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Old Jan 02, 2012, 01:28 PM
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Coaxial FPV heli - Need opinions.

Hey guys,

I'll be creating a "UAV' for use in airsoft sooner or later here. I think I'll be using the Fat Shark Dominator kit as well as a large coaxial heli. I'm not sure which heli to use yet, but I have some requirements.

What I need out of the heli is as follows.

1. Stable platform - Should be able to handle up to 5-7 mph wind.
2. Long flight time - 8-10 min is a must.
3. Load capacity - It needs to be able to easily heft the extra FPV unit.
4. Space/Size - It will need to have the storage space for the FPV unit.
5. Speed - It should have a decent forward flight speed to keep up with the action on the field and to fight wind.
6. Fairly nimble - I will be flying through wooded and desert areas; I don't want to crash.
7. Durable - I will be flying this through wooded and desert areas; it will be crashed.
8. Cost - This is not a serious FPV unit like the crazy vids we see on Youtube.
It simply needs to be easy to operate and functional. Price needs to be kept as low as possible while meeting the above requirements.

Although I don't have personal experience with the Walkera CH-47, I'm thinking that this would be the best heli available for what I need.
I am also open to other suggestions as well. Quad-copters seem interesting, but expensive and an FP might work okay as it will be better in the wind, but I think will be harder to manage for a first time FPV pilot.




Any comments and suggestions would be appreciated, Thanks guys.
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Old Jan 02, 2012, 03:05 PM
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Germantown, WI.
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A triple or quad is the best platform for your purposes. More research in the multi-rotor forum should yield a suitable platform at a reasonable cost. I don't know of any readily available coax that would fit the requirements you list. The Walkera 38# (CH47) is probably one of the worst helis you could pick. It's movement authority is poor, it's prone to blade strikes ( like 5 or 6 at a time), it's underpowered for it's size and presents a huge profle for the wind to catch.
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Old Jan 02, 2012, 04:57 PM
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I'm glad I asked, thanks for the input.

From the videos I have seen I could not tell if the Ch47 was going to be powerful enough. Everyone just kind of hovers it about a bit in the vids. No real display of FF speed.

I do think you're right in saying that the tri/qaud copters are the best platform for an outdoor FPV setup. I figured they would be, but liked the price of the coax models.
I need to mount the camera on the under-belly of the aircraft, near the nose for best visibility of the ground, which is why I liked the CH47 design as it has a hollow design and the wheels give it a long stand-off from the ground, perfect for mounting the camera.

None of the conventional style birds seem to have a good lower mounting position. However, the tri/quad copters seem to meet this design parameter.

I foresee this getting pricey...
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Old Jan 02, 2012, 05:38 PM
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Not at all. I have a friend who just built a nice triple with camera for about $250 using pretty good stuff. Of course it adds up if you need a movable mount, adjustable lens, and that kind of stuff; more channels, more servos, more electricity, etc. Hobby King sells good components (brushless motors, ESCs, radio systems, control boards and servos) for very good prices. I would do some research in the multi-rotor forum and check the FPV forum, too. You can build an awesome triple with camera mount and 6 motors for about $1700. I was really tempted when I saw one. Look here: http://www.rchobbyhelicopter.com/sto...lticopter_Kits (even if you don't want to spend that much, there's lots of good stuff and good info on the site).

I think the bulk of the expense is really the FPV hardware. That will remain the same regardless of the platform you use.
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Old Jan 02, 2012, 06:42 PM
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Would the tri-copter your friend built accommodate the use of the Fat Shark movable camera system, plus the added weight? If so, $250-$350 for the aircraft plus the $300 for the FPV is doable.
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Old Jan 02, 2012, 07:28 PM
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Germantown, WI.
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He used aluminum tubing for a frame, but you can use anything you want for a triple or quad. I've seen fiberglass, aluminum, CF, even wood. The same goes for a cradle to hold a camera. Weight is simply a matter of using big enough motors and propellers. Brushless motors come in many sizes and configurations so that's not really an issue. Your major expenses will be:

motors (3 - 8)
ESCs (3 - 8)
multi-axis gyro and control module
battery
transmitter and receiver
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Old Jan 02, 2012, 07:48 PM
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Did he use one of the pre-built frame kits on the market, or did he build his own?
Do you know what the mah rating is on the batt. he uses? Do you also know his flight times as far as batt. life goes?
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Old Jan 02, 2012, 09:18 PM
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He built it himself. It's just square aluminum tubing for arms and legs and some flat aluminum for motor mounts, brackets, etc. Nothing that can't be done with a drill and saw. I think the electronics are mounted on a plastic sheet on spacers.
I believe he started with arms about 16" long and a main beam about 24", running 4200kv motors, swinging 7" props and a 1200 mah 11.1v lipo. The tail motor tilts with a servo for more thrust. However, I believe he enlarged it quite a bit and I don't know what his current specs are.

I could ask him, the next time I see him. He works in a hobby shop and could probably build one for you. I think this was for a customer, too.

I've seen a 6 motor triple fly. That's the one with 2 motors on each arm, one top and one bottom. Those things are wicked. They flip and loop like you wouldn't believe. I've got about a dozen helis now, all single rotor FP and CP. But, my next heli is going to be a quad. If I like the way it flies, I'll probably go for one of the 6 motor triples.
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