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05-30-2014, 05:49 PM | #41 (permalink) |
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Assembled rotor head
I've filed some of the surfaces thinner to more equalise the weights of the three blade holders, and painted them. The more precise weight matching I did by gluing short lengths of solder in the "cleft" of the grips. For my mechanics, I needed to move the main rotor rearwards several cm from the fuse design position (this was to get the side swash servo hubs behind the inward pointing flange, and to get the tail rotor in a good position. So I cut the hole in the top further back, and also needed to remove part of the plywood bulkhead, especially to clear the ARB.
This head has a wide swash and bulky pushrod ends so the hole needed to be widened for clearance. Another issue is that if the upper push rods are shorter that about 16mm of exposed thread the top of the swash driver hits the bottom of one of the blade holder arms. On the other hand if the rods are much longer the outward angled rods need an even bigger diameter hole in the top of the dog house for clearance. One decorative addition may be that I'll paint matte black or dark green on the cross part of the blade holders to mimic the flex block in the "real" Starflex head.
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Nelson JR DSX9 II; Stretched Atom 500 in Bell 222 body , Stretched TRex550 in 600 size AS350 - . Trex 450 S and 550E for sport . practice.SK720 all round.. |
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07-07-2014, 08:52 PM | #42 (permalink) |
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I've had some issues getting the new head sorted. Some of them are detailed here
http://www.scalerchelis.com/phpBB2/v...177843#p177843 The image below seems to be the final compromise to get the correct pitch ranges. I shortened the swash driver (see the rectangular block part - compare with the image above). The "arms" on the blade holders are very long, which requires a lot of servo movement. I used 25 mm radius servo ball spacing.
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Nelson JR DSX9 II; Stretched Atom 500 in Bell 222 body , Stretched TRex550 in 600 size AS350 - . Trex 450 S and 550E for sport . practice.SK720 all round.. |
02-13-2015, 03:40 PM | #43 (permalink) |
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Back on track
This build came to a halt by mid-2014 due to a career change that preoccupied me (quit High school science teaching and resumed biology/horticulture research - topic: see my avatar).
In preparation for test bed flying I've bolted the mechanics to a hunk of wood as in the image. I'll need to add about another 600g of ballast to match the fuselage weight. You'll note the strange extra skid strut: I've recycled some old skids that had been cut short in the centre section for my 550 JR model (since replaced by custom scale ones) and due to the shortened centre section I decided to add an extra strut that I had. I've included a rather poor resolution blow-up to show the aluminium brackets used to attach the mechanics to the fuselage. The horizontal sections are to be screwed to the ply base of the fuselage, and then the mechanics attached via the horizontal bolts. I've included rubber grommets where the horizontal sections attach to the base. I've done quite a bit with thermoforming plastic, so I press-casted trays to hold the two 6S 3000mAh lipos, from 0.75mm PETG. I'm not sure yet how I'll make the attachments of the trays to base or lipos to tray..
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Nelson JR DSX9 II; Stretched Atom 500 in Bell 222 body , Stretched TRex550 in 600 size AS350 - . Trex 450 S and 550E for sport . practice.SK720 all round.. |
02-13-2015, 03:45 PM | #44 (permalink) |
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IS THIS IN THE WRONG SUB FORUM?
Moderators: I think this should really be in the "scale projects < 790" sub forum.
Regards Nelson
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Nelson JR DSX9 II; Stretched Atom 500 in Bell 222 body , Stretched TRex550 in 600 size AS350 - . Trex 450 S and 550E for sport . practice.SK720 all round.. |
02-13-2015, 04:21 PM | #45 (permalink) |
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Yes, it should be. Moved as requested. Hope you can get back at it soon. Take care.
Don |
02-13-2015, 07:21 PM | #46 (permalink) |
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Good to see you back on the project - very interesting test bed.
