[karla]

Got it. Thanks!
This will keep me off the streets all weekend anyway

[karla]

Puuh... finally done rewiring everything out to the wings.

I moved the ESCs from the tilt pods in to the body, just next to the FC.
Then rewired the tilt rotor servo triple cable and the triple fatter size wires out from the ESC to the motors.
Had to enlarge the wholes in the spar to get it through. Succeeded. Also made the tilt pods removable like the original design idea.   

... also need 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...

This was solved by friction of adding lots of hot glue in the wing where the spar is naked (see earlier pics). On top of the glue I pressed in the cut out foam pieces. Feels very steady and I can't force the spar to rotate even adding considerable force.

. used the same motors but a pair of brand new Blheli ESCs to start fresh
. calibrated them and motors using setup wizard for Tricopter
. all seems okay. no stuttering of motors yet.
. i kept the voltage sensor in the configuration though.

Using default PID settings from LibrePilot Vehicle setup, Tricopter.
Then set up a flight mode for Hover:
. Roll-Attitude,
. Pitch-Attitude,
. Yaw-AxisLock,
. Thrust-Manual
Took it out for a first lift off test. Trying to hover. Main idea to check CG, lift, stabilization.

Interesting initial result:
+ input controls work in correct expected directions
+ fx corrects all moves in correct directions
+ motors starts and spin smooth (up to a point, after that left motor do some stuttering in Attitude mode, not in manual)
+ tilt rotor mechanisms work fine
- seems having insufficient lift, however not really sure since if I switched to manual stabilization then seems plenty of power
- the tilt rotors Pitch was visibly oscillating, so consider to cut PIDs by half
- seems Pitch is uncontrollable, maybe CG is not far enough below the rotors, consider to rise the rotors higher or move LiPo lower.

Should I try change the left motor? It might have gotten damaged by previous experiments.
The ESC of left motor is getting much hotter than the right ESC. Both motors are hot but then again its some 35 degrees celsius here today. These ESCs have no BECs its provided by the PDB.



Also thinking What effect the Vehicle Set Up settings may have on motors when using 100% 50 or 25% of mixing for Roll. Could this make motors stutter more or less (when in attitude mode)? but why just one and not both?

[TheOtherCliff]

. i kept the voltage sensor in the configuration though.

You shouldn't have a problem with that since your ESC input wire pair is normal length.

+ motors starts and spin smooth (up to a point, after that left motor do some stuttering in Attitude mode, not in manual)
- seems having insufficient lift, however not really sure since if I switched to manual stabilization then seems plenty of power
The ESC of left motor is getting much hotter than the right ESC.

You have plenty of power in manual mode, but not in stabilized.  Motors getting hot.  It also probably jumps to this reduced power just above zero throttle.  These are symptoms of "invisible oscillation" but there is another possibility described towards the end.  There is a very fast oscillation caused by PID too high (D term at least???).  Explanation: When the throttle is very low say motors at 5%, 5% the most stabilization can do a roll is 0%, 10% or 10%, 0% but the stabilization needs to give a lot of change, it increases throttle.  The biggest increase it will do is to 50%, 50% so that it can do a roll with 0%, 100%.  This increases the effective throttle from 5% to 50%.  You give 5% stick and it actually makes the motors go 50%.

The same happens at the high side of throttle.  If you give 95%, the motors should be 95%, 95% but that only allows a roll of 90%, 100% or 100%, 90% so it reduces the effective throttle to 50% so it can do 0%, 100% or 100%, 0%.  The fact that you have plenty of power in manual, but not in stabilized is saying that you have this oscillation and the side effect is that you only have 50% power.

So when these oscillations are present, the result is that no matter where you put the throttle it is actually closer to 50% than you are asking for.  In very bad cases nearly all the throttle range is effectively 50%.  If it takes 55% throttle to take off, it will never take off.  Worse yet, if it takes 45% to take off, it will climb at just 5% throttle stick.

