
noted and agreed!
I have seen huge variations between props that are marked the same from different manufactures let along the same manufacture and size. Wood props do present another variable, some times good some times bad. APC props are definetly some of the most efficient consistant props available. however, that being said, the standard APCs are rather heavy, and I kind of have a thing about the blade profile on the E prop, certainly not to discount it, but the shape of the blade just doesnt "feel " right to me. Now the standard APC profile, like the 12.25 x 3.75 to me is a really strong outline blade. In fact a lot of my wood props attempt to replicate this shape. There is something about that blade that speaks to me.
Of course, electric power is different, I agree, and time will tell, heck I may end up with the 12 x 6 EAPC as the defacto favorite on my setup. But I do want to experiment, and an elect is a way better platform to experiment with props than a glow setup. you have all the information available to dissect its performance that is very hard to capture with a glow setup.
Dont take any of this to read that I offhandedly disagree in any way, I just want to experiment, its part of the intrigue with the elect setup for me.
Alan, when you spoke of a wood prop not loading the motor down,, I read that you think loading the motor is a good thing? or am I misreading what you are trying to get across. by Load are you refering to the measured amp draw of the prop? Would I be correct in surmising that a prop that draws more amps on the ground static will not as a matter of course draw more in flight? It would seem that the comparison of static draw to inflight draw would be one way to compare efficiency of the prop motor combination? (all this assuming the airplane actually performs in flight in a similar manner)

By the way, thanks for pushing the thought process here, I truly enjoy dissecting ideas like this

Rudy Taube · « **Reply #11 on:** September 09, 2008, 05:09:40 PM »

Hi Guys,

Walt has a very good point about not using the 14.8V in our calculations. Using a lower, more realistic, V is more accurate. Using Walt's numbers brings our ubiquitous AXI 2826-10 right where it is happy and cool. :-)

Mark, I know how you guys like to play with props, but PLEASE use the APC-E 12 x 6 for your 1st several flights. At least until you get the lap speeds and overhead pull where you want it. I tried around twelve different props and always came back to the APC 12x6 as the best, BY FAR. I have tried the expensive low pitch CF props, several brands of wood and FG and CF in different sizes, both dia. and pitch, 2 blades, and 3 blades, etc.

I think one of the hardest things for a wet guy to do is forget all he knows about props for 2C wet engines when converting to modern E power. Our motors act more like 4S wet engines and NOTHING like 2S engines. They like bigger props, both dia AND pitch.

FWIW: I think you can repitch CF and wooden props without any problems but I don't think you can repitch an APC prop and expect it to stay at the new pitch. Our experience in RC is that the APCs will slowly return toward their original pitch. This would be a major problem in ECL, having a different speed for each flight would be a real challenge, unless of course you are Brett Buck or one of the other guys out there with the "Golden Hand"!

I just looked at a few of my Eagle Tree recordings. My level flight RPM in the air is 9,050. This gives me 5.0 sec. lap speeds on 62' Eye to Eye .015 lines. This RPM is constantly changing, every second. It bounces around between 8950 and 9100. It also goes up to 9,400 for a moment. My guess is that the ESC in gov. mode still can't keep it exact. I don't know if the ESC is allowing an overshoot when pouring the coals to the motor at the beginning of a maneuver, or it is unable to stop the momentary overshoot in RPM on the down lines?
BTW: this RPM variation is NOT seen or heard during the flight. It sounds and feels like it is at the EXACT same RPM every second of the flight, and the plane NEVER bogs down, even with my ham fisted entries into the squares! :-)

Mark, please don't misunderstand me. I think that there is a lot of improvement in performance to be had with better E CLPA props than we have available now from commercial suppliers. My WAG is that it would be better to start out with a larger standard wood prop, say 13 x 6, then make it smaller with a much thinner airfoil, undercambered even. Like most of the "Prop carvers", it would take many tries to get one right, and improve on our E-APC. But that is WAAAAY more work than I ever want to do.

AFTER you get settled in with your new ECL plane with the APC, and then begin to carve your own props, please let us know how it works out. :-)

Regards,

Mark Scarborough · « **Reply #12 on:** September 09, 2008, 05:26:02 PM »

Rudy , Rudy, Rudy,, now you went and did it,, you worded it like a challange almost,, now I GOTTA make a wood prop work better,, lol
as I think I said, I do plan on starting with the 12x6 apc. But be warned,, I have to justify having all these wood props around somehow,, I mean come on, otherwise how do I explain it to Linda?
Onething that you may not realize is that I and Pat dont subscribe to all the "theories" surrounding props we both believe diameter is king, swing as much diameter as you can without hurting the motor, turn the motor where its happy. I think to many wet setups use diameter to limit speed,, and to me thats giving away traction,, after all what we want is traction going uphill, and traction going downhill, speed regulation, = traction,, anyway, it will start off with the 12 x 6,, but,, time will tell, see I spend 3 or 4 hours on a prop without even thinking about it,, so tweakign and massaging, well thats my game,,
again, thanks guys for the stimulationg exchange, all information taken to heart, and in the digestive process now,,

Alan Hahn · « **Reply #13 on:** September 09, 2008, 07:12:30 PM »

Mark,
You might want to check out my prop thread http://stunthanger.com/smf/index.php?topic=7574.0

Dennis Adamisin · « **Reply #14 on:** September 09, 2008, 07:29:01 PM »

I have variations of this discussion with my propellor artist brother all the time. To be sure it is quite possible to trick out wood props and gain fantastic performance advances. My brother has created some absolutley stunning props out of what used to be 11-6 Power Props. He's done several, and even tweaks for different weather conditions. Put them on a FP 40 and you cna kick some serious tail. He's messed around with some of our ECL props, but he's ready to get SERIOUS!

