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Programming A Remote Control for RC Helicopters

 

Programming your remote control

 

We will try and describe the most common functions on a computer radio in helicopter mode. Note that the syntax may be different on different models and makes. Some of these terms may be in the Glossary as well.



The Switches 

Idle Up 0,1, 2 (switch)

Idle Up 0, or Normal Mode as it's called, is for take-off and forward flight. Typically, this has the lowest RPM of the three idle-up settings which makes the controls less sensitive making it easier to hover with accuracy.

Idle Up 1 is your "sport" mode. It is for Fast forward flight, high speed turns with sharp cornering as well as loops and rolls. This has a slightly higher RPM, somewhere around 1600. Also, the bottom of the collective in this mode probably not set for idle on the throttle.

Idle Up 2 is your aerobatic or 3d mode. Usually, this is a symmetric throttle curve, meaning at full down on the collective, you're at full throttle so you can climb inverted. Then, in the mid stick, which would be 0 degrees of collective, you've still got plenty of power for doing tumbles.
 

Throttle Hold (switch)

This switch is used to disconnect the mixing of the collective with the throttle. By flipping this switch you can apply full collective pitch while having the engine stay at idle. You use this switch to practice autorotation and in the event of a tail failure. By cutting power to idle, the helicopter will stop spinning if the tail fails and give you a chance to autorotate to the ground. This mode usually has it's own pitch and throttle curve.

 

Throttle Cut (switch)

This switch is used to turn off your motor. Usually this switch only works if your throttle is at idle, or a very low position so that accidentally hitting it while you're flying won't force you to autorotate.

 

Trainer (switch)

This switch will let a second remote (plugged into your remote) take control of your aircraft so long as it's held. The moment you let go of the switch your remote is back in control. Usually, the instructor holds the remote that belongs to the flying aircraft and the student holds the extra remote.

 

Hover Pitch (knob)

This knob will let you adjust the pitch near the middle of the collective so that you can increase or decrease it. Ideally, you should be hovering around 6 degrees in Normal mode.

 

Hover Throttle (knob)

This knob will let you adjust the throttle near the middle of the collective so that you can fine tune your RPMs in a hover. Your target is 1550 RPM in a hover while in Normal flight mode.

 

Revolution Mixing

This mixes tail rotor with throttle (which is mixed with collective). As you add collective you need more power to maintain your head speed, but once power is increased so is the torque which means you need to add rudder. This mix lets you program in some percentages so that the remote does most of the work for you.

To set this value you want to hover your helicopter and use your trims so that it does not spin in a hover. Then, after you land you want to program in or tweak your revolution mixing so that as you add or remove power while hovering the tail stays still. How you adjust it depends on which direction your rotor blades spin. Normally, they spin clockwise, so if you add power and the helicopter turns to it's right you have too much and need less mixing. These values require a lot of trial and error. If you have a heading hold gyro you must inhibit this function because the gyro will automatically compensate for anything including torque from the motor.

In 3D mode, your revo mixing should be a v-curve similar to your throttle curve so that as you add power for inverted hovering, you're also adding revo mix.

 

Throttle - Needle Mixing

This will let you program in adjustments to the high speed needle valve at various amounts of throttle. Most people don't use this feature as it requires an extra servo.

 

Rudder Offset

This lets you set a different trim position for higher rpm modes, like idle-up 1. Since there is a higher rpm, there is more torque and thus will require a different trim setting to hold a steady hover. This is another trial and error function where you must land and tweak the settings. This function is also inhibited if you have a heading hold gyro.

 

Throttle Curves

Throttle curves tell the helicopter how much throttle to use at which collective setting. All radios come with a linear curve, so 0 throttle corresponds to 0 collective, and 25% with 25%, 50% with 50%, 75% with 75% and full collective with full throttle. This linear "curve" rarely will maintain a constant RPM, which is your goal. You can fine tune your throttle so power is applied when needed to maintain a constant rotor speed.