In your case, there is only one control that uses the motor speed to affect the control.  That is (hover) roll.  The other functions use servos.  Reduce the hover roll PID (may be forward flight yaw?) to fix this invisible oscillation.  Especially the D term.

Hover roll uses motors to affect the roll.  Yaw and pitch use servos.  These will probably all need different PIDs.

Also thinking What effect the Vehicle Set Up settings may have on motors when using 100% 50 or 25% of mixing for Roll. Could this make motors stutter more or less (when in attitude mode)? but why just one and not both?

These mixing sliders are used to reduce the roll, pitch, or yaw when 2 or more use the same "actuator".  For you, hover yaw and hover pitch use the same servo actuators, but only hover roll uses ESCs, so I would set hover yaw hover pitch both to 50% and hover roll to 100%.  Be aware that changes here affect the PIDs.  Doubling the mixer is like doubling the PID so tune after changing the mixer.

I don't know why one motor stutters and not the other.  Fix the PID oscillation and see if that goes away?  I am guessing that the stutter does not happen in manual mode.  If the stutter does happen in manual mode, then it could be the reason why you can't lift off in stabilized mode.  One motor has less power, so it reduces the other motor to keep it from tipping over.  Stutter can be caused by props that are too big or bad battery or bad connection (or too thin wire ).

In all the above when I say for instance hover roll, that is forward flight yaw.  I don't know whether you have this set up as roll or yaw.

[karla]

Wow, that was a mouthful of advice Will need to digest.
Thanks a lot!

[karla]

Hello,
Done some more experiments

1. Yes, I think there was a "invisible oscillation" problem cutting down the power and thrust to 50%.
Fixed that by lowering PIDs of Hover Roll. I know its okay since the lift generated is the same with stabilization set to manual for Roll as having it set to attitude.
Good.

2. Yes, the hover pitch oscillations was more related to the yaw PID settings being too high. Could be pitch or yaw since in hover they both move the rotors direction.
Fixed now by lowering them.
Good.

3. For the mixing table, I took the advice to put hover roll to 100%, this will only affect the motor rpm and should be fine. But for the yaw and pitch its a bit different. If set them to 50/50 as recommended the yaw is to vigorous and the pitch is insufficient. So I settled for 25 respectively 75%.
Good.

For center of gravity, I think there are two issues
1. x-axis:
it was obvious it has to be centered to were the wing spar is crossing the mid section of the craft. Otherwise nose go down or up when applying thrust to motors.
Fixed by moving the LiPo. However, this is a temporary fix. As pointed out in the previous post and picture, the design of the Mako has the CG 2 cm to the stern of the wing spar (wing spar is 2 cm aft of CG). So assuming when not in hover mode the center of lift will move to the designed CG and the weight needs to be readjusted or it will be uncontrollable and flip upwards. This can be fixed by another design of the tilt pods (tilt rotor housing). Save that for the future.

2. y-axis:
I have the feeling the pitch is not really effective and suspected the rotor tilt point is not high enough above CG.
So I tried placing the LiPo lower, under the craft. And it seems better and really promising as the FC seems to be able to stabilize it.


However, my big concern now is Do I have enough lift?
At present, giving full throttle with manual or attitude mode for motors does not give enough lift to be airborn.

Anyone good at doing the math to calculate/estimate available lift in grams?
. Lightest weight of Plane excluding cameras and stuff = 800 gram (including LiPo) but I likely like to add some 200-500gram more of stuff.
. LiPo 4S 1000mAh,
. motors 2x Sunnysky x2204S-16, 2300KV
. ESC 2 x Bl Heli 20A opto
. PDB say can take 3 Amp
. Props: 2x 3 blades 30 degree attack angle 60mm long blades from center to tip.





I am considering to fix both the CG y-axis and x-axis permanently, not by lowering the LiPo but by placing the rotor tilt higher by redesigning the rotor tilt house.
The x-axis CG can shift further stern when switching away from hover mode to forward flight, with a new design.
If I am doing that then i should also design a in a more powerful motor,
hence the need for the calculation

Anyone?

