Twinn Rexx

    Last updated on: 11-20-17

 Twinn Rexx will return in 2017 (skip to bottom for more details)


   Twinn Rexx Tandem development page  - From the beginning to today   

Summer 2006, the Twinn Rexx is a mini tandem helicopter designed to use the very popular T-Rex rotor heads and drive components. 
The goal is to make it fly with the most 3D capability as possible that is inherent with the tandem configuration.
Flight tests are under way and we will soon see what the true capabilities of this machine will be...  Stay tuned...

Also, the model is designed to give a sport scale CH47 Chinook appearance with special attention given to the accessibility
of the internal subsystems by way of a main hatch that operates like the the cargo doors on the US space shuttle.

Below is the CAD drawing and prototype pictures of the model.

Twinn Rexx CAD Drawing


Twinn Rexx 2006 Prototype Setup/Specs
Motor (initial) Align 430L (just for initial testing)  with 11T;  10 to 12 min flights with 3S 2100  
Motor (now) Medusa 028-040-2500 with 11T pinion; 8 to 9 min flights with 4S 2070 Updated 4-15-07
ESC Align 35A w/Tech Ferrite Ring Glitch Filter Updated 4-15-07
Battery TP 4S1P 2070 MAH  25C Updated 4-15-07
Servos 6 HS65HB  
Receiver Futaba R146ip Updated 4-15-07
Antenna Tech Micro Antenna  
Battery Monitor Tech LGG-1 Li-Poly Battery Monitor  
Yaw Axis Gyro Futaba GY240 (AVCS off)  
Pitch Axis Gyro Futaba GY240 (AVCS on) DCP Channel  
BEC 3.5amp Capacity at 5 Volts; Medusa MR-BEC-45035  
Controller Tech TH-2 (Tandem SW Version 2B005)  
Rotor heads Stock Align 450 XL TRex  
Main gear Stock Align 450 XL TRex  
Blades Tech 325mm High Performance Blades  
Rear Main Shaft Stock Align 450 XL TRex  
Bearings Tech High Performance Bearings  
Front Main Shaft Tech Model Products  
Driveshaft Tech 5mm Hollow Stainless Steel (Courtesy of Walt Ferar)  
Main frames 0.062 LASER cut G10     Walt Farrels LASER Cutting Service Updated 9-16-06
Shaft to Shaft Distance 20.25 inches  

Here are some pictures of the initial mockup/prototype.


  Walt Farrels LASER Cutting Service




Here are pictures of the flying prototype (click on the pic).



July 4th 2006 Update - First Flights

All things finally came together and we were able to get this bird in the air. A stock TRex 430LF motor was used since the motor of
choice is backordered 3+ weeks now.  Initial flight tests were smooth and rock solid as expected.  On the third flight, the AVCS
(Heading hold) was turned on for the pitch axis gyro and WOW !!!  what a difference.  Super stable.  The sound of the rotors wapping
the air is just awesome.  Flight testing will continue and the parameters will be tweaked to get maximum performance. This is the fun part :)

August 4th 2006 Update - Flight Testing Continues

This helicopter is a real pleasure to fly.  It is super stable and rock solid. 
We still have a stock TRex 430LF motor for now as we are trying solve a ground resonance problem More info

The two gyros are picking up vibrations right near the lift-off RPM which causes the problem to get worse.
Once airborne everything is smooth.

The weather here has been either raining, windy or to hot to fly so testing took a back seat for a while. 
This next month should be more productive.

September 16th 2006 Update - Flight Testing Continues

I recently re-designed the main frame with new sides. I beefed them up and changed to a thicker material (0.062).
The frame is very solid now. The lighter frame allowed for flexing which was causing a resonance problem.

A new problem developed though. There was a small vibration that was being picked up by the yaw gyro.
This in turn caused havoc on the main rotors which amplified the effects.  The vibration amplitude increased with rpm
which suggested it was coming from the rotor(s).

I ordered a sensitive accelerometer sensor (+/- 1.5G) that I mounted to the frame.  It allowed me to measure the vibration amplitude and frequency
(with an oscilloscope).  I used it as a guide to find the vibration source.  I simply began removing rotor components until I had the culprit red handed.

It turned out to be the front rotor flybar which was slightly off center.  I had rebuilt the front rotor head when changing the frame sides.
I did this late at night when apparently too tired.  A minor thing like this can be a source of much larger problems.

