by golly the mad man did it
Bro, forgot to pay attention to thermodynamics.
I once had an exam question that began with the phrase “ignoring thermodynamic principles…”. That question really threw me, it basically asked what would happen under XYZ situation if physics didn’t exist. How the hell am I supposed to know that?
Someone has been spending too much time on ChatGPT.
This is satire… right? I hope it is
Yet another “engineering student” who hasn’t learned his Newtonian physics yet. Which I’m pretty sure is covered in grade school, but you never know.
I’d go with second law of thermodynamics, but whatever.
LinkedIn has been shit posting goldmine lately.
The amount of emojis scream AI generated.
OR hear me out, AI was trained on these kind of posts. Emoji were overused in similar fashion before the AI bubble. Remember when crypto and NFT was all the rage? Crypto bros were all posting like this. And it worked on gullible people, so now AI does it too.
It’s funny how everyone thinks they’re AI detectives now.
Seems like satire to me. Pretty funny too.
The Law of LinkedIn:
If you think it’s satire, it’s probably actually just a really stupid individual.
Newton? Never heard of him.
mechanical engineering student
Did not pay much attention in high school
Look out for v2.0 which also features a sail on the front which you blow to go faster.
Okay, but blowing on a sail to go faster is actually a thing. Mythbusters even stated that they did their experiment in the worst method (i.e., not using modern designs and methods), and still found that a fan on a sail could make it move. It’s not free energy, but let’s not ignore how cool sails are.
This sounded very wrong to me, so I googled and apparently they had a setup where the reflected air from the sail caused a net flow in the opposite direction allowing them to move forwards. But that is less effective than just blowing the air straight backwards without a sail.
Look for the sail car video from Veritasium. With a chain drive you can out run the wind using the principles of sail propulsion.
I don’t claim to be an engineering student, why is this a bad idea? Wouldn’t he just put a “collector” of energy (like a wind turbine) on the wheels?
It could be an OK idea that just wasn’t explained right. Maybe he just wants regen braking but with one wheel for charging and the other wheel + separate battery for power at any given time. Energy would come from pedalling and hills. None of that was explained though
Maybe you can join his team!
But I can forgive a non engineering student… its impossible.
What happens to an object in motion when you collect its kinetic energy?
Okay, I admittedly know nothing about this, so bear with my ignorance. Aren’t you just moving gears? It would generally be like an auto engine where you have all of these explosions that push gears. You’re just moving the gear in one direction as a click, click, click.
On an e-bike you would be losing significant portion of energy from propelling the bike, friction, air drag and heat loss. You might be able to put a small amount of energy back in from pedaling, going down hills or even braking, but certainly not enough to make it perpetual.
Perpetual motion machine are physically impossible based on our current understanding of physics. Many, many people have attempted to create them, but they all fail from the reaaons above.
So last question, I promise.
A wind turbine collects the energy of the wind through movement. A gear can give more “force,” so I’m assuming more movement of something. If you have 2 different systems, one that collects the movement, or more “force,” and one that is making the bike move, why wouldn’t that be close to collecting as much as you put in. You’d have to charge occasionally, but not all of the time.
No, they are not separate systems and you will always have significant losses of energy to friction.
Gears change how energy is transferred, but more gears means more energy loss. Always.
With the bike, the battery (and pedaling) is the source of your net energy output. Losses from friction to the ground and air drag will be the most significant net consumers of the energy. It doesn’t matter how the rest of that energy is moved around within the system(s) of the bike.
Ultimately, what determines the distance you travel is the capacity of the battery and what external environmental factors affect the bike and by how much. Biking at 3m/s will have less air drag than 10m/s. Friction will be affected by the surfaces you go over, with something like mud taking more energy compared to something smooth like smooth concrete.
Conservation of energy, basically it’s not that it wouldn’t work “at all” or appear to anyway but that it wouldn’t work as desired. You can’t recapture the power used to propel the bike because it’s being used to propel the bike. Adding a collector increases the power needed to turn the wheels and basically makes the drive battery’s job harder, so it runs less efficiently and runs out faster, battery 2 does charge and can be run from, but in the end you end up with less range due to the stacking inefficiency and energy leakage. The closest functional system to what they are talking about would be a breaking system like electric cars use.
Turn off the engine of your car, does it keep rolling at the same speed forever?
Where are you going to get that power on a bike? Your legs. Do you really want to peddle away to charge a battery at SIGNIFICANTLY reduced efficiency, then with even more loss of efficiency discharge the battery into an electric motor? Or do you just want your energy going directly to the wheels?
