The Esky standard 6 channel TX Pitch curves

   

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The Esky 6 channel Transmitters (TX) are famous for confusing pilots, especially when they try to set up the helicopter correctly  with ZERO PITCH at 50% Throttle, and when they are trying to understand what the IDLE UP switch (and Idle up Mode) really does, and how to use (or not use) it.

Hopefully this Tip will explain it in relatively simple terms so that you will understand all about the relationships between Throttle and Pitch curves, and Normal and Idle Up modes

The diagrams below have been taken from the Esky Documentation, and hopefully will help everyone to  understand how these curves interact with each other.  (You can click each image to bring it up larger in a new window for ease of use)

In the first diagram below, you can see the throttle curves for NORMAL and IDLE UP (spelt IDEL UP by the Chinese translators) on the left, and the equivalent pitch curves on the right.  (Also note they call it 3D in one heading, and IDEL UP in others)

In NORMAL MODE the throttle curve is in fact a straight line at 45 degrees from 0% to 100%, which is a reasonable "curve" for beginners to use.  However, look at the pitch curve for NORMAL MODE at the right and you will see that Pitch range starts at 50% of the full available range and rises linearly to 100%.

What does that mean in simple terms then ?

Well, as you push the throttle lever up, it will pass through all of the points 0,1,2,3,4,5 shown at the bottom of the graph. So at zero throttle you will have whatever pitch setting you have configured it to, which is NORMALLY around -2 or -3 degrees of PITCH. As you increase the throttle, the pitch also increases gently and in a linear fashion up to the full pitch setting, typically around +8 or +9 degrees.

While this happens, the throttle is increasing linearly all the time, so this means that the motor and therefore the rotor head will spin up to a decent head speed at 50% throttle, BUT you will still have NO or VERY LITTLE PITCH on the blades, so the helicopter will NOT TRY TO LIFT OFF.

Now lets move on to the second pair of curves, marked as IDLE UP. (Well IDEL UP in Chinese)

You can see immediately that the throttle "curve" is completely different here, starting right up at the top at 100% throttle with the throttle stick FULLY DOWN.  It then DROPS to 50% throttle as you move the throttle stick UP towards mid stick.  Once you move the throttle stick above 50%, the throttle starts to increase again, and returns to full throttle with the throttle stick at 100% throttle.

Meanwhile, the matching pitch curve is still a straight line, but this time it DOES NOT START AT 50%, but rather at ZERO PITCH.  As you increase throttle, the pitch also increases linearly all the way up to 100 throttle.

Confusing isn't it ?

Well, Yes and No really.

Lets just think abut these two and see what happens when you want to make your helicopter take off.

NORMAL MODE

You increase the throttle slowly to 50%, and the rotor head will speed up to 50% of it's maximum speed, as the left hand top graph shows us.  At the same time of course, the Pitch is ALSO CHANGING.  So by the time the throttle is at point 3 (50% throttle) the pitch curve has moved to a position half way through the pitch range.  Now lets assume you have a NORMAL Pitch range of -3 to +8, the TOTAL RANGE you have is 3+8, or 11 degrees, so at 50 throttle, you will have the pitch angle that represents 5.5, or just over half the entire range. That means a pitch angle of around +2 to +3 degrees (-3 + 5.5 = +2.5)

That is just about right, as it means the helicopter will just be going a little light on the skids.

Now as you push the throttle up past mid throttle, both head speed and rotor pitch angle are increasing at pretty well the same rate.  At around 2/3rds throttle, the helicopter will be lifting off quite happily.

IDLE UP MODE

This is where it all gets tricky.  As the lower graph shows VERY CLEARLY, with the throttle stick FULLY DOWN, if you pull the IDLE UP Switch forward to engage IDLE UP MODE, you will get 100% Throttle.

