* * * MOTOR UNIVERSITY (Lab 101) * * *
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safe
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eP said:
Heat is a fact of life when riding. The small differences between peak power heat between the two controllers makes little difference when someone might pull a tall gear without realizing what they are doing. In a hub motor you can't pull a too tall gear because you are lacking any choices and in most cases you quickly move past peak and stabilize in the high efficiency area at something like 20 mph... and that's it... 20 mph. A geared bike gives too many choices and it's too hard to tell which is the ideal gear when you are riding. Often two gears feel the same, but the taller one is actually producing more heat. That's what is meant by the "Imperfect Rider"... he has no way to tell what is going on.
Air drag would increase... but the chances are that the energy you save by not pulling the wrong gear will equal the extra air resistance.
It all depends on the rider though...A "Perfect Rider" could equal or better the "Motor Current Limited" controller. The "Imperfect Rider" will produce too much heat, waste power and be in a gear that is too tall. The more "imperfect" the rider the wider the advantage of the "Motor Current Limited" controller.
Theory might suggest someone can be "perfect", but in the real world people follow what feedback they can receive and make decisions based on that. People ride by "feel" most of the time.
So when do you build your first bike?
TylerDurden
100 GW
Back to the drawing-board, Perfesser...
50A motor-side limit won't let you get where you want to go:
50*48 = 2400W * .7 = 1680W
You won't even hit 45mph. (1812W)
50A motor-side limit won't let you get where you want to go:
50*48 = 2400W * .7 = 1680W
You won't even hit 45mph. (1812W)
safe
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TylerDurden said:
My "Road Racer" is different aerodynamically than a pedal powered racing cycle that might go by the term "Road Racer", but they have about twice the drag. My frontal area is very, very small... so you need to use something like a Recumbent to approximate the real world aerodynamics that my "tucked" (legs out of the way) bike has. I get REALLY SMALL to the wind... when I sit up I can only do about 35 mph (more like a normal bike)... in a tuck it's 40 mph.
Where's that power chart from, TD?
What was the total vehicle weight used to run the numbers?
What was the total vehicle weight used to run the numbers?
TylerDurden
100 GW
fechter said:
The chart was created from kreutzotter data:
160# rider
80# bike
"road racer" on drops profile
TylerDurden
100 GW
safe said:
OK...We'll include the small profile and heavier weight.
('Zotter: short-wheelbase 'bent, 140# bike)
We'll also revise a more realistic 60% efficiency when running at 50A.
'Zotter says 1468W to achieve a 1% slope (minor accelleration) @ 45mph.
2400W*.6 = 1440W
BUST.
Even if you could maintain the speed, the heat baby... eff dropping like a rock and speed too, and then... the magic smoke. :lol:
safe said:
Are you crazy or just kidding now ??
Example please !!
At higher current limit the chances you pulling the wrong gear are much higher !!!
safe said:
A "Perfect Rider" could equal or better the "Motor Current Limited" controller. The "Imperfect Rider" will produce too much heat, waste power and be in a gear that is too tall. The more "imperfect" the rider the wider the advantage of the "Motor Current Limited" controller.
Theory might suggest someone can be "perfect", but in the real world people follow what feedback they can receive and make decisions based on that. People ride by "feel" most of the time.
So when do you build your first bike?
When i get one example a least.
safe
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TylerDurden said:
"Lowracer with streamlining tailbox" is closest to what I actually have on my bike based on existing aerodynamic results.
Try it with that...
Also, at peak power the estimated efficiency is 66.44% @ 1191 Watts. (you might as well use the real numbers)
I get 52.4 mph from http://www.kreuzotter.de but that's before adding any efficiency losses which makes my real world estimate more like 50 mph. (or less) So the eventual fiberglass fairing creation process will likely determine the top speed in the final analysis.
ShortWheelBase under seat steering, commuting equipped - 39.2 mph
ShortWheelBase above seat steering, racing equipped - 45.0 mph
Lowracer above seat steering Kreuzotter race - 49.8 mph
- - - - My Bike Should Fit Here - - - -
Lowracer with streamlining tailbox Kreuzotter race - 52.4 mph
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safe
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eP said:
What happens on a geared bike? What is DIFFERENT compared to a fixed gear hub motor?The big difference is that once you pass about 10 mph your ability to choose which rpm to run is wide open. You can select at any time what EFFICIENCY you might want to use. If you want you can hold steady on flat land in first gear and maintain perfect efficiency and low heat all day long OR you can upshift and see how much speed is possible. As you upshift through the gears you are shifting the rpms lower so that the bike must push through the peak power onwards into the efficiency peak.
But then something happens...
At some point the gear that you have upshifted to is as tall as can be pulled before you can no longer pass through your peak power. At some point you will be STUCK in rpms BELOW the peak power.
The "Motor Current Limited" controller will punish such an incorrect gear choice immedately and the rider will quickly realize they must downshift. Once they quickly downshift then the rpms rise and the efficiency is again excellent. The heat never builds up.
