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Old 01-21-2017, 12:20 PM   #61 (permalink)
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Just checked the geometry, and the pitch arms on the blade grips are shorter on the 3-blade head, 28mm vs 32mm on the 2-blade! This means I cannot use my old settings, but it also means that I need less swash travel for the same pitch angle. All other measurements seem to be the same, but it's not so easy to get an accurate reading.
I may be able to use the stock "turnbuckles" if I remove the removable main shaft collar. That will lower the head by 8-10mm, which may be sufficient. I only need to do that to set the maximum collective and cyclic throws in the BeastX; once I get that programmed I can use those settings to figure out the best servo link compromise.
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Old 01-21-2017, 12:23 PM   #62 (permalink)
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Quote:
Originally Posted by Rodan View Post
I wouldn't worry too much about that, as if you get to full pitch and full cyclic at the same time with a scale heli, it's probably too late!
I guess you are right, especially since the most extreme swash driver geometry occurs at negative collective, though that's only about -2 degrees.
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Old 01-21-2017, 12:26 PM   #63 (permalink)
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The only time you're going to be in negative pitch with a scaler is during autorotation, or sticking it to the ground in windy conditions. Shouldn't be using a lot of cyclic in either situation...
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Old 01-21-2017, 01:43 PM   #64 (permalink)
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That's true.
Well, I first have to get it set up now to get the correct pitch values stored in the FBL, by lowering the main shaft and using the stock turnbuckles.

Last edited by getsuyoubi; 01-21-2017 at 03:36 PM..
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Old 01-21-2017, 03:47 PM   #65 (permalink)
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Got it all sorted out now - I think. I did lower the main shaft by removing that collar and using the machined, fixed collar on the shaft instead. That allowed me to use the stock (false) turnbuckles, though they still gave me about -4 degrees pitch when I should have gotten zero. But all I'm interested at this point is relative changes, namely +/- 9 degrees collective pitch and +/- 8 degrees cyclic. So I just zeroed my pitch gauge at whatever it read at mid stick (50%, or supposedly 0 pitch), and set the collective and cyclic limits in the BeastX.
Then I raised the shaft to its nominal height by installing the removable collar, shortened the servo linkages by 2 or 3 millimeters, leveled the swash, and installed the mechanics in the fuselage. Now I have no more binding at simultaneous full collective and full cyclic inputs, and I can even go full negative (-9 degrees) collective and simultaneous full cyclic, and there's still a tiny gap between the swash driver and the swash! So, at my -2 degrees pitch it's certainly no problem at all anymore. Re-calibrating the limits in the BeastX was the key to success, and I have to thank Rodan for raising doubts about my claim of equal geometries.
Now I just need to order longer turnbuckles, 53mm rods instead of the stock 42mm.
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Old 01-26-2017, 08:29 PM   #66 (permalink)
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Installed the plastic tail unit using a hose clamp, and made the cutouts in the vertical fin. I don't need to worry about it staying in place thanks to the peg that fits in the hole on the tail boom, but that tightening screw mechanism on the clamp is a tad too wide and won't allow the tail fin to sit properly. I'll have to see what I can do about that; just gotta grind away a millimeter or two off that screw.

Edit:
Maybe instead of that hose clamp I can get away with a beefy zip tie? It doesn't take much of a clamping force to keep the tail unit in place - actually, none, as long as the two halves don't separate by a millimeter or so. I also still have the lower peg in place that's meant to mount the vertical fin on the pod-and-boom, and doubles to clamp the unit together. Together with a zip tie that should be enough, shouldn't it? Of course, this would be a second zip tie, not the one that attaches the tail boom to the fuselage.
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Old 01-28-2017, 09:52 AM   #67 (permalink)
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Just tried some more to make that hose clamp fit, and it looks like it's not gonna happen. The problem is that the tail control rod binds against it in neutral position, so it would fight against having zero pitch on the tail.

