bluefoxicy

For an average person, what's the normal power output to cruise? How does it change with speed? Or is this a heavy variation thing? What about take-off?

I'm curious now because I was thinking on e-bikes and the Trek Ride+/Bionx stuff. Their stuff basically has a 25%, 50%, 100%, 200% setting. When you pedal, it takes your power and adds that much. If you output 100W at 25%, you get 125W on the wheels; at 200%, you get 300W on the wheels. It's a constant multiplier.

What this means to me is that I'd be more comfortable going faster with an eBike. I mean, if it adds 100% power, and I'm usually going to cruise at 10mph on a 1% grade, then I'll now cruise ... faster. If it takes 100W to keep 10mph, I'm now producing 200W; if that translates to 14mph (wind resistance ... it won't be 20mph), then now I'll always cruise around at 14mph.

Well, I find that blah.

So I was thinking, what if the program on the eBike's computer was a bit smarter? Besides the obvious problems with rough cut-offs (it should smoothly back off when you're approaching any electronic speed limit, not just dead shutdown at 20mph), I have some ideas for the bike program.

The main one is of acceleration, hill climbing, and take-off. I can cruise at some speeds on level ground, whereas other speeds I can't maintain because it takes--of course--too much power to overcome wind. Going up a hill, again, I can cruise up the hill at lower speeds easily, same thing: lower gear, lower speed, same amount of power going in to overcome gravity. Trying to maintain a higher speed, or trying to speed up, requires increased power; an electric assist is only useful to me here.

My thinking is obvious: if the eBike kicked in its assist when it saw power input go past a certain level, it'd give you a nice, sporty bike. It's still human-powered... to cruise. An easy take-off is still an easy take-off; maybe you even set it to require even higher power to kick in from 0-3mph. But if you really shove on those pedals, the motor kicks in and gives you a much higher peak power. You can blast out from stop lights, accelerate rapidly, climb hills, and cruise at higher speeds; but if you're taking it easy, the motor just never kicks in.


So I'm now curious. You folks with power meters, when you lay on those pedals hard to take off quick, does your power meter register a huge spike in power? What's it look like relative to your normal cruising power? How about when you climb a hill maintaining current speed? When you rapidly accelerate?

In other words, do your electronic doo-dads show numbers that support the feasibility of this idea?

As a side note, I think these would be interesting for speed-controlled (i.e. by having twists and curves) endurance races. The battery only lasts so long, so you'd have to be smart about using it: blast off when you can, cruise at high speeds, but then you can reverse the motor and use it in "training mode" where it acts as a regenerative brake to charge the battery. Make the race far too long to last on a single charge, and now you can use the power assist but you'll also want to make use of the regenerative training mode to power it back up...

crackerdog

Electric bikes follow the same rules of physics that every thing does. You use more power accelerating fast, you use more when fighting the wind resistance ie, the faster you go the more wind resistance. The fancy control you are looking for is a throttle control.

rscamp

Sounds like a reasonable approach to me. However, not everyone would want assist to only kick in at a threshold value. I find it more fun and involving to have independant control of the throttle, for example...

adamtki

I had the same thought. I don't like to use the battery if I'm just casually riding around. But I'd like it to kick in at a certain threshold of power. I checked around my Bionx setting, but it doesn't have that. The closest thing is having a minimum speed at which the motor kicks in. Send the suggestion to Bionx. I'm sure it shouldn't be too hard to add that feature.

Leisesturm

Nice idea but after few months you would realize that the motor only came on once in all that time but you were carrying around 30lbs of battery and motor... ...