I on the other hand am extremely conservative about props - I like REPEATABILITY over everything else. I think this is enough to scare me off a re-pitched prop. I read about some folks twisting a prop by hand and heating it with a hard dryer... brrr! If I was ever to bother with repitching I would want a multi-station pitching fixture with controlled heat environment to bake it into submission. Still that's a lot of grief to go through - much easier and MUCH more repeatable to just bump another 100 rpm into the ESC!

Wood props have a notoriously wide variation in pitch, and a lot of wood that can be trimmed away for E-power - but can you do it TWICE? Three times or more? Exactly the same way? Probably, with a suitable set of templates and pitch fixture. However, I think that molded props SHOULD have a much narrower range of variation than wood. If you want to modify a prop and make it repeatable then start with a stable platform.

At the risk of agreeing with Rudy (no, not that!

) I would start, an APC. Longer term I expect to evolve to modified APC's - with a few milliamps of waste trimmed away by my propellor artist!

Rudy Taube · « **Reply #15 on:** September 09, 2008, 11:18:06 PM »

READERS NEW TO ECL: PERSPECTIVE and "Nerd Alert"

Please keep in mind that the standard AXI 2826-10 + CC ESC + JMP or Z4 Timer + APC-E 12 x 6 prop, is = to or better than any .40 to .50 wet power system out there. It will fly any CLPA plane under 60 oz. T.O. weight. IT IS ALL YOU EVER NEED TO FLY UP TO AND INCLUDING THE EXPERT CLASS.

Please keep all this "QUEST FOR THE LAST .0001% OF POWER" in perspective. ...... Most of what you read here on Robert's excellent "E" forum is stuff on the BLEEDING edge of our ECL technology. Please do not think you need to know, or use ANY of this "nerd" stuff that we are talking about. If it interests you, that's great, but it is NOT needed to get into ECL and fly successfully! Being a nerd can be cool, at least some of us nerds like to think so ;-), but sometimes we can get carried away and our nerd side takes over and we go out of control and lose all sense of perspective on what we are doing, and how it looks to the outside "real" world!

Now, back to finding that last .0001% of improvement!

Mark,

Yikes! 3 or 4 hours carving 1 prop? I can't even imagine doing that. .... I guess that is what makes you an artist with beautiful planes, and me a hack with OK planes.

Alan,

Thanks for the "review" post. I reread it, good info there on props. I still think that Walt is on the right path with his Twin ECL. The too big disks out there with CR props really works. I can't wait to see the Bob&Dean twin CLPA plane when it is completed. It should be a real world beater. I hope they make it E powered.

Dennis,

I am honored when one of you CLPA legends agree with me.

Thank you for making the excellent point about REPEATABILITY. That is the #1 advantage of E power, and I would hate to lose it by having a hand carved prop that I know I can not duplicate if it is lost.

I like the idea that my APC works great, I have identical spares, and I can get one at any LHS for < $5 ...... and it does not take 3 to 4 hours to make one.

I am sure your talented family can make improvements on our E props, and that is great for our hobby and will help move us forward, but what we have now is very good. I have let some national level pilots fly my ECL plane and they are all impressed with the power "as is". They all had

&@* things to say about the "trim" (or lack of, I have not done anything at all!) of my plane, but they all loved the constant, "freight train" like, power from start to finish!

Regards,

Mark Scarborough · « **Reply #16 on:** September 10, 2008, 07:55:08 AM »

Rudy,
3 or 4 hours includes finishing the prop, and really thats probably a little on the strong side. Most times when I do prop work its while sitting on the couch watching a ball game with the girlfreind so time passes quickly. as for repeatability, yes that is one major thing that needs to be considered when doing this. In all honesty, small variations have pretty much nullified themselves with these props on a wet motor,, I have managed to create fairly good clones. However, a wet motor responds differently to a load so I dont know yet. As I mentioned on the phone last night as I casually burnt up an hour of your evening, I plan on starting with th 12 x 6,,, HOWEVER, playing the prop game is fun for me, its entirly possible that I wont come up with a wood paint stick that will fly the thing better than the apc does. But if I dont try, then what am I supposed to do while watching the Hallmark movies with Linda for crying out loud! actually watch them, yeah whatever,, lol
As for need for a backup prop, well now, if you dont kiss the ground with a tip, or crash the plane who needs a backup,,,,,,

