Let's talk torque

mike killay

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Feb 17, 2011
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Advancing years and living in a hilly district means that I need greater torque.
Crank driving is the obvious answer and I have one.
But I need more.
Now a certain well respected member has advertised kits and at one time advertised a 350 watt motor, but has now withdrawn the advert.
My next bike will probably be built by myself and I will need a kit.
I am not at all interested in speed but need maximum grunt.
Does a 350 or even 500 watt motor offer more torque?
 

soundwave

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May 23, 2015
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1000w bafang hd will do 160nm with a 30a controller ;)
 
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D8ve

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Jan 30, 2013
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Change the gearing, a small crank ring and big ring at the back
 

Nealh

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Gearing is one option.
350w @ 22/25a or 500w @30a will give good torque esp in a BPM and a CST, however you will need a good celled battery.
A 5 or 6P 30Q is one option or look at Sanyo PF or GA's.
Alternately 25a bbs01 from EM3, will still need good cells.
Xiongda 2 spd hub , which d8veh states it acts as a winch up hills.
 
D

Deleted member 4366

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Basically, whatever motor you get, the higher the current, the more torque you get. If you want a crank drive, there's the 25 amp "250w" one from Em3ev, or you can choose any of the illegal ones up to the BBSHD, and if that's not enough, there's others.

For a hub-motor, a 500w Bafang BPM at 48v and 25 amps would probably stomp the lot of them, but only on hills up to 30%. If you want sort of legal, the Q128H at 48v and 20 amps is pretty handy, and, with slightly more complicated installation, the 48v Xionda is a winch.
 

anotherkiwi

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Jan 26, 2015
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As always http://www.ebikes.ca/tools/simulator.html using the custom options is pretty accurate. You have the BPM and CST motors in the motor list, add in a custom controller and battery and simulate to your hearts content :)
 
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D

Deleted member 4366

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The problem with trying to simulate hub motors is that each model comes in lots of speed variants. If you use the wrong version in the simulator, you get meaningless results. A 328 rpm one is completely different to a 201 rpm one except that they're the same size and shape.

A 201 rpm one will storm up hills, while as a 328 rpm one will overheat and stall out. A328 rpm one can do about 27 mph, while as the 201 rpm one will struggle to go much past 15 mph. They might just as well be different motors.

This is the concept that people seem to be struggling with. The winding speed (kV) Is a critical characteristic of any motor. Just about all the other performance characteristic depend on it.
 
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Danidl

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The problem with trying to simulate hub motors is that each model comes in lots of speed variants. If you use the wrong version in the simulator, you get meaningless results. A 328 rpm one is completely different to a 201 rpm one except that they're the same size and shape.

A 201 rpm one will storm up hills, while as a 328 rpm one will overheat and stall out. A328 rpm one can do about 27 mph, while as the 201 rpm one will struggle to go much past 15 mph. They might just as well be different motors.

This is the concept that people seem to be struggling with. The winding speed (kV) Is a critical characteristic of any motor. Just about all the other performance characteristic depend on it.
... Absolutely correct.. which brings me to your evident antipathy to crank driven motors. Since a hub motor is only optimum at a single road speed, as an electric motor is only optimised for a narrow band of rotation speed, why do you assert that crank drives will be only of comparable efficiency. ?
A crank driven motor using gears will have perhaps 7,8,9 10 to , 21 different road speeds at which it will be working at optimum efficiency.
This is not a point scoring question, I am genuinely interested in your opinion.
 
D

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Since a hub motor is only optimum at a single road speed, as an electric motor is only optimised for a narrow band of rotation speed, why do you assert that crank drives will be only of comparable efficiency. ?
The first part is sort of correct, in that all motors have a particular speed at which they're most efficient. That applies to crank-motors as well as hub-motors, except that a CD can hit that optimum speed once in each gear. The second part is not right. Hub-motors are relatively efficient over a broad band of speed, and they also have a relatively broad power band, which makes them a good solution for E-bikes. Whatever applies to hub-motors and bike speed, applies equally to crank motors and pedal speed. The chance of you knowing what speed to pedal to get optimum power of efficiency is pretty slim. Even if you did know what it was, you'd still struggle to hold the pedals at the right speed. I tried it with a Nuvinci to try and understand why crank motors weren't more efficient than a hub motor with the same battery, controller, speed and rider weight, but I couldn't improve the efficiency. maybe it gained a couple of percentage points that were lost by the Nuvinci - who knows.

The point I was making is that if you want hill-climbing, a 201 rpm motor will give you good power and torque up to 15 mph. There's no point in having a 300 rpm motor and restricting it to 15 mph. On the other hand, if you want to go 20 mph, you'd be better using a 270 rpm motor, but your hill-climbing would be compromised a bit. Many OEM hub-motored bikes are designed for 20 mph or more, then restricted for the European market, which means that many are not ideal, though still adequate for most people.

