Comparisons? WattHrs/mi/lb. @ speed

Matt Gruber said:

after break in my PSEV is silent.
my mbike tensioner rattles a bit, but it disappears at 20mph.
new it was annoying i'll grant u that. like loose change in my pocket, NOT LIKE ICE!

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Ja, I've watched Randy's vids and his is fairly quiet. My motor gears whine. A hub is quieter tho.

Matt Gruber said:

Tyler
my psev is11 amps @24v 15mph 62#+144
my mbike is 10a@17mph36v 132# +144.
but 20a @25mph @53v

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11Ah & 24V =264Wh / 15mi = 17.6WhMi / 210lbs = .084WhMiLb @15mph

10Ah x 36V = 360 / 17mi = 21.17Wh/mi / 276lbs = .076WhMiLb @17mph

20Ah x 53V = 1060 / 25mi = 42.4Wh/mi / 276lbs = .154WhMiLb @25mph


Kinda interesting... (I'll have to go back and see what Reid was getting @ 24V on his Currie)

Thanks

I've been surfing back through some old topics to get samples of other members' setups.

Generally, the setups are somewhere in the .07 - .08 range for Wh/mi/lb. @ around 10-15mph.

A few actually get down into the .05x range, but it takes specific figures for good evaluation,and I was guesstimating many of the weights and Wh figures.

At the risk of another pissing contest, I'd be very interested to see more figures on Randy's bike... It would be good to see solid figures on range and power consumption. I don't imagine there are notes, but you never know.

Randy's bike is a prototype of sorts. It may have potential, it may be a dud. The trick will be sifting the facts from the hype. Figures in the .01x - .02x ranges require validation to be regarded as having credibility.

Generally, the setups are somewhere in the .07 - .08 range for Wh/mi/lb. @ around 10-15mph.

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Probably the case because most systems, and most of us, are around the same weight. But to get a more accurate efficiency picture you should ignore weight. Once a mass is moving at a proscribed velocity, it keeps moving at the same velocity until acted upon by another force (one of those Newtonian laws I'm pretty sure... ). Since these measurements are mostly on the flats, with your system, a 500lb bike/rider combo will score a much higher efficiency ratio than a 250lb combo, even if the actual electrical energy --> kinetic energy efficiency of both systems is the same. Weight would become a factor were these measurements derived from acceleration or hill-climbing observations, where inertia and gravity respectively would resist the motion of the heavier system more, causing the heavier system to expend more energy doing more work for the same result as the lighter system.

Moving the weight is the goal of the systems. Everything else supports or detracts from that work.

With real-world samples, weight will always be present and varied, so it should be accounted for.

i'm impressed with the bike calculator.
it predicted 750w 25.3mph

i did 25.1 at~736w

Moving the weight is the goal of the systems. Everything else supports or detracts from that work.

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No, accelerating the mass takes energy, once it's moving the only energy needed is to overcome friction -- mostly tire and wind resistance in our case. This friction does not appreciably increase or decrease with the mass (weight) of the bike.

<a href="http://en.wikipedia.org/wiki/Newton's_laws_of_motion">Wikipedia entry</a>
Newton's first law: law of inertia

An object at rest will remain at rest unless acted upon by an external and unbalanced force. An object in motion will remain in motion unless acted upon by an external and unbalanced force.

This law is also called the law of inertia.

The net force on an object is the vector sum of all the forces acting on the object. Newton's first law says that if this sum is zero, the state of motion of the object does not change. Essentially, it makes the following two points:

* An object that is not moving will not move until a net force acts upon it.

* An object that is in motion will not change its velocity (accelerate) until a net force acts upon it.

The first point seems relatively obvious to most people, but the second may take some thinking through, because we have no experience in every-day life of things that keep moving forever (except celestial bodies). If one slides a hockey puck along a table, it doesn't move forever, it slows and eventually comes to a stop. But according to Newton's laws, this is because a force is acting on the hockey puck and, sure enough, there is frictional force between the table and the puck, and that frictional force is in the direction opposite the movement. It is this force which causes the object to slow to a stop. In the absence of such a force, as approximated by an air hockey table or ice rink, the puck's motion would not slow.