The heli now flies like a dream and is rock solid.  It is hard to describe how realistic it is and the sound the rotors make especially from
the area where they overlap.  It has that characteristic "wapping" sound the full scale birds make. 

I am still using the stock Align 3550KV motor with a 3S 2100 battery.  Flights are about 8 or 9 minutes with gentile flying.
We have an AON 4S motor on order and are waiting for it to come in.  It can handle 400 to 500 watts which should really get this bird moving.

Here are the latest pictures with the new frame (click on the pic).


October 23rd Update 2006 - Flight Testing Continues

The weather has been either windy or raining lately.  We are now looking at kits becoming available late spring or early summer 2007. 
There will be a number of choices:  Partial kits to full kits in both metal and plastic versions.
The final power system is still under development (weather permitting) but will most likely use a 4S battery and motors from AON or Medusa.
The design of the Twinn Rexx frame and mechanicals are pretty much finalized and tested.
The CH47 body mold construction is underway.

Here is the latest video.  Note: It has been moved to a different server.  Update your links.


January  3rd Update 2007 - Flight Testing Continues

We now have 3 test pilots flying and testing the Twinn Rexx. 

The 4S power system is much more powerful than the previous 3S motor. 
I had to add a second drive shaft support since it was flexing too much and I believe it was responsible for some torsional resonance problems.
We recently received the new laser cut parts to begin testing.  See the pics below

A new version of TH-2 software is being tested as well.  It now has a digital filter on the rudder channel that filters out high frequency vibration induced noise
from the gyro.  The filter has 4 settings - off, low, medium and high.

Looks like summer 2007 for a release. No exact date yet. Base kits without the rotor heads will run $250 to $275 (estimated).
Plastic rotor heads will run around $175 and metal heads around $300.
No electronics/electrics included.


Latest CAD Drawing



Twinn Rexx  Surgery



New Drive Shaft Dual Supports



April 4th Update 2007 - Flight Testing Continues

We now have 6 test pilots flying and testing the Twinn Rexx. 

The motor mounts have entered production.  They will be stamped (CNC punch) from 0.074" stainless steel plate.

The users/assembly manual has been started and gets attention as time permits.   Not much has been done on it lately.

The CH47 body plugs are in the process of being machined (CNC).  This will produce two plugs (left and right) which will be used to make a set of
master rubber molds (female).  The master molds will be used to make the production molds from an aluminum filled epoxy.  We will try to get
some pictures of this process.


June 8th Update 2007 - Flight Testing Continues

The motor mounts are completed.  They were laser cut from 0.074" stainless steel plate and formed in a brake.  A great job done by
the Milford Fabricating Company



The CH47 body plugs are completed.  The engine plugs are in the works and are expected to be ready in a few weeks. 
The next step is to drop the plugs off at our local vacuum forming shop to get some test bodies made.  The goal is to
find the right material and thickness which provides the lightest weight and best strength.

Here are the latest pictures of the body plugs (click on the pic).

The body and engine plugs were fabricated by master model builder Butch Sickels at RS Models.


There are a number of interesting Twinn Rexx threads on various forums listed below:

Twinn Rexx pics from IRAQ Pre-production Twinn-Rexx build pictures


August  25th 2007 Update - Flight Testing Continues

We currently don't have a release date.  We expect it to be later this year.

We finally got the test bodies delivered.  They came out great and the plugs won't need any modifications.
The mounting system for the body to frame is still in the design process.  So far, it looks like it will be light and simple..

The engines are on hold right now (Butch had to stop work on them) and will be offered later as a separate kit.

The servos will need to be mounted differently than shown in the pics so far.  Most will need to be mounted so the flange
is on the inside of the frame sides.  The rear "E" servo has been relocated into the body cavity.  The rear tower just doesn't
have enough clearance.  The existing mounting hole is still provided and can be used without the body.

Trimming the body from the molded sheet was easy with a #16 blade.  The wide blade allows you to use the body as a guide.

Here are the latest pictures of the body  (click on the pic).


Note: The body is only taped on and is not in the exact scale position yet.


November  4th 2007 Update - Kits will be rolling out this month   Updated 3-23-08

Twinn Rexx kits will begin rolling out later this month.  Those on our waiting list will be contacted first. 
It may take a while before all of these commitments are satisfied.  We will do our best.

