Tech Model Products TH-2 XPR Tandem RC Mixing Software Support Documentation

CCPM Mixing types	Supports 2, 3 and 4 point
Number of servo outputs	8 total, 4 front and 4 rear
Servo reversing	All 8 outputs
Servo centering	All 8 outputs with +/- 12.5% travel
Required inputs	4, Aileron, Elevator, Rudder, Pitch
Optional inputs	1, CH5 used as DCP input source
Input gain control internal	6, Aileron, Elevator, Rudder, Pitch, CH5 (DCP) with 0 to 100% range; Elevator as DCP source +/- 100% range
Input gain control external	5, PT1..PT4 and the X input with 0 to 100% range
Yaw compensation	Enable/Disable control; Input is elevator with gain +/- 50%
CP layout control	Select swashplate up/down will increase/decrease CP
Front swashplate layout	Select the E servo to face front/rear (3-point only)
Rear swashplate layout	Select the E servo to face front/rear (3-point only)
CCPM mixing type	Select 3 or 4 point mixing
Yaw Filter (low pass)	Select off, low, medium, high
Tx Frame Sync	User setting that can be any combination of inputs - default is the pitch input

Control axis swash plate movements:

Roll         - Left/right tilt of both swash plates.
Pitch       - For/aft tilt of both swash plates plus a blend of DCP (differential Collective Pitch) of both swash plates.
Yaw         - Differential left/right tilt of both swash plates.
Vertical - Symmetric Collective Pitch change of both swash plates.

Note: DCP input is a program mix (Transmitter) with Elevator master and CH5 as slave.

Radio Settings

This section describes what the settings in your transmitter should be.

In general, start off with the servo travel (travel volume, end point, etc.) set to 100% for aileron, elevator, rudder, pitch and CH5.
This will give you a good starting point. Servo reversing will depend on how you installed your servos and the brand as well.
All CCPM swashplate mixing must be turned off in the Tx. Initially, all other mixing functions should be turned off as well.

After you have things working, you can then add programmable mixes done by the TX.

Software Control Settings

The TH-2 XPR Tandem Control Software uses control settings as programmable parameters to allow customization
for many different applications and model types. These control settings can be modified, loaded, saved and shared
with other users using our Tech Link software. Details of the control settings are listed below.

Servo Reversing

Modify Settings - 1

Functions:

Set servo direction normal/reverse.

Each of the eight servo outputs can be reversed individually.
This function works in addition to the reversing done in the transmitter.
Click on a box to select.

Servo Centering

Modify Settings - 2..9

2 - Servo Centering Front Ep Output
3 - Servo Centering Front A Output
4 - Servo Centering Front E Output
5 - Servo Centering Front P Output
6 - Servo Centering Rear Ep Output
7 - Servo Centering Rear A Output
8 - Servo Centering Rear E Output
9 - Servo Centering Rear P Output

Functions:

Set servo centering position -12.5..12.5 percent (-125 ...125 microseconds)

Each servo output center (servo neutral position) can be adjusted by+/- 12.5 percent.
This function works similarly to sub-trims in the transmitter.
Click on an arrow button or drag the slider to change.

DCP Input Source/Gain

Modify Settings - 10

Functions:

Select DCP input source
Adjust gain -100..100 percent

The DCP function can have it's source come from the CH5 input or from the elevator input.
The best choice is to have CH5 as the DCP input which will give the most flexabilty.

Elevator input selected as the source:
The gain is set by the internal gain setting in this dialog.
Note that the gain is bipolar which allows the DCP function to work the same or opposite as the elevator.
The DCP function uses the raw elevator input without the elevator input gain applied so the two functions
operate independently.

CH5 input selected as the source:
The gain source selection and internal gain setting are done in dialog "18 DCP Channel Input Gain (CH5)"
When CH5 is the DCP source, its more flexible since CH5 can be a slave mix off the elevator channel with the
mixing done in the transmitter (Tx) which allows the mixing gain to be easily set in Tx and the DCP input gain set internally.
Another approach is to use an external gain source, PT1..PT4 or the X input to set the DCP input gain.

Note: One or more input gains can be set to the same external gain source.
For this software, all five external gains have a positive range of 0..100 percent.
The internal gain settings can only be set via USB with Tech-Link.

Front Swashplate Servo Layout (3-point)

Modify Settings - 11

Functions:

Selects position of the E servo

The front swashplate layout can have two possible configurations where the E servo is in the front or in the rear.
This setting only applies to the 3-point swashplate selection in dialog "19 CCPM Mixing Type".

Rear Swashplate Servo Layout (3-point)

Modify Settings - 12

Functions:

Selects position of the E servo

The rear swashplate layout can have two possible configurations where the E servo is in the front or in the rear.
This setting only applies to the 3-point swashplate selection in dialog "19 CCPM Mixing Type".

Collective Pitch Layout

Modify Settings - 13

Functions:

Select CP swashplate movment

This setting specifies the direction which the front/rear swashplates movement (up/down) changes the collective pitch
to increase or decrease. Both swashplates must move the same way.

Aileron Channel Input Gain

Modify Settings - 14

Functions:

Adjust internal gain 0..100 percent
Select gain source

The input gain source can be selected as internal or to one of the external sources - PT1..PT4 or the X input.
The internal setting is only active when the source is set to internal.
Internal gain settings can only be set via USB with Tech-Link.

Note: One or more input gains can be set to the same external gain source (shared).
It is your choice on how to assign them. Write down your settings for use when away from the PC.
For this software, all five external gains have a positive range of 0..100 percent.

