# Using Monopods for city travel utilizing linear induction motors

Prathyush
TL;DR Summary
Using monopods, for flexible and personalized scalable transport infrastructure.
This is another open ended question, exploring a space of design concepts, in similar spirit to this.

I want to explore monopods with regard to travel in densely populated cities(even possibly intercity travel). The main idea is to use small personalized pods to travel in tubes(or tracks).

The main design considerations and motivations are as follows,
1. The pod diameter is ~2 m just enough to comfortably seat a single person.
2. The pods can attach to each other dynamically to reduce air drag, by reducing the normal surface area per pod.
3. The tubes are made light weight, use minimum material and require minimum structural support. This allows the tubes to easily use available volumetric space.(unlike heavy infrastructure for required for rails and fly overs).
4. Pods are light( I am imagining under 100KGS), not sure what kinds of constraints will actually be imposed by physics.
5. Easy switching, between different tracks without significant speed loss allows.
6. The limits to speed mainly comes from radius of curvature of tracks, and ideally designed to be fast while keeping limits of acceleration to human comfortable values.
7. In principle allows for point to point travel cheaply, especially in crowded places like Apartment/Office complexes.

Some things/questions that need careful analysis
1. The efficiency of Linear Induction motors seem low. This is in part because of gap between primary and secondary. At this point I could not distill the main results from literature.
2. Two different track designs are possible. First carries current/energy as a part of the tube/track structure. Second uses a simple aluminum tube, with structural supports. There are different trade offs, in terms of pod cost vs track cost.
3. Switching between tracks at speed may be complex to engineer.
4. Air flow and ventilation problems can add significant complexity and weight.
The idea has been explored under the topic Personalized rapid transit and worth exploring independently.

Mentor
The issue here, in keeping with the spirit of the prior thread, is you are focusing on the wrong problem. The problem here isn't the efficiency of the motor, it's the cost of the infrastructure. This isn't a new idea and that problem never changes. Ask Elon Musk how his Hyperloop is going.

phinds, tech99, Rive and 1 other person
Prathyush
The problem here isn't the efficiency of the motor, it's the cost of the infrastructure. This isn't a new idea and that problem never changes. Ask Elon Musk how his Hyperloop is going.

This is not a hyperloop, which is vacuum sealed heavy and expensive.

Isn't a simple aluminum tube(or rail) with structural supports(sufficient to carry ~200 kgs of load every meter ) among the cheapest infrastructure?

The main design principle to minimize cost of infrastructure by reducing load bearing capacity.

Trains made sense(still do) when they were constructed, 2 rails on ground are very very cheap.
They don't make as much sense as over ground infrastructure, because you need to construct load bearing capacity for several thousand tons.

Prathyush
I had originally thought tubes are better, I realized a simple aluminum rail is sufficient, and cheaper.

You can use a double sided Linear induction motor, with battery on the vehicle.

Lots of details I don't understand, It's a sufficiently complex problem. But I believe(subject to further analysis) it is one of the cheapest flexible and lightweight point to point infrastructure you can construct.

Mentor
I had originally thought tubes are better, I realized a simple aluminum rail is sufficient, and cheaper...

Lots of details I don't understand, It's a sufficiently complex problem. But I believe(subject to further analysis) it is one of the cheapest flexible and lightweight point to point infrastructure you can construct.
After sufficient further development you will find you have re-invented trains.

You keep saying aluminum. Planes are made of aluminum because weight matters a lot. For terrestrial infrastructure, weight doesn't matter enough to spend more to make it lighter.

If a moderately sized city needs 10,000 of these running simultaneously, wouldn't it be better to put more than one passenger in each "pod"?

Vanadium 50, pbuk, Bystander and 1 other person
Staff Emeritus
If a moderately sized city needs 10,000 of these running simultaneously, wouldn't it be better to put more than one passenger in each "pod"?
I agree, but it is even more extreme. During rush hour, up to 50% of the population will need transportation. How many pods? How main rails? would you need for a city like Tokyo with a population more than 37 million?
The limits to speed mainly comes from radius of curvature of tracks
If there is no vacuum, then the air drag becomes the dominant consumer of power. Drag increases roughly as the square of speed. Temperature of air and oxygen levels of the air in the tubes become a problem.

