Kwad copter, anyone tried this?

[Redacted]

Hello I’ve  recently built up a quadcopter using only stock parts. While as surprisingly easy as this was to build, managing the motors / props within the assignable function groups has been quite a challenge.

Example: There’re four electrically driven rotors with three blades each. Two motors (diagonal of each other) spin CW while the other motors spin CCW. All four motors are throttled using my assigned throttle within the group manager.

Now while this does fly it has to be maneuvered using the SAS. Most of my attempts at controlling each individual axis or torque of each motor either does nothing or results in uncontrollability. Only axis i have managed was Pitch, and its response was very much like a real quadcopter. (Surprisingly) This was done by controlling each blades angle of attack to provide the amount of Pitch angle desired. (Motor speed kept constant once in flight) Obvious, this would be better if the speed of each motor could be varied to manage the copters orientation. Unfortunately, the rotors spin-up is pretty slow and thus far hasn’t allowed me to alter the main throttle input for each individual motor via the keyboard (Roll, Pitch, Yaw) control inputs.

 

Ultimately, my plan is to have a fully functioning quadcopter (or as close it it as possible) while using my Taranis X9 as the “Joystick” input. I currently do this with a few other flight sims and thought I’d give this a try here as well. Keep in mind that such a system once mastered; would be the ideal way to explore a planetary body remotely. (Assuming it has an atmosphere)

 

Anyone have experience with the rotor / prop control such as I’ve described above? 

 

Thank you in advance!

 

Redacted

Edited October 19, 2019 by Redacted

[Redacted]

Will post a few pictures and a like to the design Monday.

[Redacted]

Tried most of the day to get the copter controllable via torque manipulation. Fact is that the motors change too slow for this to be viable.

I did however make a version that uses SAS and ACS thrusters to control it's orientation.

https://steamcommunity.com/sharedfiles/filedetails/?id=1894442770

[CBase]

If you read the two tutorials about VTOL and helicopter, you will find that they mainly use the blade angle to control lift exactly for the reason.

This is even more true for quadcopters as you can use yaw and pitch directly if choosen well.

[Redacted]

On 10/20/2019 at 9:38 PM, CBase said:

If you read the two tutorials about VTOL and helicopter, you will find that they mainly use the blade angle to control lift exactly for the reason.

This is even more true for quadcopters as you can use yaw and pitch directly if choosen well.

Yeah, i have discovered that...

Was able to get Pitch (prop angle) and Yaw (Torque manipulation) working but Roll does some really strange stuff. It appears as if the rotor attempts to have opposing Roll Lift on each of its sides. When this needs to be each side of the Copter. Quad ends up fighting itself instead of Rolling. Now as for the other Axis, the motors response time is way to slow and the props can stall rather easily at higher forward speeds. For strong counter torque, the props either need to be at a high angle of attack or the rotors spun  past 200 rpms.

Sucks that motors, props and most other things are limited to one type of input / axis as KSP would be awesome for a little Quadcopter race. Would love to have direct input mixing available for the motors / props.

Edited October 21, 2019 by Redacted

[CBase]

Actually for roll the easiest solution is to simply use a reaction wheel. The required torque for roll is usually small enough and KSP reaction wheels are strong

You can make pitch and yaw work via authority limit from the blades if deploy them. Depending on rotation you might need to reverse deploy and/or use negative autohority limit. This way you can keep part count and rotating mass down. Angle Prop sounds like you added a servo to control blades. Although it does work mostly, SAS will not affect these.

Basically disable all control and enable only these:

     p

     |

y - + - y

     |

    p

 

I do have two KAL on my quadcopters: one for engine control, which spins up RPM and torque and one for lift (collective) which controls authority limit. The engine control is bound to simply switch control key and collective to throttle control. This way it controls very much like a rocket engine VTOL.

For figuring out the right configuration use F12 aerodynamics and very low RPM, so it stays on ground and does not crash, but you will see forces direction.

[Redacted]

Thank you for the constructive inputs but I thought the point was to make this work without the reaction wheels?

[CBase]

Depends I am building quadcopters to move around on planets with atmosphere, but without oxygen for jet engines. So my target is to keep it really simple and light weight and I don't care about realism.

However after reading your answer I looked quadcopter definitions up: https://www.dronezon.com/learn-about-drones-quadcopters/how-a-quadcopter-works-with-propellers-and-motors-direction-design-explained/

Since I am building in VAB, I had a different understanding of roll and yaw. Only a forward facing command module in SPH will conform with standard definitions. In regards of the official terms for quadcopters, you can roll and pitch with MCS for blades. Yaw is tricky as I doubt KSP Control Surface Control understands it right. But maybe... I will test it...

Anyway adding blade angle via servo control and a KAL will work to influence rotors as described in above report. Just keep in mind that you need to mentally replace RPM with angle of incidence for the blade since KSP motors are to sluggish for RPM control.

 

[IkranMakto]

12 hours ago, Redacted said:

Thank you for the constructive inputs but I thought the point was to make this work without the reaction wheels?

STOCK, WIP
My most complex quad-copter without reaction wheels, 8 rotors. I used KAL-1000 for each axis control ( pitch | roll | yaw | thrust ). Rotor speeds are constant - 350 rpm. It is able to fly 60 m/s forward and hower precisely without changing control, balancing or triming. 



I can't show my basic Quad-copters because I used Tweak scale for them and deleted this mod after updating to ksp 1.8

[Redacted]

@IkranMakto While this is really nice, it's still cheating by angling the rotors.

