Throttle & Pitch Curves Explained

Introduction

Many new heli fliers quickly become confused setting up throttle and pitch, this is no surprise as there are a lot of variables to take into consideration and also a lot of it is down to the type of flying you will be doing. This guide is only a brief outline and general guidance of how to do it the best way to learn is to go and experiment with your own machine.

I will start of by talking about how to set the pitch up, in a nutshell there are really two different distinctive way of setting up a pitch curve. One of these for 3D and the other one for “normal” flying so to speak.

3D Pitch Curves

A 3d curve is the easiest to set up in is simply a straight line with equal amounts of positive and negative pitch, for example the pitch at bottom stick would be –10 and the top would be +10. Normally if flying 3d all the flight modes I.E normal idle up 1 etc will have this curve. This pitch curve would have you hovering at about ¾ of the stick travel. (See Graph)

The setting in the radio for this type of curve would be would be 0-25-50-75-100 assuming you have 5 point curves other wise it would be 0-50-100.

Normal Pitch Curves

Setting the pitch up for normal flying is a little different as they are not straight lines and also different curves are normally used in normal, idle up 1 and idle up 2.

For normal mode you ideally want –1 to +10 of pitch, but as said at the start a lot of this is to do with personal preference, the +10 will stay the same but instead of –1 some people may have 0 or –3. The shape of this curve is not a linear one. The best way to describe it is to show you the graph of it (see graph).

As you can see the curve starts at –1 then increases to about +5 at this point the stick will be just above half way and the helicopter should be in the hover. The graph from there then flattens out slightly this is because it gives you more control over the height of the helicopter when in the hover as the pitch will be less sensitive. The graph then continues up to +10. You want the whole graph to be smooth you don’t want sharp edges so to speak. The best way to accomplish this is to use the expo setting on the pitch curve if you have one.

The radio settings for this curve depends on the available mechanical pitch, ok sounds confusing well let me try to explain. If you have a mechanical pitch range of –10 to +10 and you want a pitch curve like the one mentioned above then the radio settings will be some thing along the lines of 45-65-75-80-100 because 50 is half of the available mechanical pitch hence this will be 0. So the radio setting will change depending on the pitch range you have on the machine.

Idle up 1 uses the same curve as normal but the throttle curve is different we will see this later on in the throttle curve section.

Idle up 2 pitch curve is the same shape as the normal curve but instead of a negative value of about –1 a value of –5 is used instead. This curve is used for basic rolls loops etc hence the –5 just enough to keep it level inverted. You still want the curve to be a smooth shape so some other the lower points may need tweaking to keep it so.

Ok so I hope you all understood that and have decided weather to use a 3d curve or normal curves. We will now go onto how to set up the throttle curves.

Throttle Curves

Ok then onto throttle curves, the simple theory behind this is to give a constant head speed through out the whole pitch range. Sounds simple enough lets have a look how it is done.

As common sense would suggest the more pitch there is the more throttle needs to be applied. So lets put that theory into practice with the 3d pitch curve. Remember that the 3d pitch curve is a straight line from –10 to +10.

3D Throttle Curves

Ok so we need to get the helicopter of the ground first so we need a curve that will do this. This is what the normal mode curve is used for. It will always start at 0 and go from there. The normal mode throttle curve should look something like this:

As you can see the throttle curve is almost a straight line. The trouble is every bodies throttle curve will be different depending on what head speed you wish to run and how powerful your set up is, so this is only a very rough shape of what it should look like. The most important thing is that the head speed stays constant once of the ground. It is normally better I think to start with lower values and increase these to the desired head speed.

Moving onto what the throttle curve should be like in idle up 1. Again the pitch curve is a straight line but we now want the head speed to remain constant when the throttle stick is bottomed I.E the helicopter is inverted. For this a v shaped throttle curve is used. Typically the 2 extremes of the curve full positive and negative have 100% throttle and in the middle is about 50% the other 2 points are about 65% or what ever values gives a constant head speed. It should look something like this:

Idle up 2 is some times used by some people to give a different head speed from idle up 1. I personally don’t use this but if you wish to the 3 middle values will just be slightly higher i.e 50 would be 60 and the 65 would be 75.

Normal Throttle Curves

The throttle curve for normal flying in normal mode is very similar to the 3D one in respect to the shape and the numbers. It starts to differ when we get into idle up 1.

In idle up 1 we want the head speed to stay the same during a decent so for that we don’t want to drop the throttle all the way back to zero as in normal mode. The curve will tail of when we get to about 25% throttle (see graph).

In idle up 2 we want the throttle curve to almost look like a tick. This little kick of throttle at the bottom keeps the head speed up for doing rolls etc. If you look back to the pitch graph you will see they both resemble each other.

Governors

Ok lastly we will talk about the use of a governor. A governor keeps the head speed at a certain rpm and it is completely independent of the throttle stick position.

So how do we set up our curves using a governor. Firstly the pitch curves are no different than without a governor. So we can pass over this aspect of the setup as it is already covered.

The throttle curve is generally handled differently for normal mode and idleup. Normal mode needs to allow the motor to shutdown at low stick. Where as idleup wants to keep the motor RPM constant regardless of where the throttle stick is placed.

Normally the governor is controlled by what percentages you place in your throttle curve. The percentage value will correspond to a specific head speed. As an example 80% throttle may equate to 2500 rpm. You will need to work out what percentage you need to set using a tachometer. The governor will hold the set RPM providing the percentage is constant across the whole throttle stick movement. Even if you give the helicopter lots of pitch the governor ill compensate by automatically increasing throttle to hold it's set RPM. Therefore the throttle curve in governor mode tends to be a flat line as we want the RPM constant and not fluctuating. The difference between normal mode and idleup is that normal mode starts at 0% (which enables the motor to stop at low stick). Idleup mode does not start at 0% but instead low stick has a value exactly the same as the rest of the throttle curve. This means that whether you are at low stick or high stick the governor will maintain a preset RPM based on the percentage value.

In order to illustrate this a little better here is the normal mode graph:

You can see that below 20% throttle the governor will start to slow down with low stick being 0% throttle (motor stopped). Above 20% throttle and the governor is active and holding whatever RPM 80% throttle happens to give. Just to reiterate you discover what percentage needs to be set using a tachometer. If headspeed is too low then increase to 85% across the board and if it's too high try 75%. By trial an error you will eventually settle at a percentage value that gives you the headspeed you want. You should aim for this value to be 80% or higher as below this and your motor is not running as efficiently as it could. In this instance a different motor pinion may be appropriate.

The idleup curve is different as illustrated below :

As you can see, in this curve the governor is active across the board and will hold the pre-set RPM regardless of stick position.

Generally beginners find it much easier to setup governor mode as the ESC handles all of the throttle to pitch ratios on your behalf. Where as curves requires careful trial and error to get an optimum throttle to pitch relationship.

So there you have it, throttle and pitch curves de-mystified :)


( 62 Votes )


Add this page to your favorite Social Bookmarking websites
Digg! Google! Live! Facebook! MySpace! Twitter! TwitThis Joomla Free PHP

RSS Feeds

HeliTuning - Blog