To make a credible feasibility design, you will need on the order of 1000 man years of thinking and calculating.

russ_watters
Prathyush
After sufficient further development you will find you have re-invented trains.
Probably, but got to attempt.

You keep saying aluminum.
I mentioned aluminum rails, to use as secondary for linear induction motors. Not specifically because it is light weight, but that's a bonus.

I agree, but it is even more extreme. During rush hour, up to 50% of the population will need transportation. How many pods? How main rails? would you need for a city like Tokyo with a population more than 37 million?
Assuming the pods can travel at 60 m/s, packed next to each with a center to center width of 1 meter. I am imagining the pods get attached/detached to each dynamically other like roller coaster carriages.

You can get 60 pods passing though a point per second. In hour it can handle a traffic of 60*60*60 = .2 million pods. Because they are tracks and pods are designed to be light weight and low cross section. You can design to stack them vertically and horizontally. So 5-10 tracks can handle traffic in the order of million passengers per hour. And suitable for Urban needs.

This is an optimistic estimate, taking into account switching makes it much more tricky. But in the principle, it could be designed keeping with no stoppages using computer algorithms.

Number of pods, is based on number of users during peak+ extra. I am imagining the pods are much cheaper than a car, and cost closer to a motor bike.

If there is no vacuum, then the air drag becomes the dominant consumer of power. Drag increases roughly as the square of speed. Temperature of air and oxygen levels of the air in the tubes become a problem.
I realized I was being stupid, to consider of tubes over rails. The monopods are designed for minimizing cross section required for a single human to comfortably travel. Because many pods share the same cross section, the drag can be significantly minimized. Similar to a train with lower cross section.

I am looking at speeds around 60 m/s, for densely populated urban areas. At a = 4 m/s^2, you are looking at a radius of curvature of about a KM. Drag is a problem at larger speeds. I don't know how far the monopods can be pushed.

wouldn't it be better to put more than one passenger in each "pod"?
Personalized rapid transport has been explored, and some versions have more 4 passengers.(ex sky tran, is under consideration by governments and private industry). I am trying to design something with the flexibility of a car and advantages of a mass transit.

For instance something like a basic rail, can be directly integrated apartment and office complexes, where a lot of people use it. If a great switching can be built, each it is effectively point to point travel with no stops. If there is sufficient number of people that want to use it, a rail can built connecting to larger network. That is why I bent on minimizing the cost of the rail and support.

To make a credible feasibility design, you will need on the order of 1000 man years of thinking and calculating.
I agree it's a hard task. But I want to explore the question to some degree. Get some ball part estimates.

Staff Emeritus
You can get 60 pods passing though a point per second.
Are you out of your mind? Suppose a pod is 8 feet long. It's probably more. Suppose you need one foot between pods. It's probably more as well. 9 feet x 60 /s = 540 ft/s. That's 370 miles per hour!

A minimum turn radius for a railroad is 410 feet. That's 22 g's on a turn. Do you want to kill your passengers?

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sysprog and russ_watters
Staff Emeritus
You can get 60 pods passing though a point per second.
Whoopee. Just imagine the terrorist salivating over that idea.

Prathyush
Are you out of your mind? Suppose a pod is 8 feet long. It's probably more. Suppose you need one foot between pods. It's probably more as well. 9 feet x 60 /s = 540 ft/s. That's 370 miles per hour!

A minimum turn radius for a railroad is 410 feet. That's 22 g's on a turn. Do you want to kill your passenegrs?
I had assumed it was 1 meter long, because it seats only one person, and they are attached to each other.

You can change the assumptions. If you want 9 feet ~ 3 meters, you can get 20 pods per second. Or 20*60*60 = 72000 pods per hour. Which is still good for an urban setting. Especially because you can stack the tracks vertically and horizontally.

I am thinking of a design which comes as close to a chair on a track as practically possible.

A minimum turn radius for a railroad is 410 feet. That's 22 g's on a turn. Do you want to kill your passenegrs?
I am imagining 60 m/s on straight tracks. If you want to turn you need to lower the speed significantly.

