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Post by killioughtta on Oct 11, 2010 8:03:20 GMT 1
Hello, Guys. I'm undertaking a project to build one of my favorite airplanes: the DeHavilland Twin Otter. If I go through with it I will be using DOW blue foam to build an airfoil wing and full fuselage; in other words: a very scale Twin Otter. Since I know you guys are the best at answering questions in a manner that is easy to understand and at giving the best feedback, I'd like you to give me your opinions and, specially, answer some questions I have about a two-motor setup.
First, I's like to know about amp draw and ESC amperage I'll need for the motors I'm planning on using. I plan on using a pair of Turnigy 28-30 1350 kv motors with props 6 or 7 inches long. By what I've read, that should draw about 12-16 amps, depending on prop pitch and type (SF, sport, etc.). I'll be using 7 cheapo servos like the TG9s and HXT009s, 2 Zippy 2150 mAh 3S 35c Lipos.
Will 20A ESCs do the job? I'm thinking of getting 25A ESCs to be on the safe side but I'm not sure if THAT's even enough.
Can I use a Y-lead to join the ESCs/motors to ONE channel on the radio? Will that cause any problems?
This model will have a 48" wingspan and I'll be building it from nothing but 3-views. I sure wish I could find some plans but I've had no luck finding any for a 48" Twin Otter.
I'm looking forward to hearing from ginginho and flydiver, among others.
Thanks in advance for your feedback!
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Post by Dillzio on Oct 11, 2010 8:34:12 GMT 1
my thoughts are that if your motors are running at 16 amps each, a 20A ESC per motor should be fine. Just make sure the ESCs keep cool, and if possible don't use the BECs in them, they generate heat. I can't think of any reason why you can't just put a Y-harness adapter on the receiver's ESC channel and hook both ESCs together by the Y-harness, both ESCs should work fine off the same signal. The only thing that would require special concern is the BEC - when you have two BEC's hooked up together they can compete with each other and don't work well together. If they are both identical linear BECs then I think it would be OK, but to be on the safe side I'd recommend removing the BEC wire from BOTH the ESCs and just using a UBEC. The more I read about that hextronic UBEC at hobbking the more I wish I got it instead of my crappy Turnigy one, www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=3735&Product_Name=HXT_UBEC_5/6v_output,_5.5~23v_Input Although, if you're running 7 servos you might want something even bigger. It might be possible to divide up the servos so that some were powered by one BEC, and the other BEC ran some other servos and the reciever, but considering how complicated it makes matters, when I built my cub I decided to just hook everything up to one BEC (the UBEC), and leave the one in the ESC unused. With 7 servos, hopefully you won't be using them all at once anyway so 3A will probably suffice. Don't forget to use carbon spars in your plane, they are easy to install (just put a cut into the foam, then push them into the cut with a bit of epoxy) and it makes them fully sick! My cub seems to be near on indestructable now. |
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Post by killioughtta on Oct 11, 2010 21:12:54 GMT 1
Thanks, Dill. I think 20A ESCs could work but I'd like to go bigger just to be on the safe side. 25 or 30 should do.
FYI: The servos will be 2 ailerons, 2 (or 1) flaps, 1 rudder, 1 elevator, and 1 nose gear.
If I can't run the two motors together on one channel, I'll have to give up another channel like steering or flaps. OR I might sell something of value to buy a DX7. I don't know. This is a long-term project spanning the likes of 4-6 months. I just want to be sure of everything before I start it.
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Post by ginginho on Oct 12, 2010 16:14:51 GMT 1
Sorry I haven't replied earlier Erwin, I've not been on the board for a few days. As for a setup, the details of TSII I have, and as fitted to a mate's are as follows:
Motors are Suppo 2210-12 (1400Kv, Max current 16A) spinning MA 7x4's. These are linked to Hobbywing 18A ESCs, mine mounted in the fuse, his in the nacelles. This setup pulls 32A at WOT. Both ESCs are fed from one channel and both have the red wire removed. A 3A (Hobbywing) BEC provides power to the servos, of around the 12-15g weight size. I fly on a single 2250 20C Loongmax pack and get nice performance, my mate parallel's up a couple of Ebay (Mystery??) 2200 packs and flies like a loon (vertical etc). Both have quite a few hours of air time, niether have suffered any problems with these setups. Mine also has home brew U/C fitted (I think you've seen it on here) and generally flys with the spy cam so has a fair amount of extra weight over a normal build. I don't know the overall weight I'm afraid.
I have the nose wheel steering running off the same servo that operates the rudder, that might be worth thinking about. Just use an arm with two opposite tabs, the rudder off one side, the wheel off the other (as it's a nose wheel it needs to turn opposite to the rudder, if tail-dragger it needs to turn the same way). It saves on needing another servo and the fun and games involved with mounting it and connecting it up. If needs be I'll try to get a photo of it, although I may have already posted that a while back. The TSII has a WS of 1420mm.
