EC135 Scratch Build

Here is a build thread on the T3 EC135 heli!



My next build project is an EC135, one of the prettiest helis in my eyes with its flowing lines and smooth curves. I've chosen the T3 variant as it loses the vertical end plates on the horizontal stabiliser and the lower bit of the vertical tail below the fenestron duct, so hopefully the tail section is a bit lighter on this version despite the horizontal stab being a bit wider.

Because I wasn't satisfied with the transparency of the windows of my Jet Ranger build, I decided to try to print the windows and the fuselage separately. This has the advantage of being able to use different materials for fuse and windows, and allows for optimising the slicing of each window. The downside is that this means more design work and a more complex build process. I've also tried to introduce a few more details into the printed parts such as ducts, vents and rails.

The design work was done in Fusion 360 and is largely complete at this stage unless I discover something else during the build that needs to be modified. I was talked into doing a 1:18 scale by fassla, who also suggested which motors to use for the main and tail rotors. The main rotor is a direct drive arrangement, and I am using the 4 blade rotor head that Microheli makes for the Blade 230s. I'm using the main shaft, swash and servos from the OMP M2, and the Heliflight3D flight controller.

Here are a few screen shots from Fusion 360, with posts to follow as I start assembling the printed parts.

Last edited by Jim T. Graham; Mar 01, 2021 at 02:19 PM..
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Feb 22, 2021, 05:36 PM
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g monkey's Avatar
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EC135 Scratch Build - 2

Most of the parts have been printed using a PC blend, Polymaker Polymax, which is similar to Prusa's PC Blend and is easier to print than a pure polycarbonate. This filament has some very good mechanical properties: it is stronger, tougher, and has a higher glass transition temperature than either PLA or PETG. It also prints very well.

The fuselage front, mid and rear, tail boom are all modelled as shells, and were printed using a 0.6mm nozzle.
The vertical tail, horizontal stab, landing gear, motor and FC mounts are modelled as solids, so the perimeters and infill must be set to appropriate values in the slicer. Most of these were printed with a 0.4mm nozzle, as well as the Fenestron fan.

Some of the other components:
Tail motor: BetaFPV 1404 3800kV
Main motor: T-Motor 4006 380kV
Rotor head: Microheli 4 blade head for Blade 230s
Swash: modified OMP M2.
The OMP swash is smaller than the Microheli swash that comes with the 4 blade head. This was used because it just fits within the doghouse, and it also uses a slightly beefier main bearing. I designed and printed a new centre piece that holds the four Microheli ball joints, and then the Microheli head links are used from the swash to the rotor head. A 0.25mm nozzle was used for this bit as it quite a small piece.
The main shaft, collar, servo linkage rods, servos all come from an OMP M2. The servos were arranged at 120 degree intervals around the main shaft with a geometry such that the swash and servo arm movement is in the same plane and nearly parallel.
Feb 24, 2021, 01:04 AM
slideways at warp speed
kiwi_craig's Avatar
Looking great. So loosely based on the blade 230 or OMPM2
Feb 24, 2021, 07:08 AM
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g monkey's Avatar
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In a way, as some of the OMP M2 parts are used and it uses direct drive for the main rotor. She is a bit larger (and fair bit heavier, but we whisper that) than the M2.
Feb 26, 2021, 03:48 PM
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fassla's Avatar
Looks great - looking forward to see the bird flying ;-)

Did you succeed to test current setup on a trainer heli already?
Setup is great - just going to print latest version of tail rotor for a flight test series on my trainer.
I will do testing with same motors, same rotorhead, but Spektrum 2070 Servos and 3 different FBL: uBrain / uSpirit / AR6335
Mar 06, 2021, 02:40 PM
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M2 test bed

In my efforts to see if I could build it, I had neglected to give some thought to the question 'will it fly'! Of course, fassla is right - a test bed makes sense to see if these components will work together, or indeed at all.

I knocked up a test shroud/stator that could be bolted to the M2, lopped off the tail motor and set about installing the BetaFPV tail motor and Microheli 4 blade head to my hapless M2. I had already installed a Heliflight3d flight controller, so the only component that is different to what will be on the EC135 is the main motor, which is the original M2 item.

