I am new to the entire EV field (as in I'd like to electrify my bike, never done that before). I've been looking at the various options available, mostly hub motors vs chain motors (also called currie). Here is a brief comparison based on theory only:
Hub > chain for efficiency because of additional friction losses with chains.
Chain > hub for versatility because of the ability to bolt a different sprocket if you need a different power/speed ratio.
Hub > chain for reliability because of the sealed nature of hub motors (i.e. chain motors should be kept away from rain, mud, etc, while hub motors run under all conditions).
Is all of the above correct? Again, my estimations are based on theory only. Practice often is different from theory, however, so I'd appreciate comments by people with practical experience with hub and/or chain motors.
Thanks,
Alex
Hub > chain for efficiency because of additional friction losses with chains. <-- This is only correct under power but the Hub motor has much more drag when coasting or pedaling without using the motor. Over all the Chain is more efficient.
Chain > hub for versatility because of the ability to bolt a different sprocket if you need a different power/speed ratio. <-- Also you can use the bike gears with the motor and change ratios and keep the motor in it optimum efficiently range.
Hub > chain for reliability because of the sealed nature of hub motors (i.e. chain motors should be kept away from rain, mud, etc, while hub motors run under all conditions). <--Well I can only speak for my bike, which has a can motor at the bottom bracket, and I have never had any problem in the rain and I don't go in the mud as it is a street bike.
These are mostly from my own experiences and I am sure someone out there has a different opinion.
Chas S.
My Bicycle Pages
Your setup would mean the torque of the motor is transfered over two chains to the real wheel, which would result in even larger losses. Still, that would be very convenient, I think. Is there a kit that does that, or is it a pure DIY idea?
There is only 1 chain, and if a chain is properly maintained the losses are very minimal. The Cyclone Kit is one of the better bottom bracket drive kits. Using the gears of the bike you get the advantage of having low gears to haul you up steep hills and the high gears to give you some additional speed. The cyclone kit is geared to top out at about 20MPH but they do offer a gear change which will give you about 27MPH top speed. You simply have to tell them you rear wheel size is a 20" wheel and put it on a bike with a 700c wheel. There are other designs which do use 2 chains to allow you to keep all of you front chain rings which gives you a wider gear selection. I find 9-gears to be quit sufficient. Using an 11-34 Mega range cassette the following would be the approximate speed of the Cyclone kit in each gear:
Gear MPH
As you may have deduced, I prefer can motors. The only hub motor I ever road was a 2000-watt brush less motor running at 48 volts (a heavy scooter). I did not like the cogging effect of the motor (jerkiness) during coasting and acceleration from a stop. As far as acceleration and speed, I was unimpressed. My can motor bike (500-watts) is quicker with only about 5MPH less top speed. I would have thought a 2000-watt motor should be much better. My bike accelerates from 0 to 20MPH in 14 seconds, this is no neck breaking acceleration but it is faster than the 17 seconds of the 2000-watt hub motor I rode.
Again this is my experience only.
Chas S.
My Bicycle Pages
I ride a brushless hub motor. there is some cogging, but it's less than the cogging normal from the freewheeling chain. If it was a geared, brushed hub motor, the internal freewheel would release and it would have no drag at all. A chain drive has the drag of either the freewheel, or it's own cogging effect in the case of a 2 chain setup.
The advantage of a chain drive is it may be more efficent, as you can fine tune it so it's peak efficancy matches your planned crusing speed. They also can be setup to produce more torque.
the down sides are the noise, the extra brakets, the noise, the chains, the noise, gears, the noise, chain tensioners, again the noise, and it generaly looks like a kid's science project.
Hub motors In general are very efficent. in some cases, they are more efficent at their optimum speed, but less efficent in the other ranges. in the case of the brushless, they are near to completely silent when running. Brushless have no moving parts except the bearings, and being the wheel's hub, they tend to hide in plain sight really well.
the down sides of the hub motors is a lack of ability to tinker with tuning them, and lower torque.
Drunkskunk,
Thanks for you views, it's good to hear from someone with a different point of view. I wonder if you could elaborate on the following:
I have never felt any cogging using a chain drive motor so I don't know where you get the idea of cogging with a chain. If there is no cogging with a geared hub motor with a freewheel then how can there be any cogging with a chain when they also use a freewheel? Why would the freewheel on a chain have any more drag than the freewheel in a geared hub motor. When you coast the chain does not turn so that can't have any effect on the drag. I just do not understand your statement. I agree with the remainder of your post. The biggest advantage of a hub motor is how quite they are as long as you don't pedal. However there is no more noise with the single chain drive system than there is from a normal non-powered bike that is being pedaled or when you pedal with the hub motor. The real noise comes from the reduction gears used by the motor not the chain. If I lived in an area where there were no hills a hub motor would work just fine for me, but I live in a country setting with many hills and the hub motor would just not have the torque to get me around as well as the geared chain drive motors do. I think the real question to ask is two fold. Do you have hills and how important is the stealth to the rider? I would say if you have lots of hills, like in my case, stealth would not be that important. If you live in a flat area the stealth could be more important.
Chas S.
My Bicycle Pages
You have a point, a chain drive with a reduction gearset would need a free wheel. my experiance is with low RPM chain drive motors, that used the motor gear to the rear gear as there only reduction, and used a gear that either bolted to the hum, or the spokes on the left side of the rear hub.
Cogging is a factor of back EMF, basicly, the motor acting like a generator, and the current it generates resists turning. Its higher in higher winding motors, or large motors, and can be nearly eliminated with a good controller, or even better, but having the hotor wires go "open" when not in use. my Center tapped dual C-lyte has a switch position that lets me open the circuit to the motor, and eliminates cogging completely.
If you were to connect the chain drive motor as you say the cogging effect would be amplified by the gear ratio of the motor to the wheel so I can see what you mean. I also thought cogging could be decreased by decreasing the amount of iron or steel used in the manufacturing of the motors armature. I thought the larger the motor and the more Iron and or windings the more cogging would be present. I think either a controller that opens the wires or a freewheel is the best way to prevent cogging. You might want to look at the Cyclone Kit to see a better way to use a chain drive motor. There are other methods but I think they all use a freewheel. The only ones I have seen that don't are DIY machines.
Chas S.
My Bicycle Pages