Two types of balls

Balls insertion tool

The advantage for the hex type is easy to install. You can hold the screwdriver with the ball in one hand, and the other hand holding the parts to secure the ball. It is widely used in the 450 class heli.

But in the 300 class, the ball is smaller, and the neck of the ball is small as well. So, you can find that the biggest complain is the during a crash, the neck is broken and the thread is left in the parts. Then your parts become useless, and is having great cost if it is a CNC one.

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Handmade tool

Before measurement, we need to have some parameters.

1. Distance from blade hole to tip (L)
2. Distance from spindle shaft to tail boom. (h)
3. DIY a card board / Blade holder for the measurement (As shown in the photo). This will be the pitch meter of yours.

Step:

1. Adjust to the pitch you want to measure.
2. Rotate both blades to the back, on top of the tail boom.
3. Keep the flybar at horizontal level. Measure the vertical distance between both blade tips (d) by your DIY meter.
4. Done. Follow the calculation below, base on the algorithm shown in the photo:

Explanation diagram

You can see, with this calculation, a big measurement error (a few mm) will give tiny difference (less than 0.5 °) in the calculated pitch angle. So, you may feel free to measure the (d) roughly. This will still give you an accurate pitch angle.

One for note is that one blade will go up for +ve pitch, while the other one goes up for -ve pitch. (which blade goes up depends on the delta angle of the head setup)

Small Tips: Construct a table and put it in your purse. Like the one shown. You will get the pitch angle easily, no need to take sin every time!

Small Tips:
Distance-to-Pitch Table

Real Pitch angle over measurement

Besides the accuracy, there is another important advantage for this method. The ACTUAL value of pitch angle. For any practical design, the head will have free play in pitch, because the joint need to be smooth and thus have slop. So, when measuring the pitch (distance d), try to hold the lower blade instead of the flybar or upper blade. This will cancel the free play of the head and gives you the exact value of pitch when the heli is in the air (without loading).
When measuring 0° pitch, try to hold both blades so that the free play gives same (d) for +ve pitch and -ve pitch. And that will be mechanical mid-point for 0° pitch. (Of course, it will be -ve for real value)

Limitations:

1. Blade must be straight.
2. Blade is tight at the blade grip, not loose, no free play
3. Blade has no fixed pitch. (Some blades have pitch angles)

So, what you exactly need is a DIY cardboard or Blade holder, plus a table for your own heli. And that will save you a few bugs plus giving you more accurate value.

Parts:

Linkage A / B / C – as shown in the figure
Linkage D – Linkage between CCPM servos and swashplate
Pitch Slider – slider between swashplate and hub
Timing pin – The pin that keep the pitch slider sync with hub
Mixer PS – Mixer arm at the pitch slider
Mixer BG – Mixer arm at the Main Blade Grip

Assumptions:

1. Swash mix at 60% for Elevator, Aileron, Pitch
2. Hitec HS65MG servos travel as reference. Servos with similar travel limit (E-Sky, Towerpro) should be working fine with the steps. Other servos with different travel limits may have the need to adjust the swash mix first.

Aim:

Setup the rotor mechanically so that 0 ° pitch appears at pitch curve 50%

Step:

Caution – Setting pitch need to move the throttle stick up and down and the rotor may start if it is not locked.

1. Turn on Radio. Connect the battery, and make sure you locked the throttle or disconnected the motor.
2. Set the pitch curve to 50% output. You may set it to 50% flat horizontal line, or move the throttle stick to the 50% output point.
3. Install the servo horn. Try to make all the horns as close to horizontal as possible. (You may leave the horn screws at the moment. Secure them later when the battery is disconnected.)
4. Adjust the Trim, Sub Trim, or Servo midpoint at the Transmitter so that all 3 servo horns are in horizontal position.
5. Do NOT connect linkage D. Adjust Linkage C, so that the slider could have at least 5mm movement for both up and down side. (i.e. Linkage C is controlling where the pitch slider stay at 0deg pitch.)
6. Move the swash up and down so that Mixer PS stay horizontally. This is what the length of Linkages D should be. Adjust Linkage D so that the swash keep the swash at that level. Note that the 3 linkages should keep the swash horizontal as well. If the Swash is tilted, you need to have cyclic input while hovering.
7. Install Linkage D. Now, the 50% pitch slider position is set.
8. Keep the blade grip at 0°pitch by a blade holder or DIY card board. (Refer to another article: How do we measure pitch)
9. Linkage A & B are in pairs. Adjust them so that Mixer-BG becomes horizontal. Make sure both pairs are in same length. (Better measured by a caliper)
10. Done. Set the pitch curve according to your style and keep the blades in track by adjusting Linkage A / B.

Reference:

~ 500g AUW, 4° pitch will give you around 2800 rpm for 255 wood blade at hovering.

Some pilots find that it is hard to insert the screws to the parts, which they easily slip away. Here is a tip. Take the mixer arm as an example. Decide which hole you are going to use. Also which side you wish to secure the ball (The mixer arm are able to secure the ball at both sides to get different flying characteristics). In this example, we use 2nd hole from the right. (fig. 1)


Use the tiny screw driver to drill it 2 rounds (fig. 2) to make the mouth of the hole a bit bigger (fig. 3). Then insert the screws and the ball then secure it. (fig. 4)

Fig.2

Fig.3

Besides, if it is allowed that to put the parts horizontally on a flat surface and secure the ball top side down, it will be easier as well.

Fig.4

Please understand that we need to use tiny screws for ball link to keep the angle big enough for high performance. Hope these 2 tips help.