4 ms·

You make some great points. FWIW, they don't really relate to the original post I was disagreeing with, but great points nonetheless :) A few thoughts back:

by mft_ 5y ago

You make some great points. FWIW, they don't really relate to the original post I was disagreeing with, but great points nonetheless :) A few thoughts back: A) There are plenty of (heavy) bikes out there with a front caliper and a rear brake activated by reverse pedalling. Suspect a similar compromise would work, and a decent front caliper/brake level pair isn't heavy. B) In theory, simplifying the drive-train doesn't just subtract the mass of the chain - there's also a freewheel mechanism, rear cassette, chain wheels (usually 2-3), front and rear derailleur, multiple cables, handlebar shifters... and of course, the cost/complexity of purchase and fitting for these items. This would be quite a considerable weight, especially when we're talking about bottom-end components. C) Agree totally, but (for the sake of this discussion) the comparison isn't just the drive-train of a standard bike - it's a whole standard drive-train, plus a hub or bottom-bracket motor - as deployed in current e-bikes. Current Bosch BB motor assemblies seem to be ~6.3 - 7.1 lbs each. [1] D) Agree - ideally, there's no need for a display at all - a simple e-bike could just work. [1] https://www.bosch-ebike.com/us/products/drive-units https://www.bosch-ebike.com/us/products/drive-units

johnwalkr 5y ago
A) I agree regenerative braking plus a front brake could be a reasonable compromise. This is actually a pretty good idea. Could be simpler than trying to have some algorithm decide when to use dynamic vs mechanical braking. Front and rear brakes feel different already so it might be pretty intuitive to operate. B) Potentially those other things are subtracted, but a lot of e-bikes get rid of a lot of those components too and keep either a single speed with motor assist, or use a 3 speed internal gear hub. Really, if you're making the argument for a cheap, decent bike, you have to compare against the single speed option. The article didn't go into this detail but as long as the battery has juice, single speed e-bikes with motor assist don't have a big disadvantage compared to multiple speeds. C) And in this article a bottom bracket generator is required (about 2-3kg, more likely 3 for a "Corolla") plus a hub motor (also 2-3kg and more likely 3 for a "Corolla"). So it's "drivetrain plus motor" vs "generator plus motor" with some room for discussion about how many drivetrain components are involved. Until I read your reply I didn't even think about the fact that this proposed e-bike needs a hub motor instead of a BB motor, so it loses some more efficiency there automatically. D) I think front/rear lights are probably required for many jurisdictions and ought to be permanently fixed to the bike in any decent design to take advantage of the battery and be harder to steal, and battery level indication is of course required. A speedometer and programmable speed limiter would be good things to include if you want to make an e-bike that can be sold in as many places as possible without changes.

by mft_ 5y ago

johnwalkr 5y ago

A) I agree regenerative braking plus a front brake could be a reasonable compromise. This is actually a pretty good idea. Could be simpler than trying to have some algorithm decide when to use dynamic vs mechanical braking. Front and rear brakes feel different already so it might be pretty intuitive to operate. B) Potentially those other things are subtracted, but a lot of e-bikes get rid of a lot of those components too and keep either a single speed with motor assist, or use a 3 speed internal gear hub. Really, if you're making the argument for a cheap, decent bike, you have to compare against the single speed option. The article didn't go into this detail but as long as the battery has juice, single speed e-bikes with motor assist don't have a big disadvantage compared to multiple speeds. C) And in this article a bottom bracket generator is required (about 2-3kg, more likely 3 for a "Corolla") plus a hub motor (also 2-3kg and more likely 3 for a "Corolla"). So it's "drivetrain plus motor" vs "generator plus motor" with some room for discussion about how many drivetrain components are involved. Until I read your reply I didn't even think about the fact that this proposed e-bike needs a hub motor instead of a BB motor, so it loses some more efficiency there automatically. D) I think front/rear lights are probably required for many jurisdictions and ought to be permanently fixed to the bike in any decent design to take advantage of the battery and be harder to steal, and battery level indication is of course required. A speedometer and programmable speed limiter would be good things to include if you want to make an e-bike that can be sold in as many places as possible without changes.