The person in the post is trying to come up with an infinite source of energy which is not possible.
If you are drawing energy out of a system them that amount of energy is removed from the system. A freespinning gear won’t generate electricity. It has to be pushed, which requires more energy from the power source, and is always a net loss because of friction.
That is before the added weight of the additional batteries.
So trying to get energy back from a moving cycle will result in a less efficient bike.
Alternators exist on a car, why not on a bike?
You can power lights or a phone charger with a dynamo connected to the wheel and minimally noticeable drag/resistance. You can recharge a drivetrain with regenerative braking which requires high end motors to use the motor like a dynamo
Yes, you can collect some of the kinetic energy and put it back into a battery with regen braking, but most of the energy put into such a system will be lost to heat/friction, drag, drivetrain inefficiencies, battery inefficiencies, recovery inefficiencies, etc.
In the lunatic post, he’s not talking about regen braking. He’s talking about using the same system that moves the vehicle to simulatneously charge a battery. Which means you’re taking some of the energy which would normally move the vehicle and shunting it into a recharging “circuit” - which introduces even more losses.
The end result would be a machine that is less efficient.
Just assume a perfect world, and we won’t loose any energy!
… Though we won’t gain any either. -,-’
Regen braking is on every single electric car. But it’s incredibly inefficient and costs a lot of money to add it.
On a 60k car? Yeah it’s worth it. On an $500 ebike? No, not at all.
Alternators don’t exist on electric cars. The closest is regenerative breaking, which powers the car by slowing the car down.
Oh shit you solved it!
I was being sarcasmic.
🥵
So we just need to put something on the bike to power the alternator…I know, an engine! Why has nobody thought of this before?!
It would wash out. Any energy collected would be at the cost of resistance. So add fans to add wind resistance. You could collect energy from coasting and braking, but that’s just tech we’ve been using for years in cars, and it comes at the cost of movement. It actively slows you down because the energy has to come from somewhere. And since energy conversion is hardly one-to-one (loss to heat, etc), storing it into a battery and then pulling it out again means you won’t gain as much as you lose.
Energy cannot be created or destroyed. If you are generating energy, you’re taking it from somewhere, and on a bike, it’s from your forward movement.
Okay, I get that, but wouldn’t the collection be a separate system? The energy is being created by the battery, then a separate system collects the energy.
Because its all the same energy, and the contraption just slows down.
But if you’re on a hill, you’ll go much faster, thus storing more energy.
Yes, you could collect energy while coasting down a hill, but it would slow you down. Which is fine if you want to slow down; this is the basis for regenerative braking. You might be thinking that a pinwheel spins like crazy in the wind, and that’s just free energy. But a pinwheel doesn’t store anything. To store energy, you need to add resistance, and the more you add, the more energy you collect and the harder it is to spin the wheel.
So at the end of the day, you’ve got a fan at the front of the bike that is either spinning quickly with little resistance and storing little energy or one that is spinning slowly and collecting more. And the slower it spins, the more pushback there is against your forward movement.
Despite there being two batteries, this is still a single system which uses energy to propel the bike forward and collects energy by preventing the bike from moving forward. They offset. The only way to have the energy to propel the bike is by introducing energy from another source (not related to the movement of the bike) such as a battery charged ahead of time or calorie loss of the rider (active pedaling).
Thank you for this detailed explanation. I appreciate it. That’s exactly what I was thinking about, a pinwheel.
Now you’re introducing potential energy (a hill), which will be used up (or rather be fully converted to kinetic energy) once you reach the bottom, and you’re going to need the same or more energy to go up that same hill again (depending if you take resistance into account).
We already have tech for capturing kinetic energy for later in the same battery used for driving called “Regenerative breaking” (cuz’ the motor is used as a generator in place of brakes, and you’ll need to drive said generator by capturing some of your forward motion/kinetic energy).
EDIT: In other words: You could just start on a really high hill and you’d be able to use the weight of the bike and yourself as a “battery”, never needing any actual battery/motors/wiring/etc.
Imagine it like this, you have two glasses of water, labeled “speed” and “chemical.” You can only transfer water between glasses. And messily. It’s a sum of water, a specific weight of water between the two glasses that you own. In placing the water elsewhere, you haven’t done much besides lose a portion in the transfer. You can absolutely do what you’ve said! It will, unfortunately, just be a transfer from the speed to the chemical glass. You’d just lose a bit in the transfer.
It’s a bad idea because he’s essentially talking about a perpetual motion machine.
