Electric Bikes - Too many hub motors - which do regen??
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07-08-08, 07:57 AM
Okay after reading for about a week now about various hub motors I still do not have the following answers:
1) Which is better for effieciency (most miles per battery charge) front or rear hub motor?
2) What hub motors will do regenerative braking? Will they all do this with a well designed controller?
3) Is the Golden, or the Crystal, or other motor any different in the hands of an engineer who can inspect and reject it early, if any defects in the delivered product are noticed?
07-08-08, 08:57 AM
I'll give my opinion about the part of your question I have direct experience.
Forget about regenerative braking. Unless you're doing a range test under controlled conditions regen is simply not worth the trouble. Best case might reclaim 10-15% energy expended but the HIGH risk is that you will cook expensive batteries and/or controller. Maybe both before you know it.
Regen is a great concept on paper and in discussions but in practice it's a different matter.
No difference in efficiency between front/rear drive. Except if front wheel loses traction which may happen under some conditions.
07-08-08, 11:01 AM
I second BroadwayJoe. Regen - at this stage of consumer technology - is nothing more than a marketing phrase to differentiate between products. It does not make a real world difference.
The question you should be asking about the difference between front and rear hub motors, is to ask which mount better addresses the:
1. Strength of the frame under load.
2. Centre of gravity on the bike
3. Load on the axles
4. Ease of access for maintenance
In my personal opinion, the front hub motor mount is better because it distributes the weight of bike more evenly between the front and rear axles - especially when you put the battery at the rear. Imagine if you put the battery and motor in the rear, the bicycle will have such a rearward bias that it will negatively affect handling compared to a bike with the additional weight spread out between two axles.
The rear axle is also uneven due to the cogwheel set. If you peddling while the motor is turning, it only adds to the uneven torque exerted on the axle. If you have a front motor mount, this is less of an issue.
The majority of hub motors today will advertise as 500W or 600W - some with peak watts as high as 1000W. Efficiency can be expressed in either speed or distance (range). For maximum range, you will want to using it as pedal assist or pedelec. This means peddling along with the bike and turning on the throttle when under a headwind, under load, up a difficult incline or to maintain a higher cruising speed. This will greatly multiply your range.
Second, tt is the type of battery that determines range per charge and not whether the motor is a front or rear hub. For maximum range per charge, you will want to get LiFePO4 - Lithium Ion Phosphate. Be warned they are not cheap. If you do not need ultimate range (meaning you have localized riding activity), sealed lead acid is more cost efficient for miles-travelled.
07-08-08, 11:34 AM
Okay on the information about REGEN. Will just ignor that as a factor for now, as the science is not there yet to do this perfectly. Looks like we need better circuitry design (to switch back and forth between regen -charging, and burning watts) and better batteries to make this work.
Did figure that the battery being a Li-ion-iron-phosphate was the most efficient. Thanks for confirmation on that. Also thought that a front wheel drive would be better for efficent balancing.
Have read that some can get 50 good miles out of LiFePo batteries of the optimal size and weight. Reading they cost maybe $350 with charger?
07-08-08, 11:57 AM
Even if you had perfect circuitry for regen, the net benefits would be 0 or even negative because any gains you get is offset by the cogging (electromagnetic drag) effect that's inherent with these motors. To bypass the cogging effect, you'd have to have a clutch type of mechanism that would engage only when you're using the motor or regen braking and let the wheel freewheel the other times. None of the hub motors that I know of do this. THey do freewheel but they're dragged down by the cogging effect.
With that said, regen braking is great for braking. That's the main reason I like it. Most of the time, you just need to slow down slowly and you can use the regen for that and save on your brake pads. And they're great for controlling speed on long descents without wearing or heating your brake pads.
Regarding front and rear, another benefit of a front motor is that it's easier to remove the wheel for flats or maintenance.
07-08-08, 01:47 PM
"Reading they cost maybe $350 with charger?"
Hmmm. The answer like many things in life is - it depends.
Read about batteries and use the rules there to estimate the type of riding and distance you plan to travel. To simplify:
a. Volts = how fast you can go or speed. It also means how quick you can get there. Many motors and controllers can run one step higher than their official capacity (24V run at 36V, 36V run at 48V). If you plan to run 36V at 72V, you will mostly likely need a new controller (old one will fry) and a new charger that will charge at the new voltage of your battery pack). The faster you go, the better brakes, tires, condition the bike better be in for your safety.
b. Amp. Hours (Ah) = range. This is how long the battery pack can sustain an constant draw of electricity. High volts but low Ah means you can go very fast but your range is will be less. The key to a good commuting experience is a sustained average speed not peak speed. This factor will come into play if you are not able to recharge at the destination before the return trip home.
In choosing your batteries, you want the Volts that you intend to run matched with more Ah that you calculate from the ebikes.ca page. More Ah is always better than less Ah. This ensures you won't have the battery die on you with your type of use.
Another good reference is www.batteryuniversity.com. Read and understand the difference performance characteristics of battery types so you understand the risk and reward each type brings.
07-08-08, 09:40 PM
Regent can work but the complexity and processing power required to do it correctly simply isn't there except for MIT lab projects. I've got a regen Xootr that can cook a fully charged battery and/or blow pricey electronic components. Under the right conditions it's extremely cool to slow yourself down with electric but one mistake... Another downside is that you still gotta have conventional brakes anyway so it's not a part/weight/simplicity saver either.
Lithium is the eBike battery chemistry of the future. They are perfect match for our needs. SLA is okay to start but once you get a good commuter design ironed out go lithium. Prices keep falling but I would estimate $1,000 for 20-30 mile range with modest eBike motor. Charging and balance are the main issues with these packs.
Youtube is a great way to see some good ideas to roll your own. Don't forget to search "ebike" along with "electric bike" and pedelec.
I like front motors too for the reasons our friends here have mentioned. One more cool thing is that it makes you All-wheel drive.
It seems to me that using regenerative braking as a drag brake is being over looked. There are many e-assist bikes around with the combined rider weight of 320 lbs or more. Using the motor to help brake the bike isn't a bad idea in my opinion.
07-09-08, 07:21 AM
FWIW I just ordered a Crystalyte rear wheel Out Runner kit with a Lithium Polymer 37V 10.5 Ah battery. I plan to install it on my Specialized Rockhopper. I'll be mounting the battery in a triangular shaped battery back that mounts inside the frame of the bike towards the front. The battery is fairly light at 6lbs, but the front mounting location will help better distribute the weight and offset some of what the motor adds to the rear. I prefer RWD. My car is AWD, but sometimes RWD is just more fun! Actually, I don't think I would like the feel of having a heavy front ended bike. The added time to change the rear tire is not that big of a deal to me. My mountain bike tires have fairly aggressive tread and are less susceptible to punctures than a road tire. I'll be commuting roughly 22 or so miles one way to work on flat roads/sidewalks. This battery has a reported range of 25-30 miles with no pedaling. I expect to pedal assist for a good portion of the commute. I can charge the battery at work.
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