Amp draw and FE Calc

[RayR]

Guys,

At our fun run several weeks ago, I was testing some props and wanted to know if FE Calc was accurate at calculating amp draw. Below is an amp draw chart for my Delta Force 33 with a 1515/1Y, 4s2p Flightpower 25C 5000's spinning a de-tounged X640 through a wire drive. The boat was running terrific, well aired out and guesstimated speed in the low 50"s.

I installed my Eagle Tree for the first time and did a couple of laps. FE Calc was set with hull type hydro/performance since it assumes too much drag on a mono and it said I would draw 88 amps @ 93% efficiency and guess what, right in the middle of the real data.

You may wonder why the amp draw decreases as the run progresses. This is mostly due to the cells warming up. They where installed at ambient, which on that day was about 82 degrees. A good case for pre-warming cells.

All the best,

Ray

[ReddyWatts]

It calculates 99 amps in my FeCalc when using your info. We must somehow be using some different data. The hull type selection is interesting. That could also be caused by the 4 pole motor.

[RayR]

The likely culprit is IR value for the cells. I will recheck it when I get home, but I think it is correct.

Ray

[ReddyWatts]

It is interesting to see a 30% difference in 2 and 4 pole motor torque. The same difference in amps you see when you change it from a mono to hydro hull.

2-pole stator of 80-mm diameter and 90-mm length will output around 1.7 Nm torque; a 4-pole motor will output 2.3 N-m torque.

IMO FeCalc needs to be updated to have a 2-4-6 pole motor option selection.

[RayR]

If you have a way to update it, please do.

When it was first offered up to the community, the guy who wrote it got so inundated with change requests he updated once and dissappeared.

I was just tryin to suggest a way for folks to keep from melting down equipment via a simple available calc. The IR value for the LiPo cells is correct.

For those that do not know how to edit the FECalc data file, here is the file I am using currently for FE Calc, just replace the data file with this one. It contains many of the currenty available motors.

All the best,

Ray

[RayR]

Data File

FE Calc Data File

[ReddyWatts]

I use it all of the time for 2 pole motors with lipos and its calculations are in the ball park. I have had problems with the Neu motors amp calculations.

I wish someone could update the program. It is a great tool for the FE hobbiest.

[Raydee]

I use it all of the time for 2 pole motors with lipos and its calculations are in the ball park. I have had problems with the Neu motors amp calculations.

I wish someone could update the program. It is a great tool for the FE hobbiest.

What do you usually find.....that FE calc is to low or to high?

[ReddyWatts]

The calculated amps are higher than actual Neu motor readings. I plugged Fluids 60 mph Mean Machine Neu motor setup in FeCalc and it reads higher amps than actual. If I change the hull like you did, it is within 10 amps of what he stated. Interesting.

[RayR]

That's because the drag coeffienct in the program for hull type is way too large. If memory serves me correctly it is 20% for hydros, 25% for cats/tunnels and 30% for mono's.

Although, overestimating amps draw certainly keeps one in the safe zone.

Ray

[ReddyWatts]

But it works great on 2-pole Feigaos and KB45 setups.