The "Battery Current Limited" controller will allow the rider to continue with his bad gear choice and stay below the peak power rpms while the bike heats. The rider has no idea this is a bad thing because the extra low end torque sends a "false signal" that everything is okay. The rider accepts the extra low end torque as a wonderful thing and continues on in a tall gear. The result is massive heat buildup and inefficient energy usage.
This chart sums up an example of how the "Imperfect Rider" on the "Battery Current Limited" controller bike will tend to use his powerband.
The results for this simulation are:
"Battery Current Limited" controller average heat - 568 watts. "Motor Current Limited" controller average heat - 466 watts....again, the "Imperfect Rider" is very human and flawed and is following his feel of the bike. The bike has misled him to do the errors, but if he had some kind of ammeter to watch he might have been able to realize how to do things better. The "Battery Current Limited" controller gives feedback to the rider that says:
"Tall gears are okay" (even when they aren't)
eP, one day you will built your first bike and get on it and begin to ride and you will experience all the things I'm talking about. If you build the geared electric bike you will know this, but if you build a hub motor bike you might never come to understand what I'm saying. So you have a long road ahead of you learning in practice how powerbands are used on the street. You need more "real world" experience and less theorizing... :wink:
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TylerDurden
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safe said:
The "analysis" is a complete fallacy. :lol:
The peak power of an electric motor brings excess heat, beyond it's ability to dissipate. That is why motor load-ratings show three primary power-points: peak, rated and max efficiency. Peak power is indicated in ratings to describe the motor's ability to start from a dead-stop. The "higher peak power output" (at the wheel) shown in the spreadsheets is a function of raising the current-limit to 50A (from 40A). Sadly, both limits can be above a motor's rated-load, and the difference is simply how fast it burns up. The "study-guide" author prefers to shut-off the motor before meltdown (in most cases). In the real-world of electric motors, torque=heat. A motor should be selected based on the load and torque demands. The wise choice of motor meets the torque demands, while within the motor's ability to dissipate the heat generated from startup through continuous duty. Gears can be used to reduce the load at the motor, but the trade-off will be speed. That is how gears work, since the time of the pyramids.In the chart below, an average* e-bike's power-demands are illustrated. A Unite 1000W 48V motor's power output is shown in the red and green areas.
The slope axis can also be considered as acceleration.
The green area is within the rated-load of the motor (26.7A) at the motor's rated efficiency of 78%. The motor can run continuously in the green area, and the bike will achieve the speeds at the given slopes.
The red area indicates the power output up to 50A with an unlikely efficiency of 70%. Everywhere in the red area, the motor will build-up heat and eventually fail; unless cooled in some fashion, or shut-off before meltdown.
*average: 160# rider, 80# bike, "road-racer on drops" profile
safe said:eP said:
The big difference is that once you pass about 10 mph your ability to choose which rpm to run is wide open. You can select at any time what EFFICIENCY you might want to use. If you want you can hold steady on flat land in first gear and maintain perfect efficiency and low heat all day long OR you can upshift and see how much speed is possible. As you upshift through the gears you are shifting the rpms lower so that the bike must push through the peak power onwards into the efficiency peak.
[/i]
Which gear is wrong at flat ?
Could you give us an example ?
safe said:
Which rider: Perfect or perfectly Imperfect ?
safe said:
How much rpms rise ?
And what level efficiency reach ?
Could you give us an example ?
What is the signal for Imperfect rider to switch the gear ? Is this speed drop to zero ?
safe said:
Example please !!
At what slope ? or at flat ?
I'm sure the same low rpms you can get at one gear lower at your cripled bike.
So give us an real example.
safe said:
What is the false signal for Imperfect rider ?
Example please.
safe said:
This chart sums up an example of how the "Imperfect Rider" on the "Battery Current Limited" controller bike will tend to use his powerband.
The results for this simulation are:
[/i]
Is it kind of joke ?
I see over 90% of the time your cripled controller will send false signal to Imperfect rider and 156% heat also.
Example please.
safe said:
They ok for your Imperfect rider at cripled bike as you have higher current limit.
So it is still possible to ride at low rpms and over 40A current when normal bike long ago gave signal to rider to change the gear to lower.
safe
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TylerDurden said:
In the "real world" one uses a range of rpms in the acceleration of an electric bike. One needs to think in statistical terms because it's the amount of time spent in the different rpms that determine heat. Whether you are on a hub motor or a geared bike your rpms will vary depending on the terrain. Your "perfectionist" argument is silly... you can't be perfectly in the rated load all the time.
TylerDurden said:
Again, the choice of 50 Amps over 40 Amps is purely an option for the rider. The truth about "Motor Current Limiting" is that it suppresses low rpm inefficient power that produces a lot of heat. As refered to above, we need to think in terms of statistical profiles of how a motor is used in real life. Peak power is seldom held for long because the rpms tend to swiftly rise. (because power produces acceleration) The model needs to be more complex than what you are presenting.
