Using Monopods for city travel utilizing linear induction motors

[berkeman]

I've stayed away from this thread because it is frustrating for me from an engineering perspective, but Prathyush could you please compare and contrast your proposal with the new public electric scooter paradigm? You seem to be wanting to propose a new individual transportation paradigm, and this new one would seem to satisfy what you want to do?

https://www.dailybreeze.com/2018/08...munities-and-rev-up-turmoil-for-some-leaders/

 

[Prathyush]

Honestly electric scooters are pretty good. They have an extremely low foot print per person.

The drawbacks are you can't sit. They can't travel at 60m/s. They have a very low range. They are constantly at risk of colliding with something or someone.

Add dedicated set of interconnected highways for these scooters to move seamlessly. Add some sensors to detect other scooters, and integrate it with maps for automated driving. Batteries are expensive, might as well put them on a maglev track for power delivery.(and you can remove the motor) Finally add a chair, and you basically have the system I am proposing. It's the limit where everything becomes as lightweight as practical.

A computer controlled Aerodynamic chair on a maglev track is basically the proposal, It's enough to cover a very large pc of traffic use cases.

 

[256bits]

They use roughly 15-20 trains per hour each carrying like 5-6K passengers.

15 trains x 5000 passengers/train == 75000 passengers.

With the pod system, with each pod 1 meter in proposed length, that is a pod lineup of 75km at the station, to start the rush hour, elementary speaking of course.. Do you need 75000 pods at this one station?
How many pods need to be at other stations awaiting passengers?
What would be the recycle time( ie return trip) to reduce the number of pods?
How many pods can be accessed at the station? ( If the length of the station is 100m then pods accessed wound be 100 ).
Do they all have to be filled with passengers before the group can move from the station pit onto the track?
If 100 pods can be filled at as a group, and it takes 1 minute for a passenger to enter, then 75000 passengers can be moved in 750 minutes ( 12 hours ). Is there any way to reduce the wait time from 12 hours to something reasonable?

 

[sophiecentaur]

Main things are point to point transport and light weight infrastructure.

I have an idea that your proposed system would not, in fact, be lightweight or cheap, at all. You are taking in terms of some very high speeds, tight curves and the need for high acceleration rates. That makes the system nothing like a slow speed, single A-B line. All the supports would need to handle high transverse loads for the cornering you propose, serious possible collisions and malfunctions and the passenger pods would give limited protection (from falling to the ground as well).

You have fallen in love with the idea of maglev and so have we all but is hasn't taken off yet for condensed network projects which would necessarily involve low speeds. Good (viable) Engineering hangs on finding the weakest link in chains of ideas and can't afford to get carried away with schemes based on a single attractive idea. Earlier, I made a trivial remark about a possible funfair application but actually that would be one way to get the idea established for limited real applications - but not a major facility in a city.

 

[Prathyush]

15 trains x 5000 passengers/train == 75000 passengers.

Couple of general points about a realistic city like Mumbai.

1) Mumbai is a linear city in the dense areas.(map enclosed). Local trains operate at a max speed of ~80 KM per hour. Curvature of tracks should be more than 3.6 KM to operate the pods at 100K per hour at 60m/s. ( I don't think Mumbai lines so straight). At a speed of 20 m/s your throughput will be about 30000 - 35000 pods per line. (pods are arranged into trains separated by a safe breaking distance)

When you are comparing throughput numbers it should be noted that systems achieving 100K passengers per hour, people are pack more than 5+ people/m^2. Personalized pods are an order of magnitude more comfortable. If you consider seated local trains your throughput is significantly lower.

2) In the system I am proposing you won't run every line at 100 K passengers per hour. It's similar to high speed highways and ordinary roads. You have slower lines connecting into faster ones. And if you are approaching 100K/hr you would add more redundancy into the system and lower the throughput. One advantage of light weight design is lines can be vertically stacked. It also has a small volumetric footprint for tunnels (can be designed fit in a 2 m dia).

