Energy recovery for e-bikes

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efeballi
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by efeballi

With the recently surfaced news that Sea Otter will be hosting an E-bike race, something came to my mind. As an avid follower of Formula 1, I'd like to see some energy recovery systems on the bikes. In a crit where you brake into every corner, you're actually converting your valuable watts into heat, into every corner. Maybe with ERS, you wouldn't have to brake and deposit some of that energy somewhere, and use it at the corner exit, or some other time when attacking etc. Same could be applied for descents, red lights etc.

There are, of course, some technical hurdles:
-location of the ERS. Rear wheel hub would need rigid connection to the frame to be able to generate backwards torque. ERS at bottom bracket would require constantly spinning cranks, impractical, especially in corners. Separate harvesting and deploying systems may be considered, but would add weight.

-control of deployment/harvesting. Where, and how hard should the ERS harvest and deploy energy? Should it be automatic, or under rider control?

I know this is currently highly impractical and also against the spirit of the sport. But think about it, could actually be fun. Riders sprinting and using ERS to flash out of corners.

Discuss. Maybe I'm too much into F1.



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robrud
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by robrud

I haven't done any calculations but just from my engineer's perspective the weight penalty wouth outweight the actual benefit of added energy.

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euan
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by euan

There are already ehubs out there that use energy recovery to recharge the battery. The one that springs to mine instantly is the Zehus Smarthub, which personally has been the only e-assist or ebike I've ridden and actually enjoyed.

It does a little bit of energy recovery when coasting, but if you back pedal then it goes into full energy recovery mode and provides a degree of braking ala a coaster brake. The way the assist comes in is not controlled by the rider and only up until 15mph but it feels very very very natural. It only comes in when you actually need it, so if you are soft pedalling there is no assist and then its progressive from there. Feels fantastic just starting from dead.

efeballi
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by efeballi

Sounds great, this.


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AJS914
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by AJS914

If you are only braking for corners in a crit, you are in the back of the pack. And if you are 80 guys back in the pack you probably aren't going to win anyway. :-)

efeballi
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by efeballi

That was my F1 thinking that kicked in. Crit racing is the closest thing in cycling to F1. And if you're also braking in the pack, even better. More power for your attack.


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mattr
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by mattr

Except the hardware to store the energy is out of all proportion with the amount of energy it is storing.

Most hybrids have 50-120 kilos of battery to store the equivalent energy that you'd get out of a litre or so of fuel......... so once you stick the motor in, you're ending up with a not very powerful 200 kilo powertrain, the same "extra" weight would do far more good invested in a better engine....... but legislation doesn't allow it.

So for a bike, where the retardation energy is minimal (KERS needs a relatively large mass decelerating by quite a lot to get into an efficient phase) the hardware would be relatively heavy, to give a miniscule boost.........

A bit of charging on overrun/coasting on an e-bike is probably as far as the tech can go these days.

efeballi
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by efeballi

I know, that's the biggest technical challenge to overcome.
So with the current technology, we have a 63 kg ERS on F1 cars weighing 702 kg with driver. With a crude estimation, this amounts to 7.18 kg on a 80 kg bike-rider combo. Acceptable? Certainly not.
Looking at a power perspective, the F1 internal combustion engine provides circa 650 hp versus the 160 hp of ERS, with the same line of thinking, the bike ERS would provide 73 W with a 300W sustained power output from our legs. But please note that this power figure is dependent on deployment strategy, you can deploy more power for a shorter time or deploy less for longer.
Is 73 W worth an extra 7.18 kg on the rear wheel? I can hear you shout "NO!" This is why the technology needs improvement. But I still think it can add a new aspect to cycling, maybe in 20 years' time.


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Marin
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by Marin

Plus, F1 doesn't do it because it makes them faster, they do it for marketing reasons :D

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