Radical new electric bike drive system requires no chains or belts | Hacker News Reader

Radical new electric bike drive system requires no chains or belts

electrek.co

28 pointswatchdogtimer20 comments

if this can be made lo-tech, without any software and hi-tech gadgetry, then it's a killer.. even if 10-20% less efficient. Most people don't need racing.. It won't need any gears and switching them anymore, as electrical motors have mostly same torque on whole range ; The force of pushing pedals does not need to match the uphill - as long there's something in battery ; And one can keep pushing downhill regardless of speed, and that energy will not be wasted..

The racers (pure bikers) won't be interested in battery assist either. For the vast array of use cases that ev bikes enable (basically, go to the Netherlands for all the things they do with bikes) for decarbonized, fun, short trips, this eliminates a vast amount of headaches.

This drivetrain has regen braking, a vastly simplified consumer experience, and MIGHT enable solving the other #1 problem with bikes: security. You can effectively lock the motor with a chip and an app inside a frame so it won't go anywhere, and even stealing it in a van and hauling it elsewhere to get it working isn't worth it.

I’ve been thinking about how this could be retrofitted to an existing frame. The generator is too big but it could be mounted in front of the crank shaft under the frame and then be connected via simple gears or a short chain. This would still have said benefits.

I think the possibility to choose when to save energy and when to put it out you mentioned is possible with a conventional e bike but not all bikes support this due to legislation.

if the generator can be made thinner, to be put instead of the 2-or-3 pedaled gearwheels (5-7cm?), would be fine. And Can be quite larger diameter, and any shape, it won't rotate

If that 5% figure is correct then this is pretty amazing.

Do you automatically get regen if you're going downhill? Some ebikes require backwards pedalling to trigger that.

I'd been looking at belt drives which apparently aren't as efficient as a well lubed clean chain, but may perform better than a neglected chain.

Racers pedal at around 90rpm, commuters pedal around 60rpm. Small generators are not efficient until 5000rpm or so, so this will need a two or three stage planetary gear to increase the rpm by about 100x. Each stage loses around 3%, so that's at least 6% gone before we even get to the electrical losses. I think this system will end up only being 80-85% efficient pedals to wheel.

On a manual bike you really notice a 5% efficiency change, like after you clean and oil your chain. On a electric bike I doubt you would notice.

Put a small battery on board and you can pretend it’s 100% efficient. For a time.

Basically this is the same thing as commonly used for diesel electric trains and diesel electric submarines, but replace the Diesel engine with your pedaling.

Not a terrible idea, but significantly less efficient than a chain. I’m not sure if I like the idea or not, honestly; I’d have to ride one myself. I’ve currently got a Shimano Steps cargo bike and enjoy it, but that’s a traditional electric assist. With the complete decoupling that would feel odd, at least at first.

The article says it's only 5% less efficient. Not that bad for the tradeoff

> As he explained, that means the rider would either need a 5% larger battery to get the same distance, or experience a 5% shorter range compared to the same bike with chain drive.

That's a weird way to specify efficiency of assisted e-bike, because battery->motor efficiency doesn't change, but pedals->motor efficiency drops significantly. I wonder which one they mean.

> The motor isn’t particularly powerful at just 250W, though that’s the EU limit for electric bicycle motors in Germany.

That’s really quite low given that this is the total output including input from the rider.

Also, this type of bike will not operate at all if the electronics malfunction. As the proud owner of an ebike that regularly glitches and can neither assist nor shift (!) when glitchy, losing power entirely would be even more annoying.

250W is simply not true.

The directive says that the motor (when preheated) may not exceed a temperature rise of 25°C over a certain period of time, nothing else. I sure don't understand why all people talk about 250W. Its a myth.

My pedelec (bosch perfomance line CX motor) definitely peaks at over 1kW of power (plus my power), so for example uphill I have a combined power output of around 1500 W.

> pedal cycles with pedal assistance which are equipped with an auxiliary electric motor having a maximum continuous rated power of less than or equal to 250 W, where the output of the motor is cut off when the cyclist stops pedalling and is otherwise progressively reduced and finally cut off before the vehicle speed reaches 25 km/h; (https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex%3A...)

The key is continuous rated power, which is measured with the temperature-controlled method over 30 minutes (https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:42...), and thus it can have a way higher peak-power, and manufacturers have a lot of leeway massaging the system design to formally keep in that limit. So both "there is a 250W limit" and "my bike gives out way more" can be true.

> A Schaeffler representative explained to Electrek that the Free Drive is approximately 5% less efficient than chain drives.

Isn't this just describing battery to motor-on-wheel efficiency vs. battery to motor to chain to wheel efficiency - for when you're not pedalling?

What about the loss incurred on the pedal-generator and electric power transmission side, for when you are pedalling?

I think if you don't pedal then it will just coast. E-bikes for the german market don't have any "throttle" feature, and will always only provide support while pedaling vs providing power on their own.

They could use this for an all wheel drive mountain bike.

Didn't get how it's moving the wheel without chain

Pedals charge battery, battery drives motor. 5% less efficient than chain drive.

I wonder if this would remove some of the design constraints seen in folding bikes.

The frame, wheels, and handlebars are the main annoyances; but I feel the gear and chain system limits the frames.

Every folding bike is somewhat bulky, and I’d love to see one that neatly packs to the size of a small personal overhead luggage without sacrificing safety.

belt drives and chains are on the same plane as the frame, so I don't think it would allow much more design freedom to reduce bulk. It may afford other design freedom, but I don't think bulk reduction will be significant.

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