4) Designing a system for a city like Mumbai needs one central line through the heart of city. Possibly connecting all the way to a neighboring city called Pune towards which there is a lot of traffic. We are looking at around 150 KM of central track with lots of population centers along the way to split into. This is very high throughput line and you stack multiple lines into a fortified central line, with well designed ventilation and safety and something that can survive atleast and an RPG attack. Safety has a heavy price tag for sure.

You can also imagine different designs with low throughput dense lines and high throughput lines.

Do you need 75000 pods at this one station?

Abstracting out from the details of a complicated city. Let's consider a simple linear city(dimensions 5KM*60 Km). The other side of this problem is a difficult problem in computer algorithms, graph theory and dynamic routing. Attaching and detaching pods at a safe breaking distance is very complicated but solvable problem. I will make many simplifying assumptions.

Primarily let's examine theoretically how a pair of to and fro lines operating at 100K passengers per hour and local stations connecting to them.

Lets assume 10 pc get off at a station at a given time. So 10K passengers per station per hour. Ideally if you are looking at 10K passengers per hour.(~1 million per day). You would add another station a KM or two away joining into the network. A cost of 100 million(all inclusive) to attach a new station to the network, and 10 cents per station per passenger you are looking at a payback period in years.

Still, its important to demonstrate that 10K passengers per hour(or 3 passengers/s) station throughput is comfortably achievable. I won't design the layout, but explain the main ideas.

How many pods can be accessed at the station?

Firstly you don't have stations on the high speed line. It takes about 2KM to accelerate to 60 m/s. So they will be distributed stations connecting to the network.

Every station will have a buffer capacity of pods, to adjust for statistical fluctuation. We need to estimate a typical buffer capacity. I will take your assumption of 1 minute per passenger. I will assume a 5 minute buffer, for seamless throughput. You need ~ 5*180= 900 pods of buffer per station. You would organize them into a bunch of lanes so multiple passengers can get in and get out parallel.

If the buffer gets too low you can route empty pods from a nearby station, 5 minutes is ample time, especially if you can use predictive algorithms.

Do they all have to be filled with passengers before the group can move from the station pit onto the track?

Once the front pods in a lane are filled, they will be organized into train, with persons going furthest placed first and personal going least distance on the fast line placed last. The pods towards the end of the train can break off from the end.

The space on the high throughput line will be divided into 200m chunks for safe breaking distance, and the train will join into one of the empty 200 m chunks. And the next train can be prepared. You can also dynamically built/split trains on the fast line.

What would be the recycle time( ie return trip) to reduce the number of pods?

Every station will have it's balance of incoming and outgoing pods. You can route them from the closest stations with excess buffer capacity. At the extreme end, it will be time for routing from furthest station.

All the supports would need to handle high transverse loads for the cornering you propose

Centuries of work on structural engineering can figure out less than 1/10th of vertical load applied as lateral load.

from falling to the ground as well

You could in principle add parachutes to pods, but that's probably a tad bit too heavy(~15-20 Kgs) and expensive(1k-2K USD). Airbags are an absolute necessity. You can design around single points of structural failures, by suitable redundancy. It's a detailed structural engineering problem, worth examining. Ideally you design in a way that single fractures don't break the system and they are monitored and quickly replaced.

You have fallen in love with the idea of maglev and so have we all but is hasn't taken off yet for condensed network projects which would necessarily involve low speeds.

I agree, I am not saying it is better than present day infrastructure. But I want to make a case that it deserves the 200 Ph.D's worth of effort that @anorlunda was talking about.

I made a trivial remark about a possible funfair application but actually that would be one way to get the idea established for limited real applications

You have LSM roller coasters already.

 

[Vanadium 50]

I've stayed away from this thread

Don't! You know abut trains!