THAT IS FLAT OUT HEAD SPEED - INSTANTLY

Now we all know that this scenario is NOT GOING TO BE A GOOD THING TO DO, as the first thing that will most probably happen is that the motor will try to spin up to full rpm immediately, the rotor blades have a lot of inertial to stop them being spooled up that quickly, and the typical result is that you hear a nasty noise, and then find that you no longer have ANY TEETH LEFT ON THE MAIN GEAR, which is really not too surprising.

The IDLE UP THROTTLE setting is designed to allow you to have a reasonably CONSTANT HEAD SPEED, which allows you to fly inverted and do all sorts of other things, but clearly you need to find a way to be able to switch to IDLE UP MODE safely.

The other thing to note is that the total pitch range in IDLE UP MODE is typically -8 to +8 degrees, so a range of 16 degrees is available, as opposed to the meagre 11 degrees total range we get in NORMAL MODE.  THIS IS IMPORTANT TO REMEMBER, as -8 is a lot of NEGATIVE PITCH.

Well, all you need to do is to compare the top NORMAL graph and the second IDLE UP graph to spot the solution.  There is JUST ONE POINT WHERE BOTH THROTTLE LEVELS ARE THE SAME, and that is at mid throttle. (point 3 on the bottom range)

You may also have spotted that once you are up to 50% throttle, there is no difference on the throttle curve (only) all  the rest of the way up to full throttle, so you can indeed switch between NORMAL and IDLE UP modes anywhere from mid throttle to full throttle, BUT DEFINITELY NOT BELOW 50% throttle stick.

However, there is is a teeny little flaw in this apparently excellent plan.      

Take a good look at the pitch curves...   

Yep, your dead right, in IDLE UP MODE there is NO POINT AT WHICH THE PITCH CURVES CROSS AT THE SAME SETTING.

As you can see from the pitch range values I have added, in NORMAL MODE at 50% throttle, you will have around 2 to 3 degrees pitch. If you switch to IDLE UP MODE at this throttle setting, the pitch is going to go to zero, or possibly a little less, which means that although your skids were just getting light on the ground in NORMAL MODE, the pitch has dropped, and there may even be a small amount of negative pitch which will pull the helicopter downwards a bit.

This is not a particular problem, but you need to be aware of it, and ready for it, especially if you switch between modes at higher throttle settings, as the difference in pitch becomes more marked


Click image for larger version in new window...

CLICK IMAGE to enlarge in a new window

GENERAL POINTS

There is one trick you can use to help yourself out here, and that is to use the Pitch Adjustment Knob that is on the top left of all Esky stock TX's.  The graph immediately above shows what effect this knob has on the PITCH CURVE.  I think it is fairly self explanatory, in that it shows that you can change the position of the diagonal pitch line upwards or downwards throughout the entire range.

This means that if you INCREASE the value on this knob by turning it clockwise, the overall pitch range will be HIGHER, but this means that due to the higher loading, the head speed will DECREASE, and vice versa.  The change you make here effects BOTH NORMAL and IDLE UP MODES in exactly the same way.

Please do NOT FORGET if you set this knob to anywhere but 12 o'clock, then the pitch change will be different when you switch between NORMAL and IDLE UP Modes.

If you have the 35MHz TX (it is not on the 2.4GHz TX, as it has been replaced with a gyro gain control instead), you can also use the right hand knob on the TX to further adjust the Pitch to a more realistic "curved" line instead of the straight line we have seen so far.  (Most computer radio users have curves more like these)

The change this knob makes is not large, but it is a useful control to try to match the helicopter setup against your flying more closely.

Click picture for full size diagram in a new window...

CLICK IMAGE to enlarge in a new window

WHY YOU USE IDLE UP WHEN DOING THE MECHANICAL PITCH SETUP

This should now be really easy for you to answer by yourselves - just look at the graphs again....

Quite correct, it is ONLY IN IDLE UP MODE that 50% Throttle stick equals exactly 50% pitch, and this is the ONLY SETTING we are interested in when setting the pitch range.

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