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Towards helping me understand hybrid ebikes, part I

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Towards helping me understand hybrid ebikes, part I

Old 11-20-07, 07:00 AM
  #1  
pengyou
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Towards helping me understand hybrid ebikes, part I

Hybrid bike: a bicycle capable of being propelled to relatively high speeds by both pedaling and/or the power of a motor. My definition of a hybrid bike does not include some of the commercially sold ebikes that do have pedals but only provide enough pedal force to get the bike started, say 3-6 mph.

I am trying to understand how power from pedaling a bicycle and power from a motor on the same bicycle interact. I do not know all the right words to use, so please help me out a bit Also, please note I titled this part I. I am trying to take this in small steps to try to stay on topic, focusing on more detail on one issue at a time and then moving onto parts II, III, etc for other parts.

I have an ebike now with some pedaling capability. The pedaling seems to be designed mainly for starting up because the gearing is very low.

I can start pedaling the bike from a standstill. If I start motor-power and pedal-power at the same time I feel the two work together - I accelerate faster than if I only used motor-power or pedal-power. Once I reach about 3 mph I feel that my pedaling is less useful (I have decided it is less useful because I feel much less resistance when I am pedaling). I also have to pedal much faster at that point to feel any resistance at all on the pedals, maybe more than 120/second. Once I reach a speed of about 6 mph no matter how fast I pedal I cannot feel any resistance at all so it seems useless to pedal at all.

If I raise the gear ratio is it likely that I will continue to feel resistance (continue to contribute power to the wheels by pedaling) when I am pedaling even at 6 or 7 mph? and if I raise it even more is it likely that I will feel resistance at 8 or 9 mph?

Can I make a general statement that in order for my pedaling to do any good I have to be able to provide more force than the motor is providing?
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Old 11-20-07, 07:47 AM
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Is there any sort of amp meter, amp hour meter, watt meter on the bike or could you put one on it? Depending on the battery chemistry it is possible to see just by the voltage if your effort is helping but that isn't very accurate.

Some kind of metering device would help measure how much energy is coming out of the battery to propel you at your 6mph so you could see how much power is getting used from the batteries when you don't pedal and then run the same course/street/block and see how much it uses when you do pedal. With this you could even find the sweet spot where your pedalling at a comfortable RPM and effort level and the bike is going the speed you want on the least amount of battery power.

I would think that if you are pedaling and feeling some resistance you should be lessening the power getting used from the batteries. Of course if pedalling makes you go 0.1 mph faster then the motor alone it could be your power is for that 0.1 mph and the motor is doing the first 6mph. The answer to your question is really what is keeping me from buying anything right now since it isn't really all that well known. An ebike today can't make my commute alone although I do it with just pedalling. I'd like a little help though but don't would like it to be a shared effort not just the motor or me dragging the motor/batteries.

The bionx is the only electric bicycle I understand how it works at the moment as it increases the power you apply by a set percentage. It is $$$$ though which is why I don't have anything.
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Old 11-20-07, 08:03 AM
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Thanks! Your idea of the amp meter sounds good but I want to wait a bit before I get to that level of details. I am looking for that "sweet spot" but I want to understand some of the principles of the interaction between the motor and pedals before I start testing, and just become more knowledgeable about the subject in general. BTW, that sweet spot for my bike seems to be around 4mph...hence the question about raising the gear ratio to raise the speed of the sweet spot. But does the controller come into play in this equation as well?
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Old 11-20-07, 09:01 AM
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I'm curious about how that works as well. I see all these ads saying how much farther it can go if you do some pedaling. But when you pedal are you dragging the motor and batteries or is it making the motor go faster?
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Old 11-20-07, 10:59 AM
  #5  
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I'm curious about how that works as well. I see all these ads saying how much farther it can go if you do some pedaling. But when you pedal are you dragging the motor and batteries or is it making the motor go faster?

When you pedal, the bike either goes faster or uses less power. Say you have a bike that goes about 15mph on flat ground at a power level of 250 watts. If the motor puts out 250 watts the bike goes that speed, but the bike also goes the same speed if you put out 125 watts and the motor puts out 125 watts. (you'll get double the distance for the same amount of battery power.)
If the motor puts out 250W and you put out 125W then your speed will go up a few miles per hour.

Essentially, Pengyou, a hybrid (pedal-electric or any other combination) can be made to take full advantage of all of its power sources at the same time and it doesn't matter too much whether one power source is a tenth as strong as another or whether they're equal, etc. - whatever number of watts the motor transmits to the wheel, PLUS whatever wattage the pedals transmit to the wheel, is what will determine how fast you go.

But in order for your ebike to take advantage of pedaling the pedal-gearing has to be right. Regardless of the speed of the bike, your ideal pedaling speed when you want to put out a moderate amount of effort is something like 90 revolutions per minute. If your effort level stays exactly the same, then your efficiency probably goes down to 0% at 120rpm (most of your effort is used up just moving your legs around, none of it helps the wheels move).

