The Brennan self-balancing monorail [video]

143 points2
Animats2 days ago

There's a model railroader who builds these things.[1] They balance and corner fine.

With one rail, the models can't take power from the rails. They run on AA batteries.

There's also a drivable 2-wheeled gyro-balanced car from the late 1960s.[2]

These things work, but wobble too much. With active control, though...



Doxin13 hours ago

> With one rail, the models can't take power from the rails.

That immediately has me thinking about what sort of zany pantograph mechanism you'd need to get overhead power working. You might be able to get away with a really wide pantograph that has the right curve.

dsego1 day ago

And here I thought that the gyro motorcycle that appeared a decade ago was a novel invention.

jacquesm1 day ago

That second one is just gorgeous. That guy has every reason to look as smug as he does!

Animats22 hours ago

It really is gorgeous.

It's really a new build; the original had been abandoned and then hacked into being a no-gyro 3-wheeler. There are some parts from the original in the new one.

JKCalhoun1 day ago

Yeah, not a stretch to imagine someone could make a Star Wars Landspeeder version.

Jolter2 days ago

Well, that was the most annoying commercial break ever.

philsnow1 day ago

yt-dlp has sponsorblock integration, just saying

btbuildem1 day ago

Yeah that was pretty jarring

ethagknight1 day ago

Some things im curious about with this concept.

1) why not mount the gyro horizontally? 2) would the addition of a very large (say 10ft diameter) primary load bearing wheels (like a bicycle) assist with stability at speed 3) video mentions a need for gyros in each car, I wonder if such a system could only require a complicated active control system in the front (and maybe rear) car, and the rest could have simpler 'passive' gyro arrangements to assist in relative stability to the active controls? 4) could modern control systems materially improve upon this? For example, an all-electric drive for the intermediate gyros off a primary power unit is pretty trivial. 5) why wouldn't they want the flywheels higher up, like mounted over the roof? quicker reaction time and more force per rotation?

Thats all for now.

Levitating2 days ago

Wait, this isn't a Tom Scott video?

toxik2 days ago

Didn’t he quit?

Ballas2 days ago

He didn't quit making videos entirely, he only "quit" releasing them to a set schedule.

tgsovlerkhgsel24 hours ago

... but hasn't released a single video since then, yet.

franky472 days ago

That's what I was expecting too.

Fervicus2 days ago

Quite remarkable. Too ahead of its time? Wonder why it never got revisited

modeless2 days ago

Seems like the requirement for gyroscopes in every car would be a deal breaker.

neom1 day ago

Could you make a gyro car? Akin to a locomotive? I don't exactly know how it would work but I was thinking we have locomotives so we don't need to put engines in every car. The thing I'm thinking about is that the gyro is kinda both a measurement device in a way, and also the system that actuates. Could these systems be separated, simplified, and scaled-down? I don't know, I'm not an engineer, just thinking aloud. :)

jerf1 day ago

With the technology of the time I do not believe there is a solution.

Modern technology might be able to turn the car couplings into something that can actively manage their tilt relative to each other, thus allowing them to propagate the balance beyond a single gyro car, but there's a lot of PID-controller-type [1] math that would go into determining if this was even possible with real, physical objects trying to control things the size and mass of train cars in a train track environment. The computations are probably not that difficult in 2024 but trying to actually deliver the correct forces in a timely manner may be difficult if not impossible. There aren't always solutions, or practical solutions, to the PID equations in the real world.

Plus, I'm sitting here imagining the size of the electric motors we're trying to torque the cars against each other with and it's hard not to say that we're better off just having two tracks and putting those motors on the wheel themselves. (Which then collapses to having a locomotive setup like we have now.) In the "power/control/price" triangle we're basically forced to take the max on power and control, so these are going to be ferociously expensive if they can be built at all.

And there's some bad failure cases that I just don't know that you can mitigate. Having 30 minutes after power loss to evacuate passengers is generally going to be enough, but cargo can't be evacuated on that timeline. And that's not the only failure case. A seized gyro is going to be catastrophic and even a single one could take the whole train down, even with that PID control system (which is going to be a stretch even without also having to build in buffers for failed gyros).

The fact that a 2-track-train can just sit there for extended periods of time with no power is one of those advantages you don't even think about until you try to take it away.

Guy was a genius though. It's basically an analog computer that keeps itself upright that you can ride. The final design is amazing with its judo-esque approach to using physics against itself. But I don't think it can be scaled up much beyond "neat tourist attraction". I'd ride one as a tourist attraction, though.


neom1 day ago

Can always count on you for a fantastic reply Jeremy. Thank you.

Indeed, the more I think on it the more difficult the edge cases seem, I hadn't even gotten to the power out thing, although from thinking on the spinning cube conversations in this thread[1], I had thought about magnets as a failsafe mechanism, but at that point....

"The fact that a 2-track-train can just sit there for extended periods of time with no power is one of those advantages you don't even think about until you try to take it away." <- This heh.


meche1232 days ago

Because you have to replicate the same complicated mechanism for all the cars. Moreover, if a gyro in one of cars malfunctions the whole train is at risk.

Another problem is that the system is reactive, meaning that there is a lot of shaking and balancing that is quite unacceptable - think about drinking a cup of tea in such a wobbly train even on straight lines, while on curves it's not staying horizontal by design.

Yet another problem is that it can't share the current infrastructure without major switch changes while sharing the infrastructure the other way around is impossible.

And in the end all of this effort for trying to fix a problem that doesn't really exist, at least not in Europe where most of the rail infrastructure was already built 100 years ago.

