RunRyder - For same head speed, is lower Kv and bigger pinion better?

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e-Electric Motors & Controllers > For same head speed, is lower Kv and bigger pinion better?

rdalcanto
Key Veteran
Location: Salt Lake City, UT

Are you better off going lower Kv and bigger pinion, or higher Kv and smaller pinion for 3D (same head speed at 100%)? Does lower kv give you more torque?

Thanks,
Rick

Team MRC & Magnum Fuels

08-14-2006 Over year old.

HOMEPAGE

Rob_T
Elite Veteran
Location: Tualatin, OR - USA

KV and KT (torque constant) are directly connected - increase one and the other goes down by the same ratio (ie double one and the other halves).

What this means is that given 2 identical motors except one has a higher KV than the other, if you change pinions to match the heaspeed the performance will be identical.

In practice, low KV motors have more turns of thinner wire than high KV motors, so selecting a high KV motor usually means picking a motor with less resistance. Motors with lower resistance bog less under load than motors with high resistance.

So, in a particular motor size, the highest KV variant will give the most power for 3D flight if it is geared correctly. The limit is when you reach gear ratios which are impossible without adding an additional stage to the transmission.

Rob
Eco8, Piccolo Fun, Shogun, HB Elite CP, Trex 450XL CDE, Swift

08-14-2006 Over year old.

mikeflyz
Senior Heliman
Location: Westlake Village, CA

Rob,

I thought that the KV of a particular motor was INVERSELY proportional to the number of windings in the stator, ie, the fewer windings, the higher KV. The Hackers' dash number is the wind number, correct? Don't the higher dash numbers (more winds) have lower KV and increased terminal resistance?

It seems like the classic way to increase performance with the motor is to reduce the winds, decreasing terminal resistance and gearing appropriately. The heli will bog less, deliver more torque resulting in more current through the ESC, so it would be a good precaution to make sure you're not overloading the ESC with the new setup.

Reducing winds is not all gravy; efficiency is reduced with fewer winds generating more heat, particularly at high current/high torque scenarios.

Mike
MA Fury Extreme, Logo 600 and T-Rex

08-16-2006 Over year old.

Rob_T
Elite Veteran
Location: Tualatin, OR - USA

Mike you got me! I mixed up the high and low KV in my third paragraph, so what I said about winding resistance (that high KV motors have less resistance) was correct, but wasn't explained by what I said immediately before. I'll edit it so that it reads correctly.

Rob
Eco8, Piccolo Fun, Shogun, HB Elite CP, Trex 450XL CDE, Swift

08-17-2006 Over year old.

mikeflyz
Senior Heliman
Location: Westlake Village, CA

Just wanted to make sure my eyes weren't tricking me.

Mike
MA Fury Extreme, Logo 600 and T-Rex

08-17-2006 Over year old.

Pistol_Pete
Elite Veteran
Location: Tampa Bay non-Buccaneer

some info here

<><>...the lunatic is in my head...<><>

08-19-2006 Over year old.

HOMEPAGE

rdalcanto
Key Veteran
Location: Salt Lake City, UT

Thanks everyone. But what I wanted to know was if the higher torque of the lower Kv motor was precisely offset by having to spin a bigger pinion in order to achieve the same head speed.

Rick

Team MRC & Magnum Fuels

08-19-2006 Over year old.

HOMEPAGE

Rob_T
Elite Veteran
Location: Tualatin, OR - USA

In theory yes, the torque difference is exactly offset by gearing. In practice the high KV motor may perform better.

Rob
Eco8, Piccolo Fun, Shogun, HB Elite CP, Trex 450XL CDE, Swift

08-20-2006 Over year old.

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e-Electric Motors & Controllers > For same head speed, is lower Kv and bigger pinion better?

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