For instance Chou Shinkasen has a minimum radius of 8 KM. If you are looking at 410 ft ~ 125 m you need to lower the speed to something like 20 m/s.

I haven't considered the terrorism angle. But, isn't there a terrorism risk for any kind of mass transport infrastructure?

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Staff Emeritus
Just imagine the terrorist salivating over that idea.
One squirrel can kill thousands of people.

Staff Emeritus
If you want to turn you need to lower the speed significantly.
No, everybody has to lower their speed significantly.

This looks like a solution in search of a problem. It reminds me of the guy here who felt that the problem with farming in developing countries was that there weren't enough robots.

nsaspook and russ_watters
Prathyush
One squirrel can kill thousands of people.
You need to optimize and design for safety.

I am making a case that the basic idea is worth exploring i.e cheapest and lightest possible infrastructure, coupled with the lightest possible pods. It makes more sense than flyovers and overground rail, which are designed to to hold a load of several thousands of tons of weights.

Even if a single track can carry 7200 pods per hour, such a system could makes sense. That's pods separated by 10m traveling at 20m/s. You can easily build many such tracks by stacking if a particular route is very busy.

The track are light weight, and you are not trying to carry many thousands of tons of weight, that is main argument. This coupled with modern computer electronic switching systems can make a compelling case, for flexible dense infrastructure.

No, everybody has to lower their speed significantly.
I was looking at the limit of very straight and long tracks. I have to think about more about the switching systems.

Prathyush
This is what I have in mind currently. It can be designed in many different ways.

Prathyush
The company Transit X designed similar concepts based on similar principles. They published a handbook.
Skytran is another company attempting this

I did not verify their claims but, they claim

"The empty pod weighs 45 kg (100 lbs) and can achieve better than 0.23 liters per 100 km (1000 MPGe). A cargo pod carries freight and holds a standard 1.22m x 1m (48”x40") pallet with a max payload of 1000 kg (2200 lbs)"

Staff Emeritus
You have largely not given us the same courtesy and addressed them.

The "handbook" talks about a rate less than 1/700th of what you are talking about.

anorlunda
Prathyush
You have largely not given us the same courtesy and addressed them.
hmm... I will respond in detail soon

The "handbook" talks about a rate less than 1/700th of what you are talking about.
The handbook estimates the capacity as

"Line capacity is the number of people that pass through some point. Maximum capacity on a single guideway is 30,000 pph — the equivalent of 16 highway lanes. This assumes shared pods with an average of 2.7 passengers per vehicle and pod trains with three pods per train."

which is in the ball park of what I was talking about. I made an optimistic estimate of 0.1-0.2 million per hour on a straight track, if switching mechanism can designed to handle such a capacity. I was arguing even 7200 pods per hour is significant, and presents a potentially a workable solution.

If the handbook is to be taken seriously the cost is also compelling.

"The capital costs for a podway are approximately US$4M per km ($6.4M per mile), including
physical infrastructure (pods, guideway, stations, interchanges, maintenance facilities, and
operations centers), as well as soft costs (planning, permitting, and environmental impact
assessments). Capital costs are low due to: less material, and lower construction and land
costs."

Reaching a density of 1 station every sq KM is a compelling target

Prathyush
wouldn't it be better to put more than one passenger in each "pod"?
I will consolidate main points into this post. If there is anything I did not address, please let me know. The numbers can be significantly refined, corrected and revised.

In am looking at some variant of the design outlined in post 15.
1. Vehicle Weight overhead Transport infrastructure comes with a weight overhead, starting with weight of the vehicle to weight of loaded tracks.

A ball park estimate for a 12 train carriage+Engine weights ~ 100+12*20 = 340 tons, assuming 5500 passengers per train you have a weight overhead of ~60 KG's. (estimates vaguely based on Mumbai local network at rush hour)

That's an optimistic estimate. And it may be closer to 200+ KG's in many real world implementations.
I think pods weighting under 60-80 KG's should not be hard to design. In the most basic sense it's a chair on an aluminum secondary with added details.

