day_fiend

My Feedback: (1)

Yep, I really don't know. I used to think that you just had 4 servos in your radio, and they are what recognized when you moved each stick either forward and backward or left and right. But it sounds like there are servos on the actual heli too. If so, what are they for? And how many are there?

Charlie

Your right, the servos go on the heli. They are what controls the heli so you can fly it. They look like these.

-pkh-

My Feedback: (2)

Wow, that's the "newbiest" newb question I've seen in any RC forum I've cruised!

That's OK, though, we all gotta start somewhere, sometime!

Servos have a motor and a gearbox inside, which gears down the motor rpm to provide slower, higher torque, shaft rotation. They also have a position sensor and some control circuitry inside that allow the servo to sense the output shaft's angle or position, and turn the motor appropriately to achieve the desired angle/position. So if your RX is telling the servo to rotate to, say, a 45 degree angle, the servo drives the motor in the appropriate direction until it gets to 45 degrees, and then stops. If you grab the shaft and try to move it from the 45 degree position, the servo senses the movement and drives the motor to fight you to get it back to 45 degrees.

day_fiend

My Feedback: (1)

So are servos only on the heli, not on the radio?

Hummer Man

yep... only on the Heli, boat, car, truck, or airplane. Not in the radio...

-pkh-

My Feedback: (2)

The TX almost always comes with a compatible RX, and sometimes with servos, too. This is just because you need all of them to get started... Electric cars need RX/TX/1servo (steering), nitro cars need RX/TX/2servos (steering and throttle), planes typically RX/TX/4servos (elevator, aileron, rudder, & throttle... I believe) and helis need one more servo than planes for collective pitch (5 total). You can buy a RX/TX/4servo package, and then a gyro/1servo package and have everything you need for a heli.

You can almost always get a package that has what you need for your particular application, and save some $$$ over buying separatlely.

BouyanT_PooP

what is collective pitch? (i fly airplanes)

day_fiend

My Feedback: (1)

Thanks for all the detailed info -pkh-. Well since I'm on a streak of newb questions, here's another:

Why does the gyro need a servo? Doesn't the gyro take care of whatever it needs to do by itself without input from the pilot via the radio? Also, is it ok to have the 4 other servos be different ones than the gyro servo? And if so, which one would you want to be the better quality one?

-pkh-

My Feedback: (2)

The simplified view of airplane terminology to heli jargon is this:
elevator down/up = tilt blades forward/backward
aileron left/right = tilt blades left/right
rudder left/right = tail rotor pitch pos/neg
throttle = throttle
collective pitch = adjust pitch of all blades pos (go up) or neg (go down)... no real airplane version of the term...

-pkh-

My Feedback: (2)

The gyro just goes between the RX and the rudder/tail-rotor servo. The gyro provides the control signal to the tail rotor servo, and cannot move/control anything on its own. The best quality servo should probably be the tail-rotor/rudder/gyro servo. It should be very fast and have lots of torque. For the gyro to work flawlessly, it needs to be able to adjust the tail rotor pitch very fast.

Why a gyro?...

Ideally, you want to be able to move the rudder/tail-rotor stick and make the heli turn when you want, at the speed you want, and stop where you want it to. In reality, without a gyro, this isn't the case. The heli wants to rotate on it's own because of the torque of the engine & main rotor rotation. You can manually give enough tail rotor pitch to neutralize this rotation, but then when the torque changes a small amount, you have to readjust the tail-pitch again to keep it from moving. Wind, or air movement due to forward flight changes the amount of lift the rotor blades produce at a given pitch, so you have to adjust again to compensate. A gyro looks at your control inputs (from the RX) to see if you are trying to move the tail, if you are, it adjusts the tail pitch appropriately to move it. If you're not trying to move the tail (rudder stick is centered on the TX), and it senses tail movement, it automatically adjusts the tail rotor pitch to compensate and keep the tail from moving.

