The Great "Gearing vs Hub Motor" Debate

[Stevil_Knevil]

I'll exhale a sigh of relief. I've seen an awful lot of worthwhile words spilled here.. must admit that I'm leaning towards hub motors.


=^) -S

 

[knightmb]

Hill Climbing Ability (Summary)

Okay... so what?

In first gear it takes about 3 minutes to reach the top of the hill and it uses a total of 110 Watt Hours to get there with a "waste" of 40 Watt hours.

In fifth gear it takes about 8 minutes to reach the top of the hill and it uses a total of 197 Watt Hours to get there with a "waste" of 131 Watt hours.

In terms of time you save 5 minutes. (it takes over twice as long in 5th gear)

In terms of energy you save 87 Watt Hours. (the last 4 Watt hours are lost due to wind resistance at the higher speed for 1st gear)

While a hub motor with massive "hemi" styled energy could literally "lift" itself out of the low rpm nightmare, the typical small motor cannot do this and finds itself wallowing in pain. This is exactly what I've felt on my bike when I run the "tall gears" and try to climb one of the steeper hills in my neighborhood. If I switch back down to the "low gears" then not only do I climb the hill with ease, but also much faster. So low gears for hills are very beneficial. (it's not just acceleration that gearing helps)

What's "funny" here is that the bike in first gear could probably ride to the top of the hill and turn around and ride back down again until he meets up with the bike in fifth gear, then turn around and race back up again and still win and still use the same or less energy. The "tortiose" loses in this contest... the low geared bike wins easily...

If I can get my way with the national park service, perhaps in the near future there will be a way to match it up against others in real life. I've almost secured an area along Natchez Trace to hold an e-bike rally. Natchez Trace is a great ride with smooth roads, no stop lights or intersections and has a great variety of both large hills and level ride areas. Everyone here has great ideas and real world experience. I would love to see all the talent demonstrated and documented in the same place. That and it would be cool to meet everyone here in person

I'm not trying to throw this topic off, so please continue. Just wanted to add this since I've been following this topic and things are going very well with the national park service and the e-bike rally thing that I've been working on since last year. :wink:

 

[Lowell]

Could you graph that with time as the x axis and speed as a dependent variable it would be easier to read.

This is time on the y-axis and the x-axis is related to the gear ratio so for a low gearing each increment translates to a smaller speed jump and the higher gearing translates to a big jump in speed. My spreadsheet is based on rpm so since we are talking about the DIFFERENCE that gearing makes to rpm you have to account for it somehow. (maybe I'll find some better way to express it later)

Anyway... this is the time it takes for the bike to accelerate from 0-10 mph in each of the first five gear options. So the idea is that you START in one of the gears and use it as a "hub motor" like fixed gear. There's no "shifting" in this chart... it's just "fixed gear" performance at various gear ratios. This shows the advantages of proper gearing over an excessively high gear. (like one that would get you to 50 mph) This "should" be intuitively obvious because just like with a car you place it into FIRST get to get going and then shift to FIFTH gear on the freeway to get top speed. (somehow people with electric bikes think they can reinvent the laws of physics! )

The numbers are:

First Gear - 1.89 seconds @ 2621 Watts.

Fifth Gear - 2.85 seconds @ 3679 Watts.

Time saved in first gear - 0.959 seconds (85% delay avoided)

Energy saved in first gear - 1058 Watts. (40% waste avoided)

And you do this at EVERY stop... so the DIFFERENCE adds up over time...

Didn't you say it takes about a second to shift gears? Sounds like a wash to me.

When I drag race, there are usually 3 shifts, and it's amazing how much time is spent in between gears. I think on average it's around 8% of the run in a 10 second car, or so says my on board datalogger.

 

[Toorbough ULL-Zeveigh]

This is meaningless. You have to calculate the energy lost in watt-hours (not watt/hours and not watts) to compare it to the energy in the battery as measured in watt-hours.