You could design a bike instead to be a multi-speed bike which takes advantage of pedaling at about 90rpm anywhere between 6mph and 35mph, which would allow you to put out maybe 200W of power at any of those speeds. You could have a motor which was also able to put out 500W or more through that entire range. This bike would be just as fast as a bike with a motor operating at 700W (power output) but no pedals, but the bike without pedals would need better batteries.
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Old 11-20-07, 11:23 AM
  #6  
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In your other thread, pengyou I suggested that you were a good candidate for a Pedelec system. The poster that remarked that the Bionx system was the only one s/he understood was talking about a Pedelec system. You decide if the motor will give you 1/4, 1/2, just as much, or twice whatever amount of power you put into powering the bike. If the hybrid bicycle does not have a full range derailleur system OR full range hub gear system you will only be able to apply useful power at a single range of road speed usually (as you have noticed) at the very low end of things for getting the bike moving. Why? Because this is the chief source of drain on an electric systems overall performance. Hills are the other. It just so happens that accellerating from a standing start and pedalling uphill are in roughly the same speed range and therefore gear range. A manufacturer can gear the pedal system low so the rider will assist only when starting and going up hills.

If you want to do more than just accellerate the bike and want more speed on level ground then you must choose (or design) a hybrid system that provides the same range of gears for the rider that a regular bicycle does. Whether or not the motor needs to access those gears is open to debate but what cannot be argued is that you the rider need to have access to low speed as well as high speed gear ratios to be able to provide useful power at any and all road speeds and grades that you might encounter.

H
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Old 11-20-07, 11:28 AM
  #7  
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on cadence: 90RPM isn't an extreme cadence, but it'd be moving up into a good athletic cadence, depending on gearing and styling. My cadence is lower on average, but my style of cycling includes utility, touring, and cross country/all mountain. No racing. Average speed is pretty low for someone who cycles every day, 20kph. This has more to do with the fact that I enjoy not having to rush than anything

There are some systems which will scale motor input to your effort, such as BionX or the Crystalyte PAS controller adapter. There are also systems which base themselves on your cadence, such as Stokemonkey. One important point though, is that with almost any e-bike I can think of, pedaling provides input regardless, as long as its done properly.

You can move with any cadence you please as long as its beneficial to your health and if you're using the proper gear ratio in order to contribute to the motor you'll know so, as your pedals will have resistance to them. Mm, one of the reasons you feel like you're not able to contribute on those other bikes is that they don't have the proper gearing to do so, if they're getting away on you so fast. Its like riding in low gear down a hill.
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Old 11-20-07, 02:50 PM
  #8  
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The proper gearing is necessary as others have pointed out BUT if you want to have real hybrid capability you need something other than a single speed hub motor unless it is brutally powerful and then your input lessens.
I have a geared hub driven 21 speed trike and the motor is great for hills and lower speed but the moment I exceed 20 kph I am hauling the battery and motor as excess weight.
So for a multi speed motor drive your options are limited the Cyclone system will allow you and the motor to share the rear gearing and is fine for moderately hilly terrain for more gear range for both you and the motor you need to go to a Bottom Bracket drive then even with a low powered asssist you can add combined power from start to 60+ kph.
Mine is low pwered enough to allow me to just go full throttle at startup and then pedal and shift as normal, I just accelerate faster and go faster and can completely ignore the motor to the extent that I am considering throwing the twist grip and replacing it with a switch.
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Old 11-20-07, 08:08 PM
  #9  
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Originally Posted by geebee View Post
The proper gearing is necessary as others have pointed out BUT if you want to have real hybrid capability you need something other than a single speed hub motor unless it is brutally powerful and then your input lessens.
I have a geared hub driven 21 speed trike and the motor is great for hills and lower speed but the moment I exceed 20 kph I am hauling the battery and motor as excess weight.
So for a multi speed motor drive your options are limited the Cyclone system will allow you and the motor to share the rear gearing and is fine for moderately hilly terrain for more gear range for both you and the motor you need to go to a Bottom Bracket drive then even with a low powered asssist you can add combined power from start to 60+ kph.
Mine is low pwered enough to allow me to just go full throttle at startup and then pedal and shift as normal, I just accelerate faster and go faster and can completely ignore the motor to the extent that I am considering throwing the twist grip and replacing it with a switch.
Well, i've never known a hub motor to bottom out at *that* low a speed. The standard 408 on a 26" setup will work pretty well with the cyclist up to about 35kph without a problem. My setup (now out of juice) did about 41kph on its own and would assist up to about 45. Personally though, i've no desire to constantly ride any faster than 30kph. Hell, 25kph is a good enough speed for what I use the e-bike for.

However, i'll probably be using a bottom bracket drive for next years Xtracycle bike, as it'll be comprised entirely of steel and won't be used in horrible weather like the Crystalyte system is. Stokemonkey is coming back sometime, and i'd love to have one, but unless they've dropped the price on the new revision it'll still cost too much.
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Old 11-20-07, 08:41 PM
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It was a legal in Australia hub (200w max output) geared so it is a good climber but top speed is 20 kph. A 200w peak output direct drive hub is a joke unless you live somewhere flat and then why would you need/want power assist unless you are after speed which a 200w hub won't give.
Alot of Chinese market bikes are around 20kph due to their laws.
My trike is setup the same as a stoke monkey but even though the hub has an inbuilt freewheel I fitted an external one to keep the load on the pedals as normal as possible when not using the assist.
I like to keep my trike legal as it is fully faired and gets too much attention as is, any more power and it would be scarey.
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Old 11-20-07, 08:55 PM
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200w would be pretty timid on a direct hub motor, certainly. What impresses me is what Cleverchimp does with the Stokemonkey, with only 340 or 430 watts.

