*NOTE*
The original contributor, jawnn, decided to play some silly games and edited both the title of this thread and his original post to remove all the contentious and misleading information it contained. Much of it is reproduced verbatim in the quotes in my original response to it, below. This comment was added when I edited this post on 15th February 2011.
jawnn said:
Peak efficiency
All motors have a peak efficiency rpm, when powered past that rpm the efficiency goes down sharply and they start burning out. Cars use tachometers because they have so many different gears. With a single gear configuration it is easy to know what the motor’s RPM is by the speed, if you know what that peak efficiency speed is. It would be better to use a tachometer if you can get one. Actually an ammeter with a volt meter is more important.
Not at all true. Running a motor at high torque load BELOW it's reasonable efficiency rpm range will burn it out, not running it at high rpm.
jawnn said:
If you want to understand the math, go to page 105 of 'Build your own electric motorcycle' by Carl Vogal http://endless-sphere.com/forums/viewtopic.php?f=2&t=19368
I understand the math fine, but that doesn't change the fact that the statement about rpm and burning motors out is incorrect.
jawnn said:
Cheap controllers and batteries can also burn out if under sized for the maximum current flow.
Not true either. Controllers have in built current limiting, so all that will happen if you use an undersized one (assuming you don't go around modifying it) is that you'll get less power from the system. For example, if I hook up a tiny 6 FET 36V Xiechang, with it's 15A current limit, to a 5304 motor, that's capable of a few kW, then all that will happen is that I'll get crappy performance from the motor. Nothing will blow up, it just won't work well.
The same is true for batteries. An undersize battery pack will just sag under load and give poor performance. It's likely it won't last too long either, but it's unlikely to blow up.
jawnn said:
Heavy vehicles on steep hills need batteries with a high discharge rate, not cheap lead acid batteries that end up costing more than you think. Thundersky batteries are best.
What? If you want high discharge rates, then actually lead acid aren't too bad. They are usually capable of running at high rates (which is why they are used as car starter batteries, where they deliver around 10 to 15C) but they don't have a lot of capacity for their weight. In terms of current capability, lead acid probably outperforms the Thunderskys! Sure, lead acid isn't a good choice for an ebike, but that's because they are big and heavy to get usable capacity and give a decent range. Thundersky cells are, at best, average. There are many far, far better lithium chemistry cells around.
jawnn said:
Gear reductionCalculate wheel speed needed then find ratio of gears:
Wheel diameter x pi x motors peak efficiency RPM / 12â€Âper foot x 60min. / 5280ft per mile = wheel speed without gear reduction / 15mph = ? to 1( gear reduction needed.)
20mph is the legal limit for pedal assist bicycles; a motor can be forced to drive 5mph faster than the peak efficiency so 15 ‘should’ be your cruising speed if not using a Cycle Analyst http://www.ebikes.ca/drainbrain.shtml
A 20†drive wheel maybe needed for a single stage reduction, or a sheave made from a wheel rim on bigger wheels. If the rpm goes over 2000 the motorcycle chain may be too noisy.
The lower the voltage the slower the RPMs but it will increase the amperage. Most electric motors can’t be run on 12 volts because the windings can’t handle the increased amperage of the lower voltage. So they may need a two-stage gear reduction, which could loose at least another 10% of the energy into the gears.
Some pretty mixed up stuff there. The peak efficiency stuff is fairly meaningless - most PM motors have a pretty broad spread of efficiency with torque. Work out gearing for the full load rpm of the motor at the maximum speed you want to go. Full load rpm can be pulled off the motor plots with a bit of quick calculation of the drop in rpm from the no load, full throttle condition at the full load anticipated torque.
The statement about chains being noisy over 2000 rpm is meaningless. Chain noise is a function of chain pitch (which varies a great deal) and the smallest sprocket size. Big pitch chains and small tooth count sprockets are noisy at lower speeds than smaller pitch chains and higher tooth count sprockets. That 2000rpm figure doesn't make sense, I'm afraid.
jawnn said:
HUB MOTORS
Hub motors cannot use 12volts because the thickness of the wire needed for the higher current will not fit through the axle. 48-volt motors are not more efficient than using lower voltage, but it is good for a motorcycle that you don't need to drive slowly up steep hills (4 to 500lbs fully loaded).