Instead whats needed for a real quad experience, is being able to manipulate the motor torque via channel mixing. This would allow for the simplest design insofar as what hardware is required to make it fly. One big issue here though is that the electric rotors spin up / down pretty slowly and thus have to be "braked" to slow them down enough to land. (poor throttle response)

What I've been trying to build is the most minimalist copter possible then adapt it to be fold-able for transport. It would end up being a 1-Kerbal transport to fly around conducting science on Eve.

[IkranMakto]

6 hours ago, Redacted said:

@IkranMakto While this is really nice, it's still cheating by angling the rotors

Watch this GIFs again and you'll notice that angling of rotors is just a way to keep vechicle horizontal, but not to pitch or roll it. You can lock all this four servos and it will fly, but slower. Collective control is main. 

6 hours ago, Redacted said:

One big issue here though is that the electric rotors spin up / down pretty slowly

You'll get rid of that problem is you will use elevons or small wings as blades. Squad gave too much moment of inertia and too low drag to their new blades. 

I'll make simple quad-copter for you later. 

Edited October 25, 2019 by IkranMakto

[CBase]

Really interesting, could you as well somehow explain how you configure the KAL for axis control ? Redacted is right: channel mixing (or at least addition) is what is really missing as I see it.

[IkranMakto]

2 hours ago, CBase said:

Really interesting, could you as well somehow explain how you configure the KAL for axis control ? Redacted is right: channel mixing (or at least addition) is what is really missing as I see it.

It works, but in multiplicative way. If you have 2 axis from -1 to 1, f.e. pitch and roll controlling a rotor, so pressing pitch down will result as -0.5. 

Here's the craft. Flying. Slowly, not always stable, but it works without reaction wheel. 451 kg. 
It's actually foldable by locking rotors(toggle brake) and pressing control group 0
Designed for Duna, but has not enough lift. 
Enjoy
https://kerbalx.com/IkranMakto/Stock-Qcopter

Edited October 25, 2019 by IkranMakto

[Redacted]

Now thats more like it... if done well, it will be an extremely light and efficient science transport. Should be able to recharge it via 1-2 small solar cells between flights.

BTW, i like the use of the fins for the rotor blades. Maybe you can suggest improvements to the blades in other discussions? Now as for the motors poor throttle response have have found to tie the rpm and torque to the same throttle channel helps considerably.  

[IkranMakto]

11 minutes ago, Redacted said:

Now thats more like it... if done well, it will be an extremely light and efficient science transport. Should be able to recharge it via 1-2 small solar cells between flights.

Quad-copters are slow, I think VTOL or STAL plane would be faster and more efficient.

 

19 minutes ago, Redacted said:

Maybe you can suggest improvements to the blades in other discussions?

For example? I already wrote my opinion about new blades in BG discussion

 

21 minutes ago, Redacted said:

Now as for the motors poor throttle response have have found to tie the rpm and torque to the same throttle channel helps considerably.

Use blade deploy angle instead of changing RPM. More precise and faster method. 

[Redacted]

Problem with using blade deploy is that the working range is rather limited. Using them the throttle up / down would provide for a very narrow throttle range.

[IkranMakto]

48 minutes ago, Redacted said:

Problem with using blade deploy is that the working range is rather limited. Using them the throttle up / down would provide for a very narrow throttle range.

Their deploy angle is 90 degrees, that's pretty wide and more than enough because stall AoA is 15-20 degrees. Most of time you'll need to deploy them between +1 and +5 degrees using KAL controller , but not directly by throttle. 

[Redacted]

Yeah thats what i mean...

The working range isn't 90 degrees but rather 1-5. This allows the throttle range to be in 20% (positive) increments. Even with the KAL-Controller, i doubt this would allow for much in the way of fine resolution to control the throttle. Keep in mind that as the copters angle and forward momentum is increased, that the blades will quickly reach their stall angle. This is despite a real quad still being able to generate thrust at almost all angles. (Unless moving really fast)

Even then, rather than controlling each propeller it "should" be far simpler to control each specific motor. ( "If" groups could be managed as such to control orientation) Only way I see to do this would be to either having a dedicated motor mixer or by using one set of props to control "general" lift, while another set on the same rotor was used for Pitch / Roll.

Edited October 26, 2019 by Redacted

[IkranMakto]

46 minutes ago, Redacted said:

Even with the KAL-Controller, i doubt this would allow for much in the way of fine resolution to control the throttle.

It allow. I already done it multiple times. 

 

50 minutes ago, Redacted said:

Keep in mind that as the copters angle and forward momentum is increased, that the blades will quickly reach their stall angle

No, If done right of course.
 

52 minutes ago, Redacted said:

Even then, rather than controlling each propeller it "should" be far simpler to control each specific motor.

And again no. Squad messed up angular momentum, so better to keep RPM constant.

 

55 minutes ago, Redacted said:

Only way I see to do this would be to either having a dedicated motor mixer or by using one set of props to control "general" lift, while another set on the same rotor was used for Pitch / Roll.

It's pointles since an actuator/blade/motor can be controled with with multiple KAL-1000. Please, don't miss the fact that every blade in this vechicle is really bound to 3 KALs (throttle & roll & pitch), otherwise it won't be even controlable. Only Yaw is done by differential tilting.

Look, it deploys from 1 to 7 degrees 

[CBase]

Although a pretty straight quadcopter, after playing around with your stock Qcopter and looking at the KAL settings: I found the craft to be hard to control without SAS and I found no way to fly fast forward, since you are missing the collective control and the different KAL overwrite each other, so you can never have two directions at once. An additive control and bound to SAS is really what is missing for KALs for a  perfect quadcopter.

[IkranMakto]

3 hours ago, CBase said:

An additive control and bound to SAS is really what is missing for KALs for a  perfect quadcopter.

That's a big question why developers made pitch, roll and yaw axises in action groups uncontrolable by SAS.