Setup the same as a stokemonkey, on a trike? I'd really like to see that actually, do you have any pictures of it? Sounds really cool.
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Old 11-21-07, 05:24 AM
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The first is a shot of the Tongxin with the freewheel 6 speed cluster screwed on the wrong side of the motor which maintains the self tightening and gave me a chance to try slightly differing ratios.
The second shot is where it is mounted on the boom the bottle screw is probaly over kill but it guarantees that the mount does not move under torque (the Tongxin is 210 rpm rated at 160w but has a lot of torque).
The third shot is where I mounted the batteries under the seat and hanging across the frame and over the chain again using the same type of building brackets bolted together and U clamped on, the batteries are basically sitting at floor level (maybe 2" off the ground) to keep the c of g down as I like cornering at speed.
Other than the all up weight being higher the trike feels,rides and handles as it did without the batteries and motor.
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Old 11-21-07, 07:17 AM
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Geebee how much does your motor weigh? voltage? Is this a hub motor design? Do you have a URL for the mfg?

Last edited by pengyou; 11-21-07 at 07:35 AM.
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Old 11-21-07, 01:09 PM
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Originally Posted by geebee View Post
The first is a shot of the Tongxin with the freewheel 6 speed cluster screwed on the wrong side of the motor which maintains the self tightening and gave me a chance to try slightly differing ratios.
The second shot is where it is mounted on the boom the bottle screw is probaly over kill but it guarantees that the mount does not move under torque (the Tongxin is 210 rpm rated at 160w but has a lot of torque).
The third shot is where I mounted the batteries under the seat and hanging across the frame and over the chain again using the same type of building brackets bolted together and U clamped on, the batteries are basically sitting at floor level (maybe 2" off the ground) to keep the c of g down as I like cornering at speed.
Other than the all up weight being higher the trike feels,rides and handles as it did without the batteries and motor.
Nice stuff! It reminds me of this one https://youtube.com/watch?v=zlEi97dcQvk
but you managed to get the motor/battery even lower. Pretty cool.
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Old 11-21-07, 02:34 PM
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Originally Posted by pengyou View Post
Geebee how much does your motor weigh? voltage? Is this a hub motor design? Do you have a URL for the mfg?
https://www.tongxin.net.cn/en/parameter.htm
It's a geared hub (silent as it uses rollers) weighs ~2 kg and mine is 24v.
I use an after market controller as the voltage cutoff on the original was very high.
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Old 11-25-07, 03:37 AM
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this helped me understand a bit more about whether i want to use a mid mounted motor.
https://www.cyclone-usa.com/performan...18811df0b197fa
it will be my next kit, now that batteries and chargers are catching up.
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Old 11-25-07, 01:19 PM
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Originally Posted by geebee View Post
https://www.tongxin.net.cn/en/parameter.htm
It's a geared hub (silent as it uses rollers) weighs ~2 kg and mine is 24v.
I use an after market controller as the voltage cutoff on the original was very high.
I am not sure how a hub motor can function as a chain driven motor. Do you attach the cassette to the motor? Is there a freewheel in that assembly somewhere? If you flipped your setup so that the motor was driving from the lefthand side of the bike and reversed the voltage would this setup still work?

Last edited by pengyou; 11-25-07 at 01:36 PM.
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Old 11-25-07, 02:46 PM
  #18  
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Most hub motors are threaded both sides so I fitted freewheel to the left side, the motor is behind the pedals so that was the only change.
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Old 11-25-07, 02:47 PM
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Originally Posted by tidykiwi View Post
this helped me understand a bit more about whether i want to use a mid mounted motor.
https://www.cyclone-usa.com/performan...18811df0b197fa
it will be my next kit, now that batteries and chargers are catching up.
Too bad they haven't tested the 20" folding bike with the 500 watt motor yet. that's the setup I'm interested in.

On a side note- how loud are these motors? Does anyone know of a video comparing the noise to a hub motor against the noise of a chain drive motor? I've never heard an electric bike in person, so i'm cusrious about the noise levels. On that cyclone site it says their motor sounds like an electric drill. I';m all for performance and I was pretty sure I was getting a chain drive motor, but I don;t want to be sounding like an electric drill when I ride either. I might have to rethink this and get a hub motor instead...
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Old 11-25-07, 02:49 PM
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Originally Posted by geebee View Post
Most hub motors are threaded both sides so I fitted freewheel to the left side, the motor is behind the pedals so that was the only change.
You mounted a hub motor to the chain somehow? Do you have any pics to help me better understand what you are saying? I'm still pretty green with all this terminology...
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