Propeller Advice for a Dragonfly-ish Drone

[OrbitsR4Sissies]

(Moderators: I likely posted this in a less desirable place, so please move to the better thread.)

With Breaking Ground's latest goodie, propellers, I've been dying to develop a small quadricopter probe for Eve and especially Laythe.

I've landed on both worlds (probes) only a few times because of their natural challenges that match the actual moon of Titan (high gravity, thick atmosphere; large seas).

But I love rovers, and this Dragonfly-style way of navigating these worlds would be optimum for both. I have a design in mind already. But...

My problem is have too little information on using the new electric-only rotors and propellers. I can put some on, I know enough to just set them to "deploy."

But from there, the newer action and axis groups to learn how to throttle them up and down escape my understanding. The propeller and rotor settings are a bit perplexing. We're really missing game information on how to use and set these up, although I forgive Squad for this since they've done a lot of work in just getting these new features available in the first place.

I'm searched rather extensively and am aware of older threads such as

And I know of one build on KerbalX that played with the idea. I've also found a somewhat useful post that tried to explain the mechanics, as well as NASA mission discussion threads.

Does anyone have some examples or resources on the fundamentals of how to set up drone-type rotors and propellers and how to configure them for VTOL flight with the usual control keys and action/axis groups if applicable or easier?

I don't need lots of bells and whistles and can certainly complete the build the rest of the way. I appreciate any advice you have.

Edited July 13, 2019 by OrbitsR4Sissies
Clarifying - Electric rotors only

[Snark]

Moving to Gameplay Questions.

[Geschosskopf]

4 hours ago, OrbitsR4Sissies said:

Does anyone have some examples or resources on the fundamentals of how to set up drone-type rotors and propellers and how to configure them for VTOL flight with the usual control keys and action/axis groups if applicable or easier?

Well, real-life multi-rotor drones have all their multiple rotors to eliminate the complex control linkages and variable-pitch rotors of real helicopters.  They instead just have small-diameter, fixed-pitch rotors whose only control mechanism is that they are throttled individually.  They use small-diameter rotors so the blades don't have much angular momentum and the air will slow them down quickly, and thus are capable of changing RPM fast enough to provide a responsive control system.  And then they just attach enough of these small rotors to lift the weight of the thing.

You could, with some mental elbow grease, probably replicate this system in KSP using a combination of different sets of rotors assigned to various control axes and/or using manually operated KALs (IOW, you open the display and move the time line instead of running the animation).  But it would probably work better and be simpler instead to use a combination of SAS (especially for yaw) and having the blades be active control surfaces on the pitch and roll axes, with all rotor torque on main throttle so they always turn at the same speed.

You'd probably need several sets of reaction wheels and on Eve, you'll have to use electric rotors.  This brings up the question of power supply, especially for Eve.  The best way around this is to keep the craft as small as possible, so you don't have to run the motors at full throttle, thus greatly decreasing fuel / EC consumption.

 

 

 

 

 

Edited July 13, 2019 by Geschosskopf

[Foxster]

Here's a craft to try: https://www.dropbox.com/s/p4m0dbacugp5vss/Quadcopter 2.craft?dl=0

To fly:

1. Right click any of the spinning props so you can see it's PAW and pin it. This will make adjustment of the Authority Limiter easier.
2. Set SAS on 
3. Adjust the props' Authority Limiter with the up/down arrow keys. You'll want to increase it (up arrow) to about 120 to take off
4. You'll need to fiddle with the props' Authority Limiter for different heights and speeds
5. Have fun

 

 

Edited July 13, 2019 by Foxster

[OrbitsR4Sissies]

Thanks for the tips so far. 

I made a simple craft with four small rotors, set their props to deploy. Here’s where I’m probably wrong fundamentally because my rotors don’t even spin. I read to set the rotor RPM to the main throttle action group. 

The PAW shows the RPM moving with the throttle but no spin of any rotors. 

I haven’t felt this noob since I picked the game up over a year ago. Rockets be easy compared to this, and I’ve been everywhere with rovers or landers. 

