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And now for something completely different

BEB Builds a Helicopter

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john stones 119/03/2018 20:59:11
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Interesting blog B.E.B, nice to read something different. yes

Glad you've bought some ball link pliers, I couldn't see them on your tool post. Bit early yet maybe, but what training aid you going for whilst you learn, hoop or ball ended canes ? or none ?

Biggles' Elder Brother - Moderator19/03/2018 21:19:36
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Hi John, What type of training UC? A very big one I think!!

The balls on the end of canes seems to be the popular local option and I'll probably borrow a set of them from a mate. Anything that will save me a couple sets of blades would be welcome!

BEB

Biggles' Elder Brother - Moderator19/03/2018 23:48:59
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Thanks Tom. Yes I suppose the skids do look a bit tacky compared to the rest of the machine. But they do seem very strong (which I have a feeling will prove to be important)
It's likely that they will be a lot less noticeable once the canopy is in place.
BEB
Colin Carpenter20/03/2018 08:20:24
458 forum posts
34 photos

BEB. You will find the uc legs break easily if you slam it down with too much negative pitch ! Mine broke when the tail slider gave way and I put it down quickly from 18 inches or so ! I have about 3 degrees negative from memory . A cheaper fix than blades or boom .Colin

extra slim20/03/2018 10:13:12
396 forum posts
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Nice progress BEB, but you skipped over the bit I always found the most taxing in maintaining contact with the swash level tool THROUGHOUT the full pitch range... was this done just with the GPro??, I've not used one..

I also quickly found out that it was better to set the range fully at +- 12.. and then cut things down using the pitch curves on the tx

I think your heli will hover around 4 degrees with the correct head speed, and so you need your centre "throttle stick" position to be around 4 degrees for your first hover, not zero..like when you are setting up the full range.

Biggles' Elder Brother - Moderator22/03/2018 23:21:53
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Sorry I have not posted for a couple days - but I haven't progressed the build at all in that time because, as you may have noticed, the weather has marginally improved so I've been flying the last two days!! Great fun.

Your question is a good one Extra-Slim - I can only say it doesn't feature much because it was a bit of a non-event! I levelled the swash at zero, one servo was slightly low - see my post on 17-03-18 on page 4. So I corrected that using the trim function for that servo in GPro.

Subsequently, when I came to test the top and bottom of the swash travel and found that the bottom was fine, but the top had a tiny, tiny gap on the back servo. Really very small - difficult to see. Anyway I took that out with literally one click on the GPro trim for that servo. I then obviously re-examined the mid-point and the bottom. To my great delight I could see no spaces at either station!

So all in all it was a piece of cake! Now I am quite sure I can take no real credit for this. I think I have just been very lucky here and its all just fallen into my lap. Next time (hey, who said there is goung to be a next time?!) it might be not nearly so easy, but for now I am just happily plodding on and being thankful for my luck!

One fly in the ointment is that my new pitch gauge seems to have stopped working! It won't turn on. It's possible it's a battery problem, so I am picking up some new batteries for it tomorow to test that. If it still doesn't work then it will have to go back!

BEB

Biggles' Elder Brother - Moderator23/03/2018 18:05:40
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Hi,

some progress - of sorts - today that I will report later. For now I have a question:

At one point in the set up I am required to set the cyclic pitch at 8 degrees. This is shown in the panel just right of centre here:

79 trex.jpg

The idea is: I press the "Set to 8 degrees pitch" button, the blades jump to the approriate position, then I use the slider to fine tune to 8 degrees on the pitch gauge. OK, nice and clear. Only it goes to -8 degrees not plus! And the range of adjustability on the slider is around +-1.5 degrees - so no where near enough. Ideas suggestions?

BEB

extra slim23/03/2018 18:40:54
396 forum posts
47 photos

Hey BEB, good news on the leveller, shows your diligence on the mechanical side of things really paid off. 

Edited By extra slim on 23/03/2018 18:41:45

John Tee23/03/2018 20:37:45
614 forum posts
55 photos

Probably too simple an answer but the panel highlighted is negative collective pitch. positive collective pitch is to the left.

John

extra slim23/03/2018 21:50:12
396 forum posts
47 photos

Sounds like something needs reversing?

Biggles' Elder Brother - Moderator23/03/2018 22:01:24
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Hi, all suggestions welcome John! So I've just checked that out. Which of those collective panels are illuminated depends on where the throttle is. If it's at max then the "max panel" is lit and you can alter the maximum positive pitch. If the throttle is "closed" then the "min panel" is illuminated and you can alter the maximum negative pitch. If the throttle is at the mid-point then neither panel is illuminated and you cannot alter the maximum or the minimum pitch.

