Kinni420 wrote:ive done a bunch of testing while riding the bike and I find its actually more efficient at higher speeds.
14 mph 700w avg
23 mph 350 w avg
crazy to be getting more mileage out of more speed - I cant get off this damn thing LOL
I find the same thing "for the same throttle setting" and I don't think that's wrong. I expected it, and that's what the simulator predicts. I can maintain 21-23 mph using 240-270W on the recumbent. The power I need is used to maintain forward motion over the frictional losses plus wind resistance. (and BTW: I'm running 80-90 PSI in my tires)
At the higher speed, the motor generates more back-EMF, so less current flow, less power used and less available torque. In fact, if you watch on a 2810 you'll ALWAYS burn more power at low speed unless you really "feather" the throttle back. You can see this reflected in the curves on the ebikes.ca simulator. I don't care which motor you pick, the torque curve goes down and reaches zero. Power consumption rises to a maximum, then decreases
, as you reach the maximum available voltage and speed of the motor.
In the sim, these curves go all the way to zero. On my recumbent, I "enjoyed" this fact when I was pedaling my ass off to keep the bike at or above 20mph. A 250W motor would have been fine to keep me at 22-23mph on flat land. At higher speeds, as you apply more throttle, the power consumption spikes, but as the motor "catches up" with it's own rotating field, power consumption once again drops. (I'd love to see motor voltage plotted on the simulator. )
Same is true, say, when you're going down a hill and picking up speed on your own. True, you're converting potential to kinetic energy, and so the motor doesn't "have to" supply power, but that's not the only effect in play. The motor is spinning faster and generating higher back EMF as you move the coils through the PM field.
Say you're going close to the motor's maximum speed, like in your video when you go pas the radar sign (31MPH, awesome!)
You'll see it's not possible to push the motor any further with 72V. It won't take any power from the controller at all. The "cogging" of an unloaded motor generates power itself and at high speed, as the motor generates enough back-EMF to push current back through the controller, you can't go any faster.
That's the same reason the motor's max speed is in proportion to the higher voltage we apply. If I want any more than about 32mph, I gotta go above 18S. I've been wondering about making a 22S (96v) LiPo brick and see what happens with the motor. (I THINK our 25A IFRB controllers can handle that without failing...now I know what my next test should be! )
Another thing I've noticed: even though our 2810 motors aren't in the simulator, the curves for the 2808 look awfully close to the performance I'm seeing with the 2810 on a 26" wheel.
Hey, tell me: (since you're running 72VDC also) - my controller and batteries don't get hot, or even warm, when I ride. Is that what you are seeing?