That makes sense, except the collection of the energy can be less than the energy expended, like an automobile or wind turbine. Then it could be a perpetual machine.
It would be like this:
Energy in => convert to a gear that makes it way more energy => store energy, repeat.
I must be missing something.
convert to a gear that makes it way more energy
nah, see, a gear is basically just a fancy pully. it can make it easier to pedal up a hill, but only by making you have to pedal many more times to do so. each turn of the crank arms takes less force, but you have to do it many more times. it isn’t actually reducing the energy requirement, and it isn’t multiplying your energy input.
what you’re describing here would be some kind of magic.
except the collection of the energy can be less than the energy expended
The collection will always be less than the energy it takes to generate it. There no magical gear or trick to change that.
Gearing doesn’t make more energy output than the energy put in.
Yes, many electric bicycles power themselves while going down hills or costing. As for the other idea that you could recharge them just by pedaling … That exists already. Almost nobody wants it because it’s easier to plug your bicycle in. The point of the electric bicycle is to do less work, not to do more. Otherwise you would get a regular bicycle because it weighs less.
Regen braking exists, and everyone does want it, because it gives free power when you hit the brakes. The reason nobody adds it is because up until recently, you could only have coasting or regen braking, and not having to pedal literally all the time is just far more important for bikes. There’s a recent tech, freegen? Called something like that, it lets you have both regen braking and coasting,
WOOOOOOOOOOOOOOOOOOOOOOOO!
Aw man, Lemmy finally got a LinkedInLunatics instance? How long has this been here? That was like the last thread I’ve been hanging onto with reddit. Finally, this place feels like a genuine alternative 🎉
The community (which isn’t an instance!) has been there for a couple of years already: https://sh.itjust.works/post/27701
If you haven’t come across it before there is the Lemmy Explorer tool (with options for Piefed and Mbin as well): https://lemmyverse.net/communities
Welcome to the fediverse’s LinkedInLunatics, my friend!
You could harvest energy from going down hills and braking, but that’s probably not work the weight.
Electric cars already do this and I’m sure there are some smaller electronic mobility devices that also do regenerative braking. It’s not exactly a new concept.
For each second of using regenerative braking, you can accelerate for 0.7 seconds.
But how much do you actually brake when riding a bicycle? That’s completely neglectable (at least for me).
A mechanical engineering student that doesn’t know the law of energy conservation?
Techbros rediscovering old principles, a tale as old as…well, since the tech industry.
I see a lot of people clowning on this guy but is it possible that something like this could come in handy for commutes with elevation changes?
Coast to work and charge the battery, use pedal assist on the way home uphill.
Seems too niche to sell a bike for this, though.
That’s how regenerative hybrids work, IDK if a bike has enough mass though.
It does. Ebikes with regen brakes exist
I had one, and it was shit for regen braking, but also terrifying. It was a dual 1kw motor (front and back wheels both powered) bike with a car battery sized LiFePO4 battery bolted over the back wheel. Incredibly top heavy, overpowered such that the front wheel would spin on the road at takeoff, and the regenerative braking was a fixed amount of deceleration. Meaning it would put, say, 100 Newton’s of torque consistently when triggered. Want to stop from 50km/hr to zero in 10m? Too bad, this bike does it in 25m.
Want to apply just a little bit of braking? Too bad, these brakes are Boolean and they are either on or off.
I believe it was a homebrew import, I bought it off a guy who inherited it after his housemate died (not from the bike)
For context, the max legal motor size here is 250 watts (or 1/8th the power of this bike)
That’s not really how regenerative hybrids work. Turning linear motion into stored energy produces drag, aka braking, so when you hit the brakes, why not store some of that energy that would otherwise just be lost as heat in the brake pads. They’re not just finding extra energy to store for later while you travel downhill unless you have cruise control on (which is to say, unless the car is braking).
In a hybrid corolla, rolling down a hill without pressing the accelerator or breaks will regenerate the battery. Meaning the default is to always try to regenerate at least some energy and produce at least some drag. Letting go of the accelerator at some speed on a hybrid will slow the car to a halt sooner than a non hybrid would.
Well, I knew I’d leave too many loose ends explaining something before bed.
Not quite.
When you coast in a car with an internal combustion engine, you go further when you’re in neutral. Why? Engine braking. When you take your foot fully off the pedal, you restrict airflow to the engine and create a partial vacuum that the cylinders have to work against.
