[karla]

Last night my customized 104cm length wing spar arrived (originals are only 50cm).
I mounted it and centered it on the mako.



Also drilled holes in the spar in the 'engine room'


to enter the wires from the FC and drilled holes on the wing spar tips to exit the wires that will connect to the tilt house. Then fed the wires through the holes.

This is all fine, next challenge is to do all soldering for the tilt house but also to fix the wing spar from rotating, it has to be fixed even when the tilt rotors will create a turning momentum. I don't know how to best do that yet...

[TheOtherCliff]

I believe that the design of the birotor control is such that it requires the birotor to basically hover stable when the motor angles are locked (unmoving) pointing straight up.  The CG needs to be well below the props.

[kicekilla]

I believe that the design of the birotor control is such that it requires the birotor to basically hover stable when the motor angles are locked (unmoving) pointing straight up.  The CG needs to be well below the props.

some bicopters have the cg well below, but not necessary (or even preferred in my exp). On my bicopter I had the cg pretty close to directly between the motors. the servos will need to tilt the motors back and for yaw and pitch stability and motor thrust is used for roll stability.

One thing with your new spar Karla, does it pass through the CG on the longitudinal axis? if not, that is where you will have problems.


here is a video of my cc3d bicopter I made a while ago. I don't have it anymore but designing a new 250 sized one currently.

[karla]

Nice bicopter and flying site kicekilla!

That bicopter is designed to use gyroscopic forces for control right? Rotors tilting in 45 degrees angle? Thats an elegant and effective design.
This wing does not use gyroscopics for control (but will work differently, I hope



CG will be below Rotors but the way the Mako was originally designed the CG is 2 cm forward of the wing spar. That will mean that centre of lift will be aft of CG a bit (at least in hover mode). See the black dots on each side of the wings. I have been concerned about this but thinking I can move CG a bit aft with the LiPo placement...

btw I was clumsy enough to make a short on the power wires where it exits one side of the wing spar. I need to redo the wiring now 

[kicekilla]

Yes, mine was an OAT (oblique angle tilt) that uses the gyro forces to assist stability and control... but the normal trust vectoring is also used.. yours is a FAT (forward aft tilt) which uses the control /stability I stated before.


Slightly forward should actually work out pretty good. But keep this in mind... as your motors rotate forward the weight of the motor will shift your cg too so maybe shifting it back to the cg using lipo weight and then when you rotate the motors forward for fixedwing flight, the cg will have shifted back to the original cg or close hopefully.

Unless you designed your motor pod to pivot around its own cg (which is what I do when designing tilt mechanisms)

this is my latest tilt design:

[kicekilla]

just looking at your tilt pod design, it should be close enough that there wont be much cg at all. do you have a video of the tilter working? : ) I like the geared drive, I might try to do that actually. I don't know if my 3d printer can print accurate enough for the gears though.

[TheOtherCliff]

I could very well be wrong, but it seems to me that if you have positive stability (CG below rotors like Osprey?) that when hovering level, the motors will basically be pointed straight up and to make it go forward, you just tilt the motors forward and the CG pendulum allows the motors to tilt forward while it is still basically level.  No stabilization actually required.

With neutral stability (CG at same level as rotors) the CG is not helping.  Tilting both motors and accelerating laterally does not change the bank angle, so how do you make the aircraft tilt forward or backward (to maintain level) at all?  I don't think this will work at all.

If the CG is above the rotors you must constantly balance it like a top-heavy Seqway.  I think the FC can balance it.  I think you want Attitude mode and not Rate mode.  This is the scenario that is most like a normal multicopter.

[karla]

First to kicekilla,
Great you have experience in this area!
Yes mine are FAT and is controlled just like you said in post below.
My rotor tilt house design is near neutral to CG when its tilted around but not perfect. Its my first ever CAD-CAM design and 3D print I think its good enough for business though.
I will upload a video of it in action later when I have sorted the shorted slightly melted wires.
There are print shops who can print for you. In some below posts I have a link where to find one close to you and also the one who printed my gears.

Can you upload your design in a .stl file format?

