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02-22-2021 01:09 AM  9 days ago
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tintmaster

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Wichita, Ks. U.S.A.

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Tail Gear ratio
I have a Trex 700L Dominator. Trying to figure out what the tail gear ratio is. Motor pinion is 12, main is 112, so 9.33. Auto is 104, tail main is 22t, so 4.72. Both front bevels are 24t. Rea tail bevels are both 23t. Just don’t know how to figure out the final tail ratio.

Also I am trying to find an extra set of rear tail gears
Just call me Farmer Brown. 'Cause I know how to really plant 'em
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02-22-2021 02:53 PM  8 days ago
Rojoalfa

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Punta de Mata, Monagas-Venezuela

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/
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You are doing OK.
When you have several gears transmitting movement, you must make a numeration following each gear in the direction of the transmition.

Ratio = (D2/d1)x(D4/d3) x...D2n/d2n-1

In each pair of gear, you have the input gear and the output gear.

Even: output
Odd: input

When you have several gears transmitting movement, you must make a numeration.

For example, your helicopter...

1, motor pinion
2, Spur
3, Auto gear
4, Tail main
5, Front bevel in
6, Front bevel out
7, Rear tail Bevel in
8, Rear tail Bevel out

Data

1, Motor pinion 12
2, Spur 112
3, Auto gear is 104
4, tail main is 22t
5,6, Both front bevels are 24t
7,8, Rear tail bevels are both 23t

So...

Ratio= 112/12 * 22/104 * 24/24 * 23/23

Ratio = 1.979

As you were doing...

112/12 is 9.333
Motor in relation to main rotor.
9-1/3 turns on motor equivalent to 1 main rotor turn.

22/104 is 0.212
Main rotor in relation to tail rotor.
0,212 turns on main rotor to 1 tail rotor turn.

Ratio = 9.333 * 0.212
Ratio = 1.979

Remember, this ratio is motor in relation to the tail rotor.
1.979 turn on motor equivalent to 1 tail rotor turn.

/
Saludos cordiales,
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02-22-2021 06:10 PM  8 days ago
helitom

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Pine Grove, Calif, USA

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The tail rotor ratio normally refers to the turn ratio between the main rotor and the tail rotor. This number is relevant as it relates to the effectiveness of the tail rotor to control torque generated by the main rotor. For an RC helicopter that ratio is typically somewhere around 5. As noted in the above post, you can count teeth on any rotating component and do the math to pinpoint the relative ratios between any two components.

Assuming you counted teeth correctly on the tail rotor drive gear and the tail rotor pinion gear, your number of 4.72 appears to be in the ball park. A simple test is to turn the main rotor as close to one complete turn as you can and count the tail rotor turns. You should see very slightly less than 4-3/4 turns of the tail rotor with one complete turn of the main rotor.
The older I get, the fewer things seem worth waiting in line for.
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02-22-2021 08:49 PM  8 days ago
Rojoalfa

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Punta de Mata, Monagas-Venezuela

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Rojoalfa 22/104 is 0.212
Main rotor in relation to tail rotor.
0,212 turns on main rotor to 1 tail rotor turn.
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That is correct.

104/22 = 4.727

Tail rotor in relation to main rotor.
4.727 turns on tail rotor to 1 turn on main rotor.

Very interesting point.

Power is torque x rpm

Yes... We can manipulate different option for tail performance...

Rpm with differents ratios.(more popular)

Different tail blade lengths.( scale helis)

Different lengths of boom. ( CUSTOM made on P&B )

/
Saludos cordiales,
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03-01-2021 07:18 AM  2 days ago
wjvail

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Meridian, Mississippi

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💎Sustaining Member
A quick look around says the stock Align 700L Dominator tail drive ratio is 4.37:1 relative to the head. The 700X is 4.72:1 Your post suggest you have a 700L but seem to have 700X tail gears.

As for where to buy parts, my go-to for Align is often GrandRC. They almost always have 100% of what I need. -- > http://grandrc.com/Elec.-Helis-&-Pa..._478/index.html

___________________________

Reference links:

https://www.amainhobbies.com/align-...h70e20x/p501343

https://www.amainhobbies.com/align-...h70e35a/p770721
"Well, nothing bad can happen now."
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