Elon Musk’s Hyperloop and LIM Trains

RSS

Personal reflections on an earlier study of linear induction motors for transportation, along with speculations about the objectives of the Hyperloop program

 

Linear Induction Motors (LIMs), which are the basis for propulsion of Elon Musk’s proposed near-supersonic LA-To San Francisco commuter train, are interesting things.  I don’t have an opinion about the future of the proposal, but I have some recollections about LIMs and trains.  In the late 1960s, I was working for an aerospace contractor that had a government contract to study the practicality of LIM-driven trains. Some of my friends worked on the program and even managed to mangle some boxcars in a slow-motion derailment one day, so I got some education in the technology over several weeks of lunchroom conversations.

LIMS

Naturally, Wikipedia has a good write-up about LIMs.  In concept you take a rotating ac-induction motor, like the ones that have been used in ceiling fans for a hundred years or more, saw a slot in it and flatten it out.  (Yes, Tesla invented it. There’s a connection with Musk there.)

What you had in the ceiling fan was a cup-shaped metal object on a pivot. The cup fit into a slot in the stator, which was wound with coils driven by ac.  The fan blades were attached to the cup.

What you get when you flatten the thing out is this:  The cup turns into a long flat vertical rail and the active part of the motor straddles that.  When you excite the windings with ac, you get linear forces between the windings and the rail.  The idea in 1968 was to hang the powered part of the motor (It would be the stator in a conventional motor) from the railcar, have it straddle the rail, which would have been the “rotor.” And run the thing from electrified rails or a pantograph.

The research for this project got to the point where there was actually a full-scale test track with real boxcars and stuff.  Power EEs will guess that there was a real problem with maintaining an air gap, especially when the track wasn’t straight or perfectly level. But my friends got data, and that was the purpose of the program.

In a Different Century

The Hyperloop has some striking differences. The c20 version envisioned adapting LIMs to the existing railroad infrastructure, with load-hauling capabilities similar to those of a conventional GE diesel-electric locomotive. In contrast, the c21 Hyperloop is essentially a railgun with the load capacity of (maybe) a private car, with compressed air suspension.

Yet the propulsion method in a railgun is still a LIM.  Since one of the major challenges in any electric motor is minimizing the air gap, getting the car around curves is challenging.  (I can’t help but think of the famous Tehachapi Loop.)

Also, I can’t help making a connection between railgun technology and Mr. Musk’s other enterprise: SpaceX. Maybe when the Hyperloop isn’t carrying passengers between LA and San Francisco, it can be launching payloads to Lagrangian points.

So be sure to check your gate number before boarding.

Newsletter Signup

Please or Register to post comments.

What's Secondary Emissions?

Blogs from Electronic Design's Editor covering Analog and Power

Contributors

Don Tuite

Don Tuite covers Analog and Power issues for Electronic Design’s magazine and website. He has a BSEE and an M.S in Technical Communication, and has worked for companies in aerospace,...
Commentaries and Blogs
Guest Blogs
Nov 11, 2014
blog

How to Outsource Your Project to Failure 3

This article will address failure to carefully vet a potential manufacturing or “turnkey” partner and/or failure to transfer sufficient information and requirements to such a partner, a very common problem I have seen again and again with my clients over the years, and have been the shoulder cried upon by several relatives and clients in the past....More
Nov 11, 2014
blog

Transition from the Academe to the Industry Unraveled 1

There have been many arguments here and there about how short-comings of universities and colleges yield engineers with skill sets that do not cater to the demands of the industry. There have been many arguments here and there about an imminent shortage of engineers lacking knowledge in the sciences. There have been many arguments here and there about how the experience and know-how of engineers in the industry may vanish due to the fact that they can’t be passed on because the academic curriculum deviates from it....More
Nov 11, 2014
blog

Small Beginnings 5

About 10 years ago I received a phone call from an acquaintance. He had found a new opportunity selling some sort of investments and he wanted to share it with me in case I was interested. Ken had done fairly well for many years as a contract software developer primarily in the financial services sector. His specialty was writing RPG code. (RPG is often referred to as a write only language.) But he was seeing the handwriting on the wall as the industry moved on to other methods, and saw himself becoming a fossil....More

Sponsored Introduction Continue on to (or wait seconds) ×