Tech Model Products TH-2 Tandem 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	6, Aileron, Elevator, Rudder, Pitch, CH5 (DCP) with 0 to 100% range; Elevator as DCP source +/- 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

Tandem Control Software Functional Block Diagram (500 KB)

Tandem Control Software Flight Controls

The TH-2 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.

Radio Settings

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

In general, start off with the servo travel (ATV, 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. Initially, all other mixing functions should be turned off.

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

Software Control Constants

The TH-2 Tandem Control Software uses control constants as programmable parameters to allow customization
for many different applications and model types. These control constants can be modified, loaded, saved and shared
with other users using our Tech Link Software. Below the details of each control constant are listed:

Servo Reversing

Modify Constants - 1

Functions:

Set servo direction normal/reverse

This is used to set the direction on all 8 of the servo outputs.

Servo Centering

Modify Constants - 2..9

Functions:

Set servo centering position -12.5..12.5 percent

This is used to set the centering (servo neutral position) on the servo outputs.
It provides a range of +/- 12.5 percent which is more than half way on most splined servo output shafts.

DCP Input Source/Gain

Modify Constants - 10

Functions:

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

This is used to select which input is used for DCP. CH5 or elevator.
The input gain is adjustable from -100 to + 100, only when the elevator is selected as the input.

Use menu 18 to set the input gain when CH5 is selected.

Front Swashplate Servo Layout (3-point)

Modify Constants - 11

Functions:

Selects position of the E servo

This is used to select the position for the front swashplate E servo (facing front or rear).
This setting is only used if the CCPM type is set to 3-point.

Rear Swashplate Servo Layout (3-point)

Modify Constants - 12

Functions:

Selects position of the E servo

This is used to select the position for the rear swashplate E servo (facing front or rear).
This setting is only used if the CCPM type is set to 3-point.

Collective Pitch Layout

Modify Constants - 13

Functions:

Select CP swashplate movment

This is used to select whether the CP increases by moving the swashplates up or visa versa.

Aileron Channel Input Gain

Modify Constants - 14

Functions:

Adjust gain 0..100 percent

This is used to set the gain for the aileron channel input.

Elevator Channel Input Gain

Modify Constants - 15

Functions:

Adjust gain 0..100 percent

This is used to set the gain for the elevator channel input.

Rudder Channel Input Gain

Modify Constants - 16

Functions:

Adjust gain 0..100 percent

This is used to set the gain for the rudder channel input.

Pitch Channel Input Gain

Modify Constants - 17

Functions:

Adjust gain 0..100 percent

This is used to set the gain for the pitch channel input.

DCP Channel Input Gain (CH5)

Modify Constants - 18

Functions:

Adjust gain 0..100 percent

This is used to set the gain for the DCP input only when CH5 is selected as the input.

CCPM Mixing Type

Modify Constants - 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 Constants - 20

Functions:

Enable/Disable
Adjust gain -50..50 percent

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 (New in Version 2B005)

Modify Constants - 21

Functions:

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

This filter (low pass) is useful if your gyro is picking up noise from vibration. Start at the low setting first and proceed carefully since the gyro function
will be dampened (less responsive).

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.
It wouldn't make sense anyhow.
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 constants 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.