[Mangee]

Two places to check for thrust flybrushless.com or ecalc.ch.
Looks like around +-600g of thrust one motor.

Use ecalc as a multicopter to determine proper thrust for bicopter, idea.

Also have to figure out FF speed for stall and this link should help rcgroups.com

Building a VTOL but with 78" wing span so have been trying to research lots of info before I start.

[Mangee]

Just an idea but PX4.io has the E-flite Convergence coded for autonomous flight, Pixfalcon flight controller.
Its not stabilized for true hover, no tilting nacelles backward (pitch).
Might give you some ideas.

[karla]

Thanks a lot!
More to learn

Your VTOL with Wingspan of 78'', thats close to 2 meters right? Pretty big!
You design it all from scratch?

[TheOtherCliff]

Make sure you are getting full throttle command to your ESCs.  If you log your flight, you can play it back and look at an actuator scope to make sure it is asking the ESCs for full power.  You can do what you did before, and that is check the power when using Manual thrust, or when using Test Outputs on the Output page.

Make sure you don't have a throttle curve set on the Input page.  Also, AltitudeHold settings and *PathFollower settings have thrust limits if you are using Altitude Hold/Vario or some GPS flight mode.

You mentioned something a while back about one motor jumping more than the other.  If there is a weaker motor, remember that the FC will reduce power on the stronger motor to keep it level.  That is another reason for Manual having more power than some stabilized mode.

[Mangee]

Your VTOL with Wingspan of 78'', that's close to 2 meters right? Pretty big!
You design it all from scratch?

The air frame I will start with is the RQ-7 Shadow laser cut kit.
I am thinking of dropping it to 70 or 60 inch's due to the nacelles.
The design of a rotating nacelle with motor mount is the real work.
E-flite Convergence, Bananahobby V22 or Rotomast V22 style of rotating nacelle.
But yours will be flying before mine, if mine fly's at all.

[karla]

@Mangee, yes there are several FC out there, thanks a lot! I just want to do this VTOL with LibrePilot to see how far it can go and because it offers a lot more than just stabilization. I am very optimistic at the moment but will make it run with whatever fc
Good luck with your build, it looks beautiful!

Having read up on the links you send and exploring the site https://www.ecalc.ch I have calculated all is fine just need to change the props.
From 3 blade to 2 longer blades with higher angle of attack (6 inch long by 4.5 angle). Should provide Thrust theoretically for vertical continues flight with some 150g margin, without overloading motors, ESC or LiPo. Had the props at home

@Cliff, Thanks!
With the new props and new settings of the PIDs (of course), I still have some stuttering and strange behaviors of motor rpm.
But the whole project is looking more promising.
So I will really look in to your suggestions.

[karla]

Oops ... seems I was not properly connected to the internet when I got the OK on the current set up from the eCalc site

This is what it says now, suggesting
. move ESC from 20 to 30 Amp
. select a stronger and slower rpm motor
. and larger prop



Meanwhile, I will continue to experiment with the current setup since these warnings are really at the max throttle.

[TheOtherCliff]

I wonder if a pair of 2204 motors are strong enough?

[kicekilla]

I can't remember, have you tried a 3s battery and still gotten the motor stuttering?

just by "eyeballing" it and my quad experience, a pair of 2204's doesn't seem like it would be enough to hover this guy, but then again that is purely just by the looks of it.

just for comparison, my 250 quad weighs about 800g ready to fly. Its running titan 2206 motors and 5030 bullnose props on 4s and hovers at about 40% throttle. Those motors are pretty powerful and I get about 8 mins on my 2200mah.

So, it might be a bit much to hover about the same weight with half the motors (smaller ones at that).

they don't have my motors in stock anymore, but these might be a decent option.
http://www.multirotormania.com/clearance-sale/1126-mrm-titan-2208-2000kv-brushless-motor.html#idTab5

look for motors that can pull about 400g of thrust at 50% throttle.

[karla]

Yepp. Absolutely correct. Not enough motor thrust.

Thats also what the eCalc application showed clearly.
Its really great to select components by trail n error.