The exact number of passengers per vehicle is an optimization problem. PRT have been designed with different low numbers(1,2,4,6... etc.). One passenger per pod offers most flexibility, and lowest air drag. Other values could be considered, increasing it too much increases cost of supports, and reduces flexibility.

2. Track and support weight overhead Same concept as above, the lighter your system lowers the cost. I don't have estimates, but max load per m is a useful metric.

Cheaper the track, more densely you can lay. Reaching a density of 1 station per sq. KM in a city with population density of 10,000/sq KM is a useful milestone. Assuming you require 10 KM per sq KM of area. Each person pays for 1 m of track and 10000 people share a station.

Traffic could be better balanced if the network is densely laid out.

3. Motor cost This is an important expense. You can reduce the cost of copper coils required by lowering thrust and lift requirements and keeping it to a minimum.(something I need to estimate better)

4. Radius of Curvature On sufficiently straight tracks speed is limited by aerodynamic drag and magnetic drag. On curved tracks speed is limited by human limits for acceleration.

For max acceleration of 1 m/s^2, and max velocities of 5m/s 10m/s, 20m/s, 30 m/s and 60m/s the radius of curvature is 25m, 100m, 400 m, 900m and 3.6 KM. Managing the transition between different types of tracks with different maximum speeds is a switching problem.

5. Pod gap and throughput per line In limit of perfect switches, the throughput per line is given by d/v_max. Where d is separation between pods and v_max is the maximum allowable speed on a track.

d can range from ~ 1 m (limit of attached pods) to upto 10 m or so . Throughput can be suitably estimated.

If one uses extreme assumption of d = 1m and v_max = 60m/s on straight tracks we arrive at throughput of .2 million/hr. Achieving numbers close to that is a marvel of technological precision and not at all easy.

A reasonably achievable estimate would be, 20m/s and pod separation of 4m. That gives a throughput per line of 18000 pods per hour.

6. Throughput of switches Seamlessly integrating tracks of different throughput and building a high throughput switching system is a challenging task. Having mechanical switches operating at 5 pods per second is likely not viable, mainly because of friction and single points of failure.

The main task of the switching system is to seamlessly join multiple tracks of low throughput into a single track of high throughput and separate single track of high throughput into multiple track of low throughput. In most contexts throughput is mainly determined by v_max of track.

I am suggesting (a possibly novel?) use of a 2 dimensional array for electromagnets, that is capable of producing arbitrary traveling waves. This allows for each pod to controlled individually and guided to it's track without losing speed. This is something that needs to be designed, but should be possible in principle with user of computer electronics. (currently thinking about this, will explore this idea in a later post)

7. Point to point transport The main advantage of this kind of system is station to station travel without stoppages. That's a hybrid between mass transit and personalized transport. If overhead is not high, people are willing to pay for personalization of transport mode and associated time saving.

8. Safety Valid safety concerns were brought up in the discussion. I don't have fleshed out answers but I believe are solvable to a point where this system is as safe as local trains. I am first understanding engineering aspects to see what a working system looks. Limitations imposed by security and safety need careful consideration.
If you think any of my estimates are wildly fantastical, I ask you to suggest what a more reasonable estimate is for a system of this type. I stated the assumptions in arriving at the estimates. This is something I am understanding slowly and recursively.

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sophiecentaur
Gold Member
To make a credible feasibility design, you will need on the order of 1000 man years of thinking and calculating.
That's 100 workers for ten years. No effort at all for a worthwhile project. But, to be honest, the propulsion mechanics of the system are probably less important than the logistics. (I agree that a zippy tube system is fun, though.)

There's been a lot of talk about extremely high speeds but it's total journey time that counts. On a regular tube journey, many passengers spend much more time getting to and from the train. If the trains traveled at twice the speed, journey times would hardly be affected. The distance from home / workplace to transport is what counts so we need a system that replaces taxis, which pick you up and drop you at the door. They could go at very moderate pace and still improve on journey time and comfort - as long as it could all be organised properly.

If we got rid of all personal vehicles (cars) in cities and used the existing road space for a system like this, average journey speeds could go from walking speed to 'trundling along' speed and everyone would benefit.
They've been doing this sort of thing for decades in SciFi films (I don't normally quote Hollywood in an argument) but they don't deal with the routing problems and there's the rub.

