Increasing the range by Pedal Assist?

[Hillhater]

30mph requires 1000W approx continuous.
40+ mph requires 2+ kW continuous.
Average human can only output 100W continuous.
so at best you can expect a 10% range improvement at 30 mph ( 5% @ 40+ mph ) ....IF you PEDAL HARD CONTINUOUSLY.

But note that at 20 mph , which need only 200W continuous, you could extend your range by 100% !

 

[ProDigit]

I don't know,
Just a suggestion, but,
It could be that the wrong system is applied for electric bikes.
These brushless engines have a high torq at low RPMs but at higher RPMs become less powerful. also the controller plays a big role in all of this.
I had done electro mechanics in school, it was not in English, but there exists some kind of engine like a brushless engine, with the axis just being a cage, no magnets, no coils, no burshes.

My teacher explained it was a 'series engine' literally translated from my mother tongue.
The difference is that current technology is a parallel engine, which means the higher the voltage the more powerful the engine, but the RPM's are pretty much limited to the controller or phase frequency on an AC network.
In a series engine, the torq is lower, but constant. Even with a low voltage, on a zero ballast, the engine will spin out of control.
These types of engines just provide a constant, low Torq, force, regardless of RPM. If the torq is big enough to get a driver riding, they could accelerate indefinitely if they did not have the wind resistance. These types of engines might be better suited for this job, perhaps, as they're not into precision, but acceleration.

Technically if you find such an engine that can drive you 30mph (when wind resistance nullifies the force the motor is pushing the bike), when wind direction changes, speed can change too. These type of engines are also lousy performers on a hill, but could reach ridiculous speeds downhill without breaking a sweat or even overheating!

@Hillhater: It all depends, the controller limits some engines more than an engine itself limits the bike. It might be possible to go faster with a 500W engine.
Since I don't have the name of the engine I described above, best thing you can do is test a 500W brush motor, apply 48V onto it, and accelerate until the bike accelerates no more. Then you know how fast on average a 500W engine can accelerate.
When the engine has enough torq, try getting a 500W engine with a lower voltage rating, like eg,one that needs 36V to operate if that exists. Plug it on 48V, and see how fast you can go!

 

[Hillhater]

.... try getting a 500W engine with a lower voltage rating, like eg,one that needs 36V to operate if that exists. Plug it on 48V, and see how fast you can go!

With the DC motors we are considering here, once you increase the voltage from 36 to 48 volts, you directly increase its power by the same ratio. IE your 500W motor is now a 666 W motor, so naturally it will go faster.

However, the speed /power required relationship i quoted is strictly determined by the physical conditions... wind resistance, rolling resistance etc.
The power needed to cruise at those speeds is well understood and documented.
try this ..http://www.kreuzotter.de/english/espeed.htm

 

[ProDigit]

Very interesting, however I do think that the controller still plays a big role in your overall speed.

You could for instance try to see if increasing wheel size will make the vehicle go faster.
If it is true what you say, increasing wheel size should not improve speed at all.

I think many manufacturers need to see what the best wheel size is. some people only use their vehicles on flat land, and don't mind lower torq at the gain of higher speeds and more miles per charge. They should offer these vehicles with at least 2 types of tires, one with more torq and smaller tires, the other with bigger tires and more speed and miles per charge

 

[dogman dan]

Bottom line, as said above, your maximum sustainded effort unless you are on a pro bike race team, is going to be about 100w.

It's a singificant increase if you are running at 200w, to add your 100w. It is not much increase if you are running 1500w, and add your 100w for 20 feet out of each mile. What percentage of a mile is 20 feet? 1/264th of a mile .0 something%? then take 7.5% of that? now you have assisted your motor .00 something%?

You just aint getting doo doo out of pedaling a stealth bomber from the stop sign. It's nothing % added.

Discuss controllers, motor types, and wheel sizes elsewhere in another thread. They have nothing to do with pedal assist efficiency.