Most TXs have what is called revo-mix, which allows you to automatically program a certain increase in tail rotor pitch for a given increase in throttle/torque. This helps a little, but will never be exact, and cannot compensate for wind or other external forces the cause the tail to move.

Check out http://www.raptortechnique.com for loads of info on helis. Also Rays Authoritative Helicopter Manual is a great book for a newb... http://www6.mailordercentral.com/heliproz/default.asp

day_fiend

My Feedback: (1)

What is the difference between digital servos and non digital? Are the digital ones worth the extra money? On heliproz there's this combo with a radio and 5 servos and a gyro for $600, and then the same combo but with all digital servos for $700.

<EDIT> Oops, I guess they both have all digital servos. But the more expensive one is PCM instead of FM. So I guess my question instead would be: What is PCM?

<EDIT AGAIN> K, I know what PCM is now, so nevermind that. Next question though... How often do you have to replace servos? And why would you have to? I ask because I don't know whether to get some nicer 811 digital servos or some cheaper 3001 sport servos. Obviously I don't want real expensive ones if I'm going to have to replace them every week. Also, would it be ok to use 4 811 servos, then if one broke, I could replace it with a cheaper 3001 but leave the rest?

FBaity

My Feedback: (2)

Full size helicopters have servos also but they are hydromechanical or electromechanical devices that assist in flight controls. These devices give the flight controls authority and eleminate feed bach to the control sticks.

-pkh-

My Feedback: (2)

What is the difference between digital servos and non digital? Are the digital ones worth the extra money?
From what I've seen, digitals are typically faster and higher torque than analogs. I'm not sure what exactly is "digital" inside a digital servo, though. I'm sure the control circuit is digital instead of analog, but I'm not sure if the shaft position sensor is just a potentiometer (with an A/D converting the voltage to digital) or if uses another type of sensor with a direct digital output. I've also read that the digitals can have a much stronger holding torque than analogs. Analog servos require a certain amount of shaft position error to put out much torque to correct the error, while digital servos can put out max torque with very small errors.

How often do you have to replace servos? And why would you have to?
Ideally, you should never have to replace a servo. If you've chosen a servo that is appropriate for your application, you should not damage it (under normal circumstances), and it should last for years. What can happen is you can strip the gears (crash, or any other force that overpowers the servo), maybe burn out the motor (if the servo is underpowered for a particular application, or the motor constantly runs to overcome a small error for some reason). The potentiometer shaft sensor can become corroded or get dirty and cause twitching of the servo. The gears can wear down, loosening the gear mesh, and give you some slop and centering errors over time. I think you can by replacement gear sets (and upgrade gear sets) for most of the big name brand servos, so gear stripping or wear is relatively easy to fix.

From what I've read, it sounds like servos with ball bearings (BBs) are a must for helis (to withstand the loading on the shaft). High torque servos (more than 50oz-in of torque) are best to give you better response, and should last longer under the demanding loads. High speed servos give you better response/handling as well. Sounds like metal gear servos are best for strength/durability, but the gear mesh gets loose quickly, and you get more slop in your controls. Based on all of this, for my Raptor 50 I went with Futaba S9252s for my collective pitch, elevator, & aileron, and an S9254 for the rudder. For throttle, I used an S9001. The S9252s are digital, high torque, relatively fast servos, the S9254 is a digital, high torque, extremely fast servo, and the S9001 is an analog, moderate speed/torque servo.

rc12

Sounds like you need some help getting off the ground, well what I would do is find someone at your flying field that flys helis, he can usually train you on a buddy box and sometimes for free depending on how nice he is, usually after yu are finished learning to fly and you are an accomplished flyer you start looking for your own heli, most of the time your instructor knows somebody that is selling their raptor 30 or some other 30 size heli (used) but it would be all tuned up and ready for you to fly. so look for someone at your field that is selling their raptor 30 and most of the time they will give you a good deal on it too.

Good luck flying, Drew