Whatever theory says, is irrelevant anyway. I've done something like 15,000 miles on E-bikes, which includes probably 8,000 miles commuting 30 miles to work. I'm probably one of the few people that has done actual tests on efficiency, climbing power, etc, including side-by-side tests. I used to have watt-meters on all my bikes, so that I could record and analyse every type of journey. I've ridden just about every type of electric bike. I go to all the shows and try everything new as well as experiment with every type of motor. My recommendations and opinions are based on that experience, not by reading what's written on the internet or presented by some jumped up theorist. Being a graduate Mechanical Engineer and an electronics teacher for 10 years, I also have a reasonable understanding of the theory, so I can explain why things are as they are.

After all that, I prefer hub-motors for general riding around, shopping, commuting, etc. Keep your crank motors for full-suspension off-road bikes, where they're a perfect solution; off-road riding where you have 30% climbs or more; and racing (250w only).
 

Danidl

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The first part is sort of correct, in that all motors have a particular speed at which they're most efficient. That applies to crank-motors as well as hub-motors, except that a CD can hit that optimum speed once in each gear. The second part is not right. Hub-motors are relatively efficient over a broad band of speed, and they also have a relatively broad power band, which makes them a good solution for E-bikes. Whatever applies to hub-motors and bike speed, applies equally to crank motors and pedal speed. The chance of you knowing what speed to pedal to get optimum power of efficiency is pretty slim. Even if you did know what it was, you'd still struggle to hold the pedals at the right speed. I tried it with a Nuvinci to try and understand why crank motors weren't more efficient than a hub motor with the same battery, controller, speed and rider weight, but I couldn't improve the efficiency. maybe it gained a couple of percentage points that were lost by the Nuvinci - who knows.

The point I was making is that if you want hill-climbing, a 201 rpm motor will give you good power and torque up to 15 mph. There's no point in having a 300 rpm motor and restricting it to 15 mph. On the other hand, if you want to go 20 mph, you'd be better using a 270 rpm motor, but your hill-climbing would be compromised a bit. Many OEM hub-motored bikes are designed for 20 mph or more, then restricted for the European market, which means that many are not ideal, though still adequate for most people.

Whatever theory says, is irrelevant anyway. I've done something like 15,000 miles on E-bikes, which includes probably 8,000 miles commuting 30 miles to work. I'm probably one of the few people that has done actual tests on efficiency, climbing power, etc, including side-by-side tests. I used to have watt-meters on all my bikes, so that I could record and analyse every type of journey. I've ridden just about every type of electric bike. I go to all the shows and try everything new as well as experiment with every type of motor. My recommendations and opinions are based on that experience, not by reading what's written on the internet or presented by some jumped up theorist. Being a graduate Mechanical Engineer and an electronics teacher for 10 years, I also have a reasonable understanding of the theory, so I can explain why things are as they are.

After all that, I prefer hub-motors for general riding around, shopping, commuting, etc. Keep your crank motors for full-suspension off-road bikes, where they're a perfect solution; off-road riding where you have 30% climbs or more; and racing (250w only).
Thanks for your considered reply.
. My Bosch active 2 constantly monitors the motor speed road speed and torque and I suspect has a better idea than I of when to change gears, it does so by flashing an up or down arrow on the display and I follow it's advice. . This is similar to the indicators on modern manual transmission cars.
I also have a background in engineering and science, having graduated in experimental physics originally and having designed and presented courses in electronics, electrical engineering and renewable energy over a 35 year period. I would not have any of your vast experience in the area of ebikes and hence my questioning. My experience on ebikes being restricted to the two ( only) that I have, the first a hub bike from 2007 vintage and the second listed as a 2017 crank drive model, purchased last autumn.
For the short shopping trip 1 km the hub bike is fine, including the 100m height climb back home, whereas the crank bike is much preferred for the longer 30km jaunt.
 

mike killay

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Feb 17, 2011
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Thank you for all your help.
I am considering building my next bike, the mechanical side will not be a problem but the electrics will be.
I envisage a sort of 'Vicar's bike' from the 1950's similar to the Dutch Omafiets.
It will have an upright riding position, north road handlebars etc. Full mudguards and carrier, leather Brooks saddle.
I want a motor, either crank or hub, but I lean toward crank that has a lot of torque as a safety get me home feature in the event that hips and knees get bad.
Last question. I have never tried to do it, but exactly what does shunt soldering achieve, and are there any downsides such as engine over heating etc.?
 

Danidl

Esteemed Pedelecer
Sep 29, 2016
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Thank you for all your help.
I am considering building my next bike, the mechanical side will not be a problem but the electrics will be.
I envisage a sort of 'Vicar's bike' from the 1950's similar to the Dutch Omafiets.
It will have an upright riding position, north road handlebars etc. Full mudguards and carrier, leather Brooks saddle.
I want a motor, either crank or hub, but I lean toward crank that has a lot of torque as a safety get me home feature in the event that hips and knees get bad.
Last question. I have never tried to do it, but exactly what does shunt soldering achieve, and are there any downsides such as engine over heating etc.?
.. mike, I am sounding like a cracked record but the product already exists , any of the Bosch powered Dutch type bikes , fitted with a smaller front sprocket will nearly go up walls. The only downside is a reduced full speed. ...
 

