2 ms·

If you still want it to be reasonably human powered, replacing the chain with a generator+motor is a bad idea. A chain has less than 2% loss, while a motor-gene

If you still want it to be reasonably human powered, replacing the chain with a generator+motor is a bad idea. A chain has less than 2% loss, while a motor-generator set will have 10 times or greater losses. Even a few watts of loss from a generator hub is noticable... losing 10 - 20% of power would make the bike nearly unrideable for any significant distance. I'm not sure how you'd remove the handlebars and still allow steering, one key piece of bicycle steering is counter steering -- you actually steer left to tilt the bike over so you can go to the right. (for gentler turns you can shift your body weight, but if you need to make a sudden turn to avoid an obstacle, you use countersteering) Likewise, I don't see how you'd have 2 side by side wheels on a "bike" that's designed to go 30mph+, how would you stop quickly without cartwheeling?

rwmj 10y ago
I should say I'm envisaging an electric-assist bike so (some) losses would be fine since they are made up by the battery. Of course if it's 10x the loss of a regular bike that could be a problem - I've no idea if your figures are correct or represent the state of the art. > Likewise, I don't see how you'd have 2 side by side wheels on a "bike" that's designed to go 30mph+, how would you stop quickly without cartwheeling? I guess you'd stop the motor and the electronic self-balancing would do the rest (in a very hand-waving way, but Segways are an existence proof that something like this is possible, although perhaps not at 30mph).
- Johnny555 10y ago
  Here's a chart of a typical electric bike motor efficiency -- peak efficiency is about 85% at 30mph. At 15mph, efficiency is closer to 50%. (that doesn't mean you get greatest range at 30mph since wind resistance increases with the cube of the rider's speed, so is 8 times greater at 30mph than at 15mph) https://endless-sphere.com/w/index.php/EBike_Efficiency#Determining_Peak_Motor_Output_-_Simple-Cheap_Method https://endless-sphere.com/w/index.php/EBike_Efficiency#Dete... And that's just for the motor, ignoring losses in the generator. Electric bikes don't need perfect efficiency, the Specialized Turbo S has a 700W-hour battery and gives 30 - 60 miles of range (2 - 4 hours at 15mph). A human pedaling at 15mph puts out around 100W, so even if the motor is only 50% efficient, the bike can still travel for 50 miles at that rate on one charge. With a Segway, you stand well over the wheels and can shift your butt (and center of gravity) as far to the rear as possible to make an emergency stop. I don't see how you'd do that with anything resembling a seated bicycle.

rwmj 10y ago

I should say I'm envisaging an electric-assist bike so (some) losses would be fine since they are made up by the battery. Of course if it's 10x the loss of a regular bike that could be a problem - I've no idea if your figures are correct or represent the state of the art. > Likewise, I don't see how you'd have 2 side by side wheels on a "bike" that's designed to go 30mph+, how would you stop quickly without cartwheeling? I guess you'd stop the motor and the electronic self-balancing would do the rest (in a very hand-waving way, but Segways are an existence proof that something like this is possible, although perhaps not at 30mph).

Johnny555 10y ago
Here's a chart of a typical electric bike motor efficiency -- peak efficiency is about 85% at 30mph. At 15mph, efficiency is closer to 50%. (that doesn't mean you get greatest range at 30mph since wind resistance increases with the cube of the rider's speed, so is 8 times greater at 30mph than at 15mph) https://endless-sphere.com/w/index.php/EBike_Efficiency#Determining_Peak_Motor_Output_-_Simple-Cheap_Method https://endless-sphere.com/w/index.php/EBike_Efficiency#Dete... And that's just for the motor, ignoring losses in the generator. Electric bikes don't need perfect efficiency, the Specialized Turbo S has a 700W-hour battery and gives 30 - 60 miles of range (2 - 4 hours at 15mph). A human pedaling at 15mph puts out around 100W, so even if the motor is only 50% efficient, the bike can still travel for 50 miles at that rate on one charge. With a Segway, you stand well over the wheels and can shift your butt (and center of gravity) as far to the rear as possible to make an emergency stop. I don't see how you'd do that with anything resembling a seated bicycle.