 

[Alastor]

Dogman is right .There are two cases witch i have some experience in both

My ebike not the scooter like one i got in the other post is one 250 watt with pedal assist and throttle.When i took it was testing it with pedal assist the first time and with the throttle after to see the results range wise.When i was going full throttle and no pedaling at all i had a max range of 40 km tops when i was pedaling all the time and using the pedal sensor only the bicycle had a 60 km+ range with a 36v10ah lipo4 battery pack.After some more testing to double check my results i uninstalled the throttle

To the electric scooter now that is also 250 watt but way to heavy (65 kilos instead of 24 that the electric bicycle weights) when i pedal i add to the motor almost nothing because there is only one fixed gear the softer one for going uphill.After 10 kms you cant follow up pedaling because of the gear setup so its also useless and dangers trying to do so.While i do uphill the motor needs my assistance and when i pedal it gives the little push the motor needs to accelerate.That is saving me tons of energy with little effort because i help the motor when it requires it.In a case of a heavier bike or even one with an 800 watt or bigger motor is a lost cause.Same for the bomber you can pedal but what can you add to the 4500 watt motor really??

Some more sophisticated and very expensive bikes (i don't know if the bomber dose that) use the pedaling power to recharge the battery.

 

[ProDigit]

... use the pedaling power to recharge the battery.

It's actually much better as a direct drive. Generating electricity is only very little, there's a lot more loss when going from kinetic energy to electric and back, then just staying with kinetic energy.

If you want to pedal along, you'll have to have a large gearwheel in the front, and a tiny one in the back.
It'll not allow you to accelerate fast, but it's probably the only way to keep up with an engine going 25mph+

You could also have a small gearwheel in the front, for acceleration.
Since you want to pedal along, to save energy, I suppose you'll need 2 gears to unburden the motor from accelerating, and help it's burden while driving; to keep a comfortable drive. No fun pedalling like crazy to keep up with the engine, and no fun standing on a pedal waiting for it to go down, knowing you barely have torque to go forward!

24 gear Mountain bikes are the best for this! Though you'll probably only need 2 of the 24 gears.

 

[rui_fujino]

If you want to pedal along, you'll have to have a large gearwheel in the front, and a tiny one in the back.
It'll not allow you to accelerate fast, but it's probably the only way to keep up with an engine going 25mph+

You could also have a small gearwheel in the front, for acceleration.
Since you want to pedal along, to save energy, I suppose you'll need 2 gears to unburden the motor from accelerating, and help it's burden while driving; to keep a comfortable drive. No fun pedalling like crazy to keep up with the engine, and no fun standing on a pedal waiting for it to go down, knowing you barely have torque to go forward!

24 gear Mountain bikes are the best for this! Though you'll probably only need 2 of the 24 gears.

Personally 52T triple chainset and 11T-28T freewheel can give me 35mph cycling to going up the hill at ease without motor!
Its most of us have now access to 11t freewheel from ebike.ca or ebay so I would recommend it to anyone who has problem with pedalling. However, it is very dangerous to pedal beyond 30mph since it will cause bike to be unbalanced.

 

[ProDigit]

However, it is very dangerous to pedal beyond 30mph since it will cause bike to be unbalanced.

define what you mean by 'unbalanced'?

 

[rui_fujino]

However, it is very dangerous to pedal beyond 30mph since it will cause bike to be unbalanced.

define what you mean by 'unbalanced'?

Unbalanced as in you have less control over your bike compared to just throttling

 

[amberwolf]

However, it is very dangerous to pedal beyond 30mph since it will cause bike to be unbalanced.

define what you mean by 'unbalanced'?

When you pedal, the bike rocks side to side, and the front wheel "wobbles" from the weight shifts (unless you hold your arms so rigidly that you will regret it in an hour or two). The faster you go while doing this, the less stable the bike is, depending on the terrain you're on. Nice smooth sticky asphalt isn't so bad, but worn asphalt with loose bits or non-sticky concrete or dirt or gravel is harder to stay in the maneuver you're in already, while this is happening.

If you're a high-powered pedal cyclist already, and have trained yourself to ride well at those speeds while pedalling hard, then you could probably do it without a problem (other than dealing with the weight of the non-bike stuff). But most people can't pedal that fast, or at least not for long enough to worry about handling the bike at those speeds--they're exhausted and have to stop, pretty quickly.