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different pinions, how do they effect flight times?

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Old 12-12-2008, 10:31 PM
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thestratcat
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Default different pinions, how do they effect flight times?

I'm building my t-rex, they recommend a 12 tooth for sport flying, or 13 tooth for hard 3D... I'm not a 3D pilot so a 12 would work just fine, I get nice long flying times in everything else, and kind of like that... the only problem is, I only have a 13 tooth, and I WANT TO BUILD SOMETHING! lol.... how much will that extra tooth effect my flight times? I really don't need the insane power...

by the way 450SE GF is the model, stock everything... and I'm running 2200mah batteries..
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Old 12-13-2008, 11:30 AM
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Default RE: different pinions, how do they effect flight times?

By effecting Headspeed, the higher the headspeed the lower your flight time becomes.[:'(]

With a lower tooth pinion at a specified voltage, the motor doesn't have to work as hard (less load), therefore less current draw on the battery.
Think of driving a manual transmisson car with a small 4-banger, the car leaps when starting off in 1st gear (but will only take you to a certain speed). If you start off in 3rd gear, the car may "dog" off the line (if it doesn't stall), but it will take alot of load to get the car up to speed, that's is faster than you could achieve in 1st gear. The same principle applies to the motor pinion, motor Kv, battery voltage & overall headspeed.

For example: on my T-rex 500, instead of using a 6s lipo @ 22.2 volts, I'm using a 4s @ 14.8 volts. Since I cannot acheive the headspeed with the stock 12 & 13 tooth pinions the a 4 cell lipo (only 1400rpm), I geared up to a 16 tooth to start. That gave me a headspeed of around 2300rpm in ST2 @ 90% throttle, and a flight time of 18-20 minutes (all in Idle-up). When I switched to a 18 tooth pinion, I saw a slight increase in headspeed of about 20%, but flight time dropped to 12 minutes, lipo was warmer than before & motor got HOT after 1 flight. So I went back to the 16t for now.

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Old 12-13-2008, 12:47 PM
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Default RE: different pinions, how do they effect flight times?

I didn't think about the heat, I can deal with losing a minute or two of time, but don't want to lose much more.... besides that, my other heli's don't even get warm really (batteries or motors)...

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