A "watt hour" is one watt for one hour worth of energy. So if you take the battery in total it can provide it's watt hour rating times sixty minutes, times sixty seconds since watts are based upon seconds. (one amp, one volt, one second)

The percentage is what matters... there's ONLY a 1% loss over an entire hour of standard riding and that's not that bad... so relax... the losses aren't terrible...

60,000 Watts equals 16.67 Watt hours of energy... (but I see your point... is that 60,000 Watts over a second or over some other interval... I'll have to check my spreadsheet)

I'm back... the 1000 Watt loss occurs over a period of the "lost" one second of accelleration. So the numbers are good... the 60,000 Watts can be viewed as being associated with "roughly" a second. All is fine. (close enough)

So it's 60,000 Watt/Seconds... verses 1440 Watt/Hours...

If I may be frank?
On second thought, I'll be earnest.

60 kilowatts does not equal 16.67 Watt-hours as xyster has said, this is meaningless.
It's like saying that 60 miles per hour equals 16.67 miles.

I think I know what you're driving at (sometimes), but throughout this thread, in your enthusiam you have used watts & watt-hours interchangeably & referred to watts as a measure of energy (which it's not).

So if you mean Watts refer to it as Power & not energy, & if you really mean Energy, then the unit of measure is Watt-hours or perhaps Joules (Watt-seconds). If you keep those straight it will make things easier to follow. I've been hesitant to offer much because I'm not always clear on your meaning.

 

[Matt Gruber]

in 1972 i was so persuaded by a similar argument, i replaced the 3.23 open rear in my '70 318 duster with a 4.56 posi.
this really impressed my friends!
so we went down the 1/4 mile drag strip and,
guess how much quicker the et was?

My Duster felt quick and was fun, but at the track it ran the same or worse times.
Moral: when u see a chart/graph, back it up in real life.

To safes credit he has adjusted his claims based on our input.

Earlier it was GEARS WILL HELP EVERYBODY,

NOW it is
GEARS WILL HELP AT 50+ AND ON SUPER STEEP HILLS. (this is when i use a car)

If u have a normal overpass and ride at bike speeds, gears are optional, as proven by many guys here, in real life, not charts.

 

[TylerDurden]

Safe- we all love you.

The Fechmaster's crop from his mountain hide-away must have just come in today...

8)

 

[xyster]

Love it !

Safe named this thread "The Great 'Gearing vs Hub Motor' Debate". So I assume he wanted a great debate. Other great debates have had at least two sides very far apart, represented by strong personalities. I'm just trying to hold up my end of history.

 

[safe]

Great Cartoon

 

[TylerDurden]

Harris' work is great.

(I deny any involvement in its defacing...)


:wink:

 

[joystix2]

Wow just finally got on this thread. I read the last 5 pages. In my opinion to each his own. If you live in a very hilly area, have only enough room for smaller AH batts on the bike, or are building for liteness then gearing is your best option. If you don't mind heavier, live in an area with a lot of flat straights with huge bike lanes and the largest hill you encounter is an overpass like me then go with the Cadillac, like me and get a Phoenix. Also theirs the Puma motor which looks promising with power and weight. Internal GEARED HUB!!!! best of both worlds...

Ric

 

[Lowell]

Wow just finally got on this thread. I read the last 5 pages. In my opinion to each his own. If you live in a very hilly area, have only enough room for smaller AH batts on the bike, or are building for liteness then gearing is your best option. If you don't mind heavier, live in an area with a lot of flat straights with huge bike lanes and the largest hill you encounter is an overpass like me then go with the Cadillac, like me and get a Phoenix. Also theirs the Puma motor which looks promising with power and weight. Internal GEARED HUB!!!! best of both worlds...

Ric

Most of Richmond, BC, is at or below sea level, and we have excellent bike lanes. Blocks are about 800m long on the main roads and almost all the roads are in a big grid. I'm pretty sure if I lived in North Vancouver I'd want gears for the steep grades. Horses for courses...