CH47 body kits are now in stock CH47 Body

The Twinn Rexx support page is up and running.  New info is being added regularly.  Twinn Rexx support page

The Twinn Rexx parts page is up and running. Twinn Rexx parts page

Huge amount of info on the latest Twinn Rexx Builds etc.  HeliFreak Tandem Forum




April  4th 2008 Update - Kits have be rolling out   

Twinn Rexx kits have been rolling out and more are taking to the sky each week.

There are a number of great videos, build info etc. up on the Helifreak tandem forum

We are currently working on a 3-blade head for the Twinn Rexx.  It will be articulated with feathering spindles and dampers.
It has been designed using CAD and we are currently building a prototype to begin the testing phase.  There is no release date at this time.

The goal for the head design is to make it perform as best possible and to be affordable.  Also, it must be repairable/maintainable.
We are holding back on photos/drawings at this time due to our unique design.

We are also considering producing a CH46 tandem down the road.  The decision to do this depends mostly on economic factors.
If it's worthwhile then we will do it.



Dec  19th 2008 Update

No big news to report this time.  More motor trials are in the works

Reviews of the Twinn Rexx and TH-2 by RC-Heli magazine have been published recently.  These articles are available below.

Twinn Rexx RC-Heli Review

TH-2 RC-Heli Review                       (added 3-05-08)


Jan  2nd  2010 Update

No big news to report this time.  The economy has taken it's toll on sales. 

Currently all efforts towards 3-blade heads and the CH46 model have been suspended until things improve.


8+ Years Later....The Twinn Rexx Returns in 2017

May  29  2016 Update

Thank you all for your continued support and the emails asking "When will kits be available again".
After dozens or so of these emails I finally decided it's time to do a production run again in 2017.
There is no specific date yet (too early).  The project is now in the planning phase where decisions
are made that determine what design changes and features will be incorporated.

So far we are looking at:

  • Flybar-less rotor heads 2 and 3 blade
  • 500W-800W power options
  • Tandem controller - 6 axis gyro stabilization built in

At this point your suggestions are welcome.  Drop me an email.

October  29  2016 Update

  • Body kits are now back in stock.
  • Flight testing of the updated design should begin late 2016 into early 2017.
  • New CNC production fixtures/tooling are in the process of being designed and fabricated.

Your suggestions are welcome.  Drop me an email.




February 28  2017 Update

  • Body kits are now back in stock.
  • Flight testing of the updated design should begin this month as weather permits.
  • The model will support both 5mm and 6mm main shafts for compatibility with a wide variety of rotor components.
  • The TH-2 mixer and Tech-link software are getting updated as well.  Many new features, improvements and Win 7/10 compatible.
  • No hard release date yet but looking like sometime this summer....

Your questions/suggestions are welcome.  Drop me an email.  Joe


Click on the pic above to download - Latest CAD renderings


March 11  2017 Update

  • Weather here has been windy but progress is being made elsewhere.  Below is a rendering of the new "HD" (heavy duty) frame option.
    This option adds incredible stiffness and rigidity with only a small weight penalty.
  • Busy ordering parts, tools etc.


Click on the pic above to download - Latest CAD rendering


July 23  2017 Update

  • We will be offering base and HD kits sometime next month. 
  • The website has been getting updated, User manuals written etc. - All the "not so fun stuff" that needs to get done to support the products.
  • The new TH-2 XPR tandem controller is up and running with the new Tech-Link 2.0.  It will become available next month as well.


More to come.  Stay tuned....


August 11  2017 Update

  • Kits are now on sale !
  • New content has been added to the Twinn Rexx support page.  Check out the 3D models. 

Click on the pic !



November 20  2017 Update

  • The long awaited TH-2 XPR tandem controller will be for sale next week.
  • We have tested several 3-axis airplane gyros and found that the Hobby Eagle A3-L works well.
    This gyro is used for yaw (rate mode only) and optionally on aileron and elevator.
    A GY440 (GY240) type gyro is still needed for DCP and should use "Heading Hold" mode for best
  • The TH-2 XPR-G controller version which includes a built-in 3- axis gyro is in development and is currently targeting
    a release date in Q1 2018.

More to come.  Stay tuned....




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