The "Turntable Generator"


Picture 1 shows a San Francisco cable car on a turntable in action.

It takes just one / two men less than 30 seconds to spin the cable car 180 degrees. That is pretty amazing since a single-ended cable car weighs 7.000 kg and a double-ended cable car even weighs 7.600 kg (source). Weight of the turntable not included.

Picture 1 - Cable car on turntable

San Francisco cable car on a spinning turntable

Picture 1 is a screen-shot from a video of a San Francisco cable car on a turntable. Watch video.

A more extreme example: a 190 ton steam train on a turntable. Three man turn it 180 degrees in about 90 seconds. Watch video.
Picture 2 - Repair on turntable

San Francisco cable car turntable reconstruction preperations
Wondering why that relates to generating energy? Well, a 180 degrees turn in 30 seconds equals half a rotation per minute (0,5 rpm).

A direct drive gear-less generator, used for instance in wind turbines, usually rotates at 20 rpm or less and need 1000 kg of permanent magnets in order to generate 1 megawatt of electricity.

Keeping this in mind, maybe the turntable concept can be used to power a direct drive generator more efficiently.

How It Might Work

Picture 3 shows one example. Note: the housing holding the stator and drivers should be self-supporting and not "lean" on the rotor / turntable.

The rotor (picture 4 shows a Siemens wind generator rotor) is integrated in with the turntable and can be powered by for instance a pin-gear style direct driver (picture 5). This type of driver should be suitable since the rotor / turntable's speed will be under 20 rpm and 6 m/s (21,6 km/h). This is comparable to the rpm and speed of direct drive generators used in wind turbines. The use of a gearbox, e.g. a planetary gear, is optional. 

Flange-less wheels running on a rail help to keep the turntable / rotor will stable while spinning so it is possible to accurately align it with the stator and keep the air gap between turntable / rotor and stator within optimal distance. 

In order to save weight the turntable / rotor should as much as possible be made of carbon fiber or a futuristic material like aluminum that floats on water.

Picture 3 - "Turntable" generator

Design of a direct drive generator inspire by the cablecar turntables used in San Francisco
Picture 4 - Rotor Wind Generator

Siemens new direct drive gearless wind generator
Pictures 3a - 3d shows some other generator ideas e.g. the use of a double stator and are based on a turntable concept used in e.g. car showrooms which use smaller wheels but still have an impressive load capacity (see picture 9).

Picture 3a
car turntable inspired direct drive generator with flat rotor
Picture 3b
Car or train turntable inspired direct drive generator with a double stator
Picture 3c

Turntable inspired direct drive generator with a double stator
Picture 3d

Turntable inspired direct drive generator with a single stator

Picture 5 - Pin-Gear Drive

Pin gear and motorThe gear can be powered by a combustion engine, hydraulics / electric motor.

It also possible to fit the gear driver with a turbine and power it with e.g. steam for use in concentrated solar and nuclear plants. This diagram shows a nuclear gas turbine (LENR) powering a eccentric direct drive generator.

Instead of a pin gear a mono-wheel style drive should also work.



Energy Potential Indication

In order to explore possible energy potential of the idea, data from a design study (thesis) on a 2,25 MW (2 MW to grid) permanent magnet direct drive generator, spinning at 18 rpm, for wind energy applications was used.

The outside diameter of the generator laminations (basically the stator) is given as 3,9 meter (picture 6). The weight of the permanent magnets as 1,86 tons and the weight of iron (for all the generator) as 17,31 tons (picture 7).

Based on this data, for calculation purposes the diameter of the rotor is set at 4 meters and the weight of the turntable / rotor is set at ~ 20 tons (the weight of iron: 17,31 tons + the weight of the permanent magnets: 1,86 tons). A safe estimate because some of the iron is also needed for the stator.

Next: How much energy would be needed to spin a 20 tons, 4 meter in diameter rotor traveling at 13,56 km/h*? *(4 meter x 3,14 x 18 rpm / 60 seconds = 3,77 m/s = 13,56 km/h)

Picture 9 shows a container with a load capacity of 42000 kg (twice the rotor weight. It's travel speed with a load is 21 km/h (13,56 km/h needed). It is powered by 250 kW diesel engine which has a fuel consumption of 15 - 28 l/h.

A 2000 kW diesel generator consumes at full load 141,9 gal/h = 537 l/h. Source.

Thinking of the cable car video, than this engine could be strong enough to spin the rotor. Even if 4  engines would be needed, their combined fuel consumption would still be significantly less than that of a 2000 kW diesel generator.

Another way to look at it. Four 250 kW diesel engines would give it a power-to-weight-ratio of 50 watt per gram. A TGV 2N2 high speed train (380 t, 320 km/h top speedm 9400 kW) has a power-to-weight-ratio of 25 watt per kilogram. Source. There is no real difference between running a train on wheels and running a rotor on wheels.

The real question of course is: Why not use electric motors instead of diesel engines? Well that would mean.... No, we all know that is impossible. Right?

Picture 6 - Technical Data 2,25 MW Wind Turbine
Numbers on the outside diameter of a 2,25 mw generator laminations
Source: Page 9 of Anoop_Thesis_Final.pdf

Picture 7
Some weight specifications of 2 MW direct drive wind generator
Source: Page 9 of Anoop_Thesis_Final.pdf

Picture 8 - Reach Truck / Container handler
Reach stacker container handler with a load capacity of 42000 kgTechnical data

Model C4230 TL / 5
Load capacity 42000 kg
Service weight 70400 kg
Travel speed with / without load 21 / 25 km/h
Engine 250 kW diesel
Fuel consumption according to VDI cycle 15 - 28 l/h

Source technical data and picture.



Picture 9 - Technical Data Car Turntable
Specifications of a car turntable capable of holding a 6000 kg load

Picture 9 shows the specifications of car turntable with a loading capacity of 6000 kg (30% of rotor weight) and a maximum speed of 1 rpm = 1,32 km/h**(13,56 km/h needed). Power requirement 0,75 kW. **(7 meter diameter x 3,14 x 1 rpm / 60 = 0,37 m/s = 1,33 km/h).


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