Matt14x

Is it safe to assume that if a brushless motor ,( different mfg. ) uses more amps, it has more thrust ?


matt

-pkh-

My Feedback: (2)

The amp rating of a motor isn't a measure of how many amps a motor uses in a particular setup, it's just the max amount of current the motor can handle before you burn it up. In general, more power will give you more thrust with a particular prop. More current with a given batt pack voltage means more power. So if you have a given prop & batt pack voltage, and one motor draws more current than the other, the higher current motor will probably give you more thrust.

exeter_acres

My Feedback: (2)

Could also be a sign of a damaged motor.... bad bearings, bent shaft, etc. could cause a higher amp draw.... just a thought

DaveFlynn

Also, the max amps rating is sometimes more than the maximum useful amps. If you plot a graph of RPM vs Watts of an overloaded motor you'll see watts going up without an increase in RPM. I saw this on a 2215 size motor that is rated 20 amps, but anything over 15 amps just made the motor get hotter without any additional rpm or thrust. Nothing wrong with the motor, a 9x7 is just too much for it. Resulting in a shorter flight time without any more performance.

Matt14x

I'll re-write my question:
Is it safe to assume that if new brushless mtrs., propped correctly, uses more watts,measured with an in-line watt-meter, has more thrust ?

matt

Dorsal

My Feedback: (17)

That is the typical assumption, but the only way to really know is to connect a fish-scale or similar force-measurement device to take a direct reading.

Time Pilot

The kv of the motor should effect that too.

Two motors, one high kv with a smaller prop, another, low kv with a larger diameter, but smaller pitched prop, both pulling the same watts:

More thrust with the latter, more speed with the former. One transforms the watts into speed (race car), the other into torque (tractor).

Haven't done any calculations, but I'd bet that you could have a higher kv motor out-thrusted by a lower kv motor using fewer watts.

If you have a particular airplane and are trying to decide what motor to put in, that may be another question you want to ask.

Matt14x

Thankyou
It is then safe to assume ( more wattsmore ihrust.)

Of course; to be sure,one must static-test with a watt-meter and tack..

I don't have a particular combo in mind. I am looking for a way to size mtrs..

matt

DaveFlynn

I've been very surprised by the numbers from testing at times. Different mfgs use vastly different magnets ranging from N35 to N50. This effects both the torque constant and the max torque the motor can deliver.

Bottom line is, until you have a graph of power in verses power out and find the limits there are just too many unknowns.