 

[safe]

I live in a hilly area for the midwest here in Missouri. Around here you get creeks that carve themselves into the sedimentary layers of the soil so you get cases of mostly flat that are interrupted with transitions of about 50 to 100 feet in height up and down. Now "real" hills are like in Colorado (where I intend to move someday) so I'm also targeting the bike for "alpine" conditions so that I'm ready for that future.

"Cadillac"... that's a good description of the riding style of the hub motor. It's big, it's powerful, it prefers cruising over starts and stops and (due to the weight) it prefers to be kept in a straight and smooth road.

My style is "Sport Rider" which focuses on top speed, handling, acceleration, light (and balanced) weight, aerodynamics, and that hard to define sense of "sport essense". (lighter weight batteries will help a lot)

I agree.... to each his own...

 

[Lowell]

Post up some time to speed numbers for your bike, I'm interested to see them. My video cam is charging right now, and I just have to figure out how to mount it where it can view the DrainBrain and ammeter. The plan is to do a before and after zero to top speed run, and maybe some time to distance runs.

What do you think would be a good distance that everyone could agree on? 1/8th mile?

 

[xyster]

What do you think would be a good distance that everyone could agree on? 1/8th mile?

Works for me. Another way to do it is time to speed, like 35mph or so. Time-to-speed trials might be a little easier to conduct in a video-verifiable manner.
Since going up eight more volts, I've been looking forward to recording new acceleration and hill climbing vids. And I look forward to seeing video of the geared bikes in action!

 

[Lowell]

What do you think would be a good distance that everyone could agree on? 1/8th mile?

Works for me. Another way to do it is time to speed, like 35mph or so. Time-to-speed trials might be a little easier to conduct in a video-verifiable manner.
Since going up eight more volts, I've been looking forward to recording new acceleration and hill climbing vids. And I look forward to seeing video of the geared bikes in action!

0-60km/h sounds like a good benchmark.

 

[xyster]

0-60km/h sounds like a good benchmark.

OK. 60kph is just about the top speed I've gone, and feel safe going on my bike.

 

[safe]

Realistically we need to have motor classes like we've talked about before like they use in NEDRA. It's just as ridiculous for me to compare my 750 Watt bike to a 500 Watt bike as it is to compare a 750 Watt bike to a 3000 Watt bike.

I'd say that we "should" establish the motor size... because we know from all the physics (all the charts that I post) that "hemi" power can overcome all efficiency limitations and literally "dwarf" the small motored geared bikes.

The "ideal" test pits two bikes with the same power head to head and then you see if gears are an advantage. (this would best be at either 1 hp or 2 hp which are the two "standard" legal sizes for electric bike motors in America)

For example... in motorcross racing sometimes guys will start the race in second or third gear and just slip the clutch rather than have to shift , since shifting takes time. The hub motor does not need to pause for a gear change so that's an advantage.

A 3000 Watt "fire breathing monster" will beat a 500 Watt cyclone motor no matter how good the guy is with the gears...

Otherwise it's like trying to compare a 5.0 Mustang GTO verses a Honda Civic Si... the 5.0 liters will always have more low end torque, but it will also require more gas. The "big motored" hub motor bike also requires more "fuel" (energy) than the small motored geared bike. The Honda car appeals to the "sport driver" while the Mustang appeals to the "macho driver". Indy Car verses NASCAR. You get the idea...

 

[knightmb]

A 3000 Watt "fire breathing monster" will beat a 500 Watt cyclone motor no matter how good the guy is with the gears...

Love that quote :lol: :lol:

I think the debate will always continue because each has it's advantages.

Gears give you flexibility and more control. It also allows a lower power system to compete with a higher power hub motor system.