IR772

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Jun 5, 2016
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Last question. I have never tried to do it, but exactly what does shunt soldering achieve, and are there any downsides such as engine over heating etc.?
It reduces the electrical resistance.

More power goes to the motor.

But I did read in one forum where a motor got cooked after over doing this?
 

Danidl

Esteemed Pedelecer
Sep 29, 2016
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Thank you for all your help.
I am considering building my next bike, the mechanical side will not be a problem but the electrics will be.
I envisage a sort of 'Vicar's bike' from the 1950's similar to the Dutch Omafiets.
It will have an upright riding position, north road handlebars etc. Full mudguards and carrier, leather Brooks saddle.
I want a motor, either crank or hub, but I lean toward crank that has a lot of torque as a safety get me home feature in the event that hips and knees get bad.
Last question. I have never tried to do it, but exactly what does shunt soldering achieve, and are there any downsides such as engine over heating etc.?
.... As regards the shunt. The shunt is a low value resistance used to measure the current being drawn by the controller and motor. The current flowing through the shunt creates a small voltage difference which is used to estimate the current. By putting extra conductive material along the shunt, it's resistance is further reduced, and more current can flow in order to generate the same voltage. This voltage is used to limit the peak current drawn.
Now the power transistors in the controller are only capable of transferring a specific level of current, and the shunt is used to ensure that is not exceeded. These transistors have a designed safety margin and this will be eroded. When or if the transistor blows it can go either open circuit or short circuit. If any go short-circuit then a constant voltage is applied to a coil winding in the motor and it will then burn out..
 

mike killay

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Feb 17, 2011
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.. mike, I am sounding like a cracked record but the product already exists , any of the Bosch powered Dutch type bikes , fitted with a smaller front sprocket will nearly go up walls. The only downside is a reduced full speed. ...
No Danidl
I value your reply.
Just as an ex motor mechanic, I fancy building my own from the ground up.
I built my sailing dinghy, two camper vans and now feel that an ebike must be next.
The point is that I do not have to compromise, I can build just what I want and for that reason, Bosch is completely out.
For a start, a full throttle is a must because of my physical problems. Also, I want to be master and owner of the bike and not in some vague relationship with a German manufacturer.
 

Danidl

Esteemed Pedelecer
Sep 29, 2016
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No Danidl
I value your reply.
Just as an ex motor mechanic, I fancy building my own from the ground up.
I built my sailing dinghy, two camper vans and now feel that an ebike must be next.
The point is that I do not have to compromise, I can build just what I want and for that reason, Bosch is completely out.
For a start, a full throttle is a must because of my physical problems. Also, I want to be master and owner of the bike and not in some vague relationship with a German manufacturer.
.. that's a good reason, and d8veh is therefore your port of call.. good luck!
 
D

Deleted member 4366

Guest
The amount of torque you get comes more from the motor design. The rating (250/500/1000 W) means very little. You can get hub-motors that give you all the torque you'd need and more, so a crank motor isn't an obvious choice. The type of use would define the type of motor you need and its power. Look at this:


For crank-motors, there's the Bafang BBS01, BBS02 and BBSHD with a range of power to suit. GNGebike also make some interesting motor kits with external controllers.

Soldering the shunt in the controller increases the current it supplies roughly in proportion to the length you solder, so soldering 25% of its length increases current by 25%. 30% is a practical maximum, though I have gone higher.

before:



After:



Some controllers have solid state shunts that can't be soldered, so you have to calculate the resistance and solder another one over the top. they're designed to be stackable.
 

anotherkiwi

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Jan 26, 2015
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I want a motor, either crank or hub, but I lean toward crank that has a lot of torque as a safety get me home feature in the event that hips and knees get bad.
The best one at the moment is the BBS02 "250W" 25 Amp. Basically a re-branded BBS02 500W, I think that it will be my next mid-drive. https://em3ev.com/shop/bafang-36v-250-500w-bbs02-kit/ Given for >100 N.m. on the bafang site. I would couple it with a big powerful 36 V battery, say a 17 Ah or a couple of 12.5 Ah ones wired in parallel.

You can add a half twist throttle to your order as well as all kinds of other options - the new colour LCD, a 42 tooth blingring chainring, gear sensor...

I recommend a 42 or even 38 tooth chainring if you are going to be using the throttle a lot and speed is not your primary goal. You can even mount twin chainrings as I have done and cover all hill climbing or top speed needs.
 

mike killay

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Feb 17, 2011
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Thanks Kiwi,
I had looked at that one.
I didn't think of a double chain ring, but that is also probably part of the answer and helps with getting a reasonable chain alignment which is a problem on by present 8 speed bike where the 11 tooth regularly suffers chain skip.
Next problem is to find a suitable 21 inch frame with disc brake lugs and also mudguard and pannier screw holes.