Stock Rotor Techniques

[Mister Dilsby]

Can anyone share some techniques for building rotating machines out of stock parts? I have some concepts for the chunkin challenge and beyond that could use them. I understand that rotating bearings are typically made from aircraft wheels in a ring, but am unsure about things like how far to place them from the shaft, what to use as a thrust bearing, etc. Looking more for design guidelines than finished .craft, but could certainly learn something by taking apart the latter. Thank you!

Edited March 16, 2015 by Kuzzter

[Spartwo]

Landing gear are not always needed, having a bearing made from a material wrapped around a shaft is more compact although requires more effort to turn. I tend to use SAS as a turning force so I needn't worry about limited use.

[Mister Dilsby]

Thanks! What stock materials can you wrap around a shaft? Do you mean to link up a bunch of structrual parts like girders and beams and angle offset them to make a ring, or something else?

[Azimech]

Rule number one: Never let the wheels of the landing gear clip with the shaft. KSP/Unity don't respect the colliders well when loading, resulting in an immediate jam.

Rule number two: both too wide and too narrow clearance results in power loss. Too narrow means the collider mesh of the shaft pushes the wheels too much up their suspension struts, resulting in power loss. Too wide and the shaft starts too tumble, again pushing the wheels too much up their struts but now with a larger force due to an imbalace.

Rule number three: After first attaching and rotating/offset the landing gears to have the proper clearance with the shaft, launch craft, return to editor and adjust the wheels again. Due to a bug, the first time the location is not respected by KSP.

Rule number four: Four wheels per bearing is not enough for reliable operation! A shaft of 1.25m requires a minimum of six and a max of 8 wheels.

Look at some of my newest designs, for example the Whistling Gnome, over here: http://kerbalx.com/users/391/crafts

[Mister Dilsby]

Rule number one...

Good stuff, thank you! I will take some of your designs apart and see what I can learn.

[Mister Dilsby]

Here's a few more things I learned so far taking apart Azimech's ingenious Gnome engine:

1. Symmetry on symmetry. Azimech put two (symmetrical) gear bays on each of four posts with mirror symmetry, then put the four posts around the shaft with radial symmetry. This way one can adjust clearance by moving the four (or six, or eight) posts, and keep clearance constant all the way around.

2. Gear bays for thrust bearings, too. There are two wheels at each end of the shaft to keep it from moving axially. I might try this with the wheels impinging on a cone rather than the flat end of the shaft.

3. Use a separator to detach the rotor shaft from the rest of the craft. The craft must start out as one piece, then in operation the rotor and stator have to be two separate pieces. I tried using clampos first, but I suspect the magnetics were interfering with rotation.

4. SPH clearances can be (visually) deceiving. When i looked at the shaft in SPH it appeared there was lots of daylight between the gear wheels and the shaft. In operation, every wheel seemed to be in contact with the shaft all the way around. Good thing this design and SPH 'gizmos' make it easy to tweak clearance (see #1)

I'm sure I'll learn yet more as i try to build my own, scaling up to allow some 'flinging' of parts. I'll leave this thread 'unanswered' for now because I'm sure there is more than one way to skin this kat. Maybe in the end I'll have enough techniques to help someone else out someday

Edited March 16, 2015 by Mister Dilsby

[Azimech]

I've copied your findings into my main topic, hope you don't mind :-)

[Mister Dilsby]

I've copied your findings into my main topic, hope you don't mind :-)

Honored! And it worked, too: I made an electrically driven centrifugal 'chunker':

...I went with 12 wheels per radial bearing, which is maybe too much friction. The lower thrust bearing does rest on a cone with four wheels, which seems to work pretty well. I will probably add an upper bearing for a bit more stability.

Edited March 16, 2015 by Mister Dilsby

[Foxster]

All the designs I have seen or dismantled are based on this idea. A rotating drum or a couple of round items like batteries that are supported in a 3D way. The landing gears used are massless so very handy.

The downside is that the axle/engine is big. You have to cram in all those landing gears and you need a decent distance between sets for stability. I'm really, really hoping the new landing gear in 1.0 will help with this. Or we might get a stock axle - but I'm not holding my breath for that.

I keep trying different ideas though, hoping I'll find some better parts to make an axle. No luck so far but hope springs eternal.

[Starwhip]

Here's a tip: KSP doesn't care if stuff goes through struts. You can have a wall of struts around your arms or rotor and a separate ship going right through them, and it won't even notice.

[Azimech]

Confirmed. Used that trick for my stock cyclic/collective experiments.

[Azimech]

Honored! And it worked, too: I made an electrically driven centrifugal 'chunker':

...I went with 12 wheels per radial bearing, which is maybe too much friction. The lower thrust bearing does rest on a cone with four wheels, which seems to work pretty well. I will probably add an upper bearing for a bit more stability.

By chance I just tested an electric engine with my standard propeller. It achieved a max thrust of 30kN. During testing of my smallest engine, the one you looked at, I tuned it's power output from 25 to 50kN. Imagine what a 4, 8 or 12 blower could do for your 'chunker'.

Edited March 17, 2015 by Azimech

[Mister Dilsby]

By chance I just tested an electric engine with my standard propeller. It achieved a max thrust of 30kN.

Hm. Well, my real motivation in this pursuit is to develop an all-electric helicopter that will bring a (comparatively) small rocket stage to high-ish alitute on Eve. Using two large counter-rotating rotors, I might be able to get a thrust of 200kN or so... which means I can lift less than 12t off the ground... which probably means forget it.

Unless I can make a giant reciprocating engine out of docking clamps! Ha ha! Haaa haaa haaaa! *THUD*

BTW I looked at that thrust test rig earlier, and it's absolute genius. One of the best things I've ever seen built in this game.

[Azimech]

Counter rotating rotors you say ... hmmm ... I have the tech :-) I'm was the first (and until now only) person to build a coaxial rotor system out of stock parts.

But I don't think it would be of much use, the big problem is how to get it to Eve. Descent is a problem to, it would probably tear the rotor blades or overspeed the system.

And thank you for that compliment!

[Mister Dilsby]

Counter rotating rotors you say ... hmmm ... I have the tech :-) I'm was the first (and until now only) person to build a coaxial rotor system out of stock parts.

Oh no, not coaxial, I was going to go Chinook. I may be STUPID but I'm not CRAZY!

[Azimech]

LOL

Nice one!