T-REX Current Draw

[AirTrekker]

Just wanted to see how my current draw compares with the rest of the T-REXes out there.

My setup:

T-REX with Align 400LF-2500 (Not 2800!)
13T Pinion
CC35 on High-Governor with Throttle Curve set to 92.5%
E-TEC 1700-3S

I measured the Amp draw at 92.5% throttle 0 deg pitch and my setup was drawing approx 6Amps.

I have timed my bird and I get approx 11-12 mins of hovering around before the LVC cuts in.

Is the amp draw normal/low/high ? I remember reading somewhere that Mikes T-Rex with a mega was drawing something like 19Amps!

[HZM]

So coincidence, measure my amp draw yesterday during the funfly.

Mega 4T
15T pinion
etec 1700
Woodies 315mm
Rest stock

Amp draw at full - 17.7A
Temp of motor - 58 degree

Mike

[ammo]

I'm running above 20Amps with the LF400 2800, 15t, standard blade and tail.

[fuse]

HZM 58 degree?

wow!

align is cooking eggs and yours is 58 degree...

[Super-Hornet]

Fuse... because of LF got fan build in... it run cooler than the older L/S series. My L can go as high as 115Degree Celcius without heatsink and 105 with heaksink (Colco heaksink). With LF, I get around the most 75Degree.

Super-Hornet

[AirTrekker]

One thing I am trying to understand is the relationship between Battery capacity/current draw and flight time. I lost my maths skill a long time ago so can someone check to see if my formula is correct ?

Assuming
ETEC-1700 3S, Align 400LF-2500 with 8Amp average current draw
The formula I am using is Battery Capacity (in Amp/Hr) / Current Draw * 60
which is ...
(1.7/8)*60 i.e. 12.75 mins before the battery is flat ?

Now, if Mike's setup is drawing 15A on average, then his flight time should be 1.7/15*60 = 6.8 mins

Am I on the right path ?

[fuse]

hmmm i think your way of cal is correct in the matrix world.
but in real application,

align motor dont run at over 80% efficiency due to heat
mega is known to have over 80% efficiency
and mega 4 has a lower KV compared to align..
gearing also plays a part in the cal and also the source, which is the battery.
not all battery is built and charged the same. so all being equal, you are correct. but in the real world, it depends on the pilot, collective management, motor, esc- programming, heli overall weight, battery charging and etc.

so how to get the best of all these fields? is to make them more efficient!!!


cal amp drawn at 0 pitch is a mistake as there is no load induced.

just some personal input.



airT: remember nitro heli RPM always spin faster at 0 pitch then at 6 degree?

thats why you have a GOV to maintain the speed.

[Super-Hornet]

Hi AirTrekker

Normally we do not measure in 0 pitch because it is the lowest load... Just like what fuse said.

What Mike current at 17.7A is at max power for his heli. If u really want to use Ampere/Hour measurement, then we can just roughtly guess his flight time using this (Note: This is just an estimation):

If 1.700A then 60Min
3.4A => 30Min
6.8A => 15Min
13.6A => 7.5Min
17.7A approx 5.76Min

Ask Mike to do full power and measure the time. See whether is it close to the above measurement or not.

Super-Hornet

[AirTrekker]

Thanks for the input. The reason I was measuring at 0 deg pitch was becos I did not want the bird to lift off the ground with my ampmeter attached to the battery.

One question is how the heck do you measure the amp draw at full throttle / pitch ?

Do you tie the trex down or do you get a brave volunteer to hold on to the landing gear overhead with the blades running at 2400+ rpm while looking at the amp meter ?

Or ... do you run full throttle at full -ve pitch ?

[Super-Hornet]

Hehehe.... Normally we ask a volunteer to hold it. It is normally the owner of the heli. Note: Do this with caution!!

Anyway, another method that I use is that I tied my heli onto a ground or a stool (Heavy wooden Ikea type).

U can use full negative pitch also can but what if somehow your full -ve and +ve pitch is not the same? Then current drawn will be different. If your -ve and +ve is the same, u still need to tied to go ground/stool in order to prevent any accidental take off/sliding/itchy hand.

Super-Hornet

[HZM]

Yup, infact I am getting approx 7-8 mins decent flight as I move away from just hovering

I, sorry, the correct term is "We" are all using 1 "Clamp Meter" that belongs to Frank Quite a few members have them, you don need to connect in series of your batt. Just place the "Clamp" round the battery lead

1 guy will hold the bird and the other do the checking

Mike

[AirTrekker]

Wow! Looks that there are lots of brave or ?!?!?!? people around. He he he.

Will try tying the bird down and measure the amp draw again.

[X34]

I once asked the same question of how to check amp draw, most pilots here have brave heart.

I would mount an Eagle Tree FDR or a smaller version of the Astro Whattmeter to measure the draw.

[alex_bong]

where got cheapest dc ampmeter?

just wondering where to get the cheap dc ampmeter??
i just brough one digital multimeter at SLT that come with a pair of test lead and ac/dc clamp sensor (KEW MATE MODEL 2001, fr KYORITSU Japan.)
it cost S$150.

[Tele]

1 guy will hold the bird and the other do the checking

Mike

this guy gets a free haircut too