Ecalc is WAY off on amps, but right on everything else - RC Groups
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Apr 29, 2001, 01:52 AM
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realdeal's Avatar

Ecalc is WAY off on amps, but right on everything else

I have been testing my Maxcim MaxNeo13 series motors with different props and gear ratios. I have found that Ecalc predicts a MUCH higher current than I find in practice. Here are my two prime examples:

MaxNeo13D - APC-E 12x10 prop, 10-cells Pansonic 2000NiMH, 2.73:1 gear ratio.

Ecalc predicts - 52.8 Amps, 7050 Prop RPM
I measure - 32-33 Amps, 7200 Prop RPM

2nd Example

MaxNeo13Y - APC-E 14x10 prop, 21-cells RC2000, 3.33:1 gear ratio

Ecalc predicts - 50.1 Amps, 7460 Prop RPM
I measure - 34-36 Amps, Prop RPM not measured

Am I missing something? Ecalc seems to be very close on any other motor I measure or read about. It just misses these Maxcim motors by a HUGE margin in amperage. I considered that my props may be stalling in this static test since they are both fairly square, but I have noticed this phenomenon with other less square props as well. I have also bumped up the trim on my throttle channel after going to full throttle just to make sure I was getting everything I could. It never made a difference. Perhaps my batteries aren't delivering the voltage that Ecalc predicts, but the prop RPM is very close when measured.

I'm not complaining as the performance always exceeds the prediction, but I would like to know why it happens.

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Apr 29, 2001, 09:58 AM
Registered User

I have always found the same thing especially with the Maxcim. When I use Ecalc with a Maxcim and I want to fly at ~30 Amps I try combinations that show about 40 Amps in Ecalc. I normally assume Ecalc is about 10 amps high, although it appears you are finding it 15-20 amps high.
Apr 29, 2001, 10:18 PM
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Ben Diss's Avatar
Well it went the other way for me. I setup a Sp480 BB Race 7.2V with 5.5 x 4.3 prop on 8 800AR cells. eCalc said 23A, Whattmeter showed 30A.

Apr 29, 2001, 10:21 PM
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realdeal's Avatar
I measured prop RPM on the second combo today and got 6900 RPM. Ecalc will match this prediction if I lower the cell voltage to 1.12 volts per cell. It still says I should be drawing 42.6 Amps versus the 35 Amps I am actually seeing. This is much closer to the error you experience.

I am still at a loss in the 10-cell system as it is nearly exact except for the amperage.

Apr 30, 2001, 01:23 AM
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Brad Trent's Avatar
It might be the props that are throwing the #'s off. I find that all of the large APC-E props draw 10 to 15% less amps than anyone elses props, E- or not, and still give the same rpm as a similar prop. Ecalc simply may not have the right prop factor in the program.
Apr 30, 2001, 02:06 PM
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Ralph Weaver's Avatar
With that much prop pitch, the prop may be stalled during static running. This will cause low current. When it gets moving and actually "bites" into the air, the current will go up.

Ecalc, like any simulator is only as good as the data put in.