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Phil |
02-13-2015, 07:30 PM | #47 (permalink) | |
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Quote:
- I want an equivalent weight to the finished model (I realise the aerodynamics of a plank won't be the same but it's usually just for slow flying during testing). - I want to get as many aspects as close as possible to the finished model which in this case included the attachment brackets, gyro mounting, and lipo support trays. Nelson
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Nelson JR DSX9 II; Stretched Atom 500 in Bell 222 body , Stretched TRex550 in 600 size AS350 - . Trex 450 S and 550E for sport . practice.SK720 all round.. |
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02-13-2015, 10:55 PM | #48 (permalink) |
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Re-thinking about head speeds. 10T + 118T on 12S comes to 1550 - 1650 rpm at 90% efficiency and 90% throttle. I feel this is a bit high (I'm using 3 spinblades grey scale 600 mm blades). I've got the CC Edge HV 60 ESC which I hope will happily go down to 80%. I estimate it will only be pulling about 15A. I've already got two 6S 3000mAh lipos otherwise I might have gone for an 8S set up.
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Nelson JR DSX9 II; Stretched Atom 500 in Bell 222 body , Stretched TRex550 in 600 size AS350 - . Trex 450 S and 550E for sport . practice.SK720 all round.. |
02-15-2015, 01:17 AM | #49 (permalink) |
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I run mine on 8s.. 1450rpm.
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02-15-2015, 03:59 PM | #50 (permalink) |
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More on lipo trays
My c/g estimates show that the lipos will only have their rear half on the ply floor of the fuselage, so the trays are designed to be stiff and be attached to the floor by their rear half only.
- I used silicone sealant to glue lite-ply (2.8mm thick) under the trays. - Then I drilled 9mm holes through the plastic and ply to leave a cavity for screw heads that would not poke up into the lipos. - Then I glued tough 2.15mm ply to the lite-ply with "Gorilla glue" (It's the high performance wood glue - polyurethane I think that foams). This was in two pieces to leave a gap for the velcro strap. - Then I wood-screwed the trays to the temporary test-rig plank.
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Nelson JR DSX9 II; Stretched Atom 500 in Bell 222 body , Stretched TRex550 in 600 size AS350 - . Trex 450 S and 550E for sport . practice.SK720 all round.. |
02-15-2015, 04:16 PM | #51 (permalink) |
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Are the batteries going to be in front of the mechanics or beside them? I can't quite tell for sure from these pictures.
Don |
02-15-2015, 04:39 PM | #52 (permalink) | |
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Quote:
In post #43 you see the horizontal aluminium bracket at the front end of the mechanics: That is the same part you can just see behind the lipo tray in the latest post. This does intrude into the cabin space, but seems necessary for c/g. Nelson
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Nelson JR DSX9 II; Stretched Atom 500 in Bell 222 body , Stretched TRex550 in 600 size AS350 - . Trex 450 S and 550E for sport . practice.SK720 all round.. |
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02-16-2015, 02:58 AM | #53 (permalink) | |
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Quote:
Nelson I would suspect that 80% will result in a warm/hot ESC, especially in summer. NZ is not as hot as Oz, but I would think that it may get a bit too hot in summer. I would suggest aiming for between 90-95%. I don't have a 3 blade 600, but I would guess that around 1450rpm (maybe 1500rpm at a push) would be about right. I run my 2 blade 500 at 1700rpm, so I think that 1650rpm is definitely too fast. Maybe the changeover cost (ie. new price less resale of current) for a slower motor might be cheaper than a few sets of new lipos. Also bear in mind that you would probably run closer to 20-24A than 15A, with peaks up to 35A, and dropping to 8s would result in amps 1.5 times this, so peaks up to 50A, which is getting closer to your 60HV rating. Also, if your lipos are going to intrude on a cockpit, you could consider leaving them a bit further back, and getting some small round lead sinkers (balls) and packing some of them right up front (under the instrument panel maybe) as ballast. Colin
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02-16-2015, 12:21 PM | #54 (permalink) | |
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Darn... And I thought I'd done my homework before I obtained all the parts. I already exchanged the 550-kit 1220 kv motor for the 510 kv one from a TRex 600. The frame spacing is only 47mm which excludes some of the fatter motors although I have made extra cutouts in frames previously for this reason. I don't really want to go back to the 170T 0.7 gear. Any motor suggestions would be welcome. Or I might just test fly and see. Nelson
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Nelson JR DSX9 II; Stretched Atom 500 in Bell 222 body , Stretched TRex550 in 600 size AS350 - . Trex 450 S and 550E for sport . practice.SK720 all round.. |
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02-16-2015, 12:30 PM | #55 (permalink) |
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That head looks really realistic. Hoping the mechanics of it are up to your needs.
Looks great. More pics!
