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And now for something completely different

BEB Builds a Helicopter

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Biggles' Elder Brother - Moderator02/03/2018 17:44:01
14972 forum posts
1393 photos

It's cold, very cold. The "Beast from the East" is doing its worst. Its far too cold and windy to fly. It's too cold to build in my shed as, even with the heater on, I can't feel my fingers after 30mins! So what to do?

Now, some background. One of my cousin's grandchildren was bought a helicopter for Christmas. A generous gift - but completely inappropriate, the child is 5, has no experience of RC, neither do his parents, and the helicopter is a TRex 450L - not the hottest of helis, but too edgy for a child.

So, in a rush of blood to the head, "Uncle BEB" agreed to give the young man a generous donation for video games in return for the kit. And so, I acquired an unbuilt helicopter in kit form.

Now Mrs BEB has a strict "no aeroplanes in the house" rule, but she has taken pity on me in the circumstances of the extreme weather and said I can build this helicopter in the house - just this once!

This would all be fine except for one big thing - I've never built a helicopter in my life! I've built many aeroplanes (scratch, plan, kit and ARTF) I've even built a fair few multi-rotors from the ground up; but never a helicopter.

So, I'll have a go and record my progress here. The idea of this blog is that, far from being any sort of "exemplar" of how it should be done, its just going to record the learning curve of a aeromodeller trying to build their first heli! It will be warts and all, if I screw up and have to fix stuff I won't hide it. And if any of you experienced heli-builders out there spot me heading for "train crash" please shout out!

So, here we go,....... at least it's something different that might entertain while the weather is so bad! Pass the thread-lock!


David Mellor02/03/2018 17:51:30
487 forum posts
99 photos

A brave and bold decision....bravo! I'm sure you'll be just fine.


Denis Watkins02/03/2018 18:00:52
2489 forum posts
126 photos

If any part of the assembly is " ready built " BEB

Then double check this, as the bits you complete are usually fine

But " their bits " can come loose, as we assume those parts are ok

Biggles' Elder Brother - Moderator02/03/2018 18:10:21
14972 forum posts
1393 photos

Right then, here's the box with an exciting picture of a helicopter on the front!

1 trex.jpg

The kit is very comprehensive. As well as the frame etc., it includes: the servos, motor, ESC and GPro flybarless system. Basically build it and add a RX and battery and you're there.

The tool set needed is a bit different from balsa bashing, here's what I have assembled the tackle the build:

2 trex.jpg

Basically, lots of hex-drivers, screw-drivers, pliers, cutters, servo tester etc. I bought a couple of things specially; some grease (the white tube), a 1.3mm hex driver (apparently you need this - weird size!), a pitch gauge (that I'll need later) and the thing in the plastic bag is a swash-plate leveller.

The towel seems to be de rigor among heli builders going by the tutorial videos on YT. The idea is the build process is mainly small screws etc., drop one on a hard surface and its bounces onto the floor and you'll never see it again (haven't we all experienced that!) But drop a small screw on the towel and it stays there - well that's the theory anyway.

So, to start. We begin with this:

4 trex.jpg

It's the Head Rotor. As you can see it is assembled but we need to take it apart to firstly grease the two thrust bearings inside and then apply threadlock to all the screws. This was a bit of a challenge as a first task. The exploded view drawings in the manual are not very clear - and there are a lot of washers and spacers in there, not to mention 4 radial bearings and two thrust bearings.

5 trex.jpg

The picture just shows just a couple of the components around the thrust bearing. Its a doddle to take apart - it's getting back together all correctly that's the challenge.

So I made progress very slowly here, systematically laying the parts out as I dissembled it. Apply the grease then start the reassembly in reverse order - Phew!

Next up we need to fettle the pitch arms on the rotor head. We need to dissemble again, add the ball links to the turn-buckles, then reassemble with threadlocker.

6 trex.jpg

Remounted on the rotor head that looks like this:

7 trex.jpg

Why have I got a bit of string tied to one end? Well I can't get both end screws on the feathering shaft inside the unit off at the same time. So one of them is threadlocked and the another isn't - yet! The string is on the end not done and is therefore both a reminder and a marker, telling me which end to do!

