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Old 12-18-2012, 11:20 PM   #1
GeorgeFF
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Default Logo 400 Pinion Mod 0.7...

Hello friends, someone can tell me pros cons or suggestions of Pinions 12T vs 17T Mod, 07 thanks.
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Old 12-19-2012, 01:29 AM   #2
tmodelli
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Pinion is not as complicated as it seems.

So, before we get there, you have to understand the gearing concept, which includes basically 5 items:

1. Main gear tooth count (pretty static as its normally on the airframe design)
2. Motor KV (well, motor constant actually, but KV will do just fine)
3. Battery cell count
4. Pinion
5. Expected head speed

You normally know between 3 to 4 of those from the beginning. In your case, you know main gear, motor KV, battery, and head speed.

So you basically divide the main gear by the pinion, which gives you a gear rate, then multiply the motor KV by the battery volts and multiply by .89 (generic efficience), which gives you the max motor speed, then divide the motor speed by the gear ratio. That will give you the head speed.

So, (MG/PIN)/(V*KV*.89)=HS

Now that we know all that, you can see that the pinion's job is to transfer the motors torque to the mail gear, and the different sizes gives you different ratios (like changing gears on a car).

The smaller pinion's runs with more to torque and less RPM, the bigger ones goes the other way arround. So, small pinions will be better for the motor, letting them run cooler, but trading off head speed, as torque helps to get the weight of the blades spinning, and the larger ones will be the opposite, giving the motor a harder time, but increasing the head speed considerably.

To give an idea, a Logo 600 (106 tooth main gear)on 12S (50V) with a 500KV motor could spin the disks at:

So first lets get my powerhouse number: (500*50*.89)=22.250 this is how fast my motor will run with this battery, assuming an efficiency of 89%, which is not bad for a brushless out runner.

11 tooth pinion: (22250/ ((106/11)=9.63)) will be 2310 max head speed
12 tooth pinion. (22250/ ((106/12)=8.83)) will be 2519 max head speed
13 tooth pinion: (22250/ ((106/13)=8.15))=2730

Now, there are a couple factors here. 89% efficiency is pretty high. Battery volts are never at its max. There is voltage sagging and normal drop throughout the flight, governors might need a bit different gearing too, to give a wide headspeed range, and most ESCs don't have free wheeling, which means unless it is running a 100% max speed )100% throttle curve), the ESC is heating up while it commutes.

So, very long story not so short, you would need to give more info for us to tell you which head speed you would get with the pinions in question, but to choose one, you should find the one that gets you within 15% of head speed, to give headroom, which wod be the most efficient at your targeted power.

Makes sense?

Thanks,

--T

Last edited by tmodelli; 12-22-2012 at 05:00 PM.. Reason: ficed typos
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Old 12-19-2012, 06:41 AM   #3
Bullfrog98
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Epic post man
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Old 12-19-2012, 09:14 AM   #4
GeorgeFF
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Wow thanks for your time and info!!!

And i have a Logo 400 Mod 0.7 with 138T main gear, 12T pinion , scorpion 1400Kv and 25C batt , thanks again ...
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Old 12-20-2012, 09:58 AM   #5
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Nice job T.
I am lucky he lives across the street
T was referring to the cell count of the battery as opposed to the C rating.
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