UNDERSTANDING RC HELICOPTER RADIOS
RC helicopter radios have some very interesting and different features/functions than standard fixed wing specific radios. Time to learn about these features and why you can’t fly a hobby grade RC heli without them. “Can I fly a RC helicopter with my RC airplane radio?” I get this question a lot. The simple answer is “NO” – especially if you are getting a hobby grade RC heli with collective pitch - as you know by now , that should be your only consideration. You can however fly a RC airplane with a RC helicopter radio - you just won’t be using the heli specific features. So, if you were just getting into RC airplanes, but thought you would also give RC helicopters a try, your best bet would be to get a RC helicopter radio – make sense? Wait a minute... We are living in the 21st century now! Collective Pitch & Throttle – One Stick, Two Channels This is the main difference that a RC helicopter radio has over a fixed wing radio. The collective pitch and throttle are both controlled by the same stick on the radio (the left stick on a mode 2 radio). An airplane only requires the throttle to be controlled by this stick. Now this is important to understand because even though these two functions (throttle and collective pitch) are controlled with one stick, they are on two separate channels and take up two outputs on the receiver. One is the throttle channel and the other is usually the auxiliary channel. Why separate them? Why not just hook two servos up to one channel? This question leads us into the first of four other RC helicopter radio specific functions that are dependent on this separation. The throttle hold function will allow you to lock the engine throttle/speed at a pre set value – usually idle or low speed while still having full control over the collective pitch. This function is usually activated by a toggle switch on your RC helicopter radio. Why would you want this function? If you are practicing auto rotations , you need throttle hold to lower the engine power down to an idle but still have full collective control on your main rotors to perform the auto rotation. Throttle hold is also a nice safety feature for both fuel and electric powered helis because it will prevent the rotors from spinning up if you accidentally bump the throttle stick on your radio. Idle up is used for the same reasons as throttle hold – to have full collective control, while the engine is set at a constant speed – this time a high of full speed setting. This is used for aerobatics when high rotor speeds are important and also allows you to keep your rotor speed high while pulling the stick down to give negative collective pitch. This of course is required so you can fly the heli upside down. Once again, the idle up function is usually selected by a toggle switch on the radio. Some RC helicopters radios have a multi position idle up toggle switch that allows you to set more than one idle up speed for more flexibility. Computerized radios will take this one step further... The idle up or mode switch as it is sometimes called can be used to select different throttle and pitch curves giving the ultimate in flexibility - our next topics. A programmable throttle curve function simply allows you to program specific throttle output settings to specific throttle stick settings. The most basic and simple throttle curve is called a linear curve – the kind that all non computerized RC radios produce. This would mean at low stick the throttle output would be 0% At mid stick the throttle output would be at 50%. At full stick the throttle output would be at a 100%.
Computerized radios will allow you to customize this curve so you can now set the throttle speed to what ever value you want at different throttle stick positions to enhance what ever type of flying you are doing.
A good computerized radio will allow you to program at least 5 different throttle point settings throughout the range of stick movement - one setting at low stick, one at 25% stick, one at mid stick, one at 75% stick and the last one at full stick. This would be called a 5 point throttle curve. A good computerized RC helicopter radio will also allow you to see this information on a graph, just like the ones pictured above. This is important in case you mess up on one of the settings, it will be very easy to identify this mistake when you look at the graph. A graph will also make it very easy to see if your settings produce a nice smooth power curve – very important. Programmable pitch curves work the exact same way as programmable throttle curves – they allow you program specific collective pitch angles to specific stick settings. There is no single adjustment you can make to a collective pitch RC helicopter that changes how it flies more so than changing the collective pitch range. That is exactly what programmable pitch curves allow you to do, easily and quickly; to turn the same helicopter from a docile trainer to an insane 3D monster. Click here for more information on pitch set up.
