Tail Boom Co-axial Brushless motor Prop Drives - A different Angle.

We are designing a new Fixed Wing plane, all composite again, but this time with no landing gear, using a single peg bungy launch, with a parachute recovery. As w are fitting this Gimbal to this plane, we want the nose clear of motors and props. I wish to use a tail boom mounted co-axial prop, but do not approve of the possible options around - noisy and short lived gears, or Gimler belt and toothed gears, etc.All a bit complex, and awkward to locate and then house in the fuselage.

The very Nice Gimbal - Day and Thermal IR Night cameras, 640x480 Pixels. Fully Gyro Stablised. Serial port to drive and control.

So, I decided to modify a few Brushless motors and make then truly co-axial, with integrated folding prop mount, really beefy bearings, and a nice through hole for tail servo leads and lighting.

I used two HACKER Motors, A40 series, 50amp constant, one of 410kv to spind a 17x15 prop, and one of 610kv to spin a 16x8 prop, and an AXI 4120 series, also 50 amp, of 465kv for a 17x13 prop. Flight test will show which of these is best for our application.

How did I do it? Well, pictures are the best, but essentially I cut of the outrunner bell ends, machine out the inner Aluminium ball race holder, and ream out the hole to 10mm. Then I make a new bell housing, with double beefy bearings at one end, and a folding prop holder. All bonded together with locktite.  

The end results with regard to weights -

The weights are done using a standard motor, fitted with prop holder, fuselage mounting, etc, and then compared to the final weight of a modified motor.

Motor                              Standard weight             Modified weight

AXI-4120-20 465kv                  345g                            342g

Hacker A40-12S-V2-610kv      240g                             243g

Hacker A40-12S-V2-410kv      317g                             310g

As seen, there is no penalty in weight for this mod, even with a 110mm long 10mm diameter stainless steel tube through the motor centers...Through this tube is passed all the wiring for fuse to tail connections. The tube is then fitted to a holder on the fuselage, and the tubular tail boom ( actually an ALIGN 'copter tail boom - 20mm diameter) fits on the other end of the motor shaft, with a small aluminium bushing ( 4grams...)

The pictures:


The Nampilot.....

Views: 2159

Comment by Vladimir "Lazy" Khudyakov on March 23, 2016 at 1:20pm


Comment by Andreas Habit on March 23, 2016 at 1:40pm

Love the Gimbal.!

and nice work on the motor, good thing to see the coaxial Motor setup done right.

Comment by Paul Meier on March 23, 2016 at 1:46pm

Eagerly waiting for pics of the plane.....

Amazing work....

Comment by MarioSpeedwagon on March 23, 2016 at 1:49pm

Gorgeous work. Looking forward to seeing more of it. 

Comment by Rob_Lefebvre on March 23, 2016 at 6:29pm

Nice looking gimbal, is that your development too?

Comment by JB on March 23, 2016 at 9:12pm

Awesome! When can we buy? ;-)

Comment by Vladimir "Lazy" Khudyakov on March 24, 2016 at 11:37am

Joe, tell me please - why coaxial? :)))

Comment by Paul Meier on March 24, 2016 at 11:50am

@Vladimir: was asking myself the same question, was thinking that maybe he will use two motors on the tailboom, but does not make really sense to me. Lets hope the Master himself will explain (getting late in Namibia doh) ;)

Comment by Vladimir "Lazy" Khudyakov on March 24, 2016 at 11:56am


Reduce prop size? Why not use a multiblade? :))))

Comment by Gisela & Joe Noci on March 24, 2016 at 12:03pm

Why coaxial? Simple really - I want the front free for the payload.  I would therefore prefer a pusher prop type installation, and as I am not partial to flying wing type structures, a non-coaxial implementation would require a raised motor/prop structure, to clear the tailboom or nose, or a twin tailboom with prop between. I find neither of these weight efficient nor aerodynamically sound, especially since I want to use large diameter props, typically from 17inch, up to 22inch. The tailboom tube simply clips onto the motor extension hollow tube, and is easily unclipped  removing the whole tail for transport. 

Late?? In Namibia??? 02H30 in the morning is maybe a little late...

The Nampilot...


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