At this point it dawned on me that the intended heli for the 4 blade head, the Blade 230s, must be set up differently to the M2, whereby the link from the blade grip is attached to an arm coming off the trailing edge of the blade. This means that the collective pitch would decrease as the swash moves up, the opposite to the M2. I didn't really like the MH supplied head links anyway as they were printed in white PETG and were a very tight fit on the swash ball joints - and they were not symmetrical so could not be flipped over. I decided to design and print my own in black PC that would be slightly longer, and would allow me to flip the blade grips over so that the arm is on the leading edge of the blade, as per the M2.

The other thing that I noticed is that the MH blade grip arm is much shorter than on the M2 blade grip, so this results in pitch changes that are 50% greater for a given swash movement. This requires changing throws so that the same collective range and roll/pitch changes of an M2 set up are attained. I did this in the FC.

I got it all set up late in the day, so a quick hover in the garage has been all I could do so far, but she flies! The power consumption was rather high, and I got a 'low voltage' alarm after only a couple of minutes (usually I get a power/mah alarm and no voltage alarm around 6-7 minutes), but the motor is being asked to swing 4 blades that are 20% longer than stock. The main motor wasn't hot, and neither was the esc. I could not reach the tail motor inside the shroud. I should probably reduce the rpm somewhat before the next outing. She makes an interesting noise . . .
Last edited by g monkey; Mar 06, 2021 at 02:48 PM.
Mar 07, 2021, 07:32 AM
3d and EDF, some scale
MustangAce17's Avatar
This is really cool, looking forward to seeing it flying around
Mar 07, 2021, 10:50 AM
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I tried dropping the head speed to 3,000 rpm and that improved the power consumption, so I got a 3:45 flight time in before my power alarm went off (this with the stock M2 battery). The main motor and battery were a little warm but not hot at all. Not bad considering what it is swinging.

The fenestron seems to work ok and it makes a cool whistle as it winds up. It was only a hover in the garage but the tail response seems snappy enough when clicking hard right or left by 90 degrees. I put the battery as far forward as I could and taped some coins to it but it is still a bit tail heavy, so I'm sure she will handle better once properly balanced. The 135 tail boom is nearly 20% longer so that will help too, although the all up weight will increase quite a bit.
Last edited by g monkey; Mar 07, 2021 at 11:52 AM.
Mar 08, 2021, 11:32 AM
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Cyclone 7's Avatar
Very nice g monkey - great job all round!
Mar 12, 2021, 01:02 PM
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g monkey's Avatar
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Thanks. Although this is still a work in progress, if anyone wants to try printing one out they can find all of the STL files available on the link below. I'll update them if any changes are made.
Mar 12, 2021, 04:07 PM
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fassla's Avatar
I tried similar setup and I did some "low-RPM" test. Starting 2250 you can easily fly scale - no 3D ;-)
starting 2400 you have sufficent reserves. pending on weigth you can ad some 50-100 but not more needed.
Same Rotorhead, OXY2 - 210mm blades - but different tail rotor design.
Flight time with 650mAh battery close to 10min.
Mar 12, 2021, 04:20 PM
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g monkey's Avatar
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Wow, good stuff. That is very low - I'll try dropping it lower. Was this with the M2 or T-Motor main motor?
Mar 13, 2021, 06:48 AM
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fassla's Avatar
Used T-Motor which is my favorite ;-) even after 15min flight you cannot spot any warming/heat spots inside the motor.
Anyhow on direct drive the difference is in the ESC, meaning throttle value.
With M2 motor you open approx 50% vs 65% throttle when using the t-motor. ESC is more efficient when >55% open
Mar 13, 2021, 10:53 PM
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chickenhawk's Avatar
'looks like an awesome project g monkey.
Apr 25, 2021, 05:24 PM
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After a bit of time away the project is progressing again. I decided to go with a simple monochrome paint scheme, but unfortunately the aluminium colour is quite revealing of surface imperfections. At least it should be easy to see in the air. Next task is drawing panel lines, and painting vents, latches, exhaust stacks, etc. I'm also working on the windows. Printing with PVB is looking promising, although the layer lines are visible so I'm still refining the technique.

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