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Battery / ESC / Motor / Prop combination

Old 08-15-2013, 09:29 PM
  #1  
Merlotmaker
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Default Battery / ESC / Motor / Prop combination

This is probably a question that is asked repeatedly so please forgive me if this is the case.

Is there a formula or chart that one can use to determine a good / acceptable / practical combination of Battery / ESC / Motor / Prop combination?

My question arises from the following.

I am flying a Lanyu 182 TW-747-III with a 35amp ESC, 900kv motor, 12 x 6" prop using 3S 11.1V 2200mah batteries
at 3100g with a 900Kv motor this is a 1:.29 power to weight ratio

I recently crashed my Cub which had an E-Flite25 1250Kv Motor, O.S. OCA-150 50Amp 25V ESC and I used 4S 14.8V 3000mAh LiPo Battery
at 2900g with a 1250Kv motor this is a 1:.43 power to weight ratio (almost double to that of the 182)

So my questions:
If I want to use the 4S batteries from my Cub in the 182, can I just simply plug and play?
If not is there a formula to calculate which ESC will match these larger batteries for the 182s 900Kv motor?
Will it be OK to still use the 12 x 6" prop?
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Old 08-15-2013, 09:45 PM
  #2  
hayofstacks
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look at similar motors on heads up rc.

your esc should very fine. no on the prop. stepping up from 3-4 cells on the same prop will more then double your power. if I had to try it, id try an 8x4 to a 9x6 and see if it goes over the limit for the motor or not.
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Old 08-15-2013, 09:49 PM
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mclarkson
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You really need a wattmeter to answer this kind of question. You can guess and you can calculate but it's nearly impossible to actually know what will happen without actually running the setup and taking measurements.

If you watch the throttle, you're probably okay but ... hard to say for sure.
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Old 08-15-2013, 10:55 PM
  #4  
CHELLIE
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Power 25 BL Outrunner Motor, 1250Kv

http://www.e-fliterc.com/Products/De...odID=EFLM4025B

The 1250Kv Power 25 BL motor was created for for high-power airplanes weighing 3- to 5.5-pounds (1.4- to 2.5-kilograms) or 15-sized high-speed electric Formula One racers weighing up to 4 pounds (1.8 kilograms).

Product Specifications

Type:Brushless Outrunner
Size:25
Bearings or Bushings:One 5 x 14 x 5mm Bearing, and Two 5 x 11 x 4mm Bearings
Wire Gauge:14 AWG
Recommended Prop Range:8x6E to 8x8E (4S) or 8x8E to 10x10E (3S) A Rule of Thumb on props, is that you can go up 1 on the dia. while going down 2 on the pitch, example 10x10 prop, go up 1 to 11 dia. and down 2 to a 8 pitch. 11x8, go up 1 to a 12 dia. and go down 2 on pitch to a 6 pitch prop, 12x6 , a 12x6 will pull about the same amps as a 10x10 prop, or very close to it
Voltage:11.1 - 16.8
RPM/Volt (Kv):1250
Resistance (Ri):.02 ohm
Idle Current (Io):2.00A
Continuous Current:50A
Maximum Burst Current:58A (15 sec)
Cells:3S - 4S Li-Po, 10 - 14 Ni-MH/Ni-Cd
Speed Control:60A Pro Brushless
Weight:183g (6.40 oz)
Overall Diameter:35mm (1.40 in)
Shaft Diameter:5mm (.20 in)
Overall Length:Case: 54mm (2.10 in)

Last edited by CHELLIE; 08-15-2013 at 11:21 PM.
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Old 08-15-2013, 11:05 PM
  #5  
CHELLIE
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Originally Posted by Merlotmaker View Post
This is probably a question that is asked repeatedly so please forgive me if this is the case.

Is there a formula or chart that one can use to determine a good / acceptable / practical combination of Battery / ESC / Motor / Prop combination?

My question arises from the following.

I am flying a Lanyu 182 TW-747-III with a 35amp ESC, 900kv motor, 12 x 6" prop using 3S 11.1V 2200mah batteries
at 3100g with a 900Kv motor this is a 1:.29 power to weight ratio

I recently crashed my Cub which had an E-Flite25 1250Kv Motor, O.S. OCA-150 50Amp 25V ESC and I used 4S 14.8V 3000mAh LiPo Battery
at 2900g with a 1250Kv motor this is a 1:.43 power to weight ratio (almost double to that of the 182)

So my questions:
If I want to use the 4S batteries from my Cub in the 182, can I just simply plug and play?

If not is there a formula to calculate which ESC will match these larger batteries for the 182s 900Kv motor?
Will it be OK to still use the 12 x 6" prop?
You may need to use a smaller prop and pitch when using a 4 cell lipo, your amps and Watts will go way up if using the 12x6 prop, you may need to drop down to a 11x5.5 prop, only a Wattmeter will tell you for sure where your at with different prop, lipo cells, and motors, a wattmeter is a must have to protect your equipment.

http://www.hobbyking.com/hobbyking/s...arch=wattmeter
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Old 08-15-2013, 11:10 PM
  #6  
CHELLIE
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Merlotmaker Welcome To Wattflyers.

Send me some Bottles of Merlot, And I will Teach you Everything I know about E Power LOL
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Old 08-16-2013, 12:56 AM
  #7  
pizzano
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Try this:

http://flbeagle.rchomepage.com/softw..._imperial.html

Been pretty darn accurate for me and a number of flying buddies I hang with.......!