 

[sophiecentaur]

You could in principle add parachutes to pods,

A daft idea, I'm afraid. Do you realize how long a chute takes to deploy? You would need ejector seats to take the passengers of a falling pod to up to 100m in the air. Where could they come down with no user controls? On the roadway perhaps. And there would be the bad back problem too.

But all the models you seem to propose seem to compare unfavourably with existing systems in pretty well every way. There is very little room available in a city for any more systems. Any additions would have to be compatible with existing systems. That means the pods would need to drive on tarmac. The density of travellers per m² in pods is really poor compared with a train full of straphangers. etc. etc.

 

[Prathyush]

A daft idea, I'm afraid. Do you realize how long a chute takes to deploy? You would need ejector seats to take the passengers of a falling pod to up to 100m in the air.

You would attach it to the pod itself. And it would be triggered electronically by g sensors(or other automatic trigger mechanisms). The job of the parachute is to apply an emergency breaking acceleration, if the contact with rails is ever broken. Parachutes for payloads of 500 Kg's are routinely designed in the industry.

Where could they come down with no user controls?

The entire crash will happen within seconds. It takes 2 second to fall from 10m height. There is no time for user controls, or any meaningful form of guidance. If your parachute can reduce speed from 60m/s to 20m/s(or even 10m/s) at ~5 g, that's a job well done.

And there would be the bad back problem too.

What is this?

A daft idea, I'm afraid.

Almost certainly is. You are looking at a ~10-15 M dia parachute in a city environment.

 

[Prathyush]

You are looking at a ~10-15 M dia parachute in a city environment.

I believe those numbers are arrived at from terminal velocity not breaking force.

A 6 m (cross section) diameter parachute applies a breaking force of ~6.4 g at 60m/s assuming drag coefficient of .5 for a 500 kg payload. And 1/4th of that value at 30 m/s.

Even if it works well, just a random deployment of a parachute in normal operation because of sensor failure is sufficiently problematic.

You will find some useful numbers in this paper Design and selection of main parachute for Re entry Space Payload

edit: 6 meters not 5 meters

 

[Prathyush]

But all the models you seem to propose seem to compare unfavourably with existing systems in pretty well every way. There is very little room available in a city for any more systems. Any additions would have to be compatible with existing systems.

I am not sure how you arrived at that conclusion, based on what I am saying.

Safety issues I very much understand, I did rework the design adding a safe breaking distance, that's a small step.

However for throughput, comfort and easy expansion, this is a far superior concept.

In the cross section occupied by a single locomotive (~ 2.5 m width * 4 m height) + little bit extra you can fit 4 of these lines. So even at 30K passengers per hour you have similar throughput to packed local trains.

Though ideally you should take space from roads not existing public infrastructure.

That means the pods would need to drive on tarmac.

Why ? That's blasphemy XD.

The density of travellers per m2 in pods is really poor compared with a train full of straphangers. etc. etc.

You can find interesting numbers here. The corridor capacity in figure quoted is is 7.94/m/s or 28000 per hour/m.You also need to consider operational efficiencies that come from point to point transport.

If you ran a train on say 2 perpendicular tracks with a switche, you have 3 routes. A->B, A->C and A->D. If each route is equally busy you will 3x waiting time between trains + stopping time at 10 stations en route. You are looking at much longer travel times than typical track speed.

Pods can operate at typical track speed for most of the journey.

 

[Prathyush]

To the people following this discussion I wanted to add few points unique to Maglev technology and not monopods. Which may be explored as the technology becomes more mature.

For this post in specific I will assume typical 100-500 people per coach and typical train coach dimensions(~ 25m length*3m width*4 m height) and not monopods. But other concepts carry forward, fast switches, dynamically attachable/detachable coaches, high breaking acceleration(compared to much lower traction of trains) and lack of engine (track is the motor and power delivery)

There was long experimentation with slip coaches, but the time was not ripe. The unique features of maglev make point to point travel possible, with well designed contact-less fast electromagnetic switches.