Elevator Channel Input Gain

Modify Settings - 15

Functions:

Adjust internal gain 0..100 percent
Select gain source

Rudder Channel Input Gain

Modify Settings - 16

Functions:

Adjust internal gain 0..100 percent
Select gain source

Pitch Channel Input Gain

Modify Settings - 17

Functions:

Adjust internal gain 0..100 percent
Select gain source

DCP Channel Input Gain (CH5)

Modify Settings - 18

Functions:

Adjust internal gain 0..100 percent
Select gain source

CCPM Mixing Type

Modify Settings - 19

Functions:

Select 3-Point (120 degree)
Select 4-Point (90 degree)

This software supports 2, 3 and 4 point CCPM mixing. For 3 or 4 point mixing just select your choice from the menu.
For 2 -point, which has no elevator control, It can be done by two methods.

3 servo method - Select 3- point mixing and set the elevator channel input gain (menu 15) to zero.
2 servo method - Select 4- point mixing and just use the A and P servos.

Yaw Compensation

Modify Settings - 20

Functions:

Enable/Disable
Adjust gain -50..50 percent

This feature provides mixing between the elevator (master) and rudder function.
It is only useful when elevator is selected as the input to the DCP function, see dialog 10 DCP Input Source/Gain.
It provides a proportional offset to yaw to help compensate for the torque imbalance caused when DCP is applied.
Note that the gain is bipolar which allows the yaw function to work the same or opposite as the elevator.

In a tandem, the control power in the yaw axis is weaker and responds much slower than in a standard heli with a tail rotor.
DCP creates torque changes which results in yaw changes too quick for the gyro and two rotor disks to keep up with.
Yaw compensation is applied at the same time the DCP is changed thus almost canceling any yaw before it happens.
Think of it as pro-action instead of reaction. A gain setting around 20 to 30 percent is what should be needed.
Notice the gain can be adjusted by +/- 50 percent, the +/- is to accommodate different main rotor rotations (CW or CCW).
For a CW rotating front rotor, a forward stick input will reduce front rotor pitch, increase rear rotor pitch thus creating a CW torque moment.
To correct, left yaw should be applied. So, setup the yaw compensation to apply left yaw when forward stick is commanded.

Yaw Channel Digital Filter

Modify Settings - 21

Functions:

Filter settings 0= off, 1= low, 2= medium, 4= high

This feature helps to reduce noise on the rudder input. Averaging is done with previous samples to produce
a low pass filter function. The response of the rudder servo will slow down noticably as a side effect with
the higher settings. In most cases, it won't effect the flight performance since yaw is very docile in tandem helicopters.
Start at the low setting first and proceed carefully since the gyro function will be dampened (less responsive).

Tx Frame Sync Mask

Modify Settings - 22

Functions:

Tx Frame Sync Mask 1..31 (16 default)

This setting tells the TH-2 when the Tx frame is completed and to begin processing the input data.
Choose the mask value that has all of the inputs that you are using.
This setting is intended for newer FBL units that output servo data simultaneously rather than sequentially.

If your setup uses sequential outputs (PPM) you should use the default value of 16 which triggers off of the pitch channel.

Mask Value	Inputs
	Aileron	Elevator	Rudder	Channel 5	Pitch
1	*
2		*
3	*	*
4			*
5	*		*
6		*	*
7	*	*	*
8				*
9	*			*
10		*		*
11	*	*		*
12			*	*
13	*		*	*
14		*	*	*
15	*	*	*	*
16					*
17	*				*
18		*			*
19	*	*			*
20			*		*
21	*		*		*
22		*	*		*
23	*	*	*		*
24				*	*
25	*			*	*
26		*		*	*
27	*	*		*	*
28			*	*	*
29	*		*	*	*
30		*	*	*	*
31	*	*	*	*	*

Tandem Control Software General Information

The TH-2 synchronizes with the pitch channel (CH-6 on most radios) and expects it to be the last pulse
(that it "sees") in the data frame sent by the transmitter. Also, A gyro should not be used on this channel.
When setting up the DCP it helps to turn off the elevator cyclic component to visualize it better. This can
be done by temporarily setting the gain to zero (0) in the Tech Link modify settings menu 13.
When an input gain is set to 100% the pulse data from the TX is used as is and mixed. At 50%, the pulse
data from the TX is cut in half and then mixed and so on. Reducing the gain in the TH-2 when needed,
like for DCP, is better than doing it in the TX (ATV setting) since this would reduce the overall dynamic range.
The gain settings also allow you to balance the amount of servo travel from the contributing channels and
prevents clamping. The TH-2 is set to clamp at 0.90 ms min. and 2.10 ms max. to prevent servo damage
in the event of interference.

Tandem Control Software Flight Controls

The TH-2 XPR provides four basic flight controls - Yaw, Pitch, Roll and Vertical ascent/decent.
These controls map to the familiar transmitter joysticks layout (mode 2).

Yaw - Left transmitter joystick LEFT/RIGHT.

Vertical ascent/decent - Left transmitter joystick UP/DOWN.

Roll - Right transmitter joystick LEFT/RIGHT.

Pitch - Right transmitter joystick UP/DOWN.

Yaw Control

The TH-2 performs yaw control by tilting the front and rear swashplates differentially along the roll axis.

Roll Control

The TH-2 performs roll control by tilting the front and rear swashplates along the roll axis.

Vertical Ascent/Decent Control

The TH-2 performs Vertical ascent/decent control by increasing/decreasing the front and rear rotor pitch collectively (each the same).
This is known as collective pitch.

Pitch Control

The TH-2 performs performs Pitch control by increasing/decreasing the front and rear rotor pitch differentially.
This is known a Differential Collective Pitch (DCP).
It also blends in for/aft cyclic with the ratio determined by the gain settings.