Once again, just like programmable throttle curves, a good computerized RC helicopter radio will show the pitch curve on a graph for the same reasons and have at least 5 setting points – this would be called a 5 point pitch curve. Programmable throttle and pitch curves have caused much confusion, especially for those new to RC helis. After all, there are literally hundreds of variables you can set. The whole idea behind pitch and throttle curves is to produce the right amount of power for a given pitch angle based on your flying style and the machine you are flying. If you think of it that way – pitch and throttle curves are pretty easy to understand. Keeping things simple, I always set my pitch curves first. Most heli kit instructions will include the recommended pitch settings for different types of flying. I then set my throttle curves to give smooth and steady power throughout the pitch range. Like I said before, having this information displayed graphically on your radio is a big feature. You always want nice smooth pitch and throttle graphs, no erratic values or sudden changes. In short - Smooth pitch and throttle curves produce smooth flying birds. Tail Rotor Compensation / Revolution Mixing The next RC helicopter radio specific function is Tail Rotor Compensation. This is also called revolution mixing by many people. As we talked about in the helicopter theory section on the torque control page , the reactive torque loads on the heli change when the throttle/collective are increased and decreased. Tail rotor compensation as the name suggests compensates for this. Basically this function mixes additional tail rotor pitch to compensate for the added torque when the throttle/collective stick is increased. Like wise, it reduces the tail rotor pitch when the throttle/collective is decreased. On non computerized RC helicopter radios, this function is controlled by two dial knobs, one for up mixing and one for down mixing. The up setting is used to adjust how much the tail rotor pitch is increased as the throttle/collective stick is increased. The down setting is used to adjust how much the tail rotor pitch is reduced when throttle/collective stick is decreased. On a computerized RC helicopter radio, this function is programmed on a menu screen in the same way – a mixing value for up and one for down. Good radios will have two and sometimes three different settings for different types of flying such as normal, sport, or 3D. Tail rotor compensation settings are adjusted by trial and error and are never perfect - but they are better than nothing. Once again – technology is making this function obsolete. You only have to use tail rotor compensation with a yaw rate gyro . If you are using a heading hold gyro in the heading hold mode, tail rotor compensation is never used – the gyro handles the changing torque and does so with much more precision than the best tail rotor compensation settings ever could. In addition to that, you must never use tail rotor compensation if you are using a heading hold gyro – make sure your compensation dials or settings are set at zero. If not, the compensation will send tail rotor commands to the gyro. The heading hold gyro will see these commands to turn the heli and it will do just that - an endless pirouette is the result. Gyro Gain Switch The gyro gain switch is used to set the gain of the gyro or switch between two or more gain settings if your gyro has a remote gain feature. It is hard to find a gyro these days without a remote gain feature - in fact it is much harder to find a gyro that allows manual only gain adjustment. On a computerized radio, the output value of this gyro gain switch can be programmed from 0-100% so your gyro gain settings can be adjusted remotely from your radio instead of on the gyro itself. You can also switch from heading hold to yaw rate mode if your gyro supports a remote gain and mode feature. As I just mentioned, with more and more gyros using a remote gain only setting such as the Futaba GY401 , it is getting harder and harder to find a good gyro that you can use if you don't have a computerized radio with a gyro gain menu to set the gyro up. Just one more reason I strongly recommend getting a computerized radio once getting into collective pitch helicopters - gyro technology pretty much makes it a necessity. CCPM Programming I have already talked about CCPM (cyclic collective pitch mixing) in the best RC helicopter section , but it is also an important computerized RC helicopter radio specific function. Electronic cyclic collective pitch mixing called eCCPM has been made possible by computerized radios after all. Most RC helicopter radios will offer 90° and 120° CCPM modes. Some higher end radios will also offer a 140° CCPM mode. The advantages of 140° CCPM are also discussed on the CCPM page. This is something to make sure your radio has if you are getting a RC helicopter with 140° CCPM. Invert Function Switch You don’t have to worry about this one because it is a feature that has more or less been phased out. However; some higher end radios still have it, or have the ability to program the required mixing to achieve it. The invert function switch is used to reverse the collective, cyclic pitch , and tail rotor commands when the heli is flying inverted. This way, the controls are the same as if you were flying right side up. The main use for this invert function is for performing very controlled inverted hovers. RC Helicopter Radio Recommendations
If you are just getting into this hobby and are looking for a good RC helicopter radio that offers all the important functions and features that I have just talked about - the 6 channel Spectrum DX6i really can’t be beat. You simply won’t find another computerized 2.4GHz
spread spectrum
radio with as many features or quality at such a low price.
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