There are many throttle curves, one for each idle up so that you can change how much power is applied with collective.

 

Pitch Curves

Pitch curves allow you to adjust the way the collective responds to the collective control. Most people leave it linear (0/25/50/75/100) but some people like to make the middle of the stick less sensitive (similar to exponential) for example 0/35/50/65/100. This way, the middle of the collective will be much less sensitive allowing you to hover more gracefully. It's up to you if you adjust these values, but bare in mind that you'll need to tweak your throttle curves in a similar way to maintain constant RPM. Pitch curves also have their own settings for each flight mode (idle up) as well as throttle hold.

 

Programmable Mixing

This will let you set up custom mixes from either switches or controls. You can for example mix power with cyclic, since every control movement takes power which will lower the RPM.

 

ATV

Adjustable Travel Volume lets you set the limitations on servo travel so that you don't "bind up" any controls. That's what happens if your control arm can only turn so far, but your servo wants to keep going. This is hard on the servo and can break it, so you want to set the end-points to prevent it from happening. This is usually the first thing you set because it's the highest up on the priority for the servo movements. When the ATV reaches it's limit there is no other function that can over power it to make the servo move more.

 

Sub-Trim

You can use these to fine-tune the trim of your aircraft, or use them completely so that you can leave your trim settings centered. The reason you would want to do this is so you have full trim control at your finger tips if you need it, otherwise you might have to have your trim all the way left, and your flying along and something happens and you need more left you wont have any room on the trim lever. The sub trims let you always have room to trim it out in flight. It's best though to get the links physically set to as close as possible so you don't need to use sub-trims.

 

Reversing

This lets you reverse the response the servo's move to the sticks. You would use this if right goes left or up goes down, etc...

 

Gyro Gain

This lets you set how sensitive you gyro is. If the gyro is set too high, the tail will wag like a dog's tail. If it is set too low it may be hard to control and wander all over. You want to set it as high as possible, but without getting it to wag. Remember that in forward flight the blades are more effective so it may still wag when moving even if it does in a hover. I usually use 5% less sensitivity that the best I can do in a hover because of this.

 

Exponential

This will make the center of the sticks less sensitive and the extremes of the sticks more sensitive, allowing graceful hovering and snappy rolls. Most people use 15% to 25% expo, but it's only a preference.

 

 

Typical Beginner Setup

 

Normal Mode

Pitch Curve : 0 degrees / 6 degrees / 10 degrees
Throttle Curve : What ever it takes to maintain a constant 1550 RPM while in flight

(including descents)

Idle up 1

Inhibited (Disabled)

Idle up 2

Inhibited (Disabled)

Throttle Hold (For emergency autorotation)

Pitch Range : -4 degrees / 6 degrees / 12 degrees

 

 

Typical Intermediate Setup

Normal Mode

Pitch Curve : 0 degrees / 6 degrees / 10 degrees (1550 RPM)

Idle up 1

Pitch Curve: -4 degrees / 5 degrees / 10 degrees (1650 RPM)

Idle up 2

Inhibited (Disabled)

Throttle Hold (For emergency autorotation)

Pitch Range : -4 degrees / 6 degrees / 12 degrees

 

 

Typical Aerobatic / 3D Setup

 

Normal Mode

Pitch Curve : 0 degrees / 6 degrees / 10 degrees (1550 RPM)
Idle up 1

Pitch Curve : -4 degrees / 5 degrees / 10 degrees (1650 RPM)

Idle up 2

Pitch Curve : -10 degrees / 0 degrees / 10 degrees (1750 RPM)

Throttle Hold (For emergency autorotation)

Pitch Range : -4 degrees / 6 degrees / 12 degrees

 

Pitch and throttle curves are totally personal preference though. These are only possibilities. Some pilots fly all modes with the same pitch range (-10 degrees / 0 degrees / +11 degrees) This way the pilot get used to how the collective responds through all flight modes and it never changes. Many pilot actually prefer it this way, although it's the most sensitive on the collective. It requires very subtle movements to climb or descends in a hover rapidly.

