Conclusive proof gearboxes are awesome.

[Miles]

Ref: https://endless-sphere.com/forums/viewtopic.php?p=1161421#p1161421

I guess all your motors are at peak efficiency at all RPMs.

All the motors in the real world have an efficiency curve through the RPM band.


View attachment 1
It's simple math to run the motor in the efficient area of the graph to not waste power. The drivetrain losses are minor. Losses from running
in poor performance RPM areas is many times greater.

Man, I don't know about you smart guys.

I think this gives a better picture of the situation..................

 

[speedmd]

I was just trying to pin things down a bit

In my opinion and as I said, there's absolutely no point in having variable gearing for the first case, which I presume corresponds reasonably well with motomoto's expectations.

I think toolman's rather extreme case would probably benefit from a wide ratio 2 speed with one of them being a direct drive.

Agree, if you were wanting something that was excellent at near zero speed trials riding and also at wide open desert racing, a simple sliding motor sprocket change would be trick. All you would need to work out is a good chain tensioner setup that could adapt to the chain length issues.

 

[toolman2]

I was just trying to pin things down a bit

In my opinion and as I said, there's absolutely no point in having variable gearing for the first case, which I presume corresponds reasonably well with motomoto's expectations.

I think toolman's rather extreme case would probably benefit from a wide ratio 2 speed with one of them being a direct drive.

Ok, that makes sense, thanks Miles.
Just to me clear, said extreme case of climbing a 71% grade (kinda obviously) also corresponds with maximum acceleration of a 100kg total for an upright position on dirt, you would be just as likely to mono or wheelspin on a normal-ish 1250mm wheelbase dh bike. so its the maximum torque you could (mostly) ever use on dirt, and around double that (torque) may be usable on a way lower/forward positioned bike for max acceleration on bitumen, and that's likely around where Lukes deathbike lands.

Not that i expect either of those scenarios are what everyone appreciates on a nice relaxing bicycle ride, you really have to hang on tight Miles, and lean forward.

 

[alan]

Trannies can be over 95% efficient. Motors can be more efficient, but are easily pushed outside that efficiency band down into the 75-85% range. A tranny can help keep a motor in a higher efficiency operating band, and that could more than make up for the tranny losses. Note that anything other than direct drive, like with a hub motor is going to have gearing losses likely to leave the drivetrain efficiency after the motor around 95% efficiency such that an well designed multi-speed tranny is nearly as efficient as a non-tranny 1-speed drivetrain. Note also that a bicycle chain drive through a multi-gear derailleur is better than 95% and is very hard to be for efficiency.

Also note that efficiency described above is in terms of power losses from the motor to the wheels, but added weight is another kind of inefficiency not included. The added weight of a tranny may be hard to overcome with increased power efficiency.

 

[Arlo1]

Trannies can be over 95% efficient. Motors can be more efficient, but are easily pushed outside that efficiency band down into the 75-85% range. A tranny can help keep a motor in a higher efficiency operating band, and that could more than make up for the tranny losses. Note that anything other than direct drive, like with a hub motor is going to have gearing losses likely to leave the drivetrain efficiency after the motor around 95% efficiency such that an well designed multi-speed tranny is nearly as efficient as a non-tranny 1-speed drivetrain. Note also that a bicycle chain drive through a multi-gear derailleur is better than 95% and is very hard to be for efficiency.

Also note that efficiency described above is in terms of power losses from the motor to the wheels, but added weight is another kind of inefficiency not included. The added weight of a tranny may be hard to overcome with increased power efficiency.

Wrong

A transmission will only reduce the efficiency of a motor

When you design the whole system from a clean slate it will ALWAYS be more efficient without a tranny ALWAYS!

 

[DanGT86]

I have always heard that each stage of reduction subtracts efficiency. Why exactly is that? If a gearbox or jackshaft was setup to do say 10:1 in 2 stages vs a single stage with 10tooth motor 100toot rear, would the 2 stage be that much worse? Is it the addition of another shaft and bearings that kills the efficiency? I was under the impression that reductions with large size differentials between the driving and driven sprocket/gear are inefficient. So wouldn't the 2 stage have some advantage being that the driving vs driven sprockets would be closer to the same size at each stage?

Seems like as long as you have the same amount of chain on the same qty of teeth then the efficiency loss would be close to the same. Not trying to argue a point I'm just curious about some of these generalizations I have heard thrown around.