Right that's that done. Next onto the main frame assembly.


David P Williams02/03/2018 18:28:14
709 forum posts
270 photos

Welcome to the Dark Side BEB. A different kind of building from fixed wing balsa bashing but just as enjoyable I find. That really was a generous and totally inappropriate gift for a 5 year old - a seriously powerful 3D machine. Yes they can be set up to be milder, but I still find the small 450 size helis to be a bit lively for me, and the head speeds quite intimidating. I stick to 500 size as a minimum now, and prefer 600 size or bigger. As with fixed wing - bigger ones fly better.

Colin Carpenter02/03/2018 18:31:07
453 forum posts
34 photos

BEB . I built a TRex 470 recently . Surprisingly, lots of the kit came pre assembled ! Anything that rotated was stripped and re assembled to my satisfaction . The instructions were excellent . I have built many helis so had no problems . Savox servos and Spekkie AR 7200 Rx were fitted . The tail pitch slider failed after 5 flights . I didn't strip it during the build as screws were tiny fitting into plastic. Got it down ok as it was only 3 ft up at the time ! Building is easy ! Flying em ain't ! Enjoy and don't rush. Colin

Paul C.02/03/2018 18:34:09
369 forum posts
105 photos

Test flight in the living room not a good idea then winkdevil

Martian02/03/2018 19:43:54
1727 forum posts
847 photos
Posted by Paul C. on 02/03/2018 18:34:09:

Test flight in the living room not a good idea then winkdevil

definitely not I have scars on me and the ceiling to testify and you lose a surprising amount of blood surprise

Don Fry02/03/2018 19:53:18
2206 forum posts
29 photos
Posted by David P Williams on 02/03/2018 18:28:14:

Welcome to the Dark Side BEB. A different kind of building from fixed wing balsa bashing but just as enjoyable I find. That really was a generous and totally inappropriate gift for a 5 year old - a seriously powerful 3D machine. Yes they can be set up to be milder, but I still find the small 450 size helis to be a bit lively for me, and the head speeds quite intimidating. I stick to 500 size as a minimum now, and prefer 600 size or bigger. As with fixed wing - bigger ones fly better.

? In English if possible. Or just not possible.

David P Williams02/03/2018 20:04:39
709 forum posts
270 photos

I thought it was in English Don. It might have some model helicopter jargon in there, but it's still English.

Biggles' Elder Brother - Moderator02/03/2018 20:45:17
14972 forum posts
1393 photos

Seemed effecive communication to me too David! Thanks, to you, and others, for the pointers, advice and encouragement - all very welcome.

OK, onward and er,...well not quite upward yet, but we live in hope. I've been tackling the frame.

The first job was to fasten the upper and lower bearing plates to one side of the frame:

8 trex.jpg

Those bearings will take the main shaft. Again thread lock employed. While we are looking at these I'd just like to say that the standard of components and their fit is outstanding. Those bearing plates for ecample are a lovely bit of CNC milling in aluminium and they fit exactly.

Next up we add the the cross frame plates - carbon fibre again - and the ties:

9 trex.jpg

OK, time to add the other side plate. The instructions here tell you to insert the main shaft with the swash plate and rotor head (incidentally, I forgot to mention I took all the ball joints out of the swash and refited them with locktite). The idea is to gradually tighten up the second side plate whilst simultaineously checking that everything stays square and the shaft assembly still rotates freely.

So I did all that without any threadlock, then when I was happy removed one screw at a time and locktited it, constantly checking that everything was square, free and not binding. That gives us this:

10 trex.jpg

Now we have to fit the flybarless controller. As a multirotor builder I am quite comfortable with this bit - its a just a glorified flight controller as far as I'm concerned and many of the same issues apply.

11 trex.jpg

1. It has to fitted securely so it moves faithfuly with the helicopter and passes on the right motion data to the gyro etc.

