GNG, 1000W 48V BB-drive, $400

[Samd]

The argument comes up all the time because people confuse the single point efficiency of the gearbox to the linear approximation of a non-linear torque speed curve of an entire drive system.
Just because a gearbox is more complex/lossy doesnt necessarily make the overall system less efficient. Sometimes yes, often no.

 

[bee]

I'm surprised this argument is even happening, but looking back to my 2-stroke tuning days I realize that it also took me a while to wrap my head around gearing efficiency too, and I setup a few transmissions that broke records on flat ground but couldn't climb some of the hills around here

Really?

Are you honestly likening the power curves of two-cycle stinkers to those of permanent magnet electric motors? Or are you just taking the piss?

Yes because every motor has a power curve, put your hub motor on a dyno and you'll see.

 

[full-throttle]

Nope.

Yep.

Multi-speed up to 98.6% see page 5 of full article (as I mentioned 200W)
Planetary 97% typical

A typical efficiency loss in a planetary gearbox arrangement is only 3% per stage

The worst case Rohloff is a bad example since it's multi-stage
Neugart claim 96~98%

So long sucker

 

[Samd]

What's really important is the torque curve...

 

[skyungjae]

What's really important is the torque curve...

Aye, I love the usable torque. It's nice being able to climb pretty much anything with such little effort on the motor.

 

[flyinmonkie]

The efficiency argument is really only for those that are trying to squeeze the most out of a battery cycle. Hub motors have a place where they are better than a mid drive set up and vise versa.

Most people that lean towards a mid drive either live in hilly areas or want to off road, usually in a hilly area. With the small size of the motors being used, gears make what they want to do possible. If the same motor were used without running it through some gears, it would be like driving an suv with a 1.5 liter engine in second gear every where. It wouldn't last very long. It is also nice to have the extra torque or speed when you want it for what ever the reason. Cars have way more horsepower than is needed to propel them along at highway speeds so they can accelerate and get up hills. Why shouldn't an ebike?

So whether it is more efficient or not, the only way to make a small motor with less power last in those conditions is to run it through gears.

Of course there are those that just like the idea of a mid drive and that is what they want. Just like there are those that like hub motors and that is what they want, There is no problem with either of those.

Bee..

Nice work on the large pulley. Looking forward to seeing how it goes.

Clay

 

[full-throttle]

That sums it up pretty nicely. Lets get back on topic, shall we. Don't want this thread to turn into /viewtopic.php?f=47930

Yes, nice work there bee! Why did you choose 119t and not 120t? Clearance issues?

 

[Chalo]

I'm surprised this argument is even happening, but looking back to my 2-stroke tuning days I realize that it also took me a while to wrap my head around gearing efficiency too, and I setup a few transmissions that broke records on flat ground but couldn't climb some of the hills around here

Really?

Are you honestly likening the power curves of two-cycle stinkers to those of permanent magnet electric motors? Or are you just taking the piss?

Yes because every motor has a power curve, put your hub motor on a dyno and you'll see.

It's true that every motor makes zero watts of power at zero RPM. But smoggers have to get wound up before they'll deliver useful torque, and e-motors make most (or all) of their torque right from a dead stop. That means you don't have to dilly-dally around in the inefficient part of the motor's speed range for long-- it will home right in on whatever equilibrium speed it's capable of reaching. And once you get there, if your ratio is right for the task, your gearbox is only a power-wasting drag on the system.

Unless, of course, it is carefully harmonized with the human machine, in which case you trade off some maximum efficiency to get bionics in return. Stokemonkey does it; GNG doesn't.

 

[speedmd]

Anyone suggesting that a earth based motor drive system without a transmission is some how more efficient than a motor drive system with variable reduction ratios is a fool. Airplane/ boat, you can make the argument. On earth, there is just too much variation in loads to pull if off efficiently without a tranny if you wish to have a wide speed /load operating range. Bicycles can get away with the one speed because they are light and they don't go fast. The more challenging the terrain and the wider the operating speeds, the more trouble the DD motor has pulling on hills at low rpm and on starts. Solid tires are more efficient on certain surfaces, but we are not having that argument because you can clearly feel how bad the solid tires are on most terrain.

 

[LightningRods]

Here's a better angle

That looks better. We are getting some appreciation for how GNG got painted into a corner in terms of using a too small drive pulley. Every tooth added to the drive pulley requires around 6 on the driven. That's still a damn fine looking bike!

With how close the gears are to each other, I'm tempted by a herringbone gear setup

That's a really good point, Bee. I don't know how much of an appetite you have for messing with this, but there are lots of options beyond HTD5. HTD8 or 8mm pitch HTD has much better torque handling capability. Above that is the GT2 which completely outperforms the HTD belt and link chain as well. I felt constrained to HTD5 because I was just trying to solve for the drive pulley and tie into existing inexpensive driven pulleys. Since you are making everything from scratch now you really should step up to a more performance oriented belt/pulley profile.

Gears are an interesting idea. The uncompromising hard mesh of their teeth would push your process to it's limits. They'd probably be noisy little suckers, even made out of ABS or resin. It would be nice to have a sound deadening enclosure. But still, a compact, multi stage reduction that doesn't cost a fortune.... if you could do it, it would shake things up for sure.

 

[skyungjae]

How about let's all agree to disagree. Arguing theory over the internet is less than pointless. Let's get back on topic regarding the GNG. :lol:

 

[speedmd]

How about let's all agree to disagree

Or, we can "measure and analyse". Would be simple if everyone's ride behavior / goals were the same.

