``` The Gearing Advantage ```

[safe]

But we haven't heard how 50A doesn't generate heat...

I'm planning to use forced air cooling... but that's beside the point, most heat is not produced at the high end, it's at the low end. The "real world" average is what matters. I'll be able to adjust my boost level and will experiment with between 40 to 60 amps. My main interest is the gearing... I had to commit to an "estimated" boost level and 50 amps is what I'm gearing the bike for. 40 amps gets me to about 47 mph and would need a sprocket with a couple fewer teeth.

By now it's should be clear of what "steady state" riding is verses "sport" riding.

The perect solution is the Tesla style induction motor... but this is the closest you can get for sport bike performance using the permanent magnet motor.

"Steady State" riding doesn't interest me...

 

[TylerDurden]

50A is 50A... regardless of rpm.

 

[safe]

0 - 50 mph Heat Profile Comparision

It's not so simple... your heating varies with the gear you are in (or a fixed gear) and so the more realistic analysis is to look at it from a "big picture" perspective. This chart does that... you should trying thinking in terms of "constant load" rather than "steady state" because in the "real world" of sport riding you are at full throttle all the time. (or off while braking)

The reason the inductance motor was chosen by Tesla Motors was precisely because they wanted to get better efficiency "under load". It's the "under load" part that you seem unwilling to accept.

Think induction motor theory... that's the "ideal" to shoot for...

But just looking at the heat profile chart below, the 50 amp MCL stacks up pretty well even before you add forced air cooling. 8)

(there are certain situations where the MCL is hotter, but on average it's about the same)

 

[Geebee]

I just put together a tiny stoke monkey, a 16" wheeled folder with an Oatley 250w geared motor running to a 44 tooth left hand sprocket, and from a 44 r/h sprocket to a 28 tooth (low on a 7 speed cluster) rear sprocket.
This little toy will climb a 20~30% hill non stop with close to zero heat build up and very little pedal input, I then took it off road and tried some steeper hills, same result (so steep I walked back down them).
Current was being delivered by a pair of light weight alligator hook up cables, the type for electronic work and they also stayed cold.
This was just a test for a trike I am going to build, but even on the steepest slopes cracking the throttle caused the rear suspension to squat and the bike just took off, obviously with the level of gearing it was slow maybe 10 kph? no speedo.

Obvious conclusion if you have hills and want to use low power gearing is essential.

 

[ott]

And there is no better setup for this type of drive imho than a belt drive with hardened aluminum sprockets attached to a nuVinci hub. Sweeet. I'd save and get a nuvinci with dual chain sprockets. <img src="http://www.staton-inc.com/images/HPIM1345.JPG">http://www.staton-inc.com/Details.asp?ProductID=3207 This is good for up to etek power. Very nice test platform. Shift on the fly! at bicycle power.

 

[Miles]

And there is no better setup for this type of drive imho than a belt drive with hardened aluminum sprockets attached to a nuVinci hub. Sweeet.

Apart from the weight penalty of the hub itself..............

 

[safe]

NuVinci vs Tesla?

In my opinion the advantage of gears over not have gears is obvious. The advantage of infinitely smooth gear range transitions verses somewhat larger "chunks" like a regular gear set is less clear from a mathematical perspective. Mathematically the advantage of smooth gearing is a very small percentage. So in the end it comes down to performance styles:

Do you want "sport" performance?

or

Do you want "steady state" performance?

If the answer is "sport" then by definition your throttle is either 100% full or completely off almost all the time. (the exception being turns that you can't risk full throttle) For the "fully loaded" motor the better efficiency comes from the Tesla inspired induction motors that we DON'T SEE beign used yet. This is in my opinion the real future of "sport" oriented electric vehicles. (like the Tesla Roadster)

The NuVinci exists in a very narrow intellectual region of the gearing / induction motor / power load debate. The gains switching from regular gears to NuVinci will be minimal.