2. But equally it has to be isolated from vibration as far as possible - not easy!

3. It has to be installed so it is pointing in a particular direction relative to the heli.

All these are the same for flight controllers - so nothing new there for me. Looking at the unit in the photo above you can see an arrow head on the red part of the label at the top just to the right of centre. This tells us the unit must be installed so that that arrow faces the nose of the aircraft. We are going to put it inverted on the bottom cross plate we installed earlier. In the picture below we are looking from underneath the heli:

12 trex.jpg

Now there is a carbon fibre base plate that goes over that. We need to be sure that when that is in place we can still get at the USB port (we'll need that to set it up) and also to the sevo connectors and cerain additional connectors on the sides of the unit. The next three images show that we managed that for each side and from underneath for the USB:

13 trex.jpg

14 trex.jpg

15 trex.jpg

Finally we can now attach the undercarriage and we have a more or less complete frame with the flybarless unit fixed in place on a cushioned sticky pad:

16 trex.jpg

Next up is fitting the servos I think - tomorrow's job. I'm quite enjoying this so far smile


Dave Hopkin02/03/2018 20:52:23
3650 forum posts
293 photos

And here was me thinking you would be completing Mrs BEB's boat you started eons ago devil

Martian02/03/2018 21:20:52
1727 forum posts
847 photos

lovely bit of kit and the standard is streets ahead of clone kits

Biggles' Elder Brother - Moderator03/03/2018 14:42:28
14972 forum posts
1393 photos

Right then, it may be Saturday (the day wen all right thinking red-blooded aeromodellers are down at the field from first light), but the weather is still freezing cold, we had more snow overnight, and so on with the heli.

The first job this morning was to sort out my string reminder and stick some thread-lock on that one remaining screw on the rotor head. Job done, string duly removed. smile

Next up I fitted the pinion to the motor followed by fixing the motor to the mounting plate and installing the whole lot in the frame.

17 trex.jpg

The screws fixing the motor to the plate are only loose at present because apparently I'll need to fine tune the motor position to get the mesh with the main gear right. I can access the motor fixing screws from beneath the helicopter:

18 trex.jpg

These Align guys really have thought this out!

Now we can fix the servos. It is a good idea in any model to ensure your servos are centred, but as I understand it, in helicopters it's even more important. Also it's handy if you can centre the servos at this stage, just as you instal them. Recently a mate was moaning to me that he was having the devil of a job centring the installed servos on a model with difficult access. "Why didn't you centre them before you installed them?" I asked. His reply was basically around the fact that he hadn't installed the ESC and battery system, nor the Rx so he couldn't. Well of course you can!

Now forgive me if I'm teaching my grandmother to suck eggs here, yes I think this is an obvious solution too, but clearly not everyone does, so I offer it here as an aside. This is what I use to get temporary power to any servo/model:

19 trex.jpg

Yeap, its just an old 2s Lipo I had in the cupboard and very old ESC I think I salvaged out of something that met a sticky end! It doesn't have to be a powerful set up, we're only running servos off it. With this I can:

1. Bind the Rx I intend to use with the model before I instal it.

2. I can power a servo for test or centring - using either a servo tester or even my Tx.

3. I can test control links in the model and centre control surfaces.

4. I can adjust control throws

All this without having installed the model's actual power system. And in perfect safety - no big Lipo attached (even indirectly) to a motor with a chain saw on the front! Very handy. Linking it with a servo tester it is even handier:

20 trex.jpg

The picture shows me testing and centring one of the the cyclic servos for the heli. Put an arm on there, press the "neutral" button, job done. The cost? Well the battery and ESC are effectively for free. The servo tester is less than £10 - a useful addition to your workshop.

OK, back to the heli. Here is one of the cyclic servos, duly centred, installed:

21 trex.jpg

And here is the other one on the other side:

22 trex.jpg

Notice how the ball link faces in on one one side, but out on the other. I'm glad you spotted the need for that,...I didn't until after I'd fitted them sad I had to take them all off and refit the balls and servos.

Lesson to learn: study the pictures in the instructions really, really carefully!