Don't bother thinking about counter-rotating props or any of that, it's not worth it, and doesn't really work on an RC level. If a motor stops, you just gotta kill the throttle quickly otherwise the running motor will put you into a spiral of death!
One other thing, you'll love the sound of the interference that the props make, it's quite authentic.
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Gohmer
Squadron leader
Posts: 113
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Post by Gohmer on Oct 12, 2010 21:00:45 GMT 1
Are you going to use one or two batteries?
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Post by killioughtta on Oct 12, 2010 22:33:35 GMT 1
Sorry I haven't replied earlier Erwin, I've not been on the board for a few days. As for a setup, the details of TSII I have, and as fitted to a mate's are as follows: Motors are Suppo 2210-12 (1400Kv, Max current 16A) spinning MA 7x4's. These are linked to Hobbywing 18A ESCs, mine mounted in the fuse, his in the nacelles. This setup pulls 32A at WOT. Both ESCs are fed from one channel and both have the red wire removed. A 3A (Hobbywing) BEC provides power to the servos, of around the 12-15g weight size. I fly on a single 2250 20C Loongmax pack and get nice performance, my mate parallel's up a couple of Ebay (Mystery??) 2200 packs and flies like a loon (vertical etc). Both have quite a few hours of air time, niether have suffered any problems with these setups. Mine also has home brew U/C fitted (I think you've seen it on here) and generally flys with the spy cam so has a fair amount of extra weight over a normal build. I don't know the overall weight I'm afraid. I have the nose wheel steering running off the same servo that operates the rudder, that might be worth thinking about. Just use an arm with two opposite tabs, the rudder off one side, the wheel off the other (as it's a nose wheel it needs to turn opposite to the rudder, if tail-dragger it needs to turn the same way). It saves on needing another servo and the fun and games involved with mounting it and connecting it up. If needs be I'll try to get a photo of it, although I may have already posted that a while back. The TSII has a WS of 1420mm. Don't bother thinking about counter-rotating props or any of that, it's not worth it, and doesn't really work on an RC level. If a motor stops, you just gotta kill the throttle quickly otherwise the running motor will put you into a spiral of death! One other thing, you'll love the sound of the interference that the props make, it's quite authentic. Wow, Nick, thanks for all that info. The TSII has a WS of 200mm more than the TO I plan on building but it's also lighter being built from lighter foam and materials so I'll have to look at those motors as an option. I'm glad to hear there's no prob running both ESCs from one channel and I had thought about using a larger (~20g perhaps) servo for rudder and steering combined. I hope to begin building this in a few weeks. It will be a learning experience for me. |
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Post by killioughtta on Oct 12, 2010 22:36:11 GMT 1
Are you going to use one or two batteries? I'm not 100% sure about that right now. I think 2 3S batteries of roughly 2200 mAh and 30C discharge should be plenty of power for the motors I'm considering but I might be able to get away with a single larger pack of, say, 3000 mAh. That's a long way ahead and easy to decide upon later so I'm not too worried about it right now  |
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Gohmer
Squadron leader
Posts: 113
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Post by Gohmer on Oct 13, 2010 15:06:42 GMT 1
The twin setup I'm using on my P-38's has two batteries and two receivers. That eliminates a lot of wiring and Y harnesses. Depending on how many servo's you have it might eliminate the need for an external BEC.
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Post by killioughtta on Oct 13, 2010 20:29:22 GMT 1
The twin setup I'm using on my P-38's has two batteries and two receivers. That eliminates a lot of wiring and Y harnesses. Depending on how many servo's you have it might eliminate the need for an external BEC. Two receivers? Do you mean two ESCs? That's how it should be. One per motor. |
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Gohmer
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Posts: 113
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Post by Gohmer on Oct 13, 2010 20:34:15 GMT 1
Two motors, two ESC's, two batteries, two receivers. Works well for me.
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Post by killioughtta on Oct 13, 2010 20:38:40 GMT 1
What do you need 2 receivers for??
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Gohmer
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Posts: 113
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Post by Gohmer on Oct 13, 2010 21:16:16 GMT 1
Don't need two. That's the way I like to do it. I've tried all the twin motor combinations of batteries/receivers/ESC's including one ESC for two brushless motors and two motors, two ESC's, two batteries, two receivers works the best in my opinion.
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Post by killioughtta on Oct 14, 2010 1:24:55 GMT 1
I guess my question is how do you connect two receivers?
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The English Teacher
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Post by The English Teacher on Oct 14, 2010 10:38:20 GMT 1
What do you need 2 receivers for?? Why do you need two question marks? |
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Gohmer
Squadron leader
Posts: 113
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Post by Gohmer on Oct 14, 2010 14:28:55 GMT 1
Transmitter connects them. You bind them both at the same time to the transmitter model memory you want the airplane on.
Watch out for the typo police:)
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