 

[skyungjae]

How about let's all agree to disagree

Or, we can "measure and analyse". Would be simple if everyone's ride behavior / goals were the same.

Very true... even the much debated Hi Power Cycles acknowledges the benefits of a mid drive system.

http://www.youtube.com/watch?v=C05t5iDeUXc&list=UUhXHINpB6CRUVn6vxesmiLQ

The mid drive is awesome for steep offroad climbs. The hub motor loses in this aspect. If you are a DH biker and want to climb up steep inclines, go for a mid drive set up.

A company that specializes in hub motors even says, in the video, that their high power hub motor set ups can't compare to a 500w mid drive climbing hills off road.

Regardless of purpose of use, the GNG kit exists. People like it. I like it. Hub motors are great too, but both have very distinct pros and cons.

The "I don't like cats, because I like dogs" approach is not going to get us anywhere.

 

[Miles]

The "I don't like cats, because I like dogs" approach is not going to get us anywhere.

I don't think there's any doubt that you'd get up hills better with a dog... Better acceleration, too. A cat might be more efficient for cruising, though.....

 

[Thud]

CATS ftw on an icy road.

 

[Miles]

The ultimate would be a 2-speed set-up with an elephant and a cheetah, of course

 

[skyungjae]

The "I don't like cats, because I like dogs" approach is not going to get us anywhere.

I don't think there's any doubt that you'd get up hills better with a dog... Better acceleration, too. A cat might be more efficient for cruising, though.....

I'm not sure about that. The way my neighbor's cat goes up a wall when I chase it makes me think cats are more like mid drives. Don't think any dog can match the agility and burst speed of a cat. Cheetahs can burst in a sprint fast, but can't go the distance like a dog sled team.

(-_-!)

Why are we talking about this. :lol:

Let's get back to potential improvements on this GNG mid drive. :wink:

 

[speedmd]

I don't think there's any doubt that you'd get up hills better with a dog...

I would hold some store in this if dogman was saying it!

 

[speedmd]

I turned up a sample eccentric cup for the primary shaft bearings. Looks like I should be able to get about 7- 8 mm max offset with the stock bearing, shaft, bracket hole sizes.

 

[speedmd]

 

[Rassy]

Chalo wrote:

Unless, of course, it is carefully harmonized with the human machine, in which case you trade off some maximum efficiency to get bionics in return. Stokemonkey does it; GNG doesn't.

I've seen similar sentiments about the GNG since its introduction. I have my GNG on a bike with a 7 speed deraileur. If I want to cruise at a certain speed with motor assist and a comfortable cadence I either shift up or shift down as needed and match the motor speed to my desired cadence. In my opinion that's what the throttle is for. The only people that complain about the match are the one's that run at WOT all the time. Most of us don't drive our cars at WOT during take off or when cruising, so why do we think that's how bikes should be ridden?

And while I'm on my rant, the fact that the Stokemonkey doesn't use a freewheel crank does not make it more harmonized with the human machine than any other mid-drive that dose have a freewheel crank. On my trike with a mid-drive hub motor and auto shift NuVinci transmission the NuVinci is programmed to always keep my cadence between 60 and 70 RPM. The freewheel crank is seldom called into play since I like to pedal all the time. So for the vast majotity of the time it is being operated exactly like the Stokemonkey, and therefore is just as much in harmony.

 

[LightningRods]

And speaking of Stokemonkey, that paragon of human/e-bike harmony, here is a quote from their web site:

"As you shift gears to maintain normal pedal speeds, you keep the motor operating between its most powerful and efficient speeds, for several times the torque, higher top speeds, and much better range than typical electric bike products lacking variable motor gearing."

 

[Chalo]

Chalo wrote:

Unless, of course, it is carefully harmonized with the human machine, in which case you trade off some maximum efficiency to get bionics in return. Stokemonkey does it; GNG doesn't.

And while I'm on my rant, the fact that the Stokemonkey doesn't use a freewheel crank does not make it more harmonized with the human machine than any other mid-drive that dose have a freewheel crank. On my trike with a mid-drive hub motor and auto shift NuVinci transmission the NuVinci is programmed to always keep my cadence between 60 and 70 RPM. The freewheel crank is seldom called into play since I like to pedal all the time. So for the vast majotity of the time it is being operated exactly like the Stokemonkey, and therefore is just as much in harmony.

We are talking about the GNG kit, right? Tell it to these folks:

If only we could get the bb rpm down to 120rpm and make it bombproof it would be perfect!

Jack shaft NO-LOAD output @ 48V = 570-RPM, so with 12/44 second stage no-load cadence will be 155-RPM

Multi-stage reductions can give the needed cadence. It is not easy or cheap, though. And the reduction takes up more space.

I have my Norco a line with the downhill cranks still, no freewheel, and a little 500 watt brushed scooter motor, though a Curie reduction about 47 to 1, it simply does not work, a freewheel is needed! Unless there was some way to control the motor to perfectly match the rpm of the cranks it does not work.

Sounds really harmonious with pedaling! Not.

 

[full-throttle]

The ultimate would be a 2-speed set-up with an elephant and a cheetah, of course

Cats, dogs.. monkeys.. and now elephants and cheetahs FFS
All we have here in Aus is frigging hamsters

 

[rp3]

I saw chalo on a recent outing.

..