Gold Member
Each person pays for 1 m of track and 10000 people share a station.
Wh have 'stations' at all? the density you propose would involve a long walk for some people and crowds around a station. A taxi system lookalike would do the same job and reduce total journey times. Pavements (=sidewalks) could be much narrower because there would never be rush hour crowds.

Prathyush
Wh have 'stations' at all?

It's not strictly necessary. It's a cost vs comfort tradeoff.

You can easily 10X the density of boarding points and it would be under 200 m for everyone. I imagine this kind of system would be integrated into apartment/office complexes. You can think of direct to home integration also, but that might be expensive.(not sure)

sophiecentaur
Staff Emeritus
Someone noted before, you are trying to reinvent the railroad.
That's 100 workers for ten years. No effort at all for a worthwhile project
Good. When you competed that, post again and we'll discuss it.

Meanwhile random comments from the internet wrong won't help.

Gold Member
Someone noted before, you are trying to reinvent the railroad.
It's more like re-inventing Uber.
Meanwhile random comments from the internet wrong won't help.
"Send three and fourpence, we're going to a dance"
(Send reinforcements, we're going to advance.)

Staff Emeritus
Well, it's not clear what problem these PodZ solve. Other than PodZ are cool!

As @russ_watters points out, the problem is the infrastructure. If I want to have lines every kilometer or so (so the maximum walk to one is a kilometer), that's a lot of rail. If I need 8 km to turn a vehicle, that's even more rail. Having these at grade, sharing the space with pedestrians seems like a bad, bad idea.

I think that @sophiecentaur brings up an important point on total travel time. If I have a 2km trip at 170 mph (Shinkansen-level speeds) but need to add 8km to the trip to handle the turns, wouldn't it be better to go straight and slower? But now you have trains...sorry...PodZ of very different speeds on the same track. Not a good idea either.

Further, a 2km trip at 60 mph takes 75 seconds. At 170 mph it takes 48 seconds less (straight track - if you need to take a loop, it takes longer). Does 48 seconds make a difference? Especially if you have a ten-minute walk to the nearest pickup point?

If this is to replace taxis for short-distance point-to-point (perhaps getting to a train station) why does it need the same technology as replacing trains for mid-distance hub-to-hub? Because PodZ?

Prathyush
There are 2 main technical questions that are worth examining to evaluate the proposed alternative. Maglev tracks are a well researched technology.
1. What is the maximum throughput of the switching mechanism? Can it be designed without points of mechanical failure? ex using a 2d version of Maglev track, and creating arbitrary traveling waves. I believe 20000 pods per hour is an achievable target.(possibly much higher too)

2. What is the estimate for the cost savings involved with because of light weight design. Both support cost and cost of electromagnets.

If I have a 2km trip at 170 mph (Shinkansen-level speeds) but need to add 8km to the trip to handle the turns, wouldn't it be better to go straight and slower?
You are misunderstanding the system I am outlining. You have a combination of tracks with low and high curvature. Low curvature tracks are typically for long distances. These tracks fork using a suitable switching mechanism into multiple tracks of lower throughput and vice versa. Once your are on a track with lower throughput you can safely decelerate and turn. That is why I keep emphasing on the switching mechanism.

If this is to replace taxis for short-distance point-to-point (perhaps getting to a train station) why does it need the same technology as replacing trains for mid-distance hub-to-hub?
You can equally well ask the reverse question, why not take it a step further and go everywhere? This is not a definitive answer, but an attempt to understand the questions involved better.
1. Trains stop between stations.
2. Trains have a waiting time
3. Trains are heavy

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Gold Member
Imo, the system would be more like a tram network. Speed is of less consequence. I wouldn’t want a fairground ride to work and back.
Are the real advantages of (personal) maglev in this application?

this thread suffers from the problem that everyone imagines a different model. A super fast long distance train means the same thing to everyone but this idea is a bit too nebulous - albeit an interesting ‘concept’.