Reason0772 days ago

> ”while on curves it's not staying horizontal by design”

Worth noting that modern tilting trains do this quite successfully (on two rails!), in order to run faster on tracks with tight curves. By “leaning in” to curves, you make the ride more comfortable, not less.

Tilting trains are used extensively on the UK’s West Coast Main Line, for example.

danhor1 day ago

> By “leaning in” to curves, you make the ride more comfortable, not less.

That is the intention, but many people report discomfort due to the non-ideal adjustments, at least for the tilting trains in germany.

philjohn1 day ago
georgesimon1 day ago
georgesimon1 day ago

Yes, the part of the video that said this would work on existing infrastructure is entirely wrong.

It could be interesting with it's own infrastructure, though my first thought is that it might be better suited to tunnels, being able to maximize use of the tunnel profile.

1letterunixname1 day ago

And there's zero redundancy. If 1 of those piston seals or valves fail, the whole train is at risk for catastrophic failure.

Clever engineering without a necessary, defensible, competitive business advantage usually becomes either a hobby or an art project.

georgesimon1 day ago

And if one rail has a gap or defect.

kevin_thibedeau1 day ago

The double flange wheel wouldn't work with existing rail switches.

woah1 day ago

What's the benefit?

joshuaheard1 day ago

In the video it explains it only uses half the track material since it only has one track instead of two. It can also go faster since it leans into corners and doesn't derail like two track trains.

p1mrx1 day ago

> leans into corners

Modern trains do that too. eventually led to, which is being deployed for Acela in the US.

kbenson1 day ago

It also required the complex gyro for each car, not just the engine, which is why the video states ultimately it was killed. I'm not sure the situation has changed with that.

1letterunixname1 day ago

No. Watch the video.

tareqak2 days ago

Do e-scooters and the like self-balance in this way?

It would be cool to have self-balancing rollerblades.

Jolter1 day ago

Anything with rolling wheels will have some tendency to continue straight once the wheels are spinning, but they don't help to stabilize in corners. On small wheels, the effect is very small in any case, especially since the scooter and its batteries are relatively quite heavy.

arijun1 day ago

The gyroscopic effect of wheels has a minimal impact on the tendency of things like bicycles to remain balanced; the majority of the effect comes from the rake of the front wheel (i.e. that the point where it touches the ground is ahead of the pivot point of the front post).

That gyroscopic effect of the wheel works well when the whole device is wheel (think hoop rolling), but when you start adding weight that's not spinning (like someone riding a scooter), the effect falls off.

Edit: it seems that neither the gyroscopic effect nor rake are sufficient to explain bicycles' self-stability:

phyzome1 day ago

« the point where it touches the ground is ahead of the pivot point of the front post »

The other way around -- the contact patch of the tire is behind the projection of the head tube onto the ground.

I love that there are actually three different stability mechanisms. I wonder if there are others!

mring336211 day ago

see, which is an electric scooter with no handlebars.

At low speeds, a high-friction headset adds stability by damping the tendency to turn and flop.

At higher speeds, the reverse fork rake and spinning wheels provide stability.

This is my read on it, as someone that uses a 2Swift as a commuter vehicle, but the physics-based explanation may differ.

kabouseng1 day ago

I wonder if gyro drift would eventually cause problems?

croes1 day ago

What happens on a power failure?

ethagknight1 day ago

The video says the gyros would continue spinning for 30 minutes (inertia) in the event of power failure. Enough time to get the kickstand down I guess.

FrustratedMonky1 day ago

Incredible. Sometimes it seems like we were more advanced in the past.

samatman1 day ago

This is occasionally true, but that is very infrequent.

The example I like to cite is swords. Despite swords playing no role in modern combat, modern swords (the real ones, not knockoff/costume swords) are of a higher quality, fit, and finish, than anything a knight or samurai would have been able to obtain. While being dramatically cheaper, in the sense that someone would have many fewer hours to work to obtain one.

There are counterexamples of products which would have been cheaper at a given quality in the past, or readily available when they're difficult to obtain in the present. But once you rule out things made with ivory and whalebone, these are scarce indeed.

dudeinjapan1 day ago

It reminds me a bit of TRIZ thinking It's not that we were "more advanced", it's just that Brennan had a clear-headed approach to use mix of elements (gyroscopes, differential/asymmetry, pneumatics)

FrustratedMonky1 day ago

yeah, these old mechanical control devices seem like a real life 'steam punk'.

phyzome1 day ago

Where do you get that from? We still come up with crazy designs all the time (that are rejected in favor of robustness, compatibility, etc.)

JKCalhoun1 day ago

The crazy designs from 100+ years ago though were more impressive though because of the limitations imposed from not yet having electronics, computers, software.... They had to be incredibly clever mechanically. I too was impressed from the video the way the guy iterated in clever ways to address issues that came up. And, as I say, iterated within a relatively narrow realm of options.

Ads a counter-example, I watch hobbyists on YouTube these days that build and fly various R/C contraptions that would not have been do-able in the days of small gasoline engines and huge, heavy radio receivers. It's like today you can take a sheet of foam from Lowes, strap on some high efficiency brushless DC motors, double-sticky-tape on an ESC, receiver and be flying that sheet of foam by the afternoon. Too easy.

FrustratedMonky1 day ago

There must be enough people that were similarly amazed and/or fascinated to vote it to front page. Maybe my phrasing was not to your liking.

I'm sorry you've lost your sense of wonder.

phyzome22 hours ago

Are you kidding? I freaking love this invention. I just don't think it's evidence for some kind of civilizational decline.

FrustratedMonky21 hours ago
Donaldbendo1 day ago