 

 

Setting Up the Helicopter

 

First, you make the mechanical connections. You want to set up your links so they use as much physical movement on the servo and are close to centered as possible, then you use your radio to fine tune it.

 

The reason you do this is to get the most "resolution" out of your servos. They only have so much accuracy, and the more travel you can use physically, the more accurate your controls will be.

 

As an extreme example, say you have your servo geared so that only 1 degree of motion would move the rudder full deflection. Then the servo must be very accurate to smoothly transition from one side to the other. This isn't the case, there are only a finite number of steps the servo can move, and the more you use, the smoother control you will have.

 

Also, the more throw you can use, the more leverage and thus power your servo will have.

 

Second, tweak the connections so that mechanically they conform to the list of pitch ranges above; if you're a beginner, use the beginner pitch ranges etc... Ok, now say you get your pitch range to be -1 / 8.5 / 12. Slide your mechanical adjustments a bit (by adjusting the links) to be more focused around 6 degrees in the middle. 6 degrees is the optimal hover pitch, because if you're hovering and your blade pitch is 6 degrees, you must be using a good rpm from 1500 to 1600 which is what you want and when you're a beginner, you want to hover at the middle of the stick. If you're at -1 / 8.5 / 12, change the links 2 degrees until you get to -3 / 6.5 / 10. These are more practical values, closer to what you want went learning.

 

Third, use the ATV settings so that you can use as much as the servos as possible, but below the point at which they bind. (Binding is when the link goes as far as it can mechanically go, but the servo tries to move it further).

 

Before you start actually flying, you should set up your throttle hold and kill switch if you have them. These are safety features and might save your helicopter or the skin on your back. Set your throttle hold so it has just enough throttle to idle smoothly. You can use this (or kill) if you know you're going to crash or while you carry your helicopter out to the landing pad.

 

Fourth, set up the pitch curve settings on the radio to make your helicopter accurately conform to the pitch range that suits your skill level. The only reason you want -1 instead of -3 or -6 on the bottom is because no newbie is used to how sensitive the collective is and so is destined to slam it into the ground when they panic and move the left stick down more than they should. By setting this value to a high number (high as in 0, or -1 degrees compared to -4 or -10 like I use) you minimize the damage you'll do when you first panic.

 

Once your pitch range is set up and accurate, you only adjust the throttle curves from then on. You do not adjust them both here and there then and again. This makes it confusing and impossible to "home in" on a good setting. One problem at a time, so start with pitch, get that set, then work your throttle curves until you get a constant rotor rpm.

 

Fifth, If you have a gyro that is NOT heading lock, you'll need to adjust the revolution mixing (revo mix) function on your radio. This is a two step process; first you must set the 0-degree mid point as a starting reference. Once your helicopter is set up not to yaw at 0 degrees, you configure the ratio of power to rudder mixing you need when you add or take away throttle. Your helicopter manual should tell you what approximate settings to start with. It's difficult for a newbie to set this portion of their radio up, because the best way to do it is to fly up and drop the collective to 0 degrees. The helicopter will drop very fast, but by watching which way the helicopter turns on it's way down you will find out if you need to add more mixing or less mixing. This 0 degree fall is used to set your anti-torque at the lowest point of torque. After that, you set the mixing percentage of throttle to rudder; that is, the more power the more you need the radio to correct for the torque by adding rudder automatically. Same for descending, when you need to take rudder away while there is less or no torque.

 

After that, you can set expo if you like. This will help soften the center of the sticks so you don't over react, but leave room for the hard yank and bank you may need in an emergency.

 

After you get used to the sensitivity and don't over-react, you'll want at least -4 degrees on the low end so you can do an autorotation if you have to.

 

Eventually, you'll want all the range you can get, symmetric if possible.

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