Great information, it helps a lot. Is there a way to calculate prop size? Pure math and stats based, without the need to test anything? It would be nice to know what prop size to use and what thrust to expect before ordering parts. Not all motors have such information available. Log In to reply
Lots of good comments and info. Watch out for ESC 's without BEC's designated as "OPTO" --hard lesson. Question I have 50 amp esc ,can I run two 23 amp motors on it probably for ft-cruzr. Had to get a separate BEC or Could have used 4.8v pack for my recever and servos. Log In to reply
I don't know from personal experience, but from what I read it might be better to use two ESC's. That way you can mix the throttle for the two motors in with rudder. Not necessarily to use the motors to turn, but so you can trim the plane so both motors power up evenly. If you do that and use two 30amp ESC's with built in BEC, then you cut the negative wire (?) on one of them so you are only using one of the BEC to power your receiver. Using both would fry the receiver. Also, I read that it is still better to use only one battery with this set up. (Just like how you planned on using one battery to power the motors.) Log In to reply
Your BEC only powers you Rx and your servos, and the signal for the throttle. and also paralleling 2 ESC's wont kill your receiver pecasue voltages don't add unless in series. the power pin on your receiver is a rail that supplys power to all pins on that same rail. I plan on just doing a Y harness for my 2 ESC's and I will not be cutting the red wire to start. if I have issues I will cut the one RED wire. DO NOT CUT THE BLACK ONE! if you cut the black then your ESC will not work as the signal will not have a return path to negative. Log In to reply
It's really all about thrust. I've found 250W motors pulling 30 amps and generating 550g of thrust with an 8x6 prop. You need more weight an money in batteries and ESCs with higher amp pull. Then I see a motor that pulls 11amps and produces 700+ grams of thrust with a 9x5. The setup with batteries weighs less than 1/2 as much.
The moral of the story is: look at thrust numbers and go from there. Big amp draw does not always mean big performance, but it always means big weight. Log In to reply
When choosing a motor for a plane yes you obviously look at thrust numbers. but after that, is where my video plays a role, how to pair up everything else based on the motor you have chose Log In to reply
Thats what happened to me, i ordered the 265W motor and it runs on the same battery that the FT guys use, 4s 2200. I'm switching to a 4s 1600Mah for my FT 3D as the 2200 is just a tad too heavy. Log In to reply
In this video you said that your battery has a max current output of 60 Amps and that you are running a 30amp ESC that is "well within limits". Can you please explain this, because to me if your battery is capable of outputting 60 amps and your ESC is only capable of handling 30amps it seems to me that your ESC is at least 50% under capable of handling this battery.
Is watt rating on a motor equivalent to Kv?
Ie. is 1250Kv also the Watt rating of the motor?
Eg. on a E Flite Power 25 BL Outrunner Motor, 1250Kv – is this 1250Watt
No, KV is the rpm per volt of the motor.
At one volt from the ESC (this is a complex 3-pole waveform, i.e. the three leads from ESC to motor) that motor will spin at 1250 rpm. At 2 volt, 2500 rpm. So if you use a 3S battery at 3.7V nominal voltage per cell, you would be applying -->approximately<-- 11.1V (i.e. 3 x 3.7V). That would spin the motor at 13,750 rpm (11.1 x 1250).
What is interesting is that in the same size housing, motors can be wound for different KV's. If you look on HK you can see motors of something like 750, 1000, and 1250 KV. Look at their power ratings and the lower KV motors will substantially higher power (wattage). It is all in how many windings and how many magnets/poles the mfctr chooses to use. Look up Turnigy D2836's - 3 very different versions. Varies from 210W to 336W. Log In to reply
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As to the ESC "exploding", I think most refer it to as the "magic mystery smoke". ;-)
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The moral of the story is: look at thrust numbers and go from there. Big amp draw does not always mean big performance, but it always means big weight.
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Is watt rating on a motor equivalent to Kv?
Ie. is 1250Kv also the Watt rating of the motor?
Eg. on a E Flite Power 25 BL Outrunner Motor, 1250Kv – is this 1250Watt
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At one volt from the ESC (this is a complex 3-pole waveform, i.e. the three leads from ESC to motor) that motor will spin at 1250 rpm. At 2 volt, 2500 rpm. So if you use a 3S battery at 3.7V nominal voltage per cell, you would be applying -->approximately<-- 11.1V (i.e. 3 x 3.7V). That would spin the motor at 13,750 rpm (11.1 x 1250).
What is interesting is that in the same size housing, motors can be wound for different KV's. If you look on HK you can see motors of something like 750, 1000, and 1250 KV. Look at their power ratings and the lower KV motors will substantially higher power (wattage). It is all in how many windings and how many magnets/poles the mfctr chooses to use. Look up Turnigy D2836's - 3 very different versions. Varies from 210W to 336W.
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