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Jan 26, 2020, 05:31 PM
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Build Log

V Bi-copter


Recently I saw this video for the V-coptr Falcon bi-copter from Zero Zero Robotics and was intrigued.

Introducing V-Coptr Falcon from Zero Zero Robotics (1 min 20 sec)


While I'm not trying to develop my own revolutionary designs, practical applications of unique ideas do intrigue me. A bi-copter isn't common although quite a few examples of varies types have been built and flown successfully. None have been made in a serious commercial application that I know of until now.

Most of my multi's are standard camera platforms or big customs. A bi-copter isn't something I've tried before and since Ardupilot has a good platform for tilt-rotor flight control, it was time to try one.

Already have some new LDPower 4114 320kv motors that will use 17x6 folding props. Decided to go simple on the motor pivots and use RDS3115MG servos. Printed some mounts for those a few days ago. Initial plans are to use 22mm CF tubes for motor arms and adjustable landing gear mounts for the motor mounts. Picked up two fuselage plates for an XK Aircam X500 for the main fuselage. While I have a few larger reptile frames that could be modded, or 450 symmetrical frames, the XK plates looked like a good starting point for various reasons.

The 22mm CF tubes will be attached to the upper and lower fuselage plates via tube clamps attached to mounts either 3D printed or aluminum plate. Still deciding. But it also occurred to me that modified webbed fiberglass motor arms could be used. They wouldn't be as stiff as the CF tubes but probably stiff enough. Will have to look into that although running the wiring inside the CF tube was always a design factor.

Plan is for a gimbal and camera out front with battery out back adjustable to achieve neutral CG. Battery will probably be 6S or possibly 5S. FC will likely be some version of Matek. Control link will likely be FrSky R9 with 400mw 1.2GHz video although I do have some 433MHz OpenLRS stuff I'm still playing with in addition to EzUHF. Just waiting for a few more parts to arrive.

This project is simply to see if a stable and practical V-copter can be built on a budget and what its performance might be compared to other similar size DIY multi-rotor camera platforms. For truly "practical" budget HD flying video it's hard to beat something like the Hubsan Zino Pro using a big tablet to allow you to see detail in the image. You know, for locating the big orange parachute of NWS balloons or the occasional downed aircraft.

More posts as the project progresses.
Last edited by XionUAV; Feb 20, 2020 at 11:31 AM.
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Jan 26, 2020, 06:32 PM
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This user is an expert in unconventional designs https://www.rcgroups.com/forums/member.php?u=725256. See also https://www.rcgroups.com/forums/show...lcon-%2A%2A%2A
Jan 26, 2020, 08:28 PM
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Quote:
Originally Posted by robca
Thanks for the link. Interesting conversation on that thread.

I'm an engineer and aviation enthusiast and started flying over 30 years ago. Used to co-pilot a Jet Ranger 206. Not that that helps with model flying but it's a fun fact. Actually, training for and flying the real thing made trying to fly model helicopters and quads fast next to impossible. The collective on model radios is backwards so when I wanted to climb I'd instinctively "pull" collective which, of course, would cause the aircraft to go in the direction opposite of what was expected thus browning the shorts. So I still fly them but usually fairly slow and methodically. No quad racer-boy antics for me. Have no problem doing silly-fast stuff with fixed-wing. Probably because "pulling" climbs, like it's supposed to.

The engineering side is at least as fun for me as flying. Designed what I dubbed "Rotary Air Brakes" for one special purpose UAV. Have designed and built stuff others laughed at but actually fly extremely well. At this point I have around 100+ aircraft of all types and sizes just because I find the different aspects of the hobby so much much. Having a 3D printer and designing my own parts has been hugely helpful. Recently finished a strut actuation system for an FX-61 tail-sitter project in the works. Couldn't have done that nearly as easily and cleanly with old-school tooling and milling.

Anyway, the V-copter design will no doubt have inherent instability issues during abrupt forward or reverse flight reversals because there's little to nothing to stop the pendulum movement of the fuselage. However with at least reasonably modest control inputs there's no reason why it shouldn't generally fly fairly well, as long as the FC is tuned properly.

All things to find out when the props start spinning.
Last edited by XionUAV; Jan 26, 2020 at 09:39 PM.
Jan 27, 2020, 04:28 AM
Registered User
The servos will wear quickly, regardless how much you overestimate them, it's a completely unusual working mode for a hobby servo.
I would rather turn this design into a tricopter, with the smallest tail prop you can adapt, even 3" will be enough for pitch and yaw.
Jan 27, 2020, 11:18 AM
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The Robot servos are heavy duty, metal geared, dual bearing and sleeved on the opposite side and designed specifically for heavy load changes so I don't see them wearing any more than any other servo used on an aircraft, such as servos for ailerons that receive constant changes from a flight controller (granted the loads on those servos are generally less although the size of the servo is also generally much smaller). Plus my design is a low-hour proof of concept build, not a 10,000 hour commercial aircraft. If I was designing this for commercial use then the motor pivots would be on bearings with a geared shaft and geared drive probably more like the original design.

