Apparently you didn't look very closely at the charts above.Leeps wrote:Gears are better for climbing hills, however from a performance perspective the hub motor wins.
A motor is a motor. If you gear it up you get the power peak higher, if you gear it down the power peak goes lower. It's that simple. The bottom line is that motors run best when the voltage and the rpm's are in a certain "efficiency zone". With gears the "zone" is moved up and down and so you can be certain to have coverage everywhere.NickF23 wrote:There is also generally a differnce between a geared hub motor ie fixed gearing and direct drive hub motors.
I posted the chart above.NickF23 wrote:...looking forward to the chart
Problem here. Your hubmotor model has the same basic parameters as my actual ebike. I've tested my ebike up hills and made acceleration tests I've presented on video (I'll do the hill climbing videos soon)...Maximum speed at 15% grade: 7 mph verses 17mph
Maximum speed at 10% grade: 15 mph verses 23 mph
Maximum speed at 5% grade: 38 mph verse 38 mph (the hub peaks here)
Maximum speed at 0% grade: 48 mph verses 58 mph
MOST hills are less than 10% grade. 10% is a very steep hill... and I know (because I used to ride up a mountain on a road bike with a published grade) that MOST moderate hill climbs are at 5%.xyster wrote:I've climbed 15% (or darn near) grades at 20mph from a dead stop, and 10% grades at 26mph from a dead stop.
But as the rpms rise you have to spread the same power across a larger number of "radians per second" so the torque actually drops as the rpms rise. You end up calculating the INTERSECTION of those two curves and that is what determines the actual top speed. (this was explained in the first posting)xyster wrote:You're also forgetting that the lower wattage output occurs at lower speeds...as the motor gets itself slowly up to speed, more power lets it climb faster...at the wheel.
Hill climbing power and acceleration rate is a function of power, not torque. As torque decreases, to a point well established on these graphs, voltage rises faster than torque decreases. Hence power rises with rising rpms, and so does hill climbing ability/acceleration rate. That's why gears work to provide more torque at the expense of rpm's (voltage) where it's needed most!But as the rpms rise you have to spread the same power across a larger number of "radians per second" so the torque actually drops as the rpms rise
This doesn't sound right. I thought all the PWM does is allow the bike to run at lower speeds efficiently. A direct drive brushed hub motor with no throttle and a simple on off switch would have no less torque than one with a throttle.safe wrote:Let's talk about Torque
The "PWM Current Warping" effect (Buck Converter) definitely has a LARGE effect on this low end torque area and this does give some credibility to the idea of using the hub motor and abandoning chains and gears. Were it not for this effect it would be impossible.
xyster wrote:How much power in watts can a bicycle chain drive system handle?
Please note (again), I'm not arguing that gears are not far more efficient over a normal range of rpms... just that high-end, available hubmotor systems can climb hills just as well if not better than high-end, available chain drive systems. If true, the power factor cancels on both sides of the hubmotor vs. chain drive equation, leaving as most important ancillary factors such as efficiency (gears/chain drive wins big time) vs. simplicity and its close cousin, reliability (hubmotor wins).