I have tried in all three conditions now, being careful to "release" the GPro's pitch position hold in each case, and the result is the same, -8 degrees. sad

Just check me out on this guys in case I'm doing something stupid. I've shot two short videos. The first simply shows the controls moving. It designed to help you confirm to me that, as I believe, I have everything moving in the right direction, here it is (BTW ignore the fact that I keep referring to the GPro as the GoPro - old drone habits die hard)

So, are they all correct? I think so.

The next video deals with what happens when I come to do the cyclic pitch and shows it going to -8 degrees instead of +8. Here it is:

So there we are, bamboozled!

BEB

PS Good word that - bamboozled!

Biggles' Elder Brother - Moderator23/03/2018 22:05:17
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Yes - that's what I thought extra slim, but, unless I'm wrong, all the controls move the right way?

One reversal was necessary to achieve that, as I showed in a much earlier post, and that reversal was done in the GPro, not the Tx, which is the recommended way so that the controller knows about it and can presumably take it into account in cases such as this - only apparently it ain't!

BEB

Biggles' Elder Brother - Moderator23/03/2018 22:14:21
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Ah - it appears I am not alone!!!

**LINK**

Maybe my heli isn't level? I'll experiment tomorrow!

BEB

PS Or later tonight if I can sneak away!

Biggles' Elder Brother - Moderator23/03/2018 23:46:02
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OK, sneaked away!

I think I have cracked it! I very carefully levelled the heli in the fore/aft and left/right directions by using shims (bits of paper!) under each of the main skids and the tail skid. I used the top surface of the motor can as my datum (as Fassbinder does in the video in the link above). The rationale behind this is that we want the main shaft to be absolutely vertical - that way the digital pitch gauge (which is using gravity as its datum - ie vertically downward) will be giving us angles relative to the main shaft - albeit through the proxy of the motor can. We can justify saying the motor can is a good reference to the main shaft because they are both fixed in place onto the same precision machined bearing block.

OK with the heli level to the global axis of gravity, I repeated all the pitch settings, collective (zero, max and min) and cyclic (aileron, blade fore and aft; then elevator, blades across the heli. Only small adjustments from zero were needed here. I then came to the dreaded cyclic "set to 8 degrees" bit and,....it worked - went to about 8.5, I could then trim it.

Phew. TBH I think the instructions are a bit vague in this area. There is absolutely no mention of the cyclic aileron/elevator zeroing at all! Nor is the importance of levelling the heli mentioned (but in hind sight maybe that's obvious given that digital pitch gauge uses gravity as its datum). Anyway - we are finally there and I lhave learned a lot - every cloud and all that!

BEB

Biggles' Elder Brother - Moderator24/03/2018 00:06:30
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Well, after all that excitement, did we do anything new today? The answer is "yes", not a lot but a significant bit!

After the set-up we need to move to the screen in the GPro software that deals with Flight Parameters.

81 trex.jpg

Oooohhh, just look at all those interesting sounding parameters: "Elevator precomp", "Tail Acceleration %" - Mmmmm. But what about that really useful looking button at the bottom right that applies the "Beginner Settings" - oh yes please, that will do me nicely! Hit that and all the parameters go to what is (supposed to be) user friendly, gentle, settings. So that's what I did. Progress for today? I pressed one button!

(Well I seem to have solved the the "problem" as well smile)

BEB

PS - flying tomorrow - hopefully - so back after the weekend probably.

Edited By Biggles' Elder Brother - Moderator on 24/03/2018 00:08:57

Cuban824/03/2018 10:11:24
1852 forum posts
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All sounds like a nightmare.............think I'll stick to flybars. BTW, get shot of the training gear just as soon as possible. I found it useful to stop the heli toppling over before I gained confidence getting cleanly into a hover and whilst making a few initial untidy landings, but things were so much easier without it.

For me, I didn't really have too much bother with landings, but the danger area, and where damage was most likely for me, was being over cautious when getting into the hover and faffing about close to the deck in the rotor downwash.

An expert heli flyer friend said to me that once airborne and flying about, a heli is very little different to F/W flying. Well, his little difference, to me, was huge. I find very little correlation in the two skills, the most prominent is that a heli lacks a dirty great wing sticking out from each side, that we 'plank' flyers unconsciously use as a visual cue to judge bank angle and generate corrective inputs on the sticks.