With real-world samples, weight will always be present and varied, so it should be accounted for.

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Sigh...guess that year of physics in college was all BS...

On flat ground, the weight is largely a non issue as most drag is aerodynamic. I just look at the Wh/km number in the DrainBrain to see how I'm doing compared to my average trip speed.

Weight matters for acceleration and especially for going uphill, but it does not significantly affect power or efficiency at a fixed speed on flat ground. The only way in which it has any effect at all is that it very slightly increases rolling resistance since heavier weight deforms the tire a little more, and the increased stress on other components could increase friction. But this would be noticeable only with a really significant change in weight, and every bike+rider here is about 250-300 lbs.

Moving weight around is all we do with bikes.

If weight is not relevant, we'd all be using SLA.

8)

weight certainly DOES matter.
However, due to the narrow range, it can be overlooked, just like you are ignoring aerodynamics, which is way more important.
This type of reasoning requires u to throw out the best and worst to find the typical.

Matt Gruber said:

weight certainly DOES matter.
However, due to the narrow range, it can be overlooked, just like you are ignoring aerodynamics, which is way more important.
This type of reasoning requires u to throw out the best and worst to find the typical.

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There are only a couple of "bent" riders here, and they do seem to show better than average results.

The rest of the field is mostly riding upright and aerodynamics can be regarded as more of a constant than weight can.

TylerDurden said:

The rest of the field is mostly riding upright and aerodynamics can be regarded as more of a constant than weight can.

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No it can't. Weight is a constant because it's similar for all of us and it never changes. Aerodynamic drag varies dramatically depending on speed, and is also affected by temperature, elevation, rider's size/stance/clothing, etc.

Remember that our bikes are not rocket-ships. Let's say you have a rocket-wheel like this:



...where the propellant is in the blue tank in the center of the wheel. It's emitted under pressure through the red tube, firing in the direction of the red arrow and causing the wheel to spin in the direction of the black arrow.

If you turned your bike upside-down and just let this wheel spin freely, it would spin at an extremely high rate as there's very little limiting its speed. Its acceleration would be very linear in other words -- after 10 seconds it'd be spinning at roughly twice the speed it was spinning after 5 seconds.

But turn your bike back over and try running with this, and all that weight would significantly affect acceleration, plus air/rolling resistance would limit the top speed, especially if the wheel's thrust is very low. It might not even start moving at all.

An electric motor, on the other hand, behaves totally differently. Turning the bike upside-down and running the motor, the wheel does *not* increase in speed at a linear rate; the acceleration decreases until the wheel hits a fairly low max speed. In my case at 48V, it's 360 RPM. But there's alot of thrust, so turning the bike back around and actually riding it, the maximum speed is 60% of its previous value.

Since TD's brain isn't computing this weight non-issue correctly, let's take it up with the bike and speed calculator.

Pic 1: 1000 watts, 26 lb bike, 32.5mph speed

Pic 2: everything the same except bike is 526lbs (20 times heavier) 29.8mph speed.

The physics is also described on the calculator page:
http://www.kreuzotter.de/english/espeed.htm

Sheesh.

Did yer Physics prof tell you to ignore factors that can effect your outcome? That's the kind of logic that gets you Challenger shuttle explosions.

Lookee...

Puttering around at 20mph with an extra 30lbs will cost you some power when you encounter even a modest grade.

According to the calculator, 30lbs cargo will need +70 more watts on a 5% grade. A 10% grade will require +132W to maintain 20mph. (A typical curb-cut or driveway apron can be 7% grade.)


Below is my frequent 9.9mi path on the gmap pedometer. Not a hilly part of the country really. (Doesn't account for driveways, curb-cuts, landscaping, stopping, starting, yadda-yadda. )


Point: my real world does not have a rocket ship, it has has topography. When I see someone's route that has no grades and no variations in throttle, then maybe I'll believe that weight is a non-issue.