I’m not saying to coast in neutral for higher fuel efficiency. It’s quite the opposite with modern engines that cut off fuel injection when it’s not needed while in gear—and it can lead to increased wear and tear on the engine as well as your brakes fading on long descents. But now you have me covering my ass on every little point, ha. You could look up hypermiling and learn about more efficient driving techniques that way!
Now obviously hybrids have traditional internal combustion engines on board that behave the way we’ve just described. The engineers have also added a level of regenerative braking that is variably applied, even when the engine is not on, so that you scrub speed at a consistent pace. Without this, descending with the engine on or off would feel drastically different, and the car wouldn’t behave as expected at all times. It’s similar to how engineers for fully electric cars have added the “crawl” mode that makes a car idle forward when the brakes are off, even though there is no actual “idle” occurring. It makes the car handle the way you expect it to, and that makes you safer.
It is nice to recapture some energy that is used during the braking process. But only if you need to brake. Otherwise, you’re stealing energy you could be using right now and turning into less energy for later. The process of converting energy into various forms is inefficient, so you will always end up with less than you started, and the more conversions you do the more you lose. Potential gravitational energy to kinetic motion energy is more efficient than potential gravitational>potential chemical>kinetic motion, plus that last step is oversimplified because having the chemical energy turn a driveshaft is actually another kinetic energy conversion compared to gravity turning the wheels directly.
Thus e-bikes could benefit from regenerative braking if the system is efficient enough to overcome the loss of efficiency it introduces via weight and drag, but not from the constant low level capture of energy that would be better used now. Because you don’t get to fuel up an e-bike when the tank’s nearly empty—any toll you pay in inefficiency comes outta your legs and your lungs.
I am not an expert and I am sure I glossed over some nuances.
I’m not sure I get your point. What do you disagree with?
My point was hybrid regen is always on (unless accelerating), if it wasn’t, the car would basically coast in neutral. I’m pretty sure hybrid car designers did the math and examined use cases to discover its more beneficial to recover some energy and not coast as much vs coast as much as possible and ONLY regen when breaking. Lightly breaking applies more regen force. Or are you saying they do this for the feeling only and regen is a byproduct… if it even matters?
I’m not certain, but I’d say applying a little drag to regen on an ebike going downhill will be more beneficial than allowing the riders to go as fast as possible downhill. They could still turn it off, just like I can put a hybrid car in neutral and skip the drag, but why would I do that?
Not really, even in this hypothetically perfect scenario. Either the hill isn’t steep enough to generate any real excess energy from rolling down it (too much drag and you’ll stop rolling) or it’s steep enough that what you collect is offset by how much energy the ride home requires. The more potential energy you save for later, the slower you’re traveling now. And you can never cross the threshold to where it’s helpful. You’re trying to steal energy from a closed loop. It’s the “bowling ball dropped from face level” problem all over again. It can never get enough potential energy from its trip away to come all the way back.
Storing pedaled energy is pointless too.
Let’s say one regular old pedal rotation propels you 10 feet.
Let’s instead store 20% of that energy for later. You now only travel 8 feet.
While we’re converting that energy, we lose a quarter of it due to inefficiencies in the process. So now we’ve traveled 8 feet and stored 1.5 potential feet.
Pedal 1000 times. We go 8000 feet and store 1500 potential feet. Stop pedaling, turn on battery support, we go 1500 feet, we get 9500 total. 500 less than an unmodified bike. That’s excluding additional system inefficiencies like the added weight of the modifications and the mechanical efficiency of the pedal assist. It’s more efficient to just pedal.
Do most e-bikes not charge from the pedals? Combine that with regenerative coasting/braking, and this isn’t really that dumb. Like yeah, obviously thermodynamics, but an E-bike with pedal charging isn’t a closed system.
Regenerative braking is not worth it on bikes… it’s worth it on cars because you are slowing down over and a half tons of weight and going much faster so there is serious amount of energy to be recovered
You’d basically need electronic braking for this to work. Which should be theoretically possible since we already have electronic gear shifts. Would be tricky to get the feel right in the transition between motor to friction.
The pedals seemed like the bigger contributor, I just added the other for a few percent.
If I’m riding an electric bike, it’s to make pedaling easier. Why would I want an electric bike that’s harder to pedal?
If you extract enough energy from pedaling to charge a battery while also travelling, you’ll definitely end up using more power than less. Which absolutely defeats the purpose.
All these “smart” ideas would already be implemented if they were actually clever and deployable. The reason no one does it is because physics doesn’t work that way.
I’ve built two eBikes and can confirm that they do not.
