Well, if you can go to: http://ebikes.ca/simulator/ you will see that motor efficiency is a strong function of motor speed. A hill that rises 900 ft in 1.5 miles is a 8.5% grade. I guess steep is relative; I was considering hills more on the scale of 15-20%.

All of these systems have their good points and bad; none are magic. Gears keep the motor at higher efficiency. If you pile on enough battery voltage and capacity to drive a direct drive bike up a 15-20% grade at 40 mph, then it will be efficient. If you are doing 20 mph up the same hill on a bike that will do 40 mph, you are putting about half the energy of the battery into heat. You can’t get around physics. The efficienty of indirect drive systems is not that dissimilar from direct drive systems; the motor does not turn when not powered. There is no cogging as found in direct drive.

” Efficiency for electric motors is zero at zero motor speed. ”

Interesting claim, if a bit silly. I’ll claim that electric motors are infinitely efficient at zero rpm. Just as silly, though a little more accurate.

BTW: my bike weights about 50 lbs. with an inexpensive mountain bike at the core. I can lift it onto the bus bike-rack easily. It will go about 15 or 20 miles at 40mph. At slower speeds it will go a lot farther. Forty mph incurs a lot of wind resistance. It will go 25mph up my steep hill. Hill is 900 foot rise in about 1.5 miles. It’s a direct drive, hub motor which is much more efficient than indirect drive systems, such as chain drives. Where direct drive fails is in allowing the bike to be used without the motor assist. The direct drive motor causes some drag, more than is acceptable for pedaling. I think that’s fixable, but haven’t had time to address it.

Richard

Not true. Efficiency for electric motors is zero at zero motor speed. You can increase power by increasing voltage or current but you have to remember that you have to take your energy source with you. If you increase voltage, for a fixed weight battery, you decrease capacity. You can buy your way out of the hole by stacking enough batteries on the bike but you don’t end up with a very nice bike. I prefer the gears. Most single gear bikes that will do 40 mph on a flat aren’t too good on a steep hill.

SM is less than 1 HP. Being “way underpowered” by motorcycle, electric dragster, train, Tesla Roadster, or even golf cart standards is what keeps electric-ASSIST bicycles light enough to carry passengers and goods, to lift over your head, to have 100+ mile range, to remain viable as 100% human-powered vehicles. There are no >1HP systems that meet these bicycle criteria. Battery technology is currently the limiting factor. Stokemonkey is a “low power” system by contemporary motor vehicle standards, but if anything, “overpowered” by bicycle standards. “Underpowered” implies comparison to a class of vehicles I don’t mean to emulate.

So, horses for courses. I have ridden a 2,500W electric “bicycle,” with fixed ratio motor gearing. The instant you touched the throttle you knew that pedaling was entirely meaningless. It weighed maybe 175lbs and had only a 10 mile range. Its human gearing didn’t work because the owner stopped using it or caring about pedaling. It felt quite dangerous to me, not having motorcycle-class brakes and other control components. It was fun, but I’d rather bike myself 10 miles than go by motor conveyance of any kind.

Leo is mostly correct. And I’m glad to see someone say it, finally. Thanks, Leo. Electric motors have much broader power and torque curves than IC engines. The do still have a curve. So perfection only happens under certain operating conditions. But you’re usually closer to perfection with electric power than internal combustion. Way closer. And many if not most electric vehicles are designed with just one gear because of it.

The interesting thing about electric power is that the curve can be changed by adjusting the input power. Voltage and amperage. Even a small, slow vehicle can be made into a dragster by electrically moving the power curve. Momentarily increasing voltage or amps in the right way. Put more battery cells in parallel than in series, or vice versa. I’ve done this with my electric bike and gotten amazing performance under vastly differing conditions. High volts and lower amps will push my cheap bike over 40mph on a flat road — well over 40mph if I was crazy enough. Higher amps will push me up my steep hill towards home at better than 25mph!

If your system is way underpowered perfect matching of gear ratios is probably essential. Otherwise, one gear is usually plenty. And if you want to turn a golf cart into a rocket ship, just make the battery configuration adjustable. One gear is fine.

Amazingly, with electric, when you push the limits this way things still tend to stay very efficient — unlike internal combustion engines. A lead foot with an electric vehicle doesn’t consume energy nearly as terribly as with it’s counterpart.

Richard

Your statement “Electric motors produce nearly the same torque no matter the RPM” isn’t true. Check the curves for any electric motor, e.g., http://ebikes.ca/simulator/ . They produce more torque at lower RPMs, but like other motors produce less _power_ at low RPMs. Electric cars/trains (and indeed some electric bikes resembling motorcycles) simply use such powerful electric motors and have such ample power supplies that variable gearing would add unnecessary complication and expense. It’s a brute force approach. It’s when you’re constrained by the desirable minimum weight and displacement of battery packs on a bicycle that you can’t afford to take a brute force approach, instead using variable gearing to make maximum power available at all road speeds.

“Electric vehicles can also use a direct motor-to-wheel configuration which increases the amount of available power. …
A gearless or single gear design in some EVs eliminates the need for gear shifting, giving such vehicles both smoother acceleration and smoother braking. Because the torque of an electric motor is a function of current, not rotational speed, electric vehicles have a high torque over a larger range of speeds during acceleration, as compared to an internal combustion engine. As there is no delay in developing torque in an EV, EV drivers report generally high satisfaction with acceleration.

For example, the Venturi Fetish delivers supercar acceleration despite a relatively modest 220 kW (295 hp), and top speed of around 160 km/h (100 mph). Some DC motor-equipped drag racer EVs, have simple two-speed transmissions to improve top speed.”

Stokemonkey works because it uses gears to multiply torque, not so much because of some “sweet spot”.

This is now a complete ‘truck’, and is used 4-6 days a week for my business (kite stall and Permaculture gardener/designer/teacher. As such it’s now very much in the very useful tool level of utility biking. I use it when teaching the alternative transport/appropriate technology module on a PDC (Permaculture Design Certificate course).

As we slide out of an unsustainable industrial civilisation, this set up may or may not be sustainable in the long run. But as a transition from cars to intensely local living, it’s ecologically light years ahead of cars regardless of what fuel they use. And unlike cars, I don’t even really need a road, as a single dirt track will do if necessary.

As a peak oil activist for over 13 years, this setup allows me to “ride my talk” in a way that’s fun for me, and has inspired a bunch of my friends to get electric assist bikes for local transport needs.

Regards
Ted Howard
Nelson, NZ

It’s because it allows the driver/rider to select the most efficient gear to take advantage of the engine’s power in any given situation. Any motorist who has driven a stick shift must be familiar with this principle.

That said, regardless of any semantic errors in the Stokemonkey’s marketing above, the same logic applies to bicycles equipped with an electric motor. End of story.

P.S.– Big respect to Todd for dealing with Hbilt’s vitriolic argumentativeness in such a classy way, even if it happened four years ago. Hbilt, if you ever read this thread again, I hope you realize what an ass you sounded like, and how genuinely unhelpful your misspelled attempt to sound smart really was.

Thanks for the great read!