 

[Arlo1]

I have always heard that each stage of reduction subtracts efficiency. Why exactly is that? If a gearbox or jackshaft was setup to do say 10:1 in 2 stages vs a single stage with 10tooth motor 100toot rear, would the 2 stage be that much worse? Is it the addition of another shaft and bearings that kills the efficiency? I was under the impression that reductions with large size differentials between the driving and driven sprocket/gear are inefficient. So wouldn't the 2 stage have some advantage being that the driving vs driven sprockets would be closer to the same size at each stage?

Seems like as long as you have the same amount of chain on the same qty of teeth then the efficiency loss would be close to the same. Not trying to argue a point I'm just curious about some of these generalizations I have heard thrown around.

Its this simple. The gears oil and bearings and other moving parts all have friction and drag causing losses. A properly designed motor that is slightly larger in size does not have any increase in drag.

 

[Chalo]

When you design the whole system from a clean slate it will ALWAYS be more efficient without a tranny ALWAYS!

The problem with that is you need a whole different motor and system for every application. It's not practical. In the real world, the compromises from "best fit" approximations are on the same order of magnitude as the compromises from transmission losses. Often they're worse.

I have witnessed for myself how a mid drive system employing gear reduction makes a better bicycle than a single ratio hub motor. That's a system that has constraints based on integration with human power, modest power output, and emphasis on low weight, so the variables are very complex. But ultimately, the geared system is better in the bicycle role.

For a pure EV (which, let's face it, is what an e-bike becomes if you don't pedal), you're probably right that a single ratio motor drive is better. But it must be a very good match to the speed, weight, terrain, and acceleration requirements of the specific application before you can say with certainty that it is better. Such a good match is easier to hypothesize about than it is to buy and install.

 

[nutnspecial]

It seems LFP, JohnCR, and Arlo are simply arguing

A transmission will only reduce the efficiency of a motor

But I don't believe anyone here has/is denying that lol. Excuse my frankness, but is this a joke?

Obviously more overhead in power transfer to locomotion (variable gearing via 'transmission') reduces energy efficiency, though in my book that doesn't and can't mean desirability/benefit of variable gearing can ever be completely cut out . . . until perhaps said 'power efficiency' has reached 100% (unity).

 

[Hillhater]

A lot of "theoryising". happening here !
What would help is a few more real world examples ( solid metal, not spreadsheets !)
I am not aware of any practical EV's with NO transmissions ..(IE .direct drive motor in the wheel) other than our Ebike examples (any cars or trucks ?)
But we all know the limitations of those, compared to a mid drive with the gear train available.
DD hubs are heavy, limited speed range, limited climbing ability, and generally need high power set up to work well
Mid drives are much lighter , wider working speed range , and better climbing/low speed performance.
Ther are many other pro's and con's for each, such as noise levels, size, cost , etc ...but that was not the focus of the discussion.

 

[Arlo1]

What we are pointing out is the more efficient and more reliable solution is to run direct drive. Or just 1 stage of reduction if direct drive is not an option. There is cars being worked on with both hub motors and and direct drive through a CV shaft with no reduction and it is the best end solution.

We are not theroizing we use real data from real transmission losses in the real world. Just take a multi gear transmission and turn it over by hand. Then do a proper load test and let me know the losses you measure.
I just spent 4 hours on the dyno with a ICE runnign a very inefficient transmission system and it was a total joke. 400cc atv motor with 13.1 HP at the wheel. My same dyno measures my diy zero at 45hp it uses the FX powertrain. And my dual controller zero motocross bike measures 87hp at the wheel. I have spend all my life finding ways to get more power to the ground.

 

[major]

To my knowledge, all the BEV cars currently offered by OEMs are direct drive. All use a single ratio reducer. The terminology for electric vehicles larger than bicycles is different and has been around for many decades. I have been associated with the engineering and technology of EVs for a long while. It has taken some getting used to on this forum for me regarding different definitions.

The direct drive non reduced motor is seldom if ever used in electric cars whether a wheel motor or otherwise located. Many have tried; all have failed. Wheel motors appear to do well for bikes and scooters, and in some industrial trucks. I don't expect to see any in cars, but know full well people will keep trying.

 

[Arlo1]

The only reason not to spin the electric motors at the same RPM as the wheel is due to the size required of the motor not weight. Just size. So most OEM car companies are designing the car with space limitations. Hub motors do exist that work but for performance cars its best to use a CV shaft and not have all that unsprung weight.