Ofcourse with putting 100+ people per coach for point to point travel becomes a lot more tricky algorithmically, because you need to group people who are roughly going the same way together.

However if you can design stations, in a way that people going to the same station (or few enroute stations) board the same coach. And using the same kind of switching mechanisms I described you can increase throughput and minimize waiting time.

There are three reasons for increased throughput, first is lower time of travel, and second is, stopping happens in a separated track and main line is always operating at typical track speed. And much lower necessary headway for safe breaking distance (because of increased breaking traction). Ofcourse you can always attach multiple coaches into trains to reduce the effect of the headway when necessary.

All of this depends of 4 concepts, fast switches, dynamically attachable and detachable coaches, increased breaking acceleration, and track itself being the engine. And I want to emphasize that these concepts aren't unique to monopods and they carry forward to coaches too. (with very different characteristics).

 

[StephenHaw]

Several observations about the monopod concept.
1. A monopod as outlined is the equivalent to a personal transport but a single seat pod isn't going to be popular with family groups traveling together.
2. As a personal transport it needs to pick up anywhere and drop off anywhere otherwise what's the benefit? i.e. from the street corner close to home to just outside the office.
3. The infrastructure needs to be constructed everywhere to give it the flexibility to customers to demonstrate how it is better than current transport systems.
4. The infrastructure is doubled to allow for bi-directional travel everywhere.

The question then becomes how would this be better than everyone being in self drive electric cars?
When it comes to technology the biggest gain is when everyone is using a self driving vehicle that is communicating with every vehicle around it, each one knowing in advance the traffic density and managing speed, each one communicating routes, sensors on the vehicles ahead detecting and transmitting hazard warnings to those around, traffic flow making traffic lights and traffic jams a thing of the past (until someone digs up the road) because each and every vehicle can synchronize their timing through junctions.
At which point no one would bother buying a self drive car they will simple order a vehicle to pick them up and drop them off and that will save on charging points with vehicles returning to a charging depot.

 

[sophiecentaur]

2. As a personal transport it needs to pick up anywhere and drop off anywhere otherwise what's the benefit? i.e. from the street corner close to home to just outside the office.

Absolutely. The Pod is not a 'mass transit' system. It's personal so I wouldn't be prepared to walk (with my family and bags) as far as the average distance to a mass transit station just to use a fancy new system. So the 'pod function' would need access to the "street corner" and that precludes any special track in a city. However attractive a transport system is, it has to be compatible with existing infrastructure. The development has to be bottom up to allow a transition from what we use to what we will use. Compatibility is essential.

 

[phinds]

The question then becomes how would this be better than everyone being in self drive electric cars?

Exactly. It definitely wouldn't be better, all things considered.

 

[StephenHaw]

When considering a mass transit system like the pod the biggest issue is normally the logistics and how to manage the end to end process of operation.

For instance we might assume that each individual traveling alone to their place of work (or wherever) arrives at the transit hub and acquires an electronic ticket on their phone with a QI code supplied.
Each pod is gated and the traveler scans the QI code at the gate, 10 seconds later a pod arrives the gate opens and they get on board. The pod already knows the destination so transports them directly to it.

With mass transport hubs queues form because of the time between trains so this pod system should be able to alleviate the wait and thus reduce queues, however this also assumes a surplus of pods to people traveling at anyone time and that all the pods are in the right place to keep the flow of travelers moving.

To that end unoccupied pods will need to be traveling around the system continuously in order to maintain flow and prevent bottlenecks and that means energy consumption will be high simply due to the need to keep everything moving whether the pods are occupied or not.

So logistics takes over in establishing the optimum number of pods needed during peak times and ensuring the right number are where they need to be at the right time based on the daily study of people arriving and leaving each of the transport hubs during each hour of the day.

 

[Prathyush]

1. A monopod as outlined is the equivalent to a personal transport but a single seat pod isn't going to be popular with family groups traveling together.