Richmond, BC, Canada. Average hight, 1m above sea level. Highest elevation 12m ASL, and I suspect it's the multi level mall parking lot :lol:

Lookee...

Puttering around at 20mph with an extra 30lbs will cost you some power when you encounter even a modest grade.

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Agreed, for then there's a net gravitational vector tugging on the vehicle.

According to the calculator, 30lbs cargo will need +70 more watts on a 5% grade. A 10% grade will require +132W to maintain 20mph. (A typical curb-cut or driveway apron can be 7% grade.)

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No argument here.

Point: my real world does not have a rocket ship, it has has topography. When I see someone's route that has no grades and no variations in throttle, then maybe I'll believe that weight is a non-issue.

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Again, agreed. But since the point of this thread seemed to be comparing efficiency values, hills and acceleration have to be standardized too. In practice this means "on the level, at a particular speed, no wind, no pedaling," else there's no comparing numbers derived from rides up varying grades at varying speeds. So, if we're doing the best we can reasonably do and comparing numbers observed "on the level, at a particular speed, no wind, no pedaling", weight becomes a non-issue.
Like Lowell notes above, we ride through very different terrains, and so there's no comparing efficiency numbers so derived, unless we all agree to ride on a "standardized track".
For this exercise, we can either agree that track is "on the level, at a particular speed, no wind, no pedaling", or we can all fly over to your house and ride around your area (Pay my plane ticket and I'd be happy to....)

xyster said:

For this exercise, we can either agree that track is "on the level, at a particular speed, no wind, no pedaling", or we can all fly over to your house and ride around your area (Pay my plane ticket and I'd be happy to....)

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...or maybe we can just post what are our general / usual experiences.

Plus, most of us have our little ant-trails we use to assess our setups' performance... anybody who wants to can post their path and elevations using the online pedometer:

http://www.gmap-pedometer.com

I'm not trying to be super-scientific, but more general. Y'know, a nooB might wonder what to expect from a bike. (Kinda like wondering if the EPA figures for a car are realistic for the day-to-day operation.)

For example: looking at the weight issue, we might figure out that going up typical grades (1%-7%) is gonna take more wattage than the little currie motors are going to provide... if you want to go faster than you can walk.

Again, if weight weren't an issue we'd all be using lead. Weight and aerodynamics are paramount. Most folks here are just throwing watts at the issues and not doing much with either weight or drag. Only Mathurin has done radical "weight revisioning". I have yet to see anyone's custom e-bike fairing.


8)

Testing REAL World figures on a heavy Huffy is to show that these figures can get better with a lighter more expensive bike as a testing platform.My worst case figure of 1 amp hour per mile UP HILL always works out to be a 2 to 3 miles per ah at the end of the round trip NOT conserving on the power.This video is the WORST case riding on rocks and dirt climbing a 2000 foot acent in 20 minutes.
.................................
The video didn't have the wide angle so when climbing the hill it was pointed at the ground too much. I will repost it soon.The trip included going down to the ocean then back to where I started in 11.1 miles using 6.4 amp hours on 72 volt pack.Also using one gear ratio.You may notice that it took anout 4 amp hours to go about 4 miles up a avrage 20* grade.with a 2000 ft elevation rise in 2o minutes.Now lets see a hub motor ebike do the same.

http://tinyurl.com/2v7m6g

Here is the video..
http://tinyurl.com/3ad8g2
http://tinyurl.com/yp8378
http://endless-sphere.com/forums/viewtopic.php?t=718

As xyster explained, we're all talking about performance on flat ground. That's what this thread is about. Obviously weight matters when going on slopes, but we all face different terrain so there's little value in factoring that in, for comparison purposes.

CGameProgrammer said:

As xyster explained, we're all talking about performance on flat ground. That's what this thread is about.

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Is THAT what this thread is all about? Well, shit the bed Martha... I'll just have to go back and start the whole thing over the right way.

