Why not use gear shifting on an emotorbike?

[owhite]

Isn’t it all in the power range also? A large enough motor to climb without gear inevitably has larger noload losses - if the needed power is low the efficiency will be really low.

ok If I build a bike with a gearbox I am definitely going to call it the "Power Ranger".

 

[scianiac]

I think a lot of the problem here are factoring in a lot of variables that we're mostly just guessing at. The idea that having multiple gears is going to make the bike super efficient is probably not true in most real world cases where you're speed range isn't actually all that wide and you probably are moving most of the time at a pretty small speed range. A reasonable sized motor geared for the speed you want to cruise at with a controller that can dump amps into for very brief moments of acceleration, unless you are demanding that much power at low speeds continuously which either means an under sized motor, a very steep and very long hill, a towing load or some combination will be quite efficient and you may only gain a few percent overall assuming you build a very low drag gearbox.

Now all of those cases I mentioned are perfectly valid but specifically for a standard use electric motorcycle those probably aren't true.

Also just because somebody has say it, pretty much all electric vehicles, including those made for efficiency and not performance don't have gearboxes and yes some of that is down to fancy motors but not most of it.

Somewhere here there is a thread that debates all of this, it's very long and covers every argument that's been made here about a dozen times, I have no idea what it was called so I can't link it. Also Grin's presentation on why hub motors are actually not as inefficient as people think they are demonstrates a lot of this with lots of very nice graphs and numbers.

 

[liveforphysics]

Let's say range and efficiency are your key metrics.

Let's look at the most efficient EVs on the planet, solar cars.

They are the ultimate Wh/mile watt sippers. You will never see a multispeed gearbox. If they did have one, it would be there powertrains largest efficiency hit.

Don't forget the original Tesla Roadster started with a 2spd. When they dropped the 2spd, they got a faster 0-60mph time, higher top speed, and significantly improved range from reduced losses.

 

[owhite]

They are the ultimate Wh/mile watt sippers. You will never see a multispeed gearbox.

Personally I think youre making my case for me. Of course they wouldnt use multi-speed gearing -- unless you wanted to be dual use -- for example if they needed to sprint AND be watt sippers.

 

[larsb]

Time to lock the thread. Won’t be more conclusive than these last few posts

 

[scianiac]

Turns out it wasn't that hard to find: https://endless-sphere.com/forums/viewtopic.php?f=30&t=47930&hilit=gearbox

What's funny is how that thread starts out as gearboxes are great and then things get real murky for the same reasons, they sound like a great idea intuitively but the truth is a bit more complicated.

And also: https://youtu.be/dxJe_gygRGU in which he does actually run the numbers in various conditions for a single speed ebike (a hub motor) and how "inefficient" it really is to not have the gears of a mid-drive.

I'm sure nobody wanted at 32 page thread and a 2hr video as homework but I found them very informative and they both contain more real data instead of only anecdotes on the subject (although boy does that thread have a lot of anecdotes too).

 

[spinningmagnets]

If you are designing a vehicle from the ground-up, and you are free to use high voltage with a large battery pack full of high-amp cells, (Tesla cars, Zero motorcycles) then I agree on using a big motor, big watts, and no gears.

However, there are a few user-profiles where it wouldn't be horrible to have a couple gears. In a conversion where you already own the transmission, there is no extra cost. Motors and high-watt controllers are expensive. For me, the biggest issue is the controllers. The large high-amp controllers typically make it expensive or hard for owners to program, and they want to keep their dealers happy by giving dealers a license and passwords to open the firmware up, plus provide a tutorial on the software.

Controllers really need to be matched to a specific motor. Conversions often try to find a good deal on the expensive parts, and they are not always easy to mate. There are drawbacks to using a transmission, but...if you are on a tight budget, the available motor, controller, and battery voltage may limit you to "X" amount of watts.

If you convert an enduro motorcycle to electric, a 2-speed can provide a lower amp-draw when you are choosing between a slow crawl up a steep hill, or top speed when you are on relatively flat and paved streets.

