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New Heli Build-Gaui X5 Formula

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I'm glad to see you two sharing information on building hellicopters. I fly mostly gliders, so they are fairly simple. This is an education for me. At times, I still have no idea what you are talking about. You know that learning curve concept? Well, I'm way down at the bottom as far as rotorwing stuff.

Where are the bevel gears, and how exactly does the 3M tape thing work? Does one of the frames holding the gears have a fine adjustment that lets you move one of the gears to set the backlash?
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I don't want to hijack the thread but I'll explain some about the gears. Take a look at the gear illustrations to see what types I'm talking about.

Rotorman's Gaui X5 has straight cut spur gears from the motor to the main gear, and then some bevel gears to get power to the tail rotor. I have a picture showing the side view of an X5. The gear mesh is set with the motor being able to move towards or away from the main gear. Set the mesh too loose, and you will destroy the main gear from lack of contact. Set the mesh too tight, and it could wear out quickly or just melt. Same thing on setting the bevel gears. Gears are supposed to have slop, but not enough/too much will shorten the life of a gear dramatically. 

Straight cut gears are make contact one tooth at a time making it really important to get them right. This type of gears work well, but usually can't handle a lot of power. They are also noisy because of the large contact  surface.

Helical gears are being used a lot more in helicopters. These gears have multiple teeth making contact at a time, and each tooth makes contact in a progression. This makes the gears quiet, and very strong. Down side to these gears is they pull in the direction of the motor shaft, and wear out bearings.

Herringbone is probably the best gear solution. They are shaped like a V treaded tire, and this eliminates the pulling/pushing forces(up/down in this case), and like helical the gears make contact in a progression. 

Bevel gears are straight cut, or helical for helicopters, and they have the same advantages/disadvantages with each type.

There are a few rule of thumbs with setting gear mesh that I've found not to be all accurate. People say to use notebook paper to send between the gears, and that should be the correct spacing. I've found that paper is not all the same, and is not all the same thickness. I tried this and ended up replacing gears because the spacing ended up too thick with a chipped tooth gears. I've never heard of using 3M tape this way to set gear mesh, but seems way too thick. I don't know, though. 

Everyone is different, but this is what works best for me. I look at the backlash of the gear, and adjust accordingly. Backlash is the slop motion of the gear before it will move the next gear. The helical gears like very little backlash, and I've had really good luck with about a 1/2 mm of backlash. Straight cut gears need a little more, but its a feel thing for sure


Motor pinion to Spur gear to bevel gears straight gear mesh

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Sorry all, I was gone the last 4 days on vacation so I haven't progressed much past the wiring, mounting the esc and fbl unit. Also all the soldering and blade balance is done but not mounted yet. Waiting for a 15 tooth pinion and I can almost spool it up without the blades on!!
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Progress so far
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On rc helicopters there are three way's of driving the tail rotor. All heli's have a pinion gear on the engine/electric motor and a main gear driving the main shaft.

The first way (and the simplest) way to drive the tail is using two separate electric motors, one driving the main rotor and one driving the tail rotor. This setup is only found on smaller micro helicopters and its downside is the tail doesn't feel "locked in" because the motors can speed up and slow down at different rates causing the tail to feel sloppy. It also has a fixed pitch (basically a prop) for the tail rotor.

The second way is using a small cog belt. Power is transferred form the pinon gear to the main gear, through the one-way-bearing to a tail drive gear with a pulley on the other end of it. The belt wraps around the pulley and goes through the tail boom to another pulley on the tail rotor shaft. This setup can be found on medium to large size heli's and uses a variable tail pitch setup using a servo and a gyro to control the tail position. Advantages to a belt drive are "locked in" tail because the tail speeds up and slows down with the main rotor, simpler to "stretch the heli"  which means running a longer tail boom and longer blades because belts can be found in a variety of different lengths. They are also a little more forgiving if the tail rotor happens to touch the ground on a rough landing. Disadvantages are (at least for me) constant belt adjustments and can create a static charge inside the tail boom which can wreak havoc on electronic's if not properly addressed.

The third and final way is using a shaft driven tail. Power is transferred from the pinion to the main gear, through the one-way-bearing to a tail drive gear,to a tail driven gear, to a set of bevel gears, down the torque tube inside the tail boom, to yet another set of bevel gears finally driving the tail rotor shaft. Thats right, eight gears from the pinion all the way to the tail rotor!!! This setup can be found on almost any size heli excluding the vary small micro's. Advantages are "locked in" tail (variable tail pitch) , and no belt adjustments. Disadvantages are bevel gears must be carefully set or as Anthony pointed out, they wear quickly. Keep in mind the tail rotor on my x5 is spinning at a 4:1 ratio to the main rotor which means at a conservative head speed of 2400 rpm has the bevel gears, torque tube and tail rotor spinning at over 9000 rpm. Improper mesh= worn gears quickly. I also forgot to mention all the gears except the pinion on the motor are plastic!! The other disadvantage is a tail rotor strike almost always results in broken bevel gears and/damage to the torque tube.

Allen
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I've flown several different types of tails, but still I prefer torque tubes over belts. I say that, and my 2 main birds are belt drive, but only because they both have self tension mechanisms. My JR Forza, and Thunder Tiger e720 has the smoothest drive train that I've seen in my life with a torque tube. My biggest gripe about a belt is the constant adjustment with temperature change and adjustment needed for contraction/expansion.  I still say if you can keep your tail out of the dirt then go with a torque tube. My 2 cents of torque tube vs belt.
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I guess it's important to keep your tail out of the dirt! :lol:

Onward and Upward.
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Thank you guys for a good tutorial on the types of gear combinations, and description of tail rotor driving systems.

Thermals---I need thermals!
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So a one way bearing will literally only rotate in one direction?
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Not literally, but will only deliver power in one direction. Similar to a bicycle pedals only giving power to the rear tire when going forward. You can pedal backwards and free wheel down hills.
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freewheeling down hill...is that like auto rotation?

Thermals---I need thermals!
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Randy, sometimes that's easier said than done. All it takes is a little gust of wind at the wrong moment and the tail rotor strikes the ground.
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Jim, that's exactly what the one way bearing allows. When the motor/engine is spinning faster than the main shaft which is driving the rotors, the one way bearing locks up. During an autorotation or what fixed wing pilots would call a dead stick the one way bearing disconnects and allows the rotors to spin without turning the motor/engine. It's hard to imagine but even model heli's can autorotate.
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I'm not a huge auto guy, but have had to do a few not on purpose. I've really wanted to do a McDoogle auto, and an inverted to piro flipping to upright auto for a long time. I almost had the guts to do them, but chickened out. :$
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Pilatuspc12 said

I guess it's important to keep your tail out of the dirt! :lol:

Haha, among other things…
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