Using a third motor would turn it into a tri-copter regardless how small the yaw/pitch prop is. I don't discount at all the fact that three props in a triangle are inherently more stable than two. Or if we go one more, four props in a square are more stable than three and the most effective and simple combination overall. That's why the quad configuration has become the standard for small hobby UAV's. I also don't discount the fact that mechanical pivots on the main drive motors introduce an additional point of potential failure. The extra weight involved for the pivot mechanics also likely offsets any weight advantage if not using pivots and utilizing a third stabilizing motor and prop.

But the exercise here is simply to see in real-world, hands-on testing how well a big V-shaped bi-copter with vectored motors might actually perform. That's all.
Last edited by XionUAV; Jan 28, 2020 at 12:41 AM.
Jan 27, 2020, 09:11 PM
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Found some interesting prop tests for the LDPower motors. On 6S the tested props jump from 15x5 to 21x12. I've never considered using a pitch that high on a multi-rotor but the chart shows that at a 3.8A draw, thrust is 2201g. Yeah I don't think so.

Looked up the real-world test spec's for a similar size and KV Cobra motor and the numbers were quite different. I trust the tests the guys at Innov8tive do. So best guess is the 17x6 props will produce somewhere around 2500g max thrust each at around 20A on 6S. The motors are rated up to 45A and 999W so larger props could definitely be used although not necessary for my proof of concept build.

Tarot makes a 21x7 folder but the grip won't fit the LDPower motors and the blade root specs are different than the grips for the 17x6. So I'll stick with the 17x6 for now. Could certainly try something like 20x10 wood props at some point though as long as adequate spacing is left between the two motors.
Jan 29, 2020, 02:34 AM
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Something else about this design that's going to be interesting to see how it behaves is having the IMU in the flight controller so far below the center CG, which is at the motors. Instead of pivoting, the IMU is going to swing while it rotates. Might work fine or it could be a mess. There's usually a program parameter for offset but it's still going to be way off center.

I remember on my S800 with Wookong they recommended installing the IMU at the back above the battery. So I guess center axis isn't always a necessity as long as the differential is set and working correctly.

Just waiting on standoffs and tube clamps.
Jan 31, 2020, 12:23 AM
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Found a more useful prop test chart for a SunnySky 4014 320kv motor. A 16x8 only draws 15A at full throttle with 6S so a 17x6 should be a little less than that. Full throttle would hardly ever be use anyway. Might try some 35A Cobra ESC's I picked up recently.
Jan 31, 2020, 10:26 AM
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Quote:
Originally Posted by renatoa
The servos will wear quickly, regardless how much you overestimate them, it's a completely unusual working mode for a hobby servo.
I would rather turn this design into a tricopter, with the smallest tail prop you can adapt, even 3" will be enough for pitch and yaw.
I would rather use swahplates so the servos don‘t need to move those huge motor masses.
Jan 31, 2020, 11:15 AM
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Quote:
Originally Posted by Woga65
I would rather use swahplates so the servos don‘t need to move those huge motor masses.
It would certainly be doable. What swash design would you use since the ones I'm familiar with require 3 servos?
Jan 31, 2020, 11:28 AM
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Quote:
Originally Posted by XionUAV
It would certainly be doable. What swash design would you use since the ones I'm familiar with require 3 servos?
Almost any 90 deg swashplate will do. Many of the toy-grade FP helicopters use only two servos. Some of them have a guiding rod on the opposite side of one of the linkages. If one linkage and the guiding rod on the opposite side is locked into place, the swashplate can only tilt in one direction and one servo would be sufficient.
Jan 31, 2020, 02:02 PM
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Quote:
Originally Posted by Woga65
Almost any 90 deg swashplate will do. Many of the toy-grade FP helicopters use only two servos. Some of them have a guiding rod on the opposite side of one of the linkages. If one linkage and the guiding rod on the opposite side is locked into place, the swashplate can only tilt in one direction and one servo would be sufficient.
Interesting idea. I've only worked with 450 up to 700 class helis and had never considered modifying a swash for pitch only. It would be a lot more complicated to build regarding motor mounting, power transfer to main shaft and supporting everything vs. just slapping a motor on top of a big servo. However, from an engineering standpoint it would be a more efficient operating design.

The robot servos are geared pretty low and have a lot of torque so they're pretty slow and smooth. I still think they're going to work fine even with the additional motor rotational mass but we'll see.
Jan 31, 2020, 04:14 PM
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Quote:
Originally Posted by XionUAV
Interesting idea. I've only worked with 450 up to 700 class helis and had never considered modifying a swash for pitch only. It would be a lot more complicated to build regarding motor mounting, power transfer to main shaft and supporting everything vs. just slapping a motor on top of a big servo. However, from an engineering standpoint it would be a more efficient operating design.

The robot servos are geared pretty low and have a lot of torque so they're pretty slow and smooth. I still think they're going to work fine even with the additional motor rotational mass but we'll see.
There are a few swashplates available for Chinook style helicopters. With one of those you could make it CP with just two servos. But those parts are expensive and made for large scale helicopters.
Jan 31, 2020, 04:42 PM
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I'm always good for large scale. However, just because a person can due something doesn't always mean they should.
Feb 01, 2020, 12:02 AM
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Quote:
Originally Posted by XionUAV
I'm always good for large scale. However, just because a person can due something doesn't always mean they should.
I prefer to keep it simple so i just removed the upper rotors from two koax toys and used the mechanics as is.

INAV powered BiCopter with swashplates (14 min 31 sec)


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