Originally Posted by Angelbaby

DIY Quadcopter Flying Witch
https://youtu.be/4GKv7ZFSLNk

Brilliant

Originally Posted by Gunslinger68

I finally finished my Bicopter built, using RCExplorers 3D print files. All parts are printed with ABS. FC is a Cleanflight SP Racing F3 DeLuxe. Had some troubles setting up the bicopter due to my lack of knowledge regarding the cli and general how-to. After two evenings searching the web I finally got the fc working the way I think it should. For the interested ones: Diff of my cli attached for persons like me who are not pros in setting up multirotors.

Motor filtering and large bi-blade props work great. The 5" tri blade props have a smaller disc area and thus have a harder time supporting the copter.

My Bicopter photo is attached...

1SB

you guys are running bicopters with Betaflight?

i dont need to start another project when there's one on my bench right now...but man that would be cool.

is it stable?

Yes I'm running Betaflight with dynamic motor filtering. https://oscarliang.com/rpm-filter/

This allows the Bicopter to fly without the shakes seen in David's RCE videos. So in that sense, yes its MORE stable then it was...

Look about 1:30 into this video for an example of the shakes:

The BICOPTER - TERMINATOR inspired RC Copter - only 2 motors? (5 min 51 sec)

That being said, you'll never be able to fly it (safely) in anything other than self-leveling mode. Best analogy would be like balancing yourself on a knifes-edge, while still being able to quickly maneuver around. To say that this is unbelievably hard wouldn't come close to attempting it in person. I've tried it once and it was one of the scariest flight experiences I've had to date. (Think flying Cuisinart blender)

In a nutshell, here's the break down for each Axis, either individually or combined.

Roll is simply a matter of motor speed and as such it has by far the strongest and quickest response. Thus it requires less P & I than the Pitch but more than Yaw. (minimal cross interaction with other Axis) Beyond the Axis order of importance, tune Roll as you’d a normal quad. (P, I and D)

Pitch control is a combination of Servo angle, CG and motor speed. Its pretty responsive so long as your not also Yawing hard. It should be setup with the strongest P & I values of the three, assuming you want the copter to remain stable. (Moderate interaction with other Axis) Tune as you’d a normal Quad except do NOT use D as this adds delay to an already slow Servo response. Case-in-point, Servos are typically 300-330hz while the crappiest ESC’s on the market are at least 100 times faster.

Yaw is a mix of Servo Differential angles and CG. While Yaw is important, it takes a back-seat to all other Terms. Thus Yaw will have the lowest term values to allow Pitch and Roll to remain dominant. Which is very important if you want the copter to be able to easily return to a self-leveled state. (Yaw has a Strong interaction with all other axis) Please keep in mind that in many situations that with Yaw, “I” drives the set point corrections, while “P” is how strong. Thus you’ll want only enough “I” to keep its orientation stable, with just enough “P” to have a rate of change that feels acceptable. Just like with Pitch, don’t use D-term unless you really enjoy flying with the shakes.

Now as you've surmised, all three axis can interact badly with each other dependent on the situation your in and which Axis are being using at the time. Example, during a high speed pass you attempt to turn sharply without first slowing down. You'll notice that while the copter is still moving forward, that its nose may suddenly drop mid-way thru the turn. Effectively the forward / up lift had been exchanged for Yaw as the Servos create more torque differential, causing the CG to fall / lean forward, possibly resulting in a crash. (Lawn Dart)

Reason for this is that the copters CG translates forward much like a helicopters and once the right amount of CG has been attained you'll achieve forward flight. After that, the motors will roll back (via the servos) to a neutral position to maintain the current CG balance and maintain forward flight. However once the Servos attempt to Yaw, past a certain point they can no long maintain the CG's current position and thus the nose drops. This is why a lot of Bicopters you've seen have either really low CG, the motors are mounted really high or it’s using a tail to help stabilize pitch.

All of this is compounded by the following design issues with the RCE bicopter.

• It has no large tail surfaces to help counter balance Pitch CG in forward flight. Sure the little fins help but they're more for the structural integrity of the frame than anything else.
  
• Yaw is 100 dependent on the same rotors used to control Pitch and Roll. A tail rotor would help but this would make it a Tricopter. However a simple rudder could help reduce the need for much Servo induced Yaw and thus help to maintain Pitch CG.
  
• The lack of variable pitch blades, which IMO would totally solve most of the copters stability issues but would make it a very complex craft to build. Example: tilt the blades to control Pitch and Yaw rather than tilting the entire motor. This would allow for smaller Servos to be used as well as decrease the reaction time from swinging those big motors around.

Things that will "help" with stability.

• Have the Axis terms (P, I & D) setup in order-of-importance, from Strongest to Weakest. Example: Pitch, Roll and Yaw. This will make tuning and flying the copter much easier.
  
• Ditch the 5" tri-blade props for 6" bi-blade props. (I use DAL 6045RN) This will increase the disk-area while reducing loading. Thus making the flight more responsive to your inputs and increase the flight times as well. Maybe swap to a lower KV motor to provide for more torque rather than top end, such as 2207-1900kv. Basically any 2207 motor would do fine so long as the KV is low. (Assumes 4S LiPo)
  
• Motor filtering is the bomb, never fly without it.
  
• Adding a custom canopy such as what I have. This not only allows you to access the electronics without taking the CF panels off but the body shape acts like a wing in forward flight. Link to files: https://www.thingiverse.com/thing:3571841
  
• Disable Yaw & Pitch D-Term as D doesn’t work well with Servos. Generally, Servos are already slow to respond but D just makes it worse due to the added loop delay. In other words, shakes and oscillations may result from processing lag.
  