Well, some sort of mixed up stuff in there again, but there is an element of truth there. For sure, trying to run thick wires into a hub, in order to get a high torque capability, is tough. This doesn't have anything really to do with voltage though. Bear in mind that a motor running on 48V at 1/4 throttle up a hill (i.e. in current limit on the controller) may only have 12V at the motor anyway.
The efficiency statement is backwards. A higher voltage for a given power will always give better system efficiency - it's why power transmission is always done at the highest voltage possible.
jawnn said:
The largest gear reduction hub motor is far from enough to do what the same gear reduction would do at 12 volts, because the difference in RPMs created by different voltages.
What? There's no reason at all why a geared hub motor shouldn't be perfectly capable of providing enough torque for the job. The rest of the statement is pretty meaningless AFAICS.
jawnn said:
The good hill climbers use three planetary gears to lower the RPMs and those gears use up as much energy as a three stage reduction. All hub motors are geared too high to keep you under 20mph and unless you limit the amps to control the speed, they are illegal. And if you are in a wreck using an illegal vehicle you will get the blame even if it is not your fault.
http://endless-sphere.com/forums/viewtopic.php?f=7&t=23357
http://www.x-tremescooters.com/techdocs/adobe/e-bicycle-fed-regulation.pdf
Loads of mixed up stuff in there, too, I'm afraid. Planetary gear reduction systems can be pretty close in efficiency to any other gear reduction method. An ordinary car auto transmission uses planetary gears, for example. The statement about hubs being geared too high to stay under 20 mph is backwards. Most hub motors are at their best below 20mph, especially geared hubs. In fact, unless you run at high voltages it's hard to get them to go much over about 25mph, providing you start out with a well-matched motor/wheel size/battery voltage combination.
The legality thing I can't comment on - here the law is 15mph and 250 watts.................
jawnn said:
If you do limit the amp flow to make them legal, you limit the hill climbing torque.
A grain of truth at last. Restricting current will always restrict torque, all else being equal. However, what's that got to do with being legal? Surely legality has more to do with power and speed than torque, doesn't it? There's no reason not to have a controller that allows the full legal power at low speed on a hill, to give maximum torque, and that also limits motor speed under lighter load conditions to restrict speed to the legal limit.
jawnn said:
The ‘Cycle Analyst’ maybe able to control the speed without eliminating the slow speed amps.
The CA limits speed by cutting back the throttle, which then cuts back the current, so this isn't right.
jawnn said:
But there is still a chance you could burn out power system if you run too many amps threw it at too low of a speed.
True, if your controller was mismatched to the motor and had a current limit that was set too high - but why would you run a mismatched system like this?
jawnn said:
A good meter will help keep your vehicle alive. A heat sensor would be good also.
Generally sound, I wouldn't disagree with either, if you're running at the edge of the system's performance capability. If you're running a fairly low power standard type ebike set-up, then it's far less valid, as the controller should provide pretty much all the protection you need.
jawnn said:
The Scott 1hp upgrade is the motor to use http://www.cloudelectric.com/product_p/mo-4bb3995.htm
That looks to be a pretty crappy brush motor, most probably based on a cheap Chinese MY series with some mods. Frankly it's hard to imagine a less efficient or reliable motor for an ebike.
jawnn said:
I have seen no evidence that hub motors are good for anything but light weight vehicles on light duty hills. Or just for racing.
Well, as hub motors are used in a very wide range of vehicles, from ebikes to massive earth movers weighing many tens of tons, I can't agree with this. A geared hub motor in a well matched low power (legal) system can climb hills pretty much as well as any other ebike of a similar power. If you want illegal speeds and good hill climbing, then driving through the gears on the bike is probably better, but I'm assuming here that this is related to a low power, speed restricted, legal ebike.
jawnn said:
And if you want more info, go to my blog: http://commutercycling.blogspot.com
Nice to see that you're spreading this misinformation around the web.......... Not so nice to see you link it back to here. I take pride in trying to give the very best info I can on this forum, so would rather it not be connected to misleading and incorrect information such as that on your blog, I'm afraid.
Jeremy
:lol: :lol: It reads like a discarded script from "One flew over the Cuckoo's Nest".. 