Look at the chart... the only gains you will get with a NuVinci are the "valley" portions of the yellow region of this chart...

 

[xyster]

Do you want "sport" performance?

or

Do you want "steady state" performance?

A false distinction, these styles are not mutually exclusive to most riders as they are for you. With a high power hubmotor, I get my "sport", and I get my "touring".

 

[safe]

NuVinci vs 8-Speed vs Fixed Gear

As a true "final analysis" of this topic I did my homework on the NuVinci and have plotted it's likely performance relative to the other options. There are definite gains if you could keep the gear ratio perfect all the time. The advantage of the NuVinci over the 8-Speed is about a 6% difference relative to the fixed geared option. The 8-Speed is 28% better than the fixed gear and the NuVinci is 34% better than the fixed gear. Is it worth it to buy a NuVinci? Hey, that's up to you, your wallet and your riding style... :wink:

Just as a reminder... on these charts the bottom axis is mph and NOT rpm. For the fixed gear case they are the same, but for the gearing options they are the final rear wheel speed after going through whatever gearing you use. (it's kind of obvious since I list the gear shift points, but a reminder is just to be helpful)

 

[Miles]

As a true "final analysis" of this topic I did my homework on the NuVinci and have plotted it's likely performance relative to the other options. There are definite gains if you could keep the gear ratio perfect all the time. The advantage of the NuVinci over the 8-Speed is about a 6% difference relative to the fixed geared option. The 8-Speed is 28% better than the fixed gear and the NuVinci is 34% better than the fixed gear.

This is all a bit simplistic. Why don't you report back when you've got some real data.

 

[safe]

This is all a bit simplistic. Why don't you report back when you've got some real data.

I've got my own bike that has validated everything I've written about so far. My shift points, power behavior have all been very close to the theoretical models. So what I've been presenting is more of the "post data analysis" than anything else. This is the way things work in practice... in the "real world". (or at least as close as a model can be made to mimick the "real world")

I collected the data first... then created (and adjusted) the models second... which is the best way to do it.

But as far as the NuVinci hub I have no data because I don't own one. Given what I see of the calculations I'll save my money becuase a 6% difference isn't worth it. That's where the theoretical models can instruct my future behavior becuase I can see that the advantage is "real" but likely small compared to a regular 8-Speed gear setup.

 

[Miles]

Do you have any figures for the efficiency of the different gears of the S.A. hub gear?

Do you have any figures for the efficiency of the Nu Vinci across its range?

 

[safe]

Do you have any figures for the efficiency of the different gears of the S.A. hub gear?

Do you have any figures for the efficiency of the Nu Vinci across its range?

I've included all that into the theoretical models. I'm assuming that the efficiency of the NuVinci is roughly equal to the 8-Speed. Gears introduce about a 5% loss compared to not having them. All models are approximations... they are to give you a basic framework to make decisions. Upon this framework we see that while the move to gears is a big step... a big advantage... the secondary move to a CVT is only a small improvement on top of that. Philosophically I don't see the big advantage to taking that last step.

At some point I see throwing all this into the garbage and starting over with the Tesla style Induction motor. Those motors can achieve 94% efficiency and PREFER to be under load. For "sport" riders load is everything and "steady state" is not very important.

The law in America is 750 Watts, Canada is 500 Watts and Europe is 250 Watts. The best way to utilize those legal limits is with an Induction motor. (if you want "sport" performance)

Full power all the time... now that's the future.... 8)

(because the law is very restrictive)

Motorcycles and mopeds are allowed much higher limits, so for them they can avoid a lot of the performance "tweeks" we need to pay attention to in order to retain our bicycle classification.

The easy way is always to produce illegal (over the limit) power... :wink:

And looking at the chart again it's obvious that this motor is ILLEGAL as I'm presenting because it's waaaaaay over the power limit. I'd be better off with a 250 watt motor and getting 750 watts out of it. (this chart shows over 1000 watts most of the time, despite the fact that it's a legal 750 watt rated motor)

 

[Miles]

Do you have any figures for the efficiency of the different gears of the S.A. hub gear?