I spent many, many hours learning to steer correctly with the heli flying sideways or briefly when flying towards myself. Just when you think that you've cracked it, you'll make and error and frighten yourself half to death. A good tip I did get, was to put a bright stripe on the front of the canopy, it helps to keep your concentration on the nose of the machine and works wonders when you need something quick to orientate on when things go a bit pear-shaped. Saved me a lot of repair time.

Edited By Cuban8 on 24/03/2018 10:12:47

Denis Watkins24/03/2018 10:33:51
2567 forum posts
129 photos

I thought I had this heli flying sorted in the past, as both mentors flew either concentrating the canopy forward or amazingly the tail rotor aligned behind.

I was scuppered one day watching a really cool guy flying scale and asked him how he did it.

" Oh, I just fly the rotor disc " he replied

Cuban824/03/2018 12:06:39
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Before I began flying helis, I thought that 'flying the rotor disc' would help with orientation. In practice, I find it does a bit, but not as much as with fixed wing, which is odd.

Watching the tail is not a good idea and a bad habit to get into.

Biggles' Elder Brother - Moderator24/03/2018 12:07:16
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Thanks for the pointers chaps. I have just set up a sim to get a little practice on. First go reveals it does indeed feel very like a multi-rotor with the stabilsation and self leveling etc. turned off. That means I was able to manage a reasonable hover. But hey - that's on a sim and we're all heros on the simulator aren't we?! But at least it will give me some preparation, I'm not relying on it for more than that though.

I've just noticed something else about this setting the cyclic to 8 degrees thing. In adjusting to close to what it expects the position to be it moves both blades in the same direction - ie they remain in one plane. Very odd. So that means if you measure one it will indeed be at negative incidence and you will get about -8. If you measure the other one it will have a positive incidence and measure +8! Go figure that!

I don't understand what we are doing here to be honest. I understand the previous screen:

It moves the swash to mid-point and we set the collective to zero. Fine.

Then we basically check this is good for the cyclic "trueness" by measuring zero with the blades arranged both fore and aft and across the heli. This checks that the blades are moving in one plane. Fine.

We then go to the next screen and set the max and min pitch from a 45 degree pitch curve in idle-up2. Yes, great, understand it all so far.

Then we do this set to 8 degrees thing for the cyclic - yer what?

I've done it, I've done what it tells me to, but I don't understand what its doing. Why specifically 8 degrees? If it's cyclic why only in one position? A mystery - unless you know otherwise!

Not much left to do now.

1. Balance the blades

2. Reinstate the bottom plate which I removed to make access to the GPro easier.

3. Do an all round check up that all screws are fully home and threadlocked.

4. Insert the top Jesus bolt with threadlock, thus finally fixing the rotor head on. (I don't want to be like the chap in the video earlier!)

5. Solder a XT60 onto the ESC. I have batteries on order - they are bit strange 6s 1500mAh! - they are due on Monday. Solder XT60's on them.

6. Fit the canopy.

7. Tweak the Tx programming.

That's about it. Should be ready to maiden next weekend all being well. I have an experienced heli-flying clubmate on stand by to do the final checks and maiden it to be sure its OK. Then I'll take the plunge, better get some more sim practice before that! Right now though I'm off flying - the weather is quite nice here, for a change.

BEB

Tim Meakin 124/03/2018 19:42:21
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Posted by Biggles' Elder Brother - Moderator on 24/03/2018 12:07:16:

Q1: I've just noticed something else about this setting the cyclic to 8 degrees thing. In adjusting to close to what it expects the position to be it moves both blades in the same direction - ie they remain in one plane. Very odd. So that means if you measure one it will indeed be at negative incidence and you will get about -8. If you measure the other one it will have a positive incidence and measure +8! Go figure that!

Q2: Then we do this set to 8 degrees thing for the cyclic - yer what?

I've done it, I've done what it tells me to, but I don't understand what its doing. Why specifically 8 degrees? If it's cyclic why only in one position? A mystery - unless you know otherwise!

A1: Think of Ailerons on a plane. Bank left, one side goes up the other side goes down.

Collective = both up and down together (more or less lift).

Cylcic = differential to get roll and fore / aft pitch.

A2: Most FBL controllers need to be taught the sensitivity of the mechanical setup.

By setting a fixed number of degrees (here 8, BeastX is 6), then confirming, the FBL knows how much servo rotation was needed to get that deflection. If the resolution is too coarse or too sensitive, you have to alter the mechanical gain in the horns / servo wheel / linkage. Then the FBL is calibrated to your specific mechanical setup.

Hope that helps.

Great build log.

Cheers

Tim

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