Biggles' Elder Brother - Moderator Posted March 24, 2018 Author Share Posted March 24, 2018 Tim, firstly welcome to the forum! And thank you very much for that - got it I think. So basically, what your saying is the FBL unit simply needs one point on the curve to effectively "calibrate" the cyclic - ie how much swash tilt equals how many degrees blade pitch? In principle any point would do; but obviously, in the interests of accuracy, it sensible to pick one well diplaced from zero. They picked 8 degrees, they could have picked 7 or 9. So the GPro knows how much swash tilt (servo movement) causes 8 degrees, from the geometry then it could work out say how much tilt (servo movement) creates say 3.5 degrees of blade cyclic pitch, or any other value for that matter. I have that right, yes? BEB Quote Link to comment Share on other sites More sharing options...
Tim Meakin 1 Posted March 25, 2018 Share Posted March 25, 2018 Thanks for the welcome. This is a nice Forum. Yes, you have got it exactly right. The FBL only knows how much servo rotation it is requesting. I doesn't know, on your particular heli, how far out the link is on the servo horn, what is the diameter of the swash input (bottom), or swash output (top), or length of main grip arms, etc. So you go to 8 degrees measured, and tell the FBL this is it. Now it knows the mechanical gain and how much servo travel provides how much change in pitch at the main blade. They use 6 or 8 or other very similar number because that is close to typical maximum cyclic pitch. Cheers Tim Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted March 27, 2018 Author Share Posted March 27, 2018 Well I think we are in the final straight now. Couple of jobs done today: The batteries have a arrived. They are a bit of a strange combination, a 6s that is only 1450mAh capacity. They must be the smallest 6s battery I've ever seen. Talking of the their size they are in fact custom made for the 450L - exactly fit very swish! There is just one fly in the ointment, they have Deans connectors on them! I've never got on with Deans - but it's easily fixed,.... Nice sparkling new XT60's! Of course the heli itself has to be tricked out in new gear as well,.... Having satisfied myself that the swash is level, that the pitch range is right, that the cyclic is calibrated, the time has finally come to fix the rotor head in position. This is done with three screws, one of which is the infamous "Jesus bolt",....here it is: They are shown in place in the picture below. The pair at the bottom effectively make a locating clamp, whilst the one at the top is the "Jesus bolt" that passes not just through the rotor head but through the shaft itself as well.. Remember all the hassle I had with the lower one? This one went in first time - no problem. Much easier access of course. OK, that's it for today. Just a short afternoon session between other jobs. BEB Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted April 4, 2018 Author Share Posted April 4, 2018 Hi, sorry I had an enforced lay-off, due to "circumstances outside my control"! But back to business now. The first part of today was about blade balancing. I looked at quite a few videos and websites to gather some info here and basically what I found rather surprised me. The vast majority of folks believe that if they put the blades on a balance and they stay horizontal then they are balanced - job done. This isn't strictly speaking true. There are at least two possible reasons why a pair of blades could be out of balance: 1. They differ in weight - i.e. one is heavier than the other 2. Even if they were the same weight their CoG could be at different locations It is possible (likely) that the two effects would be present simultaneously, in which case they could, in principle, cancel each other out as far as a simple balance test is concerned; the blades would appear to balance but actually be "out" by some way due to a combination of these effects. So, to start I took my two blades and weighed them on my "drug-dealer" scales and then balanced them individually to find their CoG. I determined the following: Blade 1: mass=29.4g, CoG @ 198mm from centre of rotation. Blade 2 mass=29.2g, CoG @ 196.2mm from centre of rotation. So, there is a definite, and measurable, difference. Next I put the two blades together on the balance - and sure enough blade 1 went down. OK. Now the mass difference between the two blades is 0.2g, I can cut a bit of tape that weighs 0.2g easy enough - but where do I stick it (answers on a postcard please to,....). Seriously, what I'd like to do is find a position to put the 0.2g of tape that not only makes the two blades weigh the same but also makes their CoG's be at the same distance from the centre of rotation. So, I did some sums,.... Here is the basic situation: P is the centre of rotation - effectively the main shaft. Blade 1 is to the right and blade 2 is to the left.So blade 1's mass of m1 acts at its CoG at x1 from the centre and similarly blade 2's mass of m2 acts at x2. The mass m3 is our bit of tape weighing 0.2g and is at some distance x3 from the centre. The objective is to find x3 and hence know where to put the tape. The basic mechanics and algebra is simple enough and gives us: The problem is this doesn't always have a useful solution - e.g. x3 could lie off the blades = like 2 metres away!! Anyway the long and short is that