Cliff,
I have no idea at this point in time but what you say seems logic
This build is your first case, have positive stability, CG below rotors.

[karla]

I re-wired the shorted things this morning.
Original idea was to make the motors detachable for easy transportation, but I realized it will be just too much wiring taking too much space and create drag, so I soldered them hard in to the frame.

Here is a video of the tilt rotors and the controls in action in hover mode

https://www.youtube.com/watch?v=zQPpcAR2nvg&feature=youtu.be

Coming this far I am a bit reluctant to take it to the field and try it out...
But that is the next step of course.
Bit concerned about the 'coughing' of the left motor...

[kicekilla]

Cliff, I misspoke, my CG (along the vertical axis) was definitely lower than the motors/pivot line due to my under-slinging the battery. Not excessively but not centered. it was roughly centered longitudinally thought which gave me the close to level flight attitude.

I agree that the further the cg is lowered the more natural stability it will have, but at some point maneuverability will be overpowered probably haha. 

I am curious to see what happens now with the cg  centered vertically. I will probably do some tests with different cg position once I finish building my 250 bicopter.

and yes on the bicopter in the video, I always flew in attitude mode. I don't remember trying rate, but will experiment with my new one.

[karla]

Finally took it for an intended first test hover.
Problems.
The motors did not perform much over 40-50% of rpm before disconnecting and did boot up beeps.
I tried 
. recalibrating the radio transmitter/receiver
. recalibrating the ESCs
Then I disconnect all servos from the FC to only test the motors.
They did start now and then but 'coughing' like in the video I uploaded before.
However, after some 3 min of trying, then the wires on other side of the wing started to smoke and melt

Question: is it mandatory to keep a thicker wire diameter on the power wires from the PDB and the ESC/Motors?
I think too thin wires (servo wire type) might melt if the motors are consuming too high current, but not causing the problem.
Any thoughts?

I am thinking to try another brand of ESC (Litlebee 20A) to see if they can work better with these Sunnysky x2204S-16, 2300KV motors than the current ones (Bl Heli 20A). However, don't have much hope this will fix it...

[TheOtherCliff]

Which wire got hot?  (From ESC perspective) Was it signal (servo) wires or input power wire pair or output power wire triple?

Generally, you need to maintain the same size of wire as comes out of the ESC.  The only ones that are allowed to be thin wires are the signal (servo) wires.

If any of the wires are too thin, it will cause hot wiires, power loss, motor stuttering and motor resets.  If wire sizes are OK, the problems you mention can also be caused by using props that are too large or a battery that can't provide the desired current at full power.

I know that @Mateusz uses the LittleBee ESCs.  I wouldn't think that is the problem.

[TheOtherCliff]

One other thing is that it is that long ESC power wires can cause inductance problems.  I have heard it recommended that if you need to extend the ESC input power wire pair a long way, that you put some ESC capacitors (same as on ESC input) (low Equivalent Series Resistance) across the wire pair in the middle of the length.  I also heard that it is better to extend the ESC output wire triple (don't use capacitors there ) than the ESC input wire pair.

It should not be a problem to extend the ESC signal/servo cable to the lengths you need.  Even to several meters.

Adding a voltage/current sensor to a system with long ESC input wires can cause ground loop problems.

[karla]

Thanks a lot!
Seems to be a lot more to this than I first imagined 

Hm yes the problem here might be the thin and long power cable pair going to the ESC.

. The wires getting hot (this and last time) is not the signal wires but the power wire pair going in to the ESC (V and Grd). I have these wires as thin as standard servo wires to more easily fit them inside the wing spars. The 3 wires out from the ESC to motors are fine, short and default size.

. I do have a voltage/current sensor between the LiPo and the PDB (hm, so this could cause some ground problems).

So I should use thicker, default size power wires to ESC and also consider to make the wire out from the ESC to motors longer rather than the power pair wire going in to the ESC. Maybe also remote the voltage/current sensor.

[TheOtherCliff]

Your main, real problem is the thin ESC power input wires. 

The other stuff I mention for things to keep in mind if you have future issues.  I wouldn't change them until I had further issues.