This chainless drive system could revolutionize e-bike designs

Schaeffler’s Free Drive system converts pedal power into electrical power.
Image: Schaeffler

We don’t often write about bicycle components, but it’s not everyday that an innovation like the Schaeffler Free Drive is announced for pedal-assisted e-bikes. The so-called “bike-by-wire” system, first spotted by Electrek, dispenses with the need to string a chain or belt between the pedals and wheel hub. It’s an all-electric drive system that allows for entirely new bicycle designs with fewer moving parts.

The Free Drive system works by converting the rider’s pedaling power into electrical energy via a small generator housed between the pedals. It then delivers this energy to the rear wheel (or wheels) via cables strung inside or outside the frame of the bike, rather than sending it mechanically through a chain or belt. Excess energy created by pedaling is fed back into the battery. The end result is a power system with fewer moving parts to complicate construction.

The Free Drive system is sold to bike makers as a set of optimized components consisting of a 250W hub motor, the pedal generator, battery, and interface unit. And while the technology could have serious design implications for commuter and city e-bikes, Free Drive’s biggest and most immediate impact might be on cargo bikes.

A chain-free drive system would remove the need for unwieldy designs like that of the Tern cargo bike (above).
Image: Tern

Cargo bikes come in some unusual designs in order to create space for freight. These designs often require absurdly long chains slung between the pedals and rear derailleur. These can snag or soil clothing, and slap about noisily over any bumps. Tern cargo bikes, I’m looking at you.

Electric cargo bikes have the potential to transform cities by replacing those hulking delivery vans that block traffic and pump the air full of pollutants. So, anything that accelerates the adoption of e-cargo bikes is welcome news, indeed.

A prototype electronic cargo bike from BAYK fitted with a Free Drive system.
Image: Schaeffler

Schaeffler recognizes this opportunity by replacing the chain drive of a Bring S cargo bike from BAYK with its Free Drive system. The bike is on display at the big Eurobike trade show happening now in Frankfurt, Germany.

Comments

Sounds very interesting. Though I wonder what it a like to bike with this. I mean, if you don’t have an immediate feedback from the street as you pedal.

It’s not really a bike, it’s an electric motorcycle with a foot-operated charging crank.
That disconnect is going to be disconcerting.

I don’t consider anything with a throttle a bicycle nor should they be regulated the same as human powered vehicles. You’re probably correct that these will be something other than a bike.

Yeah this smells like a device to skirt a loophole in the law. We already see more of these type of "bicycles" on the streets of Amsterdam ever since 50 cc 4kW gasoline scooters have been banned from the bicycle paths and after helmet laws started applying to those vehicles.

The best thing about a chain is that it is nearly 100% efficient. Nearly.
We’ve seen driveshaft bike drivetrain designs, and unfortunately they’ve been underwhelming because they were somewhere around 90% efficient in transmission of power.

I didn’t see any claim of efficiency for this pedal by wire drivetrain but I will go on a wild guess here and assume it is probably no more than 80% efficient; meaning 100W of pedal power input will only result in 80W wheel power output. Absolute deal breaker in my opinion but unfortunately a physical limit of mechanical to electrical (and then the reverse conversion) efficiency.

Geez; wonder why no-one ever thought about this revolutionary bike train design…

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

I find their "5% less efficient" claim extraordinary.
My understanding is that electric motors are at best 90% efficient. So doing a double conversion as is the case here will yield at best 81% efficiency (90%*90%). And that’s at the optimum RPM and load, any variation in speed and load will increase amperage and thus energy losses.

I’m calling shenanigans on the manufacturer claim…

yeah, definitely needs to be tested. It’s certainly less efficient, but technicalities aside, does that really matter to the rider when it’s a pedal-assisted e-bike if they get a design they like, with range they like, and are able to ride further while arriving at their destination sweat-free?

Agreed, not everyone is part of the lycra army trying to go as fast as they possibly can under human power. I want my bike to get me around not to prove my worth.

The other way to look at it is that the battery is used to supplement that missing 10-20% efficiency. Then it will be no different than a chain bike but far less liable to break due to fewer moving parts in exposed areas. I wonder how far you could get with the equivalent supplemented efficiency on typical roads. Considering breaking and and coast phases are just wasted on a chain bike with no battery to charge you might go very far indeed.

I think this is a great idea.

I think the issue with this system is that obviously you will get much less range for a given battery capacity.