Ok Ok before the flames, I know, I have been burned at contests , in fact three contests in a row, when I buzzed one of my wood props on takeoff, and then had to adjust on my second flight,, I DO know how important backups are, thats why I take 4 airplanes to a contest,, lol

Alan Hahn · « **Reply #17 on:** September 10, 2008, 08:26:03 AM »

Mark,
I hope you get extra points for being the COP (carver of the prop

)

Mark Scarborough · « **Reply #18 on:** September 10, 2008, 08:30:25 AM »

ROFLMAO, thats goo Alan,, maybe I will petition for that, hmm
perhaps a new debate is on the horizon, I mean after all, Isnt that true craftsman ship,, shouldnt I get rewarded,, ,,,,,,,,,,,,

Dennis Adamisin · « **Reply #19 on:** September 10, 2008, 10:08:26 AM »

Mark:
I think Alan is holding out for WOM points* After all WOM & COP points could help him make up for ARF & BOM...

(huh???)

(*Winder of the Motor)

Rudy:
I'm only a legend in my own mind.

I converted & flew my first ECL scarcely just over a year ago - I am but a "grasshopper" in this field!

We're finding another perspective on repeatabiity: my nephew has been able to take data he's collectd on the Oriental (9" to 11" props, 3 different motors, 3 different ESC's, etc) and he is remarkably accurate in PREDICTING usable starting points for setting up new airplanes. In the case of the Vector and the Swinger, he came up with the RPM settings that generated the lap times within 0.1 seconds of target. I think the repeatability and dependability of ECL effectively REMOVES the power system as a point of concern in preparing & campaigning a new bird.

I have no proof of this, only supposition: I have a hunch that when using a governor some degree of prop performance shortfall can be tolerated because it can overcome by the governor.

There are more great IC engines available now than ever before. However I have come to believe that IC engines are NOW obsoleted by what's available in electric. As Rudy pointed out, you can easily procure and install FIRST CLASS ECL systems; though we will always have the 1%'ers pushing ahead a little more each time...

Mark Scarborough · « **Reply #20 on:** September 10, 2008, 11:08:58 AM »

****There are more great IC engines available now than ever before. However I have come to believe that IC engines are NOW obsoleted by what's available in electric. As Rudy pointed out, you can easily procure and install FIRST CLASS ECL systems; though we will always have the 1%'ers pushing ahead a little more each time...****

You know in all honesty, Im not sure my pursuit of the magical wood prop equivelant is even what its about for me. I am competative, but, I have this little drumbeat inside my head that doesnt seem to sync with anyone else, well at least very few

I have only been playing the stunt game for less than two years, and I understand the benefits of using what is proven, but just like I design my own stunters,, (see my bf 109 thread, and my Gee Bee profile) its almost more about the personal expression for me. Of course, I do have this fantasy of uncovering some magical secret that will make me a stunt icon, but then I thought I would have money too by this time in my life, so what the heck, its my fantasy I can live there if I want to! lol

Really , these forums are a godsend though, they allow an instant transfer of knowledge that wasnt even thought of before! As for me, I love to debate and discuss, it expands everyones scope of knowledge so bring it on!

Dennis Toth · « **Reply #21 on:** September 10, 2008, 12:55:30 PM »

Mark,

I have been playing with about 8 different style props over the past 6 months and so far the APC E 12x6 is the strongest pulling prop of the bunch (RevUp, MAS, TF Power Tip, and APC 12.25 x 3.75). I have tested them in stock and modified configurations and the only one that comes close is the Top Flight Power Tip 12x6. The TF has a Philips entry and narrow blades, it draws a little more current but it does pull. To make the RevUp pull the same lap time I had to go the a 7" pitch, which brought the amps to the same level as the APCE and worked pretty good. Seem the APC E 12x6 has an effective pitch one inch more than the flat backs (and the APCE 11x5.5 for that matter). I have modified this prop by cutting and repitching in several sizes and they all pull the ship the same in level flight, only when you get up top to you notice the difference the extra diameter makes in holding the speed.

On repitching, as Dennis pointed out all heat pitchable props want to move back to the molded pitch, but repitching has been going on for many years and works fine. They don't move back that fast and if you check them once every few months it's fine. The regular APC props take a lot of heat and heat soaking to get them to repitch. CF props and the APCE props don't need much heat and hold the pitch well. I know there is some question as to keeping the blades in true plane, I know it seems like once you heat them they should move out of plane but they don't if you just twist them to set the pitch. Obviously if you force the out of plane movement they will go out but I have never heard of anyone that heat pitches having a problem. As far as the stock pitch on any of these props go it is like the balance, close but if you put stock APC's, APCE's, CF, or wood on the pitch gauge only a very small % will have both blades pitch the same. Bottom line is if you think it is important to balance a stock prop then you should check the pitch on both blades.

Best, Dennis

Author Topic: Motor Specs (Read 2335 times)

Alan Hahn

Alan Hahn

Alan Hahn

Alan Hahn

Alan Hahn