Flettner Rotor for small craft - Design and Build Prototype

[rwatson]

The story so far.
Without a machine shop, and not living in an industrial area, organising things are tedious.
For example, I decided to make the axle support system from 6mm aluminium. The one Local aluminium welder, had a large sheet of 6mm, that he wanted to charge 1.5 times the cost of a new sheet.
That was a lot of money, and I still had to chop it up.
I found I could buy 30x20 6mm 6061 plate squares on Temu.
Then I got into the electronic side of the system, and built a test rig. Once again, all the 24 volt switches, wire and fuses were available on Temu.
All item took from 4 to 6 weeks to deliver. Often I would order unsuitable items, and have to re-order better ones.

The event that slowed me down , was realising that the main axles that supports the Aluminium flywheel was bent. It could have happened when I spun the big disk unbalanced, or it could have been bent from new.
I thought that I should move the bearing from 200 mm from the actual wheel carrier, to much closer to the end

Of course, the axles shaft 60 mm from the end, wasn't parallel, nor machined for a bearing.
I toyed with the idea of welding up some extra thickness, and then machining it down, but opted for a bearing adaptor.
View attachment 197990

 

[rwatson]

This thread is very handy for referring inquirers and trades people to, as I develop the concept.

The latest stage was getting the bearing adapter made, thanks to a reasonably priced local fitter and turner I discovered by accident. ( He was also able to take most of the bend out of the axle, that may have been caused by unbalanced speed test. )


The concept is a method to better support the "Drive Wheel" at the end of the main shaft.
The Go Cart axle had the bearing location quite a way back from the wheel carrier, that supported the large Aluminium "Drive Wheel"



When I ordered the bearing adapter, you can see I was planning to use a Taper Roller Bearing.
The difficulty I encountered was creating a Bearing Holder for it. That would have taken about $100 to get machined, but I could buy a whole new Y bearing and holder for under $50.
On impulse, I bought a Y bearing, that has a bearing holder available. The load specifications are still way better than I need, but it has the flexibility of coping with small shaft variations, as well as having a suitable bearing holder.


The other side benefit, is that the bearing and holder are designed to accept grease/oil lubrication, which could be handy under it's more loaded location.

When assembled with its adapter, it looks like this

 

[rwatson]

Finally installed the Bearing on the end plate of the Truss,



and then inserted the axle, and mounted the wheel carrier plate



Then, I need to build a platform to support the bearing for the lower end of the axle

 

[rwatson]

The upper end of the tower mechanism is installed and completed.
Aligning the two bearings took some doing. I found my little Dremmel with a carbide bit was super useful in "adjusting" holes in the aluminium components.



Next is to install the smaller axle at the lower end of the tower, join the two with an aluminium tube, add the electric motor, braking system and speed controller.

The aluminium "plate" holding the lower bearing took a lot of ingenuity to shape and install between the tower girders.
Its a "hammer" tight fit to reduce vibration and movement.

 

[Deane W]

Hello, Thanks for posting the details of this project. I am just now collecting information and parts to build such a rotor into a small iceboat.
I will use Sodium Ion batteries because they work well in cold tempertures.
In looking at your drive system, I have what looks like the exact same scooter motor and gearbox that you show. Mine says it is rated at 350 watts.
I also see you are reducing the RPM to the rotor by the go-kart sprocket. This will result in insufficent RPMs as the output of my similar scooter motor
is only 175 RPM no load at 12V which should yield 350 RPM at 24V. Now the chain and sprocket will reduce that by about 1/3 = 116 RPM. Have you considered this?
I also wanted to see if you have seen this video of a very successful small boat. Looks like it moves right along in a light breeze.

I think your aluminum truss is way overbuilt for something as small as a canoe. You can see he just uses an unstayed aluminum tube! Also, look at the small size of his motor. It is an RC brushless motor by Eflite.

