ChopperAddict's Hints & Tips

CHOPPERADDICT SPECIALISES IN THE BUILDING, REPAIRING & 
SETTING UP OF R/C HELICOPTERS AND RADIOS

   

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INFORMATION - Everything you might want to know about the IDLE UP switch

This page is dedicated to the "infamous" IDLE UP switch, what it is, how it works, how to use it, and what not to use it for.

Firstly, it is often called the "DEVILS SWITCH" by many of us, and for very good reasons as we will show as we progress.

Its main function is to allow us to switch the head speed from a normal curve starting at zero to a much higher starting point.  This allows us to have a more constant head speed when flying, while still having full pitch control, which is the way full size helicopters always work.

On stock transmitters such as the Esky and others, you cannot adjust the normal or IDLE UP throttle curves, and if you accidently hit the IDLE UP switch with the throttle fully closed, the motor will instantly attempt to spool up to about 60% throttle.  THIS IS OF COURSE VERY DANGEROUS

Imagine what will happen to you if you are standing in front of your helicopter, maybe on the bench, and you hit this switch.  The helicopter is going to spool up really fast, the rotor blades are very likely to hit you, with serious injury a possibility, and then the helicopter will try to take off all by itself.

Now one plus point (if you can call it that) is that most main gears will not accept the sudden and vicious acceleration and in most cases, the main gear will strip its teeth, which may save some damage, but means you are going to have to replace the main gear at the very least.

So the MORAL here is to ALWAYS ensure that the IDLE UP switch is firmly in the OFF POSITION whenever your radio is switched on, unless you really mean to use it.  Many pilots put red tape around it, and many other actually TIE IT BACK in the OFF position to ensure it cannot be turned on accidently.

Most radio systems claim to have a safety feature that will inhibit the ESC from initializing correctly if you accidently connect the LIPO while the IDLE UP switch is on, but DO YOU WANT TO TRY IT OUT FOR REAL ?  I don't for sure.

OK, now we have talked about the dangers inherent in the DEVILS SWITCH, let's look at what it is and what it is to be used for.

On a stock transmitter, you should only ever switch it ON when the throttle stick is at 50% at least.  Then the change in head speed is not too marked.

The good points of the IDLE UP switch

Once the switch is ON, the head speed will continue to be pretty fast, even when you pull the throttle right back, and this is in fact very useful, as we will now see.  The reason is because although the head speed doesn't drop away to nothing, the pitch of the rotor blades is still performing basically the same as it does in NORMAL mode.  In fact, most stock transmitters actually provide a pitch range that includes more negative pitch in IDLE UP mode.

So when you think about it, as you are landing in NORMAL mode the head speed slows down more and more as you pull back the throttle.  Equally the pitch is also reducing, so as you reduce throttle more and more, the amount of lift is reducing quite rapidly due to the combination of pitch and head speed.

In IDLE UP mode however, the head speed is staying at a preset speed that probably represents about 60% throttle, so only the pitch angle is changing.  This gives you far better control over the helicopter.  Equally at the hover, the head speed is nice and constant despite the small changes in pitch you will be giving it.  This makes hovering smoother and more controlled.

Finally, and the major reason for the IDLE up system, is that when you start to fly circuits and perform simple aerobatics, it is very much easier in IDLE UP mode, and indeed, some manoeuvres like the roll require that you use negative pitch as the helicopter reached the inverted stage.  When you think about that, to get negative pitch you have to pull the throttle stick all the way down, as it also controls the pitch...

Therefore, you cannot possibly have the throttle turning the motor off at the same time, hence the need for the IDLE UP setting, as you still have power to the rotor head, but you can also apply negative pitch at the same time.

The bad points of the IDLE UP switch

Accidental use can cause damage to your helicopter, damage to yourself and/or to others around you.

In the event of a crash, the last thing you want is to have the helicopter beating itself to bits on the ground because the head is still being spun at 60% throttle.  Therefore, if a crash is inevitable, you need to either switch the IDLE UP OFF, or better yet, if you have one, hit the THROTTLE HOLD switch quickly.

Using the IDLE UP with a programmable Transmitter such as the Spektrum DX6i 

Once you move up to a decent transmitter system, the IDLE up system is actually far more useful, and if you DO  NOT WANT TO USE IT, you can protect yourself easily by making the IDLE UP and the NORMAL curves identical, so that throwing the IDLE UP switch will have no effect.

Typically, the IDLE UP throttle curve will start at around 50-60% throttle, and most pilots set it so that at a certain throttle setting, both curves are the same so that switching between them is not even noticed.  The same applies to the pitch curves.

If you also have a better ESC that provides a GOVERNOR MODE, you can use the IDLE UP curve to set the governor to whatever speed you want.  In this case, the throttle line is usually a totally straight, horizontal line set to the throttle speed  you want the GOVERNOR to hold.  Most often this is about 90-95%.  You can do this, because part of the ESC's duty when switching to governor mode is to spool the head up to that setting slowly, avoiding the massive wrench when used with a normal ESC.

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