This afternoon's adventure is going to centre all around the tail rotor - looks scarily exciting in the manual! Back later, with a fully assembled tail rotor,..... I hope


Steven Shaw03/03/2018 15:15:57
206 forum posts
105 photos

Yes, and with the servo tester you can let them cycle for a while to let them "burn in".

servo testing.jpg

Biggles' Elder Brother - Moderator03/03/2018 18:00:48
14972 forum posts
1393 photos

Yes indeed Steven, and you can "soak test" any servo you're not 100% sure of in the same way. All very handy, for very little touble and money.

OK, I promised this would be "warts and all" and I'll keep to my word - I've screwed up!

Remember me being so pleased with myself that I'd finally spotted that the balls on those two cyclic servos faced in and out respectively - that I'd changed them to "make them right"? Well, rubbish - they were right in the first place!!! Grrrrrrr.

Those two both face inward, the third one does face outward. I'm finally sure of that! And it makes sense, those two are connect to a symmetrical pair of balls on the swash for "ele and aileron", while the third connects to single ball much further back, on the centre line, that controls blade pitch I think. Doh!

So, half the afternoon has been spent very cautiously and carefully rethinking all this out, studying the manual and systematically putting it right. As in the picture below. Sorry its a bit blurred, I didn't notice at the time I took it, probably because I was a bit blurred too! Anyway I've arrowed the points in question. The two top arrows are the original cyclic pair - both face inward - and the outward facing singleton is on the bottom:

23 trex.jpg

To be fair to me,....the manual could be clearer on this point. This sort of thing demontrates the limitations of a manual describing a complex assembly using only diagrams and no words. Generally they do a good job, but there are limits.

So, having lost quite a bit of time I haven't achived as much as I wanted, but there is some further progress. I have connected the ESC and mounted it on the battery cover:

24 trex.jpg

With a bit of a struggle I've managed to fit the boom bracket at the back:

25 trex.jpg

This was difficult because I couldn't get it in with the frame assembled and tightened up - impossible. I had to loosen the screws at the back of the frame to give myself a little wiggle space to get the bracket in. This should really go in before the two halves the frame come together perhaps?

Finally, I fitted the anti-rotation bracket (apparently!)

26 trex.jpg

I think this stops the top half of the swash plate assembly from rotating.

OK, that's it for today. Not bad. A bit of a hiccup, but I managed to spot it (eventually wink 2) and fix it, so no real harm done. On to the tail next.


David P Williams03/03/2018 18:22:38
709 forum posts
270 photos

The linkage balls on the two forward servos should be symmetrical about the centre line of the heli and give a pretty much vertical linkage to the swash. Similarly, the rear one should be on the centre line.

If you were using a 'standard' radio with pre-determined heli settings, then this would be selected as '120deg CCPM' in the radio menu, and the 'ail', 'ele' and 'pitch' servos are connected to the relevant channels on the rx. The servos do not individually perform their designated function, the TX mixes it all so they all move correspondingly to produce 'aileron', 'elevator' and collective pitch functions, so for example to change collective blade pitch (for up/down control) all three servos will move up and down in unison.

With OpenTX you're on your own smiley, but I'm sure there's a ton of YT stuff about how to set this up.

Mike Blandford03/03/2018 18:57:38
324 forum posts
8 photos

Both er9x/ersky9x and openTx have a "Heli" menu (unless with openTx you have selected "No Heli", where you select the "120" swash option (off, 120, 120X, 140 and 90 are available).


Andy4803/03/2018 19:55:50
1274 forum posts
65 photos
Posted by David P Williams on 03/03/2018 18:22:38:

With OpenTX you're on your own smiley, but I'm sure there's a ton of YT stuff about how to set this up.

See here for setting up a heli on OpenTX (download the How To section)


Gary Manuel03/03/2018 20:00:35
1430 forum posts
1284 photos

And here's me thinking that you opened the box and found a helicopter in theresurprise

It's suddenly become a lot MORE attractive to me now that it involves building it Meccano style.

Watching with interest.

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