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Electric Stunt => Gettin all AMP'ed up! => Topic started by: bruce finley on August 12, 2015, 07:13:50 AM
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This E stuff is all so confusing to me...
So what is the difference in terms of run between a 2700 mah 3s and a 2700 4s using a 1000kv motor?
Is there a magic temple of E CL that I can peruse to find enlightenment??
Bruce
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Hi Bruce, Go to the top of this forum (getting all AMP'ed Up) and take a look at the sticky threads there. That will give you some good information. Also, look for Norm's Cook Book (used to be there too but it has been moved).
The K value for a motor is the number of RPMs per volt for the motor unloaded (no prop in this case) and 3S and 4S refers to the number of cells in the battery. Which battery you choose for your 1000K motor will depend on how many RPMs you need for your application.
Finally, post your questions here (with as much detail as you can provide) and you will get helpful replies (guarantied) much better than mine!
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A 4s has 4 lipo cells in series, each at 3.7v nominal, 4.2v fully charged. So total voltage is 14.8v nominal, 16.2v fully charged.
A 3s is 11.1v nominal, 12.6v fully charged.
The voltage multiplied by the Kv of the motor gives the rpm, but without the propeller attached.
I know this may be confusing, but it will get easier.
The 1000kv motor you have probably will work best with a 4s, unless you want to fly with a large prop, then a 3s might be better for you.
If you use the same prop with 4s that is appropriate with the 3s, you will burn up the motor probably, because the amp draw well be much higher.
Hope that helps you.
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The 1000kv motor you have probably will work best with a 4s, unless you want to fly with a large prop, then a 3s might be better for you.
If you use the same prop with 4s that is appropriate with the 3s, you will burn up the motor probably, because the amp draw well be much higher.
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This is exactly the type of explanation I am looking for. TY Chris
This is a big help in understanding the new world ~^ ~^
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A 4s has 4 lipo cells in series, each at 3.7v nominal, 4.2v fully charged. So total voltage is 14.8v nominal, 16.2v fully charged.
A 3s is 11.1v nominal, 12.6v fully charged.
The voltage multiplied by the Kv of the motor gives the rpm, but without the propeller attached.
I know this may be confusing, but it will get easier.
The 1000kv motor you have probably will work best with a 4s, unless you want to fly with a large prop, then a 3s might be better for you.
If you use the same prop with 4s that is appropriate with the 3s, you will burn up the motor probably, because the amp draw well be much higher.
Hope that helps you.
Is there a chart that gives prop sizes etc to motor to battery?
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If you can get your hands on the July 2015 issue of Model Aviation there is a very good article that talks all about the basics of Lipo Batteries that is worth reading.
The big thing to realize is that the Mah number tells you how big your fuel tank is, the higher the number the longer you can fly. And the other item you learn quickly is that all of the Lipos are different sizes so there is no std size of Lipo battery
I put some information on our club website about Lipo batteries that might be helpful
https://lafayetteesquadrillecl.wordpress.com/lafayette-esquadrille-cl/cl-models/lipo-batteries-and-safety/
Fred
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Is there a chart that gives prop sizes etc to motor to battery?
If you're flying stunt the really super quick way to get a motor sized to a plane is to look at the motor manufacturer's recommendations for 3D. 3D RC seems to have very similar demands on the motor as CL stunt -- so there you go.
There are so many variables that a one page chart would, at best, be limiting and at worst it'd just plane be wrong. Your best bet is to go through the "List Your Setup" thread and look at similar airplanes -- if you use a similar power system then you've at least got a good starting point.
And we're a friendly bunch of guys, so you can ALWAYS tell us what combination you're planning on using and ask for opinions, and you'll get guidance.
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If you're flying stunt the really super quick way to get a motor sized to a plane is to look at the motor manufacturer's recommendations for 3D. 3D RC seems to have very similar demands on the motor as CL stunt -- so there you go.
There are so many variables that a one page chart would, at best, be limiting and at worst it'd just plane be wrong. Your best bet is to go through the "List Your Setup" thread and look at similar airplanes -- if you use a similar power system then you've at least got a good starting point.
And we're a friendly bunch of guys, so you can ALWAYS tell us what combination you're planning on using and ask for opinions, and you'll get guidance.
Good ideas Tim, Thank you! y1
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Hello Bruce.
Happy to help.
Regarding the chart you are seeking, some motor manufacturers do publish a chart, cobra and scorpion being one....
Search p-calc/brutanas on Google, and you should get to a program that has some older motor and battery and prop combinations, and you can play with that and see how changing the battery number of cells effects the amperage, thrust, rpm, etc.
Just remember that watts = power (essentially), and there's no substitute for not enough.
A handy equation is Volts x Amps = Watts (not taking into account losses for inefficiencies).
If you have a certain number of watts needed to fly your plane, say 500w, and you have a 10v battery, you're going to need to draw 50 amps to get you there.
The same motor with twice as many cells, at 20v, will give you 500w when you draw 25 amps.... but in these radical examples, the rpm and prop sizes will be very different. The low voltage setup would need a pretty large prop, and the high voltage setup a much smaller prop....
I'll see if I can find you a link to the p-calc program.
A watt meter, that plugs in between the battery and ESC, is a very helpful bench test tool for any e power flying.
Regards,
Chris