SteveFree energy mod!
When the battery runs out, you pull over and “pedal” to recharge the battery, then you’re good to go again!
I don’t own one of these, but that sounds actually useful if for example I’m about to climb a big hill and want to pedal at a less strenuous pace (but for more time) than would be needed to overcome the slope.
Assisted modes already exist, and regenerative braking already exist
logiBut do e-bikes have regenerative braking? I haven't seen that. I've been thinking that it would just be too heavy and clunky to be worth it.
teftToo heavy? You just run the motor in reverse which turns it into a generator and adds friction to do generative braking. There really isn’t any added weight.
Bikes normally have freehubs, a ratchet on the cassette (sprockets) of the rear wheel, when you stop pedalling the bike freewheels, without that the pedals would keep turning.
This makes driving a motor from the wheel impossible without heavily modifying the normal bike mechanics. That’s why regenerative braking on e bikes is rare.
Tlaloc_TemporalNot if you have a hub motor. Those don’t interact with the gear system at all.
Only very cheap e-bikes have hub motors. They’re not a good idea precisely because they don’t interact with the gearing system. So you lose that functionality.
It’s not worth losing access to gearing just to get regenerative braking because the amount of power being used isn’t worth trying to recoup.
Motors are generators when run inversely:
Motors = put in power to get rotational movement
Generators = put in rotational movement to get power
You already have the heaviest parts on the ebike - motor and battery, just need some capacitors and charging circuit board which are light and not too big.
Cheap electric bikes I’ve ridden with regen breaking slow you down quite a bit.
It’s not difficult to get regenerative braking on a bike it’s just difficult to get regenerative braking on a bike that’s any good. Hub mounted motors are the least efficient type of motor because it’s just directly driving the wheel at whatever speed it can output, with no access to gear ratios. E-bikes that forgo generative breaking in favour of a more efficient motor designs achieve better speeds for any given amount of power usage.
So yeah you can absolutely do it. But it’s not a good idea for reasons that have nothing to do with the weight.
miguel
pelespiritI 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?
Brave Little Hitachi WandWhat 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.
KazuyaDarklightConservation 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.
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.
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.
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.
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.
henfredemarsLooks like it could even be AI style with all the emojis.
Either way, thanks I hate it.
You could harvest energy from going down hills and braking, but that’s probably not work the weight.
Unironically, I would enjoy a bike that I could pedal at a constant speed, charging the battery all the while. Give me a display that indicates my pedaling speed so that I can tailor my exercise and you’ve created a moving stationary bike. I hate having to stop at lights and whatnot, so a rotation-based stabilizer would be nice at speeds below 10 km/h as I pedal the equivalent of 30.
Really, it’s just unfortunate that the engineering doesn’t work out for momentum->chemical energy unless you’re biking at a professional level and willing to cruise slowly or charging the battery at home. Bleh
zaknenouAs someone who sucks at physics, I’m convinced that Trollface has proposed so many solutions around the internet to provide free energy, but the capitalists are conspiring to sabotage him, just as they did to N.Tesla.
idunnololz
Swedneck
VictoriaI am not well versed in modern electric bikes. Do they offer regenerative braking yet?
driving_croonerMy e-bike dosen’t have it and it’s sounds pretty complex to add efficiently on a bike. It’s just take like 5 hours to charge in a normal output. And every corporate building have outputs for e-bike so I can charge while working.
Perpetual motion machine aside, where tf is bro going that the range of an ebike isn’t enough, but the speed is
Mechanical engineering student huh? Good to know he didn’t attend class on day 1 of dynamics
UnderpantsWeevilMechanical engineering student huh?
1 week
This is a normal trajectory for college freshmen. Get introduced to a bunch of basic ideas. Spitball and try to see how you can apply them. Start running into all kinds of caveats and engineering hurdles. Go back to class. Bother the RA. Maybe actually learn more about what you’re trying to accomplish. Become a better engineer.
AvicennaUnrelated, but the pedaling cadence people have on ebikes bothers me. I’m always seeing folks in a high gear slowly pedaling. I’m like dude you’re sacrificing watts! Pedal faster on a lower gear, you’ll use the same energy but go faster.
I thought it was the other way around, where doing the higher force version results in higher efficiency, so you use more energy to achieve the same effect (when you use the lower gear and pedal more). It’s easier to generate force but takes more energy to apply that force over the same diatance (because the converted distance you’re applying it to on your end is longer).
So like regenerative breaking for e-bikes? Except that such a thing already exists.
Apparently regenerative breaking efficiency in bikes is rather limited (small motors / generators, high friction). It still increases the range a fair bit (enough to be a better investment than bigger batteries), but efficiency is still not as high in bikes as in bigger vehicles which can drive more kinetic energy into bigger generators with better individual wheel control
Some paper says ~25% extra range in bikes at the high end vs ~50% energy savings in Japanese trains. Different units for those numbers, but you can infer that trains has much more efficient regenerative breaking because that number indicate a doubled range for the same amount of energy used.
Sterile_TechniqueThis is dumb as shit ofc, but it gave me an idea that’s probably nearly equally dumb as shit:
Regular bicycle, but with an extra gear that can selectively connect to the chain or wheel or w/e, that’s connected to a coil torsion spring on a kind of ratchet release.
Basically you flip the switch when it’s a good time to rob some energy like when you’re on level ground or going down hill. That energy makes you a tad less efficient (but you don’t care cuz it’s level or downhill), and uses that energy to wind up the coil torsion spring up until a max amount of torque is stored.
Fast forward a bit: now you’re approaching an incline, so you flip the switch the other direction and that torsion spring regurgitates that energy back into forward motion, giving you a nice forward burst when going up a hill.
Not free energy by any stretch, but a strategic use of what you’re already spending.
Feel free to explain why this is a horrible idea - I’m about as far from a physicist as it gets.