Ecalc vs Pancake Motors

[ewr]

I've heard that eCalc is way off when calculating the amp draw vs prop size for pancake motors..can anyone confirm this, and maybe explain why? Id think since it asks for the number of poles, case length, voltage, and max A limit that it couldn't possible mess that calculation up??

I'm wondering because I entered in the specs from my most recent Hex build with 4830 480Kv motors which have a maximum amp limit of 31A and the manufacturer recommended props for it are 14x5-15x5, while some people say they even use 17x5.5 on them......but eCalc is telling me I will pull over 60A at full throttle with 15x5.5's! In order to keep the A below 31 I have to input a prop size of 12x4.5....surely these motors can handle more than that though???? I'm confused!

Attatched a picture from the calc for reference.

ThanksView attachment 12395

 

[ewr]

whoops pic too small.
View attachment 12396

 

[schoeds]

You need a lower KV (320-390) or a lower voltage battery with those numbers. Those are some odd numbers you have plugged in for battery, however...

 

[ewr]

Thanks for the reply, Schoeds.

Well the motor is meant to be run on 6s so I don't think I can go lower...and the only lower Kv they offer is 420 which would give me around 1800 less RPM...but again, the manufacturer recommends 14-15" props.

Doing some more digging I found some prop test charts and they run up to 16" props on them and the Amps seem to stay in check.

Decided to just do some tests myself also so I ran one motor with a 15x5.5 prop up to full throttle for 10s and came up with 36.2A Max (and that's static with me holding down the motor which I think gives a higher A and W reading than in flight) and 8090RPM which keeps the prop tips well within the limits....so after doing a real world test it seems eCalc IS way off when it comes to these motors....wonder why?

Oh, the battery numbers I put in are a little off...I run a 6s2p setup using 2 8000mAh 6s batteries....I just entered in the numbers for 1 16000mAh 6s....so the "battery" specs section at the bottom is correct except the weight is only half of the real weight...but the AUW number I have is the correct one so I don't think that even matters.

View attachment 12404

 

[Electro 2]

I've never used E-calc, so I don't know, but is pole count included ? "Pancake" motors typically have a higher ple count than "normal" motors. This is, of course, why they are pancake shaped. For 6 cell biggies, it's typically 22. This said, I have trouble believing any reasonably mathmatical algorithm is going to yield consistant, correct, results. On any real aircraft with any real pilot/flying style, there are sooooo many variables.

 

[ewr]

I've never used E-calc, so I don't know, but is pole count included ? "Pancake" motors typically have a higher ple count than "normal" motors. This is, of course, why they are pancake shaped. For 6 cell biggies, it's typically 22. This said, I have trouble believing any reasonably mathmatical algorithm is going to yield consistant, correct, results. On any real aircraft with any real pilot/flying style, there are sooooo many variables.

Yes I explained in the first post that it takes into account number of poles, can length, diameter, cooling, voltage, max watts or amps...so I figured it couldn't go wrong! but apparently it can lol. I entered in 22 poles.

Thanks

Eric

 

[Electro 2]

Actually, unless I see hard, measured, numbers on a motor prop combo, I wouldn't put much stock in it. Maybe you can find someone who has the very motor you're thinking of and have him shoot some curves (if they have a test stand) and let you know. On my last build, I was very fortunate. A forum member in Italy put up a fairly complete set of curves on the very motor I wanted to use. My work was done for me!