Why doesn't the math for prop size and cell count match add up in Ecalc

[GlitchGR]

Hi,

I'm new to the electric motor world. I've been using the ecalc's Xcopter and filling in the variables with manufacturer information. I often find that it says the prop will stall or draw too much amperage, or that if i use a 4 cell vs 3 cell that the motor is over it's rated current. Is this something that i'm doing wrong or are the manufacturer's misrepresenting their specs?

 

[jes1111]

Impossible to say without seeing exactly what you are doing - try posting some screenshots.

I've found eCalc to be very good - but it does need to be understood and set correctly.

 

[GlitchGR]

Here's an example I threw together of what I'm seeing with some of the motors I've tried using with ecalc. It's probably my doing but it would be great if someone would point out where I've gone astray.
View attachment 6190View attachment 6191

 

[Blacksails]

You'll only ever be drawing that 24A at max throttle. At hover your drawing 8.78. So you'd be fine flying about normally, but would stress your motors if you had to use max throttle to get out of a sticky situation.

Also your IR is wrong. 0.063 rather than 0.036.

Where did you get your 1A @ 10v?

 

[GlitchGR]

Blacksails,

Thanks for pointing out that i transposed the numbers in the IR. The 1. amp was pulled from iflight's website though apparently this is a slightly different motor the one that i had been looking at was a 2814Q this is a 2814M. Okay good to note that maximum throttle numbers aren't critical but should signal caution. I would probably just limit the throttle so that the max keeps it in the motors design specs. since i would likely only lose 5% or so at the top end.
Or is this something considered in advisable? The application of electric motors vs nitro is still a bit new as are learning the pitfalls in matching them for a given purpose.

 

[Blacksails]

I know a lot of people would be happy with those motors & set up if they were using it for AP as its rare that you ever use full throttle.
I personally would prefer to find a motor that will produce similar endurance and cope with the stresses of running it flat out. You never know when you are going to get into a situation where full throttle is needed to save your copter.

I had a quick play.

Try running the same setup through ecalc with Tiger Motors MT2814-11 (710) and 12x5 / 12x4.7 props.
Better endurance and motors within their limits.

 

[GlitchGR]

Blacksails,

Yep those certainly are a better fit and still at a reasonable price, thanks for the heads up.

 

[jes1111]

I can't be sure, and the author may have fixed it - but I do remember encountering a possible bug when specifying a custom battery pack. Try choosing a standard battery pack that's close to the spec you've entered, just to make sure the figures don't change wildly.