Funny thing tho... when most people go to buy a bike, they check how much it weighs. When people talk about the X5 hubmotor or BMC Puma, they talk about how much they weigh compared to the power they produce... Funny thing about batteries... people seem to buy the batteries that give more power and weigh less...

Golly... my disk-shaped rocketship must have accidentally landed in FlatWorld, where gravity, accelleration and weight above the shoulders are nonexistant.

:lol:

TylerDurden said:

Funny thing tho... when most people go to buy a bike, they check how much it weighs.

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That's partly because they care about the effort required to go uphill, and largely because it's the only easy way they know of to judge a bike's "quality". Just lift and see how light it is. Easy! So they pay $1000 for a fork that's a bit lighter than their previous one, even though they forget about their own weight and the actual weight of the total system only decreases like 0.03%.

When people talk about the X5 hubmotor or BMC Puma, they talk about how much they weigh compared to the power they produce...

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That's because heavy motors put stress on the spokes, and heavy wheels can affect handling when turning.

Funny thing about batteries... people seem to buy the batteries that give more power and weigh less...

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No, they buy batteries that have a long lifetime, and they also happen to be lighter than Lead-Acid. Plus they need to carry their bikes to get over curbs or indoors for recharging, or in my case I sometimes remove the battery pack and take it inside to recharge. Though I'm still using SLA. And, of course, it does still affect hill-climbing.

Golly... my disk-shaped rocketship must have accidentally landed in FlatWorld, where [...] weight above the shoulders are nonexistant.

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Well you're the one that that applies to, by your own admission.

bike that's too heavy, >40kgs, lead bricks on it etc=

A real PITA to haul up a flight of stairs. Has to slow to 4km/h to struggle up anything resembling a curb. Has to swerve around potholes, sometimes into traffic. Has to be rolled back and forward to get parked in a bike rack. It's a very slow bike to hump around, sucks you dry in no time over typical urban stop & go, also amazingly slow uphill. So, you better have a motor that grossly dwarfs what you can put out cause it'll be nearly useless without it. It's really nowhere close to being as nimble as a normal bike, so you need more road width to travel the same speed. Can't be installed on a bike work stand or a car rack, because it's too heavy. Forget silly bike tricks, too. Trackstand? Keep dreaming! Wanna haul a bag of feed home? I'd think twice - it's already got a pretty heavy load. It's lost pretty much everything that makes a bike nice, instead it feels kinda like a moped or scooter.


light-ish bike, <18Kg, 3kg Li in a backpack =

Jog up stairs with it if you fancy, no need to slow down to hop on a curb, it can also hop over potholes rather then swerving. It's easy to move it around to make it fit in a bike rack. The bike is quite nimble and can keep more speed through narrow places and tricky footing. Feels like you're hardly heavier, riding a somewhat heavier then normal bike (still lighter then some of the ones I've seen here in stick form), at this weight it feels and behaves like a bike. It's a whole lot nicer then the massive bike on energy usage in urban stop & go, and much better uphill. Riding at a good clip (assuming actual bicycle speeds are concerned), you'd get 70-ish kms from 350wh, simply because it wastes so much less power and is so much more usable as a bicycle. You can do wheelies, doughnuts with it, no need for multi-kilowatts. Trackstand at a light, why not? Haul that 40kg sack of feed? If you want to...



Of course, if what you want is to ride a motorcycle while avoiding your responsibilities by calling it bicycle, this has nothing much to do with actual bicycles...

But that's all irrelevant to this thread, which was about Wh/mile. People were dividing it by weight, but weight does not have a linear effect on these bikes so that makes no sense. To exaggerate a little, it's like dividing people's test scores by their weight to calculate points per pound.

To exaggerate a little, it's like dividing people's test scores by their weight to calculate points per pound.

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Man, CGameProgrammer, pound-for-pound you have a most impressive IQ!

Heh, you do realize he missed the point of the OP, WattHrs/mi/lb. @ speed?