ACrisp1982

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Ok guys,

Here is my problem. I have a helicopter with a B28/13T brushless motor connected to a 60A ESC which in turn is connected to a 11.1V 5400mah 20C lipobattery. Here is a link to the helicopter instruction manual. Please see page 3 and 8 to see where I got my motor and ESC info. http://www.art-tech.com/english/pdf/...anual%20EN.pdf.

Ultimately I would like to know how long can I fly before I hit the dreaded 3.4v charge per cell cutoff of a lipo.

I tried a calculator "http://www.rtideas.com/battcalc/"online and it said I could only run for 5.4 minutes, seems a little short for such a large battery.

I would also like to know how many amps that engine will draw. I cannot find any info on that engine outside the instruction manual.

I am about to begin the break in for the lipo above and dont want to distroy a $65 battery the first few times out. I am new to helicopter flight and want to be able to continue the hobby with as little financial impact as possible.

Thank You for your help and knowledge.

jdetray

You asked the correct question when you asked how many amps your power system will draw. Along with the capacity of your battery, the current drawn by the power system determines flight time. The ideal way to determine the current is to measure it with a wattmeter.

If your power system draws 60A, then 5.4 minutes flight time is exactly what you would expect. See below.

Formula for Run Time

run time in minutes = (Battery Capacity in Ah/Motor Current in A) x 60

This is just a rough guide, and it requires that you know approximately how much current your power system draws. A wattmeter will tell you. The formula also needs your battery capacity in Amp Hours (Ah). Divide mAh by 1000 to get Ah.

The simplest method is to measure your current at full throttle and use that number in the formula. In reality, you probably won't fly at full throttle all the time, so your average current usage probably will be less than the full-throttle value.

So if you use the full-throttle current in the formula, it will generally give you a worst case flight time. Actual flight time will usually be greater.

Using your battery as an example and assuming your power system draws 60A:

5400 mAh battery
power system draws 60A

5400 mAh = 5.4 Ah

5.4/60 x 60 = 5.4 minutes

If, on the other hand, your power system draws 50A, the calculation is:

5400 mAh battery
power system draws 50A

5400 mAh = 5.4 Ah

5.4/50 x 60 = 6.48 minutes

It all comes down to knowing how much current your power system draws.

- Jeff