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02-16-2015, 01:21 PM | #56 (permalink) |
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Further to the power system question: By far the easiest for me would be to go to an 8S system. Locally I can get 4S batteries in 2600-2650-4200-4500 mAh. I guess the 4200 mAh has the nearest energy content to my exisiting 6S 3000 mAh packs.
As for the higher current you mentioned Colin, I understood the CC ESC ratings were continuous, so having 50A peaks on a 60A ESC should be OK. In any case I'll probably put a small fan next to the ESC. EDIT - quote from Castle: "*RC HOBBY APPLICATION RATING: 60 amps for the duration of a single 5,000 mAh battery pack with the ESC in contact with a 5 mph airflow of 25C (77F) or cooler air. Controller temperature must never exceed 100C (212F). Exceeding current or temperature ratings may damage components and may shorten the life of the ESC. Always verify system current draw at full-throttle. Decrease load or increase airflow to decrease the ESC’s operating temperature."
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Nelson JR DSX9 II; Stretched Atom 500 in Bell 222 body , Stretched TRex550 in 600 size AS350 - . Trex 450 S and 550E for sport . practice.SK720 all round.. |
02-16-2015, 03:36 PM | #57 (permalink) |
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Nelson:
You had mentioned having the 118t main gear and the 11t pinion but had also said you would look at getting the 10t pinion. If you had that, your maximum headspeed, governed (at 92.5%), would be 1597rpm, not outrageous by any means. You could easily drop it to 85% and would have a headspeed of 1458rpm. You don't need to go out and buy new batteries or a motor. I ran my AS350 with that motor, the original main gear (112), and an 11t pinion for the better part of two seasons at a headspeed of around 1600rpm. It was not ideal but the system held good and solid until I changed the motor to the 450kv, 118t main, and 10t pinion which is running at 1400rpm. Try it before dumping extra coin into the project as you might not really need to spend it or require it. Take care. Don |
02-16-2015, 03:45 PM | #58 (permalink) |
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OK thanks for the encouragement Don. I'm not going to rush into anything until I've done some trials on the ballasted test rig. I also read that dropping the PWM from 12 to 8 places less heat stress on the ESC. There's room and power to run a fairly grunty fan to help cool the ESC (and ESC heat seems to be the main issue).
Nelson
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Nelson JR DSX9 II; Stretched Atom 500 in Bell 222 body , Stretched TRex550 in 600 size AS350 - . Trex 450 S and 550E for sport . practice.SK720 all round.. |
02-16-2015, 04:20 PM | #59 (permalink) |
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You have seen how I mounted mine on the front of the frame and it does not get a lot of air movement over it. My recollections of it running in the middle of summer have temps when run with the 510kv motor at a maximum of 158F and drawing seldom more than 35A peak, averaging 15A nominal. With the current setup, it averages 13.2A, 35A maximum, and a top temperature of only 115F. with the two sliding windows and the underside hole open, only. That is the beauty of having a logging ESC. I don't keep every single flight or group of flights logged but tend to do a spot check, verified by the old fashioned way of putting my finger to the motor and ESC from time to time. There is seldom any variation and the hottest temps I flew in were in Georgia at the Southern Challenge where it flew like a champ. Hope this eliminates some concerns.
Don |
02-17-2015, 03:08 AM | #60 (permalink) |
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Nelson
I do agree that you should try it out before spending, and if you can get a 10T that would certainly help. Going to Mod 0.7 and 164T main and 13T pinion will give you less gains than a 10T. Playing with PWM is good but it is balancing act between motor and ESC temps - higher reduces motor temp and lower reduces ESC temp. A 470kV motor would be ideal, but you may not need it. I run my Long Ranger at 86% governor, and often see ESC temps of over 70°C and that is with 1x 80mm & 1x 60mm fans, whereas my Seahawk runs at 90.7% and the ESC seldom exceeds 60°C (no fans). Both run Xera 4030-470kV motors, CC Ice 2 80HV, 1350rpm and both are between 8.5 and 9kg in weight. The Seahawk draws about 10% more power as it has 4x 600mm & 4x 105mm blades compared with the Long ranger's 2x 710mm & 2x 120mm blades, so the setup that is working harder (ie. more Watts and more amps) actually runs cooler. What I get from that is that the 5% lower governor % does make a difference as the hardware is fairly similar. Colin
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