I have considered that, especially in the context of small children. It should be possible to attach 2 pods linearly to make a double pod ( in general N pods). But you need to pay close attention to tolerances in actual design. You need some kind of flex at the junction between pods for turns.

But, yes this is not designed for family picnics. You could also redesign it with 2-8 people per pod, but I am not sure if it is better overall.

2. As a personal transport it needs to pick up anywhere and drop off anywhere otherwise what's the benefit? i.e. from the street corner close to home to just outside the office.

It is intended that there is a station within less that a KM away (possibly even under 200 m), in dense urban areas. It all depends on the cost estimates per KM, once it is mass produced and standardized.

People say my cost estimates are an order of magnitude too low, but I am not entirely convinced. For instance a single concrete railway sleeper weighs like 300-400 kilos.

3. The infrastructure needs to be constructed everywhere to give it the flexibility to customers to demonstrate how it is better than current transport systems.

It should be developed in way that it is easily expandable by design. It should be straightforward to add a junction and attach to an existing network. It's a long way to convincing people.(including myself)

4. The infrastructure is doubled to allow for bi-directional travel everywhere.

Yes

The question then becomes how would this be better than everyone being in self drive electric cars?

That's a valid point. There are maglev advantages, i.e frictionless design, so no wear an tear. You don't need batteries. And cars weight like 1-2 tons, much lower energy cost. It would depend on a cost benefit analysis.

The largest expense(both weight and price) for the pod seems to be the Neodymium magnet.

10 seconds later a pod arrives the gate opens and they get on board.

I explain how a station would work in post 75. But there would be a buffer of pods in each station.

that means energy consumption will be high simply due to the need to keep everything moving whether the pods are occupied or not.

I disagree that it would too high. In the zeroth order approximation both directions are equally preferred. You need to adjust for fluctuations. In the extreme end if there is doubling of electricity cost for each user, it will still be very cheap per KM.

Compatibility is essential.

If maglev is going to be the future, we would have to re-imagine everything. Compatibility is just a transition issue. Average life of cars is some 12 years apparently. Given all combustion cars will soon be phased out in decades might as well rework the entire thing.I am trying to understand physics of maglev better. 10-20 Kilo N/m^2 is typical thrust density maglev designs can provide. If you don't use superconductors, magnetic field in order of 1 - 2 tesla limits the kind of engineering you can do. It is limited by magnetic flux of Neodymium magnets, and saturation of magnetically permeable material.( Neodymium is probably going to be the largest expense for the system)

10 KN is 1000 KG's accelerating at 1g.( Not sure what the deceleration thrust is, I don't think it is higher)

(attached graph taken from Linear Synchronous Motors:Transportation and Automation Systems)

 

[sophiecentaur]

It should be possible to attach 2 pods linearly to make a double pod ( in general N pods).

I suspect you are not a person with children.

If maglev is going to be the future, we would have to re-imagine everything.

If maglev is going to be the future it must be applied appropriately.

 

[Prathyush]

I suspect you are not a person with children.

I assume you understood I meant attaching creating a double pod with a floor space of ~1m*2m.
(width * length)

But that's a tricky aspect. Children alone could justify a very different design.

 

[sophiecentaur]

Children alone could justify a very different design.

"Force", not "Justify", I reckon.
You really should let this thing drop. You have a good solution to an entirely different problem for Urban Transport.

 

[Prathyush]

You have a good solution to an entirely different problem for Urban Transport.

What do you mean different urban transport problem ?

 

[StephenHaw]

Having used the Shanghai maglev a couple of times in the past and it is impressive to be hurtling along at 380 km/h but as far as I am aware it takes a considerable amount of energy to propel the train forward and not long after it reaches that speed it starts to slow down again.
64% of running the Shanghai maglev is just on energy, and while it's really fast and smooth its main problem is that it only goes between the airport and Longyang station so it doesn't generally get enough passengers to cover the cost of running it.