The hub motor gives you ease of use and convenience. Sure, it has it's preferred "cruising" speed so while it may not rocket up steep hills or long level areas, it's easier for someone who isn't very technical to get into e-bikes without having to be a master at the gear shifter. At the same time, it allows you to add more power to your e-bike system easily provided the frame can take it.

I love gears, all my vehicles are manual transmission. But there's something sexy about the "all in one" solution that the hub motor presents even if it's not the most efficient means of getting power to the roadway. I think both can co-exist in this e-bike world, just like auto vs. manual transmission for cars.

 

[xyster]

It's just as ridiculous for me to compare my 750 Watt bike to a 500 Watt bike as it is to compare a 750 Watt bike to a 3000 Watt bike.

You've got that new, 100 amp controller. Why not use that at 36 or 48 volts for your video? Afraid you'll lose wasting all that time shifting?

Shifting for bicycles isn't nearly as continuous or precise a process as it is for cars.

 

[TylerDurden]

There's good rationale for recording/reporting both metrics:

Time to Speed
Time to Distance

Everybody plays... some bike go up to 20kph, 30kph, 40+ , so there can be a basis for comparison at numerous levels.

Every bike can go 1/8 mile, so that would be common to all.

Perhaps in the Member Profiles we can have bike stats so the sig-files dont have to rattle on with specs like in other boards. That way, if "Sandy E-biker" posts that they reached a new peak in performance, readers can click Sandy's profile to see Sandy's bike(s) and previous benchmarks.


8)

 

[xyster]

Everybody plays... some bike go up to 20kph, 30kph, 40+ , so there can be a basis for comparison at numerous levels.

Every bike can go 1/8 mile, so that would be common to all.

Excellent point, TD. And the speed graduations can be handled in one run, counting off the speed audibly, then using the video to plot the time points. That's how I made the little acceleration chart on my stats graphic:
http://endless-sphere.com/forums/files/e_bike_projectxls_542.gif

I still need to update that chart for 80 volts anyway.

 

[safe]

Hub Motor verses 8-Speed

Okay here are the conditions:

Both bikes are using the same motor which is a Unite 1200 Watt 48 Volt with a 60 Amp controller. The 8-Speed uses all eight gears while the Hub Motor is using just Fifth Gear alone. (this is actually cheating a little for the Hub Motors benefit because it never actually equals the geared bike in top speed)

The chart has time on the x-axis and either mph or acceleration on the y-axis. The acceleration is in weird units so just use it to see the shifting points of the 8-Speed (those little wiggles) and compare it to the Hub Motors one and only peak.

On paper there is little to debate... given equal power you will always accelerate faster with gears... however the time it takes to shift might help the Hub Motor catch up a little...

And don't forget that I've got a very low frontal area (about half a regular bicycle) so my more aerodynamic bike makes these numbers very realistic. (all my previous numbers have matched my own results within a few mph) For a regular bike you would hit the wind resistance "wall" much earlier. So keep that in mind... without the aerodynamics all these gears become less important... and your results would be much worse...

 

[xyster]

On paper there is little to debate...

Then let's take the debate to the pavement already!

You didn't respond to my previous suggestion-question that to level the power playing field, you should use your 100 amp controller at 36v while I use my 35 amp controller at 80 volts.

That gives you about 800 more watts than me, in addition to gears and better aerodynamics. Come'on man, what more of a handicap do you need to put your motor where your graph paper is?

 

[Lowell]

I say run what you got, street racing style. If it rolls on the road, it's fair game. (as long as it's an electric bike of course. no JATO rockets :lol: )

 

[xyster]

I say run what you got, street racing style.

Sounds good to me! But Safe's trying to make a NEDRA event out of a little friendly competition to promote the publication of real-world empirical data after a good debate replete with reference to theoretical stats & graphs.

He's got the 100 amp controller. I think Safe just doesn't want to race because he's afraid he won't be able to shift fast enough during short acceleration tests, his all-powerful gears becoming an embarrassing hindrance.