this post was submitted on 16 Oct 2025
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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 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 braking" (cuz' the motor is used as a generator in place of brakes, and you'll need to drive said generator by capturing/braking some of your kinetic energy/forward motion).
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.
Gearing doesn't make more energy output than the energy put in.
The collection will always be less than the energy it takes to generate it. There no magical gear or trick to change that.
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.
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.
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.
All of these points are well taken, but I didn't understand it as infinite, but more like to get you where you're going.
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.
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.
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.
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.
Thank you for taking the time and patience, this explains it for me in a way that makes sense.
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?
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?!
Oh shit you solved it!
I was being sarcasmic.
🥵
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.
Maybe you can join his team!
But I can forgive a non engineering student… its impossible.
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