 

[Hillhater]

Pretty sure we can all accept that any gear train is going to have losses, but that is not the real point.
Fact is, it is not yet practical (in most cases) to propell a EV without some form of transmission/ reduction box...why ?
Arlo, where are the EV's that use DD motors even driving via cv shafts ?
E bike DD hub motors are a good example of how even a well developed system of DD wheel drive, still has limitations for practical use everyday.

 

[liveforphysics]

A lot of "theoryising". happening here !
What would help is a few more real world examples ( solid metal, not spreadsheets !)
I am not aware of any practical EV's with NO transmissions ..

Right, no practical examples...

Unless you count the highest performance standing mile EV at 204mph

Or the pikes peak EV record holder EV

Or the most efficient electric vehicle drivetrain in the world ~98%

Or the most prevalent means of EV transportation

So, if you choose not to look at the highest performing examples, most efficient examples, or the most commonly used examples, you're right in saying that direct drive only works in theory with no practical applications.

 

[speedmd]

You could easily have a 30 or more inch diameter motor driving a smaller diameter wheel via a cv jointed half shaft if torque was a issue. No sense limiting the motor package to rim or wheel sizes if torque is at issue. The only way I could see a gearbox being an advantage is if artificial limits are added into the vehicle specs limiting motor size or something like phase current.

 

[Arlo1]

Thanks Luke. I didn't know where to find all the pictures. There is other stuff going on behind closed doors and that's about all I can say about it

 

[nutnspecial]

Lfp, Arlo, John: I believe the thoughtful and applicable cases above evidence incontrovertibly the benefits in E over ICE, and are specific cases/uses where additional gearing would certainly degrade performance within intended/designed operational criteria/circumstance. . . . .

But is there evidence that variable geared power transmission cannot still have benefits such as is so obvious in less efficient ICE? (and also apparently to several here, including their examples)

Irrelevant to my example of tesla vs geared ice mclaren of similar HP simply due to unequal weights and aerodynamics imo. . . I do not see evidence a 2nd higher gear would not make huge difference for tesla if goals were shifted to (example) compete @50-150mph while retaining as much of launch as possible. ?

Remaining also (imo at least) is the broader theorization/rationality that any power for locomotion under 100% efficient will no doubt still find conditional benefit from variable gearing in power transmission -because conditional benefits just lessen while approaching 100% efficiency as evidenced by general application of gearing in ICE vs E.

Unless someone cares to address this, I find non-argument here and no need of any further discussion/explanation by me. Thanks for considering it though.

 

[Arlo1]

If tesla wanted to accelerate from 50-150 mph they would need to design the system with only 1 speed and no shifting to make it optimal for 50-150 its just that simple.

You CAN NOT compare ICE to EV ICE has 0 ft-lbs torque at 0rpm with a curved torque curve which is almost opposite of a EV!

Any time you see a variable transmission added to a EV its a band aid fix to the actual problem of not designing it properly in the first place.

 

[nutnspecial]

Thankyou very much, and although I understand the concept I find it flawed/incomplete. These three points don't help expand my perception to see my potential err, so I will have to respectfully disagree.

 

[Arlo1]

Thankyou very much, and although I understand the concept I find it flawed/incomplete. These three points don't help expand my perception to see my potential err, so I will have to respectfully disagree.

Ok give me a scenario you think a tranny is a better option then to just design the system for the desired/intended use?

Take the Tesla for instance. They use a induction motor so the relationship of rpm is not directly linked to the winding in the motor and the pack DC voltage.
But lets just say they have it working to its best ability and they leave the motor alone and just use a different gear reduction. So at 50MPH the rpm of the motor is reduced to get the motor into its performance curve a little better.

Or look at it like this. I don't know their exact numbers as of right now with the P90DL but I bet its close to 4000 ft-lbs at 0rpm and at 50 mph is fallen about 25% to 3000 ft-lbs and by 155mph its current top speed its fallen to 1000 ft-lbs.

If you were to use a transmission to make it accelerate from 50-150 better how would you do it? Would you have the gear used from 50-150 a lower or higher amount of reduction? If you gear down it will not likely go 155mph any more And if you gear up it will not accelerate as fast from 50-150? So what would you do to make it better? Either way adding a spot where you shift gears and having a second shaft that needs sliding gears will add drag at all times and more failure points. So you would ALWAYS in every gear get less range...