Do you have any figures for the efficiency of the Nu Vinci across its range?

I've included all that into the theoretical models. I'm assuming that the efficiency of the NuVinci is roughly equal to the 8-Speed. Gears introduce about a 5% loss compared to not having them. All models are approximations... they are to give you a basic framework to make decisions.

So, rather a lot of guessing. The efficiency of hub gears varies a lot, from gear to gear and the efficiency of the Nu Vinci remains unknown.

 

[safe]

So, rather a lot of guessing. The efficiency of hub gears varies a lot, from gear to gear and the efficiency of the Nu Vinci remains unknown.

My point is that no matter where you peg the efficiency (from 5% to 10%) the NuVinci is NOT going to be a significant advantage over an 8-Speed geared transmission. That's the point here... there's not enough "room" left in the performance envelope to gain much more.

You can't "magically" get performance out of nowhere. All the gearing really does is correct for the permanent magnets of the DC motor that have the annoying quality that they prefer certain rpms over others. All gears do is correct for the motors inherent deficiencies.

I'll say again...

The REAL solution is the Tesla Induction motor because it loads up really well. The permanent magnet based motors only work at their best in a narrow rpm range and suffer everywhere else both in terms of heat and efficiency. (one in the same thing) The Inductance motor creates it's own magnetism so it's "perfect" all the way through the rpms. The "ultimate" destination is the computer controller SR/VR Switched Reluctance / Variable Reluctance motor that has nothing but a hunk of iron as the rotor... no brushes, no sensors, everything is induced/controlled from the outside.

The NuVinci is a nice hub and if it performs equally or better than an 8-Speed transmission (hub or traditional) then it could show some modest advantages. But I don't see it as part of a cost effectiveness solution... what you gain over the 8-Speed might not be worth the cost.

We can say that no gearing solution will be worse than 10%... that's simply too extreme. The typical clean and well lubricated chain runs at a 98% efficiency... so a loss of only about 2%. If your losses are more then 10% you have a bicycle maintenance problem going on...

 

[TylerDurden]

Do you want "sport" performance?

or

Do you want "steady state" performance?

A false distinction, these styles are not mutually exclusive to most riders as they are for you. With a high power hubmotor, I get my "sport", and I get my "touring".

Sport Performance = riding till your motor gets too hot.

Steady State Performance = Riding as long as you like.

 

[safe]

Sport Performance = riding till your motor gets too hot.

Well you're essentially correct.

A dragster needs to be able to finish it's quarter mile and not overheat.

An Indy Car needs to be at full speed in order to get enough air cooling through their radiators or they will overheat. This is why when the Indy Cars run on the road courses they will make modifications to their radiators in order to get better cooling at low speeds.

The electric bike "sport style" (like mine) has a typical range of about 30-45 minutes at full speed. In that time the motor gradually heats up and when I'm done the motor is just getting to it's hottest point. After 2-3 hours of charging the battery is rejuvenated and the motor is cooled and you can go out again and go full speed. It's possible to do this four times in one day.

So "yes" most definitely... the "sport rider" needs to practice "heat management" and know the limits of power, heat and time and not let it get away from you...

MCL should help a lot because it makes it impossible to make a mistake. The BCL suffers from the fact that a poor gearing choice can increase heating. MCL heating is a constant.

That was the lesson of this chart:

 

[TylerDurden]

So... just how long can a 36V Unite MY1020 run @ 48V, 50A?

 

[safe]

So... just how long can a 36V Unite MY1020 run @ 48V, 50A?

With forced air cooling and MCL it might run the desired time limit of 30-45 minutes. If not, then I could lower the boost down to 40 amps. I have a feeling (just by looking at the charts) that I might be able to get away with 60 amps if I'm using forced air cooling, MCL, and only run for 30-45 minutes. That sort of thing is determined by the forced air cooling and the sheer mass of the motor... the larger the mass the slower the heat build up. Once the ride is finished you get 2-3 hours of cool down... so it works out fine.

