Helitronix > Multi-Mixer Special Edition	Printable Version

HMIX01  Helitronix Multi-Mixer SE for Multi, Tandem & Coaxial Models  $225.00 

Designed for: multi-blade & flybar-less rotor heads, dual rotor tandem & coaxial models.

The complete Multi-Mixer Instruction Manual.

The standard and special edition mixers are same physical size, are based on the same hardware footprint but differ slightly in components and contain different versions of the software. Specifically, the special edition includes the Tandem and Coaxial software in addition to the Multi-Blade software. The Mixer Mode setting is the very first item set during programming as all other settings are based from this mode. The common mode of operation is to choose the rotor head (R1/R2), then scroll to the setting that needs to be changed. While most Tandems use the same swashplate control system for the front and the rear, the Multi-Mixer SE allows any two swashplate modes to be used together.

New Features:

General Features:

The Multi-Mixer Special Edition is designed for a single or dual rotor helicopters. Single rotor helicopters will use: (S1R1 - roll (aileron), S2R1 - pitch (elevator) & S3R1 - collective pitch). Tandem and Coaxial helicopters will use R1 and R2 servo connections including: S4 - yaw (rudder).

Tandem and Coaxial are not new in model helicopters but in recent years, the technological advances in electric motors and electronic control systems has made these traditionally very complicated models much simpler to manufacture and fly. Mechanically mixed tandem models have been available from almost the beginning, but it is has been the mixing and the power plant that has given modelers the most problems. The mechanical mixing works but lacks significant adjustability. The Multi-Mixer SE now provides those same modelers the chance to break away from mechanical mixing forever and be able to fly their tandem models with confidence.

Tandem Flight Control
Tandem model helicopters obviously do not have a tail rotor and rely completely on the front and rear rotor heads for all flight control. The servos that drive the front and rear swashplates are connected to the Multi-Mixer SE and the mixer does all of the complicated mixing to control the model. Aileron is the simplest to understand as both rotor heads tilt in the same direction to move the model left or right. Collective is also simple and adds the same increase or decrease to both front and rear rotor heads at the same time to change the model's altitude. To purely rotate the model, say to the left, in terms of a yaw or rudder command, the front rotor head tilts left while the rear rotor head tilts right. Elevator is the difficult one.

DCP - Differential Collective Pitch (Tandem)
To fly forward, tilting both swashplates forward is not enough and as it turns out, is much better suited for trimming the rotor head instead of actively using it in forward flight. Through extensive prototype testing, using only DCP mixing the tandem model becomes very predicable and smooth in response. As pitch (elevator) is added the front rotor head reduces collective pitch while the rear rotor head increases collective pitch. The DCP Ratio is the percentage amount of collective pitch that is uniformly introduced to both rotor heads proportional to the amount of elevator input. Generally we start at a low ratio, and gradually add more until the model transitions into forward flight smoothly. Too much will make the model too sensitive and difficult to fly.

Elevator Ratio (Tandem)
The Multi-Mixer SE was designed to give modelers complete control over the flight system. When the Elevator Ratio is set to zero, there is no fore-aft tilt of the swashplates when the pitch (elevator) is moved. This give the modeler the chance to fly the model in pure DCP mode. However, the modeler can now experiment with limited Elevator Ratios to further trim the tandem model. Consider the condition when you are in forward flight, and you start adding back elevator to slow down and transition back into a hover. Using DCP only, the front rotor will increase pitch while reducing pitch in the rear rotor. The net effect pitches the nose up and you need to be aware of stalling the trailing rotor head. What can be useful is to be able to feed in a percentage amount of elevator to gradually slow the model without causing it to excessively pitch (rotate) fore-aft. The Elevator Ratio provides this adjustment.

Elevator, Aileron & Yaw Gyros (Tandem)
Tandem models suffer from the same stability problems in forward flight as a multi-blade single rotor head models and the complex elevator control system only adds to the instability. It is highly recommended to use an elevator and a rudder gyro to stabilize these two axis. The gyro gains will be similarly small as compared to a sport model with a standard tail rotor system. Only 5-15% gain is required on the elevator and 25-45% is needed on the rudder to dramatically improve the models stability.

Elevator ⇒ Rudder Free Program Mix (Tandem)
The last item that needs attention in a tandem model is a free program mix to eliminate a natural tendency of the model to roll as an elevator input is applied. While this is not part of the Multi-Mixer SE's functionality, it is worth mentioning. Set the Elevator as master at 100% and the rudder as the slave at 25-50% and make sure you have the sense direction correct for your model.

Coaxial Flight Control
The control system for coaxial models is much simpler to understand but will use still the DCP Ratio for controlling the yaw of the model. Roll (aileron) tilts both swashplates left and right according to the aileron input. Pitch (elevator) similarly tilts both swashplates fore and aft according to the elevator input. Collective adds the same increase or decrease to both swashplates at the same time to change the model's altitude.

DCP - Differential Collective Pitch (Coaxial)
To yaw (rotate) the model, the collective pitch on one rotor head increases while the other rotor head decreases. This creates a torque inbalance which rotates the model. The DCP Ratio percentage value controls how rapidly the model rotates by increasing the difference in pitch between the rotor heads as the rudder is applied.

Similarly, gyros can be added to coaxial models but generally are only needed for the rudder, but an elevator gyro will provide the same assistance when in forward flight.