Saturday, August 13, 2011

Helicopters: Radio Setup

Setting up your radio for heli flight

By Lood Birk

Ermelo Radio Flyers

There has been some questions as to go about setting up your radio so that it’s ready for hover, normal and 3d flight. In this article, I want to touch on just the radio setup. I will try not to be radio specific, but rather just touch on the basics like the pitch and throttle curves. What idleup1 means and so forth.

Setting up your heli on the radio is but one part of the entire exercise to get your heli in the air. What precedes the radio setup is the hardware setup. If the hardware setup has not been done correctly, no amount of fiddling with the transmitter is going to sort out your problems. Having said that, the reverse is also true. No amount of fiddling with the hardware will sort out a wrongly set up radio. So what are the setups that has to be done to get your heli airborne? Well, there is not really a lot to do. All you have to do is set up the swash plate type, the servo directions ,the sub trims, the swash plate travel, the pitch curves and the throttle curves. It all sounds like a mouth full, but not really all that complicated. So lets get cracking.

Before you start, make sure that all trims are centered and that there is no throttle or pitch curves programmed on the model when setting up a new model. Sometimes I reset the programming for that specific model and start all over again just to be sure.

The first step is to set the sub trims. This should actually have been part of the hardware setup, but I am going to just discuss this in short again. A chopper’s setup rests on one fundamental rule. This rule states that all controls must be at a right angle to the next. So, if you have a control rod that hooks onto a servo arm, the have to be at a right angle to each other (90deg). Now on servos, you never get the servo arm to correctly fit at a 90deg or 180deg angle to the servo, so we have to compensate for that by using the sub trim. All heli radios has got a sub trim function in the menu of the radio. Using this feature trim each of your servos so that it is at the desired angle. If you find you have to sub trim too much then rather see if you can find a servo horn that fits better.

The next step is to program in the swash plate type. Your radio should have a menu entry that lets you choose the swash plate types. Some radios the menu can only be accessed by pressing certain buttons on the radio while switching on. Currently there are one servo, 90deg, 120deg and 140deg are the most common ones. There are more, but they tend to be less common. Some radios tells you which servo will be elevator, aileron or pitch, but if it does not, consult either the heli instruction manual, or the instruction book for your radio.

Once you have selected the correct swash plate type, you have to select the servo directions. This sometimes is not easy as the swash mixing can interfere here. Especially when you are setting up a CCPM system. Let me try and see if I can easy the confusion a bit though. Let’s start with the tail servo. That is the easies to set the direction of. Firstly plug the tail servo directly into the receiver. Rotate the tail rotor till you have a blade pointing down. Now look at the leading edge of the rotor blade pointing down. If the leading edge of the blade moves to the left (seen from behind of the heli), the nose of the heli will move to the right. If the leading edge of the bottom rotor moves to the right, the nose of the heli will move to the left. So no you must set your servo direction in such a way that id you give left rudder input, the leading edge of the bottom rotor blade must move to the right and vise versa. As easy as that.

As to the gyro direction, it is just as easy. Connect the gyro into your system and make sure it is set to headlock mode. Center your rudder and move the helis nose to the left. The leading edge of the bottom rotor blade should move towards the left as well and vise versa. As simple as that. Do not forget to set your end points on the gyro.