 

[Deane W]

In addition, here is a different Magnus force calculator you may not have seen:
Magnus Force Calculator https://www.omnicalculator.com/physics/magnus-force

 

[rwatson]

In addition, here is a different Magnus force calculator you may not have seen:
Magnus Force Calculator https://www.omnicalculator.com/physics/magnus-force

I checked that out, thanks.

It seems a bit optimistic, (107 Newtons V 160 Newtons) and also doesn't include the Pressure/Drag contribution.

 

[rwatson]

Hello, Thanks for posting the details of this project. I am just now collecting information and parts to build such a rotor into a small iceboat.
I will use Sodium Ion batteries because they work well in cold temperatures.
In looking at your drive system, I have what looks like the exact same scooter motor and gearbox that you show. Mine says it is rated at 350 watts. "
I also see you are reducing the RPM to the rotor by the go-kart sprocket. This will result in insufficent RPMs as the output of my similar scooter motor
is only 175 RPM no load at 12V which should yield 350 RPM at 24V. Now the chain and sprocket will reduce that by about 1/3 = 116 RPM. Have you considered this?

You are correct. The Motor I am now using is this one. I had to upgrade after doing the calculations for power requirements in earlier comments.
Flettner Rotor for small craft - Design and Build Prototype https://www.boatdesign.net/threads/flettner-rotor-for-small-craft-design-and-build-prototype.67600/#post-941796



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"I also wanted to see if you have seen this video of a very successful small boat. Looks like it moves right along in a light breeze. You can see he just uses an unstayed aluminum tube! Also, look at the small size of his motor. It is an RC brushless motor by Eflite."
Yes, I actually posted that video to the main Flettner Thread. Everything Old is new again - Flettner Rotor Ship is launched https://www.boatdesign.net/threads/everything-old-is-new-again-flettner-rotor-ship-is-launched.24081/page-41#post-955567
My stated objective is to create a rig that would work in MORE than a "light breeze", that's why the much, much stronger construction.
That catamaran Rotor is just a bunch of Polystyrene blocks glued to each other.
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"I think your aluminum truss is way overbuilt for something as small as a canoe. "

Indeed it is. If you look at the comments, you will see that the Canoe and the Tower are NOT intended for each other.

 

[montero]

I appreciate your effort to build this rotor.

Have you thought about using a hub e-bike motor ?
The axle is a bit too thin for wind loads, but depending on the engine it could probably be reworked. The rotor itself would only have bearings at the bottom. Free standing rotor.
Or use VAWT generator as a engine ? I don't know if it's possible but I think so.
https://pl.aliexpress.com/item/1005008256903621.html?spm=a2g0o.productlist.main.77.77ddl1Udl1Udxh&algo_pvid=33f9864e-cf4d-4434-b194-c1513cb75281&algo_exp_id=33f9864e-cf4d-4434-b194-c1513cb75281-38&pdp_ext_f={"order":"2","eval":"1"}&pdp_npi=4@dis!PLN!1996.21!1977.94!!!491.69!487.19!@211b80f717397924455913365ecc4e!12000044392332926!sea!PL!0!ABX&curPageLogUid=MaBnYtjWXn6d&utparam-url=scene:search|query_from:

 

[rwatson]

I appreciate your effort to build this rotor.

Have you thought about using a hub e-bike motor ?
The axle is a bit too thin for wind loads, but depending on the engine it could probably be reworked. The rotor itself would only have bearings at the bottom. Free standing rotor.
Or use VAWT generator as a engine ? I don't know if it's possible but I think so.:

Thanks for the input. Here is the reason for not using the Ebike hub



and instead using



Interesting that you mention VAWT usage.

At this point, I am planning on building the rotor in 4 sections.
This is primarily to make construction and transport easier, but the curious side of my mind wonders if I can configure them to provide a VAWT solution.
For that purpose, I plan to make the leading and trailing edges aerodynamic, instead of just a joining design.
I guess I will make the decision on the vawt concept when I see how hard it will be to manufacture.