Try to use math and show me an example where a multiple speed or variable transmission would be a benefit. I have worked on 10s of thousands of transmissions and I have never seen one do this magic you speak of.

 

[liveforphysics]

Irrelevant to my example of tesla vs geared ice mclaren of similar HP simply due to unequal weights and aerodynamics imo. . . I do not see evidence a 2nd higher gear would not make huge difference for tesla if goals were shifted to (example) compete @50-150mph while retaining as much of launch as possible. ?

ICE powerplants use transmissions like crutches to help them limp around with devices that make 0torque at 0rpm.

In the example of Tesla, if they were to apply the same mass and bulk of a 2spd gearbox into the motor, they would not only have the potential to be quicker and/or have a higher top speed, but also have a higher continous power for the same mass of drivetrain. This is because the parts of your drivetrain in an EV that aren't electrical steel or copper or magnet material are not helping you convert the energy you have stored in the battery to tractive effort.

If you saw my thoughts on EV's ~8 years ago after having the first few decades of my life given to ICE racecar development, I was hellbent on tiny high RPM motors going through gearboxes and even multi-speed gearboxes. My first ebikes were 10,000rpm motors on 1:10 reductions and I thought it was a great idea, and even seriously explored many ways to add multi-speeds.

Fast forward through the last 8 years of non-stop EV RnD efforts and thousands of dyno pulls and thousands of miles on the road and racetrack finding out what actually delivers the performance. With each step towards more of the vehicle drivetrain weight budget becoming copper/iron/magnet, and less of not being copper/iron/magnet, the system performance kept improving, and amazingly so does the efficiency. Eventually on this path I arrived at a point at which I had more torque than the chassis and tire could possibly handle all the way to a higher speed than I wanted to be traveling, and it's also the most efficient and most reliable.

More acceleration than your tires can handle all the past a speed you want to be going is where putting the drivetrains mass into copper and iron rather than parasitic things can take you, and it's a nice place to be.

 

[Hillhater]

Sorry Luke, but that Selection of pics, is pretty much a Fail !...
The Drayson has transmission reduction boxes ..big ones, on each motor !
And , as with the Pikes Peak car, the Solar Racer etc, ( which i grant you are DD drive)...are all one off s, purpose built for a specific application, and limited performance parameters, run time etc ..
Proof of concept, yes,...but .hardly , proven, practical daily use vehicles.
Then we are back to the bike / scooter hub motors...(which are not what i call EVs ). but still simply demonstrate that it can be built, however, the standard production Escooters i have ridden would all be better for both more speed, and better torque for hills etc.
But why dont the flagship production E bikes, Zero, Lightening, etc,....use hub motors ?

 

[liveforphysics]

Sorry Luke, but that Selection of pics, is pretty much a Fail !...
The Drayson has transmission reduction boxes ..big ones, on each motor !
And , as with the Pikes Peak car, the Solar Racer etc, ( which i grant you are DD drive)...are all one off s, purpose built for a specific application, and limited performance parameters, run time etc ..
Proof of concept, yes,...but .hardly , proven, practical daily use vehicles.
Then we are back to the bike / scooter hub motors...(which are not what i call EVs ). but still simply demonstrate that it can be built, however, the standard production Escooters i have ridden would all be better for both more speed, and better torque for hills etc.
But why dont the flagship production E bikes, Zero, Lightening, etc,....use hub motors ?

They don't use hubmotors because it adds weight to the wheel and impacts suspension performance.

For non-in-line wheel vehicles, you can simply have a CV from the motor to hub and not have the added unsprung suspension mass effects.

Also, when it comes to existing hubmotor tech, I'm not saying most things available aren't designed to simply be the cheapest solution to make something get from A to B. As the EV industry matures, we will see more examples of people making the battery energy to tractive effort conversion into the form of force the application requires rather than wasting portions of it in post-conversion stages.

 

[nutnspecial]

Luke and Arlo: Thankyou (and kinda an 'oh snap' moment)! I was so sure of myself, but these are truly excellent replies tailored to my post. I seriously and highly treasure realization of being wrong and thus refining perspective. The bigger the better imo.

They are very thoughtful and concise/easy to understand combos of reasoning/info/quandry that are very thought provoking! I've honestly not immediately seen my err, but will give much further thought and work into the stated reasonings and posed questions!!