In an urban area with a good network the idea could work however it would operate in conjunction with other already established transport system rather than replace them.
Considering cities like New York has between 4 and 6 million people using the metro system every day with trains arriving and leaving every few minutes at peak times, the unanswerable question is how many would switch given the choice? and I think for people traveling alone, providing the network gets them to where they want to go they will use it providing the cost is low enough.

Only caveat, the cost of building the infrastructure including disruption to the city during construction and potential lawsuits for losses incurred to businesses (on the construction route and surrounding area) would be such a bureaucratic nightmare any anticipated spend will be quadrupled in actual cost.

 

[Prathyush]

Shanghai maglev

It's more useful to see Shanghai Maglev is as a test track with a real world use case.

I am aware it takes a considerable amount of energy to propel the train forward and not long after it reaches that speed it starts to slow down again.

It will take time for me source all this information, but if I recall the research I did correctly maglev is more energy efficient and lower maintenance than high speed rail at comparable speeds.

the cost of building the infrastructure including disruption to the city during construction

One aspect of this outlined project is to design a system that can fit like standardized lego blocks, that are mass manufactured and assembled in approximately 10 m/10 ton chunks. You only need to build pillars, which should have a small footprint. The entire project makes very little sense without standardized assembly line manufacturing. Easy construction is a key aspect. That's a reason why rail is successful.

But obviously standardization of anything is hard, especially maglev where there are 100's of design parameters. But worth the effort. It need not be monopods, but well developed and well researched standard design parameters for tracks and vehicles. You can fix on the pitch length, pole configuration and solenoid configuration on track, and you can build vechicles of any multiple of pole pitch easily.

the unanswerable question is how many would switch given the choice?

It doesn't make sense to compete with existing lines, only complement them or upgrade them. Designing for realistic cities is quite a different problem. But also it should be noted that many cities don't have a public transport system, and are at a nascent stages of building them.

 

[sophiecentaur]

Shanghai Maglev is as a test track with a real world use case.

It's not a test case for personal transport. It's a test case for a mass transport system. Pods would be tethered to rails and the number of interconnections would be limited - unless they could jump from rail to rail. This is where the proposal fails to achieve a replacement for the present system of motor cars.
You keep ignoring this.

 

[Prathyush]

interconnections would be limited

I see no reason why they would be limited. That's the entire point of point to point transport. You can experiment with different network layouts on a paper, test various topologies of high speed lanes and interconnecting lanes and try it out for yourself.

unless they could jump from rail to rail

I discussed the 2 different switching mechanisms. In fact high throughput switching mechanisms are key to making the idea work.

This is where the proposal fails to achieve a replacement for the present system of motor cars.

This is not intended to replace all aspects of motor cars/Road transport. But a very large portion of use cases. It's a mixture of personalized and private transport.

I feel discussion has saturated, I am repeating the same ideas again.

I'll make a post about maglev physics at some point in the future. Too busy with work right now. There are some very interesting ideas(especially stabilization and propulsion) that I am trying to grasp.

 

[sophiecentaur]

You can experiment with different network layouts on a paper, test various topologies of high speed lanes and interconnecting lanes and try it out for yourself.

That's your job as the proponent of the system. If you are prepared to have a great distance to your nearest pick up point then it's fine but an interconnection. will take up more room than the naked track. How could it possibly achieve what an untethered taxi does all the time with potential interconnections every few metres? That's the opposition to your scheme.

 

[Prathyush]

How could it possibly achieve what an untethered taxi does all the time with potential interconnections every few metres?

That was never the plan. Stations will be under a KM, and possibly as close as under 200 m.

I explained some aspects of it in post 75 for a linear city. I may add more details when I find the time. I did work out rough schematics. But the essential idea is you have large radius, fast and high throughput tracks with slower tracks from stations connecting to them and away from them.