In my idea the cams would sit between the nacelle and the spinner. It’s a two-part assembly. Fixed to the spinner, between the spinner and the nacelle, you would have concentric tubes (or arms) with holes at the bottom of each for the tethers to pass through. You would have a minimum of 2 of these concentric tubes if you use a single cam. Jutting out from the nacelle you would have the tubular cams. That is a part that can move in and out, moving in and out between the concentric tubes, depending on if you want to do cycling banking or not. It can also rotate if you need to compensate for different tensile shaft twists.
At first you could try not actuating the cams and just see if a fixed position of them works well enough.
The height of the tubes would be matched to the height difference of the cams. And say you use a single cam with a 30 centimeter height difference, you could vary the line length by a maximum of double that. You would need to extend the shaft coming from the nacelle then by 30 centimeters if you don’t allow the cam to move in and out, and by 60 centimeters if you do - unless you mount the two parts around the nacelle and spinner. So it might be better to use more cams instead, if that doesn’t make friction much worse
Still very keen to see some sort of model / sketching / toy version / patent … anything to get the physical orientation of components across more easily so that we can help you assess strengths weaknesses etc
a: threaded bolt, to raise and lower the mounting plate for the cams
b: tether
c: pulley riding on cam
d: cam
e: gear to turn mounting plate for threaded bolts, actuated by i.
f: mounting plate for cams, with threaded holes for a to actuate
g: mounting plate for threaded bolts, attached to shaft or nacelle with bearings
h: motor for bolts
i: motor, rotating cam plate depending on shaft twist
j: cover, fixed to spinner
k: nacelle, attached to shaft with bearings
l: shaft
m: spinner, fixed to shaft
n: not sketched and perhaps optional: grooves to constrain the pulley as it goes up and down
Note I make some mistakes in the sketch: You can see the pulley almost touching the top of the cover, but the mounting plate for the cams also almost touching the nacelle. So I’ve sketched the cam too tall here. In this position the pulley should be at the same height as the holes in the nacelle and cover for the tether, and there should be more distance between the nacelle and the spinner so the cam has some working distance, or alternatively you could make the plate f an annulus instead, going around the spinner. Also like I’ve sketched it here the bolts would interfere with the tethers (they should stop below the holes for the tethers anyway). Alternatives would be to replace the threaded holes with bearings that the bolts get fixed to, and the bolts going through the motors instead, or mounting the motors on the mounting plate, or annulus, for the cams instead and putting the threaded holes in the bottom, g, plate instead. Or just making the bolts shorter.
I’ve sketched a single cam. You can use more.
I’ve sketched the cam like a tube with a straight diagonal cut. More likely I think would be something like a sine wave. You can also imagine compound waves, one to do cycling banking, one to help with gravity slowdown, if that helps. Here the cam goes around the nacelle. It might also go between the nacelle and spinner.
As the spinner rotates, the tether is pushed up more and less by the cam throughout the rotation. As the mounting plate for the cam is lowered and raised, the tether is pushed up more and less by the cam. And as the mounting plate for the bolts is rotated, the cyclic banking occurs at different points of the rotation.
Brilliant Windy
Well done getting the sketch out, it seems to have opened up a whole host of possible configuration ideas.
2 questions…
What holds the nacelle or shaft from turning … Where does the torque come from so that energy can be imparted to the pulley carrier modulating the tether lengths?
Unless I am missing something… The nacelle is in line with the tensile shaft. The nacelle and cam are mostly fixed in place by the tower. The tethers go to arms, the arms are pulled on by the kites and cause the spinner to rotate. The rotation is retarded by the generator, which I haven’t drawn. So the tension required to go uphill comes from the turbine not freewheeling, or perhaps just the pull of the kites. If one kite can’t go up the cam, it is helped by the others going down the cam and rotating the spinner.
I don’t know. It seems like it would be and would be a drawback.You could think of ways to try to reduce it.
Inside the (green) gearbox there are two drums with cables that pull on the movable pulleys and so determine their position and with that the length of the tethers. You could actuate these drums with motors instead of with the cams to do testing.
Here I’ve drawn two cylindrical cams, one for each tether, 180 degrees out of phase with each other, see the next comment as to why. You could do circular cams instead, which might be easier to manufacture and take up less vertical space.
a1, a2: cams, fixed to nacelle, can be rotated. The only part drawn that does not rotate.
b: gearbox, fixed to shaft, can be lowered and heightened to increase or decrease steering, I think, if the gearbox and the steering pulleys are part of the same assembly.
c1, c2: acted on by the gearbox and lower and raise the steering pulleys
d1, d2: steering pulleys
e1, e2: drums
f1, f2: fixed pulleys
ga1, gb1, ga2, gb2: achieving a 90 degree angle in the tethers, arranged this way to reduce wind resistance
h: shaft
Not drawn: cam followers, covers, nacelle, arm, additional arms.
You could decide to do the majority of the steering from the ground so that other methods, a lifting kite or the kites steering themselves for example, have less to do.
I now use one (or multiple) cam(s) per tether, rotated 180 degrees from another. So that now tether travel of each tether is halved and tether wear is lessened and divided between the tethers. Control authority is presumably potentially raised. You can reduce tether wear presumably further by strengthening the parts that are frequently in contact with the pulleys and by varying the tether length so that different parts contact the pulleys.
Edit: I’m tending toward liking the idea from the previous comment better. The pulleys would have more distance to move along the arms for example.
Say you have 10 meter arms for example and you let the pulleys move 5 meters, you can vary each tether length by 2x5=10 meters, times 2 tethers for a 20 meter difference. At that point you could almost consider making a horizontal carousel.
Great to see the start in 3d development / design
It’s going to really help you get a feel for the physical properties / problems / relationships…
My top tip for everyone doing 3d design 3dconnexion spacemouse
using one saves sooo much time.
5m 10m arms … these sound like huge dimensions and masses to be flying
The longer the arms the better I think, at least for testing. Ideal would be if you could fly in a straight line and wouldn’t have to do any cyclic anything, second best would be to have as long arms as reasonable so you limit needed accelerations and so on and have more time to do things.
Say you’re going at 20 m/s, going in a straight line, or with arms that are 10 or 1 meter long:
Once you figure things out, you can decide if you want to make the arms shorter. You probably won’t as longer arms still should probably help with control, and power requirements, and torque transfer, and gearing / generator sizing (less need for rpm decreases from launch to flight as the flying radius increases).
This was done in SketchUp. I used to use that quite a lot. It does help. Now I try to do the same in SolidWorks or FreeCad, but you have to organize that correctly from the beginning or it gets messy, and I’m not so experienced yet, so it’s less conducive to doodling I think. Maybe I should go back to using SketchUp a bit more. Thanks for the tip on the mouse. I’ll look at some reviews.