The next step is to do your servo directions on the swash plate. The description on how to do this will vary from heli to heli, but the basics still apply. When you press the down elevator, the swash plate must tilt forward and when you pull up elevator, the swash plate must tilt backwards. I turn, if you give left aileron, the swash plate must tilt to the left and if you give right aileron the swash plate must tilt to the right. On a singe pith servo system, this is very easy to achieve, but on a CCPM system you will have to fiddle with the swash mixing as well as the servo reverse. Let us assume your CCPM system has one servo in the middle rear (call it the middle servo) and one on the 120deg left side of the swash plate (call it the left servo) and one on the 120deg right side of the servo (call it the right hand servo). The important thing you need to know is that with CCPM when you give down elevator, the middle servo moves upwards and the left and right servo moves down. When you pull back on the elevator, the left and right servos needs to move upwards and the middle servo needs to move down. When you give left aileron, the left servo moves down, the right servo moves up and the middle servo stays static. Should you move the ailerons right, the left servo moves up, the right servo moves down and the middle servo stays static. If you stick to these rules, it becomes a matter of setting your radio correctly. Not always and easy task though. So now you know which direction the swash plate must move on your corresponding stick movements and we need to change the settings on the radio so that we can get the swash plate moving in the correct direction. I suggest you use the swash mixing feature in your radio to do this. Before we do this, make sure that there is no EPA (End Point Adjustments) or trims on your radio. This will just make your life difficult. The Swash mixing is your EPA for the heli. The other thing you must remember is that your hardware setup HAS to be correct for this to turn out OK in the end. Right. You will notice that the swash mixing has three values. These are Aileron, Elevator and Pitch. You will notice that all three of them has got the same value for instance 60%. When you set these values you must keep them the same otherwise you can get unexpected swash movements which will make your life difficult whilst you fly. No say you wish to change the direction of the aileron servo, all you do is move the aileron value to -60%. This will reverse the operation. To increase the swash plate’s movement, increase the values, but be careful not to se it so much that it binds or presses somewhere when you give cyclic input.

So now you know your controls are going in the correct direction. The next thing that has to be done is the setup of the pitch and throttle curves. So, let us start with the pitch curves. In essence most radios has two settings, hover and 3D. My radio has provision for three so I normally set it up as hover, flight and 3D. I will do the flight mode as well to show you what it looks like. When setting up the pitch curves, always make sure that you work from the 50% pitch mark on your radio. At the 50% pitch mark, your rotor blade pitch has to be 0deg. The reason for this is that when you switch between flight modes and you did not set you radio and hardware to be 0 pitch at 50% input, you will get that the heli will unexpectedly climb or fall when switching modes

Let’s Start with hover. Just a quick note, the pitches I give might be different from your chopper model. Reference your chopper’s manual for the correct pitches.

In hover, you want little negative pitch to prevent the heli from slamming into the ground on landing, but enough to get you down if the wind is blowing. Mostly I use about -3 deg till about +9 deg pitch on my chopper. So the curve will look something like this…

Notice that my pitch lines always are in a straight line.

For the flight mode, I want more negative pitch because as the chopper picks up speed the rotor starts acting more like a wing and generates more lift. To be able to descend, you need more negative pitch to be able to bring the chopper down. You also want a bit more positive pitch because with practice you can do simple aerobatics in your flight mode. So the curve looks something like this …

Notice again that the lines are straight.

During 3D flight, you normally want the same amount of negative as positive pitch for that crazy upside down maneuver. So you will probably will be needing a pitch range of about -11deg to about +11deg depending on your chopper model. Thus the pitch curve looks something like this …

Notice that the 3D Pitch line is straight. No bends.

Lastly, we want to set up the throttle curves. Now the throttle curve is different to a heli with a governor that to one without. I am going to be doing the curves without the governor because you should know the principle of operation. I can tell you this though, your governor throttle curves normally runs in a straight line.

The basis to which you setup your throttle curves is to try and give you heli a constant rotor speed, so you might have to fiddle with the curves once you start flying. I am going to give you the basics though to try and help you understand the curves.

Let’s do hover first. In hover you want to have zero throttle on startup, spool it up till it’s ready for hover, but you might need that little push if you should open the throttle fully. The curve looks something like this…

This is a sample curve. You have to fine tune the engine by moving the flat part up or down to increase motor speed and tilt the flat part if you see the motor over speeding on the lower pitches but no having enough power at full throttle.

In your flight mode, you never want the throttle to close completely, so your throttle setting at 0% is going to be of such a nature that the rotor keeps its speed, but does not over speed as the chopper descends. So it will look something like this…

On your 3D throttle curve, you want your engine to produce proper thrust toward the full negative and the full positive, so your throttle setting will look like this...

As you can see, you have 100% throttle when the stick is at 0% as well as 100%. Needless to say, NEVER EVER start your chopper in this mode.

As stated before, you might have to fine tune the curves, but the basic principle stays the same.

I hope that you now understand the cyclic and rudder setup on your radio.

Happy Landings

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