Fechter has claimed to roughly double his heat dissipation rate when he added forced air cooling.

 

[Miles]

We can say that no gearing solution will be worse than 10%... that's simply too extreme. The typical clean and well lubricated chain runs at a 98% efficiency... so a loss of only about 2%. If your losses are more then 10% you have a bicycle maintenance problem going on...

No, "we" cannot.

Losses on some ratios of hub gears can approach or exceed 10%

The % efficiency will vary with the torque that you are putting through the drive-train, of course. So, for your case, you're probably right.

 

[xyster]

Sport Performance = riding till your motor gets too hot.

Steady State Performance = Riding as long as you like.

If Safe rode my bike instead of his, he'd enjoy much better performance (except perhaps handling), and the motor would never get hot, and in his state my bicycle would be just as much of a bicycle as his is in the eyes of the law. So how does "sport performance" equate to "riding till your motor gets too hot"?

 

[safe]

Staying Within The Law

Assume you aren't a home enthusiast with a modified machine that produces horsepower that is better suited for a small motorcycle or moped. Assume you are a manufacturer that needs to pass the basic set of rules that define the American, Canadian or European electric bike. No matter what the limit (750 watt, 500 watt or 250 watt) while you are operating within that limit it says nothing about how wide the powerband might be within the limit. The limits are "peak" limits... it's sometimes expressed in terms of "rated load" for a motor. The "rated load" is really a heat related term because it's the load that the motor could run 24 hours a day and never overheat. This makes things more complicated because you can exceed the "rated load" for short periods and simply take the heat "hit" to your motor. If you allow the motor to cool off afterwards you are okay, but if you keep going hard it will burn up the motor.

One way or another a "true" accepted limit is understood by the law and the manufacturer.

At this point it comes down to how that power is delivered to the road. If you use the classic fixed geared powerband the power at low rpms is not that great compared to a geared solution. Even with the benefit of the "current multiplication" the power of a reduced gear and a high rpm to the rear wheel beats the non-geared machine easily. So the simple answer is to use a standard motor and then just gear it so that the power from 0 mph all the way to top speed is very close to the legal limit. You could use a derailler, a multispeed hub, or a NuVinci hub for gearing to make that happen.

But the "next generation" of motors could use the Tesla style inductance technique and eliminate the need for gears altogether. With peak efficiencies in the 94% range under full load ACROSS ALL RPMS this type of motor is unbeatable. However, at this point in time the control systems are complex enough that the costs are too high.

Having gearing gets you very, very close to the induction motor ideal. The NuVinci approach is virtually equal to the induction motor and the only remaining question is the efficiency comparision of inductance motor verses permanent magnet motor plus NuVinci... I suspect it's only on that last analysis that the NuVinci option has to surrender to it's logical successor.. the inductance motor.

 

[ott]

34% increase in power. Yeah I'd take it. Also with the Nuvinci you can run a #35, #40, etc. chain. You could put the powerband in the middle and use the higher gears when you are outrunning law enforcement.
Yes the weight...It corresponds to the power capability of the hub- easily handling 5hp+. If you are running a powerful motor 8 pounds ain't that bad is it? (You have to take off .3 pounds of chain and rear derailleur weight

Anyway it seems like a bulletproof quality piece of work that hub. It is at least $500 for a fully built, double sprocket freewheel wheel though. It sure would be fun on a scooter!

 

[Miles]

Yes the weight...It corresponds to the power capability of the hub- easily handling 5hp+. If you are running a powerful motor 8 pounds ain't that bad is it?

Have you got a reference for that? I seem to remember a limit of something like 150 Nm for the bicycle version....

 

[Miles]

Maximum torque for the NuVinci is 130 Nm

Ref: http://www.atcnuvinci.com/docs/ATC_Bike_Datasheet.pdf