That means I have to either resort to a zip tie, or try to find a different hose clamp (narrower, with a smaller clamping screw mechanism). Any idea where I might find a smaller one?
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Old 01-28-2017, 12:27 PM   #68 (permalink)
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Align makes different length balls that are used on arms for servos. You can take one of those and mount it on the pitch control arm, which will lower the rod enough that it should clear the screw on the hose clamp. You may need to remove some of the wood to allow that to happen. Second, you can try to use two screws to hold the sides of the housing to the boom. I see there is one lug still left on the bottom and even using a short bolt and nyloc nut might help to keep it together. The cable tie can still help provided you use one that is fairly strong (40lbs. rating) as it does not need a huge amount of pressure to keep the two halves together. The ones that are on the rear around the shaft are the critical ones and they are unaltered. Take care.

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Old 01-28-2017, 01:00 PM   #69 (permalink)
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Thanks Don. I'm already using a bolt and nut in the remaining lug underneath, though I still have to replace that one with an M3 one - I only had M2 with the required length on hand. I will go through my parts bin to see whether I can find a longer ball. I had thought of that, too but was a little reluctant removing some of the wood. I guess I can always add some ply in the right place to strengthen it again.

On a positive note, my 53mm Lunsford turnbuckles arrived today, and everything works out perfectly. I get my desired 9 degrees of collective and 8 degrees of cyclic without binding, plus a blue light on the BeastX at 6 degrees, using 17mm servo arms direct-to-swash. Time to mount the mechanics on a test rig, balance the blades, and go for a test flight!
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Old 01-28-2017, 04:23 PM   #70 (permalink)
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Looking at your servo mounting, I would look for those CF plates that are used to clamp the servo from the outside. There is a small chance of the servo being dislodged as the head is really not much bigger around than the hole in the servo case. Hope this helps.

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Old 01-28-2017, 05:48 PM   #71 (permalink)
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I'm not sure I understand what you are referring to. Do you mean those CF "washers" that would prevent my servo screws from slipping through the mounting lug in the servo? I think I would have to use regular washers instead, because I'm already using two of those CF ones between the servos and the frame to push the servos a tad outside, which is pretty much all the length of the servo mounting screws allows. The reason is that these Spektrum servos are a millimeter or two too tall to fit in my 47mm wide frame without pushing against each other.
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Old 01-28-2017, 05:52 PM   #72 (permalink)
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I installed the long step on the left today. This makes the whole heli look much more "complete", it's amazing what this one little detail can do.

There is still a lot more to do on these skids. It's amazing how much detail there is - those little step bars in the rear, unused mounting brackets on the right side, and so on. I'm not sure yet how much of it I will try to replicate, though.
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Old 01-28-2017, 07:11 PM   #73 (permalink)
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In any case, while you are getting through the finishing of the body, I would add those washers to your next order. You can always make the spacers you need out of plywood as the ones in my rebuilt 550/700 are. The funny part of that build is that they only reason I installed the spacers (three of them on each side) was so that I could install the pod and boom body on while it is awaiting time for me to finish other projects. I had the ball on the lever between the the arm and the body of the servo which pretty much put the swash link vertical or very near to it. A seemingly unimportant as those washers may appear to be, they are a very important part of keeping the servos anchored in place. Keep up the work, it's getting there.