in our case it wasn't off the blades, the solution was useful, I implemented it and,.... Perfect balance. And when I came to check the individual blade CoG's there were, within the limits of the accuracy of my measurement technique, coincident. Hurrah! We mustn't forget the tail blades, in this case their weights were identical and I couldn't detect any difference in CoG,... Spot on, so I left them alone. Now, you might be thinking, hang on a difference of 0.2g and CoG difference of 1.8mm over two blades is tiny - surely that can't have any impact? I wondered that too, so again I did some calculations. I worked out the centripetal force on each blade assuming the head was doing 3000rpm - allowing for their different masses and differing CoG locations. I found the result force difference was 0.03N. That doesn't sound much - but put it this way its a sideways pull on the top of the main-shaft of just over 1 ounce doing, say 3000rpm. That would be significant - it will give my heli a little shimmy like my sister Kate! Hopefully not now though. BEB Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted April 4, 2018 Author Share Posted April 4, 2018 Today part two was nice and easy compared to the above - just sorting the battery position and fastening etc. The batteries have been fitted with the usual "fluffy velcro", and the battery tray with "spikey velcro"! That tray slots into two sets of runners either side of the frame and the cam on the top engages with the latch giving a nice reassuring "click": That all feels very secure. To release the battery you lift that red knob marked "pull unlocked" - a lovely bit of neat engineering by Align. The only other thing I did today was to remove the testing umbilical to the 20A ESC and plug in the heli's actual throttle lead. We are almost there! BEB Edited By Biggles' Elder Brother - Moderator on 04/04/2018 20:58:30 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted April 7, 2018 Author Share Posted April 7, 2018 Well, I think the picture says it all. Finished! All dressed up but (due to the weather) no where to go - yet! I have a very good heli flyer lined up to maiden her then its,....me! The final steps have been a general "go-round" all the screws to make sure everything is fully done up and some time spent re-reading the manual to be sure I haven't missed anything. Finally I fitted the canopy, which I think makes her look great! As I said earlier I have revisited the programming in the Tx. In particular, on the advice of my mentor and test pilot, I have: reset the throttle in idle-up1 and 2 to 60% and 70% respectively; set the switch warnings to require normal mode, heading hold and throttle hold at switch on and set the failsafe to all contols at zero and the gyro gain to 80%, heading hold. I have also modified all the pitch curves for idle up etc to be -2 to +8 degrees range instead of the available minus 12 to plus 12. And that's it. Done. Obviously I will report back on the maiden and my first flights - hopful not clutching a bin bag! I've enjoyed this build, something new and challenging. Many thanks to all those who have contributed and helped on the thread, it really is appreciated, But now the build is over and its time to fly, Mrs BEB can have her dinning room table back and I go back to the shed to engage in some balsa bashing. Please stop raining!!! BEB Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted April 7, 2018 Share Posted April 7, 2018 Posted by Biggles' Elder Brother - Moderator on 07/04/2018 13:01:46: Please stop raining!!! BEB I'll drink to that! Best of luck with the maiden! -- Pete Quote Link to comment Share on other sites More sharing options...
Barryorbik Posted May 12, 2018 Share Posted May 12, 2018 What's happening BEB - has it been maidened yet? Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted May 13, 2018 Author Share Posted May 13, 2018 No, I'm afraid it hasn't! A combination of factors have conspired to delay the maiden. I need to get three things in line, which until recently has been difficult - i.e. my heli flying mate, me and the weather. Now that the weather at least is playing the game unfortunately a personal factor has intervened and meant I haven't been able to go flying at all for the last week and a half! I'm getting serious withdrawal symptoms! I hope it will be soon - I'm very keen to see if I've put it together correctly and it all works OK and of course chomping at the bit to have a go! Hopefully sometime in the next 2-3 weeks it should be possible! BEB Quote Link to comment Share on other sites More sharing options...
Colin Carpenter Posted July 14, 2018 Share Posted July 14, 2018 Hello BEB . Whatever happened ??😨😨😨 Colin Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted July 14, 2018 Author Share Posted July 14, 2018 Yes, its flown and very well. With me on buddy having just the right hand stick. Very good. But FW scale comps, trying to finish a big FW project and just enjoying being out with aeroplanes flying them in this gorgous weather has taken all the time (not to mention now my daughter's graduation, my son's wedding and the compulsary week away Mrs B inststs on) As you can see, things are a bit congested! We'll fly it again and get some photos soon! Well as soon as we can! BEB Quote Link to comment Share on other sites More sharing options...
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