Prathyush
Imo, the system would be more like a tram network. Speed is of less consequence. I wouldn’t want a fairground ride to work and back.
Hmm... It makes sense to design a system with a typical max acceleration of 1 m/s^2 or so.

Are the real advantages of (personal) maglev in this application?
You can consider a wheeled design, but a system without mechanical friction has fewer points of failure and low maintenance costs.

I am not sure about efficiency, linear induction motors don't seem to have particularly high efficiency values because of end effects and air gap ( though anything above 50 pc is good enough for the purpose)

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Gold Member
It makes sense to design a system with a typical max acceleration of 1 m/s^2 or so.
I would think in terms of very little speed variation on the journey - just at start and end. All the 'weaving in and out' would be automatic and designed to minimise noticeable acceleration. It would be less scary than with some taxi drivers. We'd all be in bubbles (like cars- except we wouldn't own them; nothing to wash on Sunday mornings) and we'd socialise via screens like we do now when in motion. Journey times would often be only tens of minutes with no delays (haha). I'm back in Hollywood again.

Prathyush
As @russ_watters points out, the problem is the infrastructure. If I want to have lines every kilometer or so (so the maximum walk to one is a kilometer), that's a lot of rail.

I am not entirely sure, if it is prohibitively expensive. I will make an estimate. This is just a first attempt at arriving at such an estimate. I could be way off ( please correct me or if miss basic points).

Say we use some type of permanent magnet linear synchronous motor setup and we have Neodymium magnets(which produce about 1 tesla of magnetic field) attached to bottom of the pod.

For the motor if we use copper winding around permaalloy or similar material. If my estimate is correct, primary thickness should be under 1 cm. The density of materials of roughly 9g/cc. And primary width is 1m. We have a motor weight of 90 kilos per m. Permaalloy seems to cost like 30 USD per KG. So assume cost of motor is 2700 USD per m.

This should suffice to lift a 500 KG loaded pod( base of ~ 1 sq m).

Say it requires 400 KG of steel per m to support it. Add ~800 USD per m. For a total loaded weight of 1 tonne per m.

Say total cost is 5 million per KM after labor, electronics, switching mechanism and miscellaneous. This is a very very rough estimate.

New York has an area of 784 Sqkm. Assuming 10 KM of track per Sq Km. You get a number of 40 Billion USD. New York GDP is 1700 Billion. That's 3pc of its GDP. NY is one of the riches places in the world, but even if its 10 pc of GDP, it can be built in a modular fashion over many years.

My estimate seems be in ball park of Skytran costs, quoted at 8 million per KM in 2015 prices.

Staff Emeritus
You've never built a large engineering project, have you? Labor is a large, often dominant, part. You also need to figure out what buying all the land costs you.

Prathyush
You also need to figure out what buying all the land costs you.
Yea I intentionally excluded land costs, because most infrastructure projects have them in one form or the other.(And varies a lot city to city) I should have mentioned it in my post though. The footprint itself should be much smaller than typical rail infrastructure.

Labor is a large, often dominant, part.
In principle if you the standardize design, parts can be produced in a factory environment. Skytran claims it can be installed in days. It's different from a typical highway construction, which takes several months to a year.

But yes, this is a very rough estimate, I could be underestimating labour costs significantly.

Gold Member
You've never built a large engineering project, have you?
You should see my new kitchen.

Gold Member
Skytran claims it can be installed in days.
What proportion of the population would get to use Skytran? Its strikes me that Skytran falls between two stools. It seems to be pretty exclusive yet it gets in the way of the majority of travellers.

"skyTran is a personal rapid transit system concept"
"skyTran exists to make that dream a reality - with autonomous, zero-emission vehicles arrowing above congested streets."

Are all the travellers in "congested streets" going to pay for the elite travellers zapping around above their heads? Any system that is not useable by the whole population can't be justified. What's needed is a system to reduce the congestion and that's a matter of suitable traffic control and regulation. The Pods, as described, are actually not autonomous in the way that cars are because the pod tracks need railway / tram style points to allow changes of track. Cars can change lane anywhere along the road (driverless cars even moreso) to optimise journey time.

It seems here that the maglev tail is wagging the dog of actual requirements because it's such an attractive technology.

Staff Emeritus