[OrbitsR4Sissies]

OK, Foxster, while I couldn't load your particular craft to play (should've added it in a sandbox and not my career save) I was able to see what I appeared to need first: What and where to add parts for control in the action groups.

So you got me from complete ineptitude to this point of joy:

The little test craft does want to spin, which suggests that I should add four more rotors that are counterrotating. It also wants to drop from the sky as it begins that spin about itself, but this is a good starting point.

I'm using propellers and not helicopter parts if that is important. I did map the authority limiter but, honestly, have no idea what to do with that. If I can understand that fine-tuning, I'll have a fighting chance to send something like this to Laythe.

I guess that the authority stuff will help me fly it level but straight ahead as a drone truly does, rather than having to tilt the whole craft as much as some copters.

Edited July 14, 2019 by OrbitsR4Sissies

[Foxster]

What I did with my little craft was to offset the torque by having opposite pairs of rotors spinning in opposite directions, which means all the props of the reversed rotors need inverting. I'd guess for your craft that means pairs on opposite sides of the craft but not sure. Might need the four rotors equally spaced at 90° and the opposite pairs removed from symmetry and reversed. 

Unless Squad gets kinder with us, you will need to get the hang of adding all the props to an action group to adjust their pitch through the Authority Limit setting. Your craft will barely fly without regular adjustments to this for height and speed.  

[Geschosskopf]

13 hours ago, OrbitsR4Sissies said:

I made a simple craft with four small rotors, set their props to deploy. Here’s where I’m probably wrong fundamentally because my rotors don’t even spin. I read to set the rotor RPM to the main throttle action group. 

The "deploy" function of blades changes their pitch.  At the default authority of 100 and with the default deployment direction, activating "deploy" reduces pitch by 60^, reversing thrust.  This whole function, with suitable tweaking (like reversing direction) is very useful for planes, allowing to you manually adjust pitch to suit speed and altitude, plus throw on reverse thrust for landing.  It can also work as collective pitch for conventional helicopters, but I'm not sure it's what you want for this application.

It's a tough question which rotor function to put on the main throttle, RPM or torque.  This will require some experimentation to decide the issue.  I know at present that all rotors will develop max RPM at considerably less than full torque (at the default max engine size) so if torque is on the throttle, you can open the rotor's PAW and throttle down until you see the  RPM drop.  The question is, if you max RPM on the throttle, do you get full torque or only enough torque to make that RPM?  If the latter, then RPM might actually be better.  In either case, it behooves you to see just how much torque you need at sea level to maintain max RPM, and reduce the size of the rotor's motor to provide only that much torque at max (plus maybe a little more just in case).  This saves both weight and money, plus spreads full range of throttle position out more, so finer adjustments are possible.

[mystifeid]

47 minutes ago, Geschosskopf said:

It's a tough question which rotor function to put on the main throttle, RPM or torque.  This will require some experimentation to decide the issue

Does it matter? Put one on the main throttle (if you like) and put the other on a custom axis group. Or put them both on custom axis groups.

[Geschosskopf]

45 minutes ago, mystifeid said:

Does it matter? Put one on the main throttle (if you like) and put the other on a custom axis group. Or put them both on custom axis groups.

It MIGHT matter a lot for fuel consumption.  Once the rotor is at max RPM, having more torque than needed for that simply wastes (a lot) of fuel / EC.  With torque on the throttle, you can reduce torque to the minimum required to maintain the desired RPM and hence speed./lift.  The question is, if you put RPM on the throttle and max out RPM, do you get full---meaning too much--torque or only the minimum necessary torque?  If the latter, then cool!  You'd get the thrust/lift you need at the most fuel-efficient torque setting, so this would be easier than manually tweaking torque.  But if it's the other way, you'll waste a lot of fuel.