I'll keep you posted.

 

[montero]

Forgive my imprecise English.
My idea was to use a set like this, for example :
https://www.aliexpress.com/item/100...9WCSO6L0&utparam-url=scene:search|query_from:

The second idea is to use a vertical wind turbine generator, not the VAWT turbine itself. Generator can be used as an engine, but requires an engine controller. These generators have the appropriate structure for your rotor. In this case, the rotor will only have a lower bearing, but a solid one.The cost of a generator, special controller, batteries, and a throttle can get big , unless someone can figure it out cheaply.
Bicycle kits are cheaper and include the necessary components. Lower and upper bearings arrangment is possible.Power available , no gears, less noise and wear are the pros.

 

[rwatson]

Forgive my imprecise English.
My idea was to use a set like this, for example :
https://www.aliexpress.com/item/1005008375395489.html?spm=a2g0o.productlist.main.59.7ed6YJ3DYJ3Dsh&algo_pvid=2c62cc0e-4e58-4924-b354-3052fa745299&algo_exp_id=2c62cc0e-4e58-4924-b354-3052fa745299-29&pdp_ext_f={"order":"-1","eval":"1"}&pdp_npi=4@dis!AUD!466.97!294.19!!!291.93!183.91!@211b804117399513258627682e920c!12000044768195669!sea!AU!0!ABX&curPageLogUid=VrKK9WCSO6L0&utparam-url=scene:search|query_from:

The second idea is to use a vertical wind turbine generator, not the VAWT turbine itself. Generator can be used as an engine, but requires an engine controller. These generators have the appropriate structure for your rotor. In this case, the rotor will only have a lower bearing, but a solid one.The cost of a generator, special controller, batteries, and a throttle can get big , unless someone can figure it out cheaply.
Bicycle kits are cheaper and include the necessary components. Lower and upper bearings arrangment is possible.Power available , no gears, less noise and wear are the pros.

You will have to draw a diagram. The problem with in-hub motors, is that they need to use the existing spoke and rims, which may not be strong enough for the cylinder.
You also can only use one hub, at the top, as the bottom one will have a column going through it.
Please feel free to draw it up and specify the components.

 

[montero]

Watch this movie :

to see how the motor looks inside. At 18:11 is axle shaft. My idea is to machine new shaft. It should be as long to get a solid mount in the hull at least 0.5m or more down (where the cables enter). The upper side of the shaft should also be extended as much as the lathe will allow.
There will be a second bearing on top of the shaft.

Connection between motor and rotor base plate can be easy done with srews , threre are two collars for spokes. Serial shaft diameter looks strong enough imo.

 

[montero]

IMG 20250219 0001 — Postimages https://postimg.cc/cvYyzDJ4

 

[rwatson]

Forgive my imprecise English.
My idea was to use a set like this, for example :
https://www.aliexpress.com/item/1005008375395489.html?spm=a2g0o.productlist.main.59.7ed6YJ3DYJ3Dsh&algo_pvid=2c62cc0e-4e58-4924-b354-3052fa745299&algo_exp_id=2c62cc0e-4e58-4924-b354-3052fa745299-29&pdp_ext_f={"order":"-1","eval":"1"}&pdp_npi=4@dis!AUD!466.97!294.19!!!291.93!183.91!@211b804117399513258627682e920c!12000044768195669!sea!AU!0!ABX&curPageLogUid=VrKK9WCSO6L0&utparam-url=scene:search|query_from:

.The cost of a generator, special controller, batteries, and a throttle can get big , unless someone can figure it out cheaply..

That model you have in our link, is only 250W. I calculated that I needed much more than that, but I have no idea how big your rotor is supposed to be.
I also thought about having the motor at the top, but I was worried about the weight up high, as well as having to run the power cables, speed controller wires etc all the way up the column..