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Old 01-28-2017, 07:52 PM   #74 (permalink)
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OK, thanks, I'll get those washers then. There is no rush as I just had another setback. I had bought two sets of DT 600mm blades a while ago with this build in mind, and I even asked for the two sets to be matched by weight if possible. Well, each set is nearly perfectly balanced, but the two sets don't match at all to each other. I haven't put them on a scale yet as the battery on my digital scale turned out to be dead, but one set is noticeably heavier when I balance it against the other one. What's even worse, the center of gravity of the heavier set is about 5mm closer to the blade root than on the other set. This means I need a lot of tape on the lighter blade near the blade root to move its COG further in by those 5mm, and then even more at the COG to match weights.
I tried some packaging tape, but even 25cm was by far not enough. Is there a heavier tape around, or something totally different that I could try (I'll certainly want to paint those blades eventually anyway), or should I just give up on these and get a matched 3-blade set of Spinblades? I was planning on using symmetrical blades, though, but that probably wasn't such a great idea because there are not matched sets...
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Old 01-28-2017, 09:41 PM   #75 (permalink)
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I tried using electrical tape, but these two sets are so far off that it seems hopeless. As you can see in the pictures below, I could set the entire roll (!!!) of tape on the lighter blade to get it balanced. Obviously, this is very close to the fulcrum, but still.
I then proceeded as usual. First I brought the COG of the lighter blade to the same location as on the heavier blade. Then I added six layers of tape at the COG, but that's by far not enough. The second picture shows the situation with the entire roll on top of the lighter blade to get them balanced. It clearly had to be moved closer to the fulcrum than without any tape, but from these two pictures I estimate that I need 3-5 times as much tape at the COG. Instead of six layers, that would be 20-30 layers! Each strip of tape is about 4 inches long, which makes that 80-120 inches of tape, or 6-10 feet! This is definitely hopeless unless there is some magic trick that I'm not aware of...
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Old 01-29-2017, 12:51 AM   #76 (permalink)
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There are blade sets available for three blade heads. All are weighted and balanced as a set. I know Rotor Tech makes three blade semi-symmetrical sets and SAB, Rotor Tech, Switch, and NHP make three blade symmetrical sets. Also, Spin Blades make both symmetrical and semi-symmetrical three blade sets for 3D and for sport. Unless I personally know the fellow saying he will match the sets, I would only buy balanced sets today. There is too much time spent trying to find matching sets in two blade packages as my friend at Leisure Tech will verify. The weights have got to be within .5 grams of each set and then it becomes fairly easy to balance them. Mine are balanced to .1 grams or less of each other by static balancing. So far, I have found that I have not had to dynamically balance any sets so far but that does not mean that I'll get away with that forever. I would not bother with those blades, sorry to say. Put them aside for other two blade helicopters or a four blade head project. They will work there as two balanced sets as long as you number them to keep them from getting mixed up. Take care and good luck.

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Old 01-29-2017, 03:35 AM   #77 (permalink)
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I can find 3-blade sets from some of the manufacturers you mention, but none of them are 600mm. SAB has a 630mm set, which is the closest to 600mm I can find, but other than that I only see around 700mm.
I read in another forum that a fellow contacted Zeal, and they offered to match a set at 127 bucks. There are pictures of his helis with three Zeal blades in yet another thread, and I'm trying to get in touch with him regarding his experience with those blades. I won't know how they perform on a scale heli, though, but at least I'll know how close they were matched out of the box.
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Old 02-05-2017, 01:30 PM   #78 (permalink)
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Not much visible progress this weekend. I installed the little aluminum pegs that keep the front fuselage in place. There are only four of them, so I will probably add two more, plus two more set of magnets. Unfortunately the unpainted version does not come with that really cool magnet-actuated locking mechanism.
Other than that, I build a little test rig to test rig.
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Old 02-05-2017, 03:31 PM   #79 (permalink)
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A nice tidy test rig. Will the battery(s) go on the wood at the side? I'm thinking about position w.r.t. c/g.
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Old 02-05-2017, 06:30 PM   #80 (permalink)
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Yes, I probably have to put them on the side. I haven't installed the tail gearbox and rotor yet, but without those it turns out to be pretty much balanced without the batteries. That means I likely have to put them on the sides. In pod and boom it needed two 6s 3300mAh batteries to be balanced, though. Maybe for the test I will just use one in the front.

The reason for it looking so tidy is simple. I flew this helicopter for over a year in pod-and-boom configuration, so everything is attached to the frame. In your build you bought the 550 with the intention of installing it into a fuselage, which meant that you didn't have to squeeze everything into the frame.

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