The entire web site has many good tools:

http://www.adamone.rchomepage.com/index.html
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Old 08-16-2013, 01:56 AM
  #8  
kyleservicetech
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Originally Posted by Merlotmaker View Post
This is probably a question that is asked repeatedly so please forgive me if this is the case.

Is there a formula or chart that one can use to determine a good / acceptable / practical combination of Battery / ESC / Motor / Prop combination?

My question arises from the following.

I am flying a Lanyu 182 TW-747-III with a 35amp ESC, 900kv motor, 12 x 6" prop using 3S 11.1V 2200mah batteries
at 3100g with a 900Kv motor this is a 1:.29 power to weight ratio

I recently crashed my Cub which had an E-Flite25 1250Kv Motor, O.S. OCA-150 50Amp 25V ESC and I used 4S 14.8V 3000mAh LiPo Battery
at 2900g with a 1250Kv motor this is a 1:.43 power to weight ratio (almost double to that of the 182)

So my questions:
If I want to use the 4S batteries from my Cub in the 182, can I just simply plug and play?
If not – is there a formula to calculate which ESC will match these larger batteries for the 182’s 900Kv motor?
Will it be OK to still use the 12 x 6" prop?
The formula for horsepower input to a prop is pretty complex, requiring a scientific calculator.

Much easier to go to one of those model computer programs such as www.motocalc.com. Free for 30 days, then $39. With this, you just select your motor from the hundreds of motors in its database, put in your ESC, prop diameter and pitch, and your battery.

The program will spit out its opinion, and will predict how much current and watts your motor is running. What is important is the predicted motor efficiency. If the motor is overloaded, its efficiency drops like a rock. And will get HOT. Motocalc is pretty close, but its accuracy depends on how accurate the mfgr's motor specs are. Some of those motor specs are way the heck off.
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Old 08-16-2013, 10:01 AM
  #9  
Larry3215
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Originally Posted by mclarkson View Post
You really need a wattmeter to answer this kind of question. You can guess and you can calculate but it's nearly impossible to actually know what will happen without actually running the setup and taking measurements.

If you watch the throttle, you're probably okay but ... hard to say for sure.
+1
+1
+1
+1
etc...

Everyone else has given you good advice, but this is the one critical thing you must do to be successful in e-flight. As other have said, there are many options for calculating your power, but the chances of those calculations being 100% accurate are exactly zero.

Get a wattmeter.
Measure YOUR exact power system performance instead of guessing or hoping your system will perform just like someone elses - it wont.

Get a wattmeter
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Old 08-16-2013, 10:16 AM
  #10  
Larry3215
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I'll add a little of the reason calculations are dificult to do and why you shouldnt be surprised when YOUR power system performs differently then some other guy who has "Your exact power setup".

There aint no such thing as two exactly equal power systems.

Take motors. No two are ever exactly the same. Even two identical motors bought from the same company at the same time. Why? Mostly because they are hand wound and hand built. Small errors in winding can make significant differences in motor performance. Add in the differences in connectors, soldering ability etc.

Even with name brand suppliers I have measured as much as 10% difference in kV between identical motors bought at the same time. With the cheep stuff all bets are off.

Batteries are similar. Differences in age, how they have been charged, balanced, discharged, over heated, dented and dinged etc etc all add up to significant differences in the voltage under load that you can get from two "identical" batteries. Batteries from different mfg's can be wildly different while having the exact same "specs".

ESC's are also not exactly the same one to the next, although - again - the name brands do much better than the cheepos.

And props are not immune to this problem - they can sometimes vary a LOT from one to the next.

So calculations that make assumptions about the specs of the motor, esc, battery, prop and only guessing. Sometimes they are fairly close. Often they arer wildly off.

Again, name brands do better than the cheep stuff because their specs are usually fairly close.

The cheep stuff on the other hand often has specs that are just made up or copied from the name brand item they are cloning. They are never measured.

So..... get a wattmeter or be willing to burn up the occasional power system when the calculations don't match up to reality
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Old 08-17-2013, 03:45 AM
  #11  
kyleservicetech
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Originally Posted by Larry3215 View Post
+1
+1
+1
+1
etc...


Get a wattmeter
Yeah
GET A WATTMETER!

Or what I keep in my model airplane Chevy S10 truck is a Sears Craftsman #82369 digital AC and DC clamp on ammeter. This meter does not require adapter cables, just clamp its jaws around one of the two battery leads.

Its got current ranges of 0-40 and 0-400 Amps, sufficient for any model we might fly at our field. And, it can measure the usual resistance, volts, temperature and a bunch of other stuff. Price, around $55 or so.
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Old 08-19-2013, 05:44 PM
  #12  
Dr Kiwi
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I posted this reply to your post on RC Groups:

Highly unlikely that with 4s, you can use the same 12x6 that you used on 3s. Probably you'll need to go down an inch or two in diameter but unless you tell us exactly which 900Kv motor you are using in the Lanyu 182 we can only guess its capability.

Size of ESC will need to be determined by your motor's amp draw.

Just as an example I entered a Turnigy SK 3548-900 into DriveCalc... with a 12x6 APC E on 3s it is predicted to draw 25A (maybe 275W), but on 4s with a 12x6 APC E it is predicted to draw 41A (maybe 540W)! To stay at 25A on 4s you'd need to reduce prop size down to a 10x6 APC Sport.
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