• Disable things in the PID tab that automatically rescale or adjust the PID’s in flight. Otherwise you’ll have one hell of a time trying to tune in good values while the algorithms are changing PID’s on the fly. Please keep in mind that many of these functions are really intended for Quads not a copter with only two motors. Once you’ve a stable tune you can experiment (carefully) with those functions to see what actually helps and what turns the Bicopter into a lawn dart.
  
• Within the CLI turn off runaway_takeoff_prevention. This is a Quadcopter specific feature that has issues with Bicopters. Effectively you’ll see the copter self-disarming inflight as the software doesn't understand that it only has two motors.
  
• Use the highest Voltage your Servo can handle for the best response time and torque.
  
• Never use the flight-controllers 5V BEC to power a Servo. Unless you don’t mind burning up both!
  
• Install sOat mounts for the motors / servos as the offset will offer more Yaw torque without the need for the Servos to rotate as much. Making it much easier to turn without the nose dropping as much. https://www.thingiverse.com/thing:3166975

Here is one of my flights thats really stable.

Bicopter Fun Flight (6 min 24 sec)

From time to time I've done a few Flips and Rolls too. However the recovery is like one giant twitch (auto-leveling) and then your not really sure which direction the copter is facing. Sure FPV is possible but the cameras view is bouncing all over the place making judging the height above the ground very difficult compared to flying a quad.

Here is what FPV looks like.

Bicopter Maiden Flight (2 min 11 sec)

Have fun and Safe flying!

1SB

1SB what a great writeup, thank you! I got put on a work project and my hobby time disappeared so I didn't even check this thread until now. I think larger tail surfaces would be top of the list for a DIY version.

Originally Posted by falcongsr

1SB what a great writeup, thank you! I got put on a work project and my hobby time disappeared so I didn't even check this thread until now. I think larger tail surfaces would be top of the list for a DIY version.

Hey NP!

Forgot to add that you should NEVER power the Servos from the flight-controllers BEC as this is a sure-fire way to burn up both the FC and the Servos. Instead, use an external BEC such as the Matek FCHUB-W as this can push 7V @ 5A.

Edit: updated original post with more info.

1SB

These are two of my larger drones the one with the green props is a 350mm turning 9" props. It is installed with INAV. The larger drone 560mm with the carbon 12" props, it also is running INAV and has a full 3-axis gimbal high-def camera mounted underneath. I designed it so that the arms can be easily taken off to be able to transport onto my sailboat and packed away and not take up too much space. I also have some other ones that I'll post up here later. I'm a designer builder, can't say I'm a great flyer but love building. Hope you enjoy, if you got any questions just post it here and I'll try and get back to you.
Thanks,

hi, i make 4" toothpick build, naughty weight 46g, 92g with 18650 battery. lipo 550mah hovering time is 10min, lion old 2000mah 17 min flying time, i think with good 3400mah, flying time will be around 25-30 min.

diamond f4 flight controller
3d printer frame PickleBig4v2_4in_true_X_153mm_v1-0
2$ motors, 4300kv 1-2s
hq props
mobyla 6 canopy

so far this is just an idea. without FPV, but maybe in the future...
Worth continuing?

Originally Posted by edic

so far this is just an idea. without FPV, but maybe in the future...
Worth continuing?

awesome!
Video of flight, please (not fpv video)

Isn't that going to be very inefficient with 25% of the thrust being blocked for each prop? It's going to make some interesting noise with the overlapping props throwing air against the top plate. I wonder if it would even be stable.

Can't wait to learn what you discover!

Originally Posted by chunkslayer

hi, i make 4" toothpick build, naughty weight 46g, 92g with 18650 battery. lipo 550mah hovering time is 10min, lion old 2000mah 17 min flying time, i think with good 3400mah, flying time will be around 25-30 min.

diamond f4 flight controller
3d printer frame PickleBig4v2_4in_true_X_153mm_v1-0
2$ motors, 4300kv 1-2s
hq props
mobyla 6 canopy

What do you think of these motors? Reliable? Quality? I see them for $2 and less, but no point in buying them if I just have to replace them later.

Originally Posted by falcongsr

Isn't that going to be very inefficient with 25% of the thrust being blocked for each prop? It's going to make some interesting noise with the overlapping props throwing air against the top plate. I wonder if it would even be stable.

Can't wait to learn what you discover!

Yes you are right about everything. I think that not 25, but 35% of thrust is blocked. This was a test item, and now I'm trying to solve these problems. Firstly, I think it's worth turning the frame but 180 degrees, making the props pushing and allowing maximum access to the air flow down, mount all electronic components from above, including the battery. But then a new problem appears, too high a center of gravity. The work has just begun. I will try to shoot a video with the flight in the near future and post it for your judgment.
Here are some photos with the new version of the frame, and the insides of the first version.
P.S. sorry for my english, it's all the fault of google translator)))

My 5" Aesir II is coming together!

F7 AIO fc, gps, and Express LRS! All the good stuff...

Folding PVC frame for an octocopter drone. Heavy, but fun to build! Diameter is about 1.1 meter.
I used Naza M-v2 FC, and T-Motor MN4010 - 400 kv motors with 16.2-5.3 T-motor props.
Short first flight video:

IMG 1431 (0 min 52 sec)

Instructable for the frame build is here: https://www.instructables.com/PVC-Oc...r-Drone-Frame/