help !! with electric set up
 

Hi all

New to this forum lark, just purchased a Seagull edge ep 540 from fleabay to continue my areobatics.
Specs below.

Wing span 42.7 inch
AUW 48 oz
Wing area 376.7 sq inch

It came with an Overlander Thumper V2 T3536/5 650 Watts 1450 kv (Now discontinued) and a Top gun etronix 6-10n/c2-3 40 amp Esc swinging a 10 x 5 prop and one Overlander 3s 2200Mah 25 c Battery.

So here's the story, flow this and it only lasted 4 minutes when the Esc shut down the motor, borrowed three more same spec batteries from a another club member and same thing happened, batteries were down to 4%, not good, apologised to club mate.

Bought three more 3s 2200Mah Batteries 35-75c and a watt meter, and after feeding figures in to webcalc decided to prop down to a 9 x 6 and with new batteries charged coupled up the watt meter and this is what I get.

WOT

61.96Ap – 56.11Ap
10.86Vm - 10.57Vm
667 Wp – 600 Wp

75% Throttle

58.8Ap
10.49Vm
632Wp

50% Throttle

18.63Ap
11.28Vm
185Wp

As you can imagine this thing is screaming round and shouldn’t be drawing this much on such a small prop, I put my rubbish taco on and got 9400 rpm with the following settings.

34.48Ap
10.79Vm
373Wp

This is around where I want to be, so why is it pulling so much at WOT?

So where do I go from here, clearly the esc won’t last long and shuts down when at half throttle after a couple of minutes, too hot.

Don’t have the 10 x 5 anymore, but tried a larger prop 11 X 7 just to satisfy my curiosity and as expected pulled 71 amps at 75% throttle.

Is it the motor or Esc or Both?

First welcome!

No doubt. That is a very high kV for 3s. Should be using 7 or maybe a low pitch 8" prop.

That is simply way too high a kV. Should be much lower for that prop and plane.

Mike

Thanks Mike

I thought that too, I bought it second hand and it's just what it came with, what do you recommend something around 1100Kv?

Check out one of those computer programs for electric models, such as www.motocalc.com. This program is free for 30 days, then $39. It allows you to specify the model wingspan, wing area, weight without motor/esc/battery, and try a wide variety of motors in its database.

Then just click on motocalc's "opinions" and see what the recommendations are.

With a 3 pound model, a good number for very good acrobatic capability is around 130-150 Watts per pound. That puts your motor in the 400 watt range.
There are a lot of other brands of motors out there, some very good, some not so good. The Hacker A30 motors are expensive at $69.99, but they will perform per specifications.

Take a look:
https://www.aero-model.com/8_66_877/...-10L%20V2.html

Interesting this motor has a 1200 KV rating.

At the top end 900-1100 should be pretty good for that plane.

Mike

Using webocalc 1.7.6:

AUW: 48 oz
Wingspan: 42.7
TWA: 376.77
Flight Mission: Fast sport aerobatics
Desired top speed: 71.4 mph
Desired thrust: 48 oz
Desired Flight duration: 7 min.
Motor efficiency: Good outrunner 80%
Battery voltage 10.80 v
Desired current per motor: 33 amps
Motor kv: 1450

Results:
Thrust/weight 1.1:1
Min. Battery: 3S, 2100 mah, 17C, LiPo
Est. Flight duration: 6 to 10 min.
Suggested ESC: 43 to 50 A
Power into/out of Motor: 356.4 watts in / 285.1 watts out
Power to weight ratio: 118.80 watts/lb
Estimated stall speed: 21 mph
Wing loading: 18.35 oz/sq ft

Suggested prop Size:
APC-TE 8x6; 12490 rpm; 45.8 oz thrust; Vpitch 72.8 mph

For:
APC-TE 9x6; 12533 rpm; 64.6 oz thrust
Desired current per motor: 47 A

Thrust/weight 1.3:1
Min. Battery: 3S, 3000 mah, 17C, LiPo
Est. Flight duration: 6 to 10 min.
Suggested ESC: 61 to 71 A
Power into/out of Motor: 507.6 watts in / 406.1 watts out
Power to weight ratio: 169.2 watts/lb
Estimated stall speed: 21 mph
Wing loading: 18.35 oz/sq ft

With a 1100 kv motor:
APC-E 10x7; 9542 rpm; Vpitch 63.9 mph; 49.8 oz thrust
Desired current per motor: 32 A

Thrust/weight 1.0:1
Min. Battery: 3S, 2100 mah, 17C, LiPo
Est. Flight duration: 6 to 10 min.
Suggested ESC: 42 to 48 A
Power into/out of Motor: 345.6 watts in / 276.5 watts out
Power to weight ratio: 115.2 watts/lb
Estimated stall speed: 21 mph
Wing loading: 18.35 oz/sq ft

Thanks guys

After seeing dgholmes59 data laid out in table form, I can see now where I was going wrong with feeding data into webcalc, adjust motor amps until the yellow 1.00 ratio comes up and taking the esc as the peak amps and compare it with the watt meter data I recorded.

proping down to the 8x6 would be the cheaper option but the esc would be under strain (only rated @ 40amp - 50amp burst) at any of the setting.

so I think I will bite the bullet and buy a 1100kv motor and a 50-60 amp Esc.

I was thinking this one from Hobbyking, its in stock from the UK warehouse
Turnigy D3548/4 1100kV
SKU: D3548-41100

Spec.
Battery: 3~5 Cell /11.1~18.5V
RPM: 1100kv
Max current: 50A
No load current: 3.1A
Max power: 910W
Internal resistance: 0.023 ohm
Weight: 159g (including connectors)
Diameter of shaft: 5mm
Dimensions: 35x48mMax thrust: 2150g

3s 10.8v * 50 A = 540 Watts

So much for a ebay bargain

I really like webocalc. The prop suggesed with the yellow 1.00 ratio is usually right on as well as the other values. I bought some Flyzone planes, put them into to webocalc, and changed to the suggested props and they flew great. They barely flew with the supplied props.

How much ground clearance do you have? You might be able to run a 11x10 prop at 7680 rpm with a 900kv motor. Running about 35 amps with 50A esc. Your prop range is 7.7 to 13 and motor a kv range from 890 to 1100 kv. Battery range 3S 2500mah to 5S 1500mah. This would be for fast sport aerobatics. For fast 3D, you would need at least a 4S.

Just some things to consider. But you probably know this now since you are also using webocalc. I found a great simplified procedure on one of the forums for engineering power systems on one of the forums it you are interested, I can post it. I took all of his posts and put them in a pdf document. It is a great step-by-step procedure.

Thanks dgholmes59

That would be great.

john

I looked for quite a while for power system designing for electrics until I found this one at RCGroups. It is such a simplified approach and he included many examples for teaching. I included the link in the pdf to the original thread, but the pdf has all the important stuff for designing your own. Very interesting reading.