TylerDurden said:
Torque does equal heat... but Power is the result of torque times rpms. That's what's really more important to the geared bike than torque alone. For some reason you simply seem unable to comprehend power compared to torque and I don't know if I should laugh or cry... :lol:
Often the choice of motor is restricted by legal issues. (US 750 Watts, Canada 500 Watts, Europe 250 Watts)TylerDurden said:
It's true that with gears you can climb steeper hills for a given power output, but with less speed. You can also go faster in a taller gear than if you were stuck with a fixed gear that had to be low because of hill climbing concerns. Gears simply increase your options.
Think again about this chart... this is a more realistic statistical profile of how someone really uses a motor in the real world... think "statistical" and not always in one dimensional terms. The motor "rests" when you enter a turn and are using the brakes. It heats the fastest as it pulls the hardest, but then it cools as you rev the motor up to the high rpms. A bad shift into a too tall gear is the demon that hurts the motor.
Multiply the heat values by 100, so you are looking at peak heat in the range of 1300 Watts.
Average heat is "Motor Limited" - 466 Watts, "Battery Limited" - 568 Watts
safe said:TylerDurden said:
Again, the choice of 50 Amps over 40 Amps is purely an option for the rider. The truth about "Motor Current Limiting" is that it suppresses low rpm inefficient power that produces a lot of heat. As refered to above, we need to think in terms of statistical profiles of how a motor is used in real life. Peak power is seldom held for long because the rpms tend to swiftly rise. (because power produces acceleration) The model needs to be more complex than what you are presenting.
[/b][/i][/color]
So show us the part of your profile where current multiplication occur above 50A.
Show us slope grade/ wind and percenage in your profile for that case.
And the same for all major (percentage) cases in that part of your statistical profile.
This way we could see what your profile come from.
TylerDurden
100 GW
safe said:
This is where you are gravely mistaken and your premise goes up in smoke.
Torque produces accelleration, not power.
You could easily produce 5kW @ 10K rpm w/ little torque. Power yes, acceleration no. So what good is 5kW if you stall?
safe said:
You must be smoking crack. That motor won't even begin to cool until you are running less than 30mph. You need to get below rated load of 1281W (48V*26.7A).
You need current to accelerate. Current = heat. If your motor cannot dissipate the heat... You. Are. Toast.
:lol:
TylerDurden
100 GW
Lowell said:
Easy for you to say, but you got any numbers to back that up?
Watts?
RPM?
Nm?
Ratios?
:lol:
TylerDurden said:
It isn't the major issue torque or power produces acceleration.
The main issue of his idea is low very low gain at very limited area (percentage of statistical profile).
If Imperfect rider is so stupid to ride at low speed/low rpm/high gear, so the same stupid Imperfect rider will never switch to right gear - after stall he/she switch to the first gear which give him/her acceleration a little bit greater than zero.
The main issue is false assumption that Imperfect rider switch the gear to the right gear.
At very low acceleration the Imperfect rider could stay in bad efficiency area for much longer for the sake of higher current limit.
Wrong gear + higher current limit = much more heat.
TylerDurden
100 GW
The reverse is true too...Lowell said:
:lol:
xyster
10 MW
Lowell said:
Lowell is correct, TD is not. Higher voltages give the same torque at higher rpms. Power is the product of torque X rpms, or amps X volts. Imagine an ungeared motor generating one million N-m of torque because it's fed huge amps, but only one volt. It'll quickly rev up to a few rpm's, but no further. It could accelerate a huge vehicle very quickly to, say, 1 mph, but no further.
If it weren't the case that power is equivalent to acceleration, we would not gain acceleration by only overvolting our motors -- but we do.
xyster
10 MW
To further the point, check out the 4qd acceleration calculator.
http://www.4qd.co.uk/faq/current.html
http://www.4qd.co.uk/faq/current.html
In terms of electric motors, simple physics throws out the extremes, as you couldn't push enough amps at low voltage to produce a direct drive space shuttle mover. On the other end, tiny high RPM inrunner RC motors still have no trouble being geared down for use in cars, boats, planes etc.
http://vettenet.org/torquehp.html
http://vettenet.org/torquehp.html
Torque X RPM = power. 5kw is 5kw, so as long as the gearing is close to optimum, the power transfer will be efficient.
Look at the extremes:
A direct drive hub motor with a no-load speed of 400 mph is not going to be efficient under any real conditions since it will always be in a near stall condition.
A 5kw geared motor that has a no-load speed of 4 mph, will go 4 mph, even up the steepest hill, but will not be efficient under any real conditions, since the no-load current will be the majority of the power consumed.
Look at the extremes:
A direct drive hub motor with a no-load speed of 400 mph is not going to be efficient under any real conditions since it will always be in a near stall condition.
A 5kw geared motor that has a no-load speed of 4 mph, will go 4 mph, even up the steepest hill, but will not be efficient under any real conditions, since the no-load current will be the majority of the power consumed.
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