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Modified Twinn Rexx with rear-mounted motor

Posted 07-04-2012 at 07:59 PM by jolyboy
Updated 07-04-2012 at 08:22 PM by jolyboy (Add photos)

This blog is to keep track of my progress on the Twinn Rexx build I undertook a few months ago. There have been many issues from the lack of the availability of parts, so I have modified the design as a work-around. The only part sourced from Tech-MP is the TH-2 tandem controller, since all other parts are no longer available.

So far, the chassis has been the most challenging part of the build, but luckily I have access to laser cutting and water-jet cutting for free. I have cut two versions of the chassis - the original style of design, and a modified version.

The original-style design was reverse-engineered using CAD and measurements taken from a Trex clone (servo positions), and dimensions of the parts that would be used (ie main shaft bearings and miter gears).

When I realised that I could not source the front main shaft and motor mount from Tech-MP, I decided I could modify the design to negate the need for custom front main shaft, and utilise the original Trex 450 motor mount. The new design drives the transverse shaft, rather than the front main shaft. By mounting the motor on the rear of the heli, I was also able to mount the motor on the centreline.

For the sake of Tech-MP's copyright I will not share CAD files, but I will post photos of my design.

Here is my parts list so far:

Store Amount Description
sdp-si $40.52 5mm x 1000mm drill rod
sdp-si $56.55 4 x Miter gears, 8 xbore reducers
HKing $19.23 4 x 325mm Fiber Glass Main Blades
Ebay $3.70 XT60 Male Female Plug Connector + Red Black Heat Shrink
Ebay $2.99 Micro Screw Pitch Gauge Blades Adjuster for T-Rex 450
Ebay $6.40 RC JR/HITEC SERVO PLUGS Gold Plated x 10 Pairs
Ebay $3.10 1000mm servo wire
Ebay $42.76 6 x Hitec HS-65HB Gear Set ~HRC55013
Ebay $25.25 Hitec HS-65HB Karbonite Micro Servo
Ebay $9.56 2 x F-H45094 Frame Hardware for TREX T-rex 450 Sport align
Ebay $10.38 2 x Frame Hardware For T-Rex Trex 450 Helicopter RHS1122-SL
Ebay $5.95 Nylon Insert Lock Nuts x 20
Ebay $5.85 2x Main shaft bearings
Ebay $7.40 Flybar Rod/190mm HS1006
H King $114.09 ESC, LiPo Battery, Charger
JGF $87.50 JGF 500T Brushless Motor
Ebay $11.98 4x Main shaft bearings
Ebay $11.95 4x Main Blades
Ebay $69.23 3xHiTec HS-65
Ebay $69.23 3xHiTec HS-65
Jaycar $39.90 Copper Clad board, 300 x 300 x 1.6mm, x2
Miter 10 $24.00 Aluminium square tube, 19.5 x 19.5 x 3000mm
Ebay $33.98 2x GY48V Gyros
Ebay $247.47 Spektrum 2.4GHz DX6i
Tech-MP $163.44 TH-2
Ebay $95.98 2x ARF 450V2 Metal

TOTAL AU$1,217.38
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