Edited July 14, 2019 by Geschosskopf

[mystifeid]

2 hours ago, Geschosskopf said:

It MIGHT matter a lot for fuel consumption.  Once the rotor is at max RPM, having more torque than needed for that simply wastes (a lot) of fuel / EC.  With torque on the throttle, you can reduce torque to the minimum required to maintain the desired RPM and hence speed./lift.  The question is, if you put RPM on the throttle and max out RPM, do you get full---meaning too much--torque or only the minimum necessary torque?  If the latter, then cool!  You'd get the thrust/lift you need at the most fuel-efficient torque setting, so this would be easier than manually tweaking torque.  But if it's the other way, you'll waste a lot of fuel.

With planes it has been my experience that it is expedient to tweak torque, rpm and blade pitch separately.

Initially I tried using torque in the main throttle group without touching rpm and sure, reducing torque also reduced rpm. But then I tried reducing rpm even more with a different axis group and found that I could then drastically reduce the blade authority. This had the effect of increasing speed while using less fuel.

With rpm on the main throttle (or any axis group), reducing rpm has no effect on the torque limit.

Anyway, I think if you are going to rely on torque reducing rpm optimally or vice versa, then you will be wasting fuel. It has just become automatic to assign axis groups for rpm, torque and blade pitch.

My only experience with a quadcopter has been lifting a single stage Terrier powered rocket to a position where it could obtain Kerbin orbit. Best results were obtained by keeping rpm and torque maxed and using blade pitch to regulate (maximum) vertical speed.

Edited July 14, 2019 by mystifeid

[Geschosskopf]

On 7/14/2019 at 12:40 PM, mystifeid said:

With planes it has been my experience that it is expedient to tweak torque, rpm and blade pitch separately.

I'm not talking about tweaking in the SPH, I"m talking about what happens when you move the throttle in flight.  There is no need to do torque and RPM separately because they're linked.  And, after doing the experiment mentioned above, torque on the main throttle is clearly superior to RPM.

It works like this....   

With RPM on the main throttle, going full throttle does 2 things:  it increases RPM to max AND it increases torque to whatever the current max setting of the rotor's motor is.  Initially, even if you gave the rotor a full-power motor in the SPH/VAB, rotor torque will be zero so you have to increase torque, too, before the blades will move at all.  Which will more than likely be too much and in any case requires you to adjust both torque in addition to RPM.

OTOH, with torque on the main throttle, increasing throttle starts the motor spinning.  It will reach an RPM determined by the mass and aerodynamic drag of whatever parts you have attached to the rotor given the torque provided by the throttle.  As torque increases, RPM increases until it hits the max of 460.  For pretty much all values of rotor motor strength, max RPM will be achieve will less than full throttle.  Thus, increasing torque beyond the point of max RPM simply wastes fuel because you get zero additional thrust.  And note that you don't need a separate control axis for RPM,

[mystifeid]

11 hours ago, Geschosskopf said:

And note that you don't need a separate control axis for RPM

Unfortunately it seems that lowering the rpm limit, even so that it is still above the reported current rpm, appears to have a marked effect on fuel consumption.

Using a four engine plane carrying 2000 units of LF in level filight at 3000m and having only used torque and blade pitch adjustment so far:

Torque Limit -     16.6%
RPM Limit -        460
Current RPM -    250
Speed       -         220
Prop Authority -  44
Fuel -                    62.4mU/s (per engine)

Subsequently reducing the RPM limit to 285 produces no effect on the speed or current rpm yet appears to lower fuel consumption to 38.7mU/s (per engine).

Edit - Later had the time to watch the actual fuel consumption over the course of an in-game minute. With the RPM limit at 460 I used 15 units of fuel. Lowering the RPM limit to 285 saw the fuel used drop to 9 units. This corresponds to the fuel consumption reported by the engines - ie

0.0624 x 4 x 60 = 14.976
0.0387 x 4 x 60 =  9.288

Also, in the current configuration of this plane, I find it much easier to fly (in level flight) with a torque setting of around 25% and an RPM limit of around 300. This still gives me a fuel consumption of around 60mu/s per engine but with an extra 25m/s flying speed. Flying with minimum torque seems to produce bigger fluctuations in the current rpm and suddenly the blade pitch becomes incorrect, the speed drops, blade pitch gets further out of whack and then I'm falling out of the sky.

Edited July 16, 2019 by mystifeid