The much bigger issue however is that in places like Europe where the motor has to be rated to less than 250W you will have a real issue with this system, particularly on cargo bikes. On a pedal-assisted system as we have now, you get 250W from the motor + bursts of up to 1,000w for any decent person (arguably only in very short bursts, such as starting uphill etc.). If your total output is only ever 250W then there is no way you can have the flexibility that is needed for heavy loads or city pedaling. Meaning that this system would only ever be useful in flat areas…

Why not just buy an electric motorcycle cargo bike with a 2kw rating instead?

I just don’t really see the use case for this system

Current designs are always taking energy from the battery and never putting any back. If I could pedal with consistent resistance comfortably then I don’t mind charging that battery a bit while the bike is technically coasting.

Not sure how that will equate to less range when the batteries and hub motors are the same efficiency as current designs, but without onboard power recoup. And technically it seems feasible that this design could reinvent pedal braking to recoup power when coming to a stop as well.

Even if this is a baby step and not the most efficient, I see it as a step in the right direction. They certainly shouldn’t just give up because their first iteration isn’t quite as efficient at pedal to ground power delivery.

This claim is complete BS. They might say some part of their system is that efficient under perfect conditions. But convert from kinetic to electrical – 10% loss, convert from electric back to kinetic another 10%, now if it goes throw battery that’s another 10%. If they use an inverter to convert ac to dc, that is another 5% (most likely what they talking about). And of course the resistance of the wires. So I would be surprised if you got more than half of your effort translated into miles. Above is a perfect world scenario.

While undoubtedly a generator/motor combo will suffer loss of efficiency compared to a chain drive in theoretical terms. In reality, you get fairly low efficiency pedaling a bike. At any given time on a bike, except perhaps accelerating up hill, your chain drive will vary between fully loaded (all pedal movement results in output) and zero load (pedal movement does nothing). For example pedaling while coasting down a hill on a chain bike is 100% lost energy. In reality a pedal bike is powered in pulses, and about half of the pedal motion is too slow to actually generate any output.

An electric generator however will generate power through the full rotation of the pedals, so while efficiency is lost in the conversion from potential to electric energy and back, it is made up for by using 100% of the energy input into the system rather than about 50%.

Where this would really shine is on tandem bikes, where two people could pedal at different speeds and still both provide power.

Pretty sure that is how they’re getting their efficiency numbers, which is fair.

yes!! more innovation in the ebike space

I saw a tweet that said "In this era of gadgets and gizmos, riding a bicycle is the closest we get to operating a contraption"
I feel that a chain retains that small amount of pixie dust simplicity that makes a bicycle what it is.

Of course, innovation is well and good and anything that gets more people to bike is excellent. But there’s also the ship of theseus POV to assess this from

I will always prefer a paperback stuffed into my back pocket, but still do most of my reading on a kindle

As far as I’m concerned, a kindle is superior to a paperback in almost every way except it’s more delicate and therefore can’t be stuffed into a back pocket safely.

I’m not sure you understand what the Ship of Theseus refers to.

I understand what this reference means. If you start with a bicycle and you replace the chain, it is still the same bicycle. If you replace the chain with a generator and a motor, add a battery, maybe a twist throttle, it is not really a bicycle anymore. It’s something else that doesn’t have the "spirit" of the original.

That is not what that thought experiment is exploring though. The original philosophical question was about the inherent identity of the object as parts are replaced; upgrading parts and altering the object’s original functionality (though not purpose) is a different matter.

Those "unwieldy" chain designs are easily solved with an internal gear hub.

Is this technically an "e-bike" system, when the bike can’t be operated without the electrical system? This strikes me as more of an "e-scooter" system, where they’ve essentially integrated the throttle into the crank.

Not that I think it’s a bad idea, but the ability to be propelled by purely mechanical means is a part of the "e-bike" definition in many jurisdictions.

Also curious on the specs for the hub motor. I know 250W is a Euro standard, but what’s the torque rating? Most 250W motors have a pretty anemic 30-40Nm of torque, which strikes me as a bit low for a cargo vehicle as pictured.

Mid-drives can get away with it because 250W is the nominal top (but they can peak much higher), and the rider gets the advantage of leveraging the mechanical gears.

Absolutely agree – what happens if you run out of battery or have some electrical issue? If you can’t pedal the bike without the power on, it’s not really a bicycle the way we think about them.

Removing any ability to drive the bike yourself doesn’t seem like an improvement on design to me. And you’re also losing the torque of both other systems – a mid-drive has a lot of torque, and a hub motor bike with a normal bottom bracket you can pedal with, you can easily out-do the torque of that motor when going up hills.

If the hub motor paired to this (250 watts?) doesn’t have the torque to get up an incline you are, again, S.O.L. with no ability to use your own torque.

Agreed completely. To me, it’s not a bike if there’s no chain that allow operation without electrical power.

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