For a quad-runner on a ranch, I'd keep the 4-speed manual trans while using 52V, but on a "street only" motorcycle, I'd go for a big motor and 28S voltage, like Zero.

 

[larsb]

And also: https://youtu.be/dxJe_gygRGU in which he does actually run the numbers in various conditions for a single speed ebike (a hub motor) and how "inefficient" it really is to not have the gears of a mid-drive.
..
I'm sure nobody wanted at 32 page thread and a 2hr video as homework but I found

Thanks for the links, haven't seen them before and Justins content is always high quality. I think he proved that geared systems can be more efficient in total when you can find an improvement above the gear inefficiency, that's if you have a broad useage range (chugging up mtb paths and flat riding with the same bike). Gears could then also give "two bikes in one" for you but for just road use then yes, one gear will likely be as efficient or even better.
(The comparison he did in the video with a bbs02 mid drive with pedal bound rpm is off course not valid for an ebike with decoupled pedals or emoto so that doesn't fit so well in the thread.)

 

[Elektrosherpa]

If you convert an enduro motorcycle to electric, a 2-speed can provide a lower amp-draw when you are choosing between a slow crawl up a steep hill, or top speed when you are on relatively flat and paved streets.

For a quad-runner on a ranch, I'd keep the 4-speed manual trans while using 52V, but on a "street only" motorcycle, I'd go for a big motor and 28S voltage, like Zero.

I absolutely agree to that.
It is all about the intented purpose of your EV.

 

[owhite]

Controllers really need to be matched to a specific motor. Conversions often try to find a good deal on the expensive parts, and they are not always easy to mate. There are drawbacks to using a transmission, but...if you are on a tight budget, the available motor, controller, and battery voltage may limit you to "X" amount of watts.

If you convert an enduro motorcycle to electric, a 2-speed can provide a lower amp-draw when you are choosing between a slow crawl up a steep hill, or top speed when you are on relatively flat and paved streets.

I'm glad spinningmagnets mentioned controllers. Originally I hoped to start a thoughtful discussion about gearing in general, but I also had alternative motives. After my last build I did very much want to get away from 20s constraints. I managed to build my own controller, but 104v is right around where infineon MOSFETs fail; if I had to replace my board estimates are that it would take 40 weeks with current supply chain problems. Also disclosing my real motives, I've purchased a QS165, and I was hoping to stay in the 16s range and still maintain some good performance. I got to thinking about gear optimization since no matter what a mid drive like this will require some choices about sprocket sizes and gearing.

Finally, for better or worse, I'm pretty sure I would never have started this thread at all if I was aware of this post.

I thank everyone for their very thoughtful contributions to this thread.

 

[scianiac]

Thanks for the links, haven't seen them before and Justins content is always high quality. I think he proved that geared systems can be more efficient in total when you can find an improvement above the gear inefficiency, that's if you have a broad useage range (chugging up mtb paths and flat riding with the same bike). Gears could then also give "two bikes in one" for you but for just road use then yes, one gear will likely be as efficient or even better.
(The comparison he did in the video with a bbs02 mid drive with pedal bound rpm is off course not valid for an ebike with decoupled pedals or emoto so that doesn't fit so well in the thread.)

The other very important point he makes in the presentation is that while traveling at slow speeds and high powers the motor will be operating inefficiently but only for short periods of time as you will be rapid accelerating to a higher speed depending on the power. This was my point about the size of the motor (and vehicle weight) really matters. The motor could easily be power enough that there is no such thing as "chugging" up steep trails it's just traction limited so you have can't use all the power anyway and if you're at that point you won't be moving slow for very long.

This was the condition that I mentioned of the motor being undersized, in the case of a BBS02 it's undersized for the vehicle weight. Which we can already see many real world counters to this from people using BBSHDs pushing 4.5KW plus who mostly give up on actually using the shifting, mostly because they don't take the power well.

So the real question we're trying to answer here is for your bike, your motor, and your application does a gearbox makes sense? A hard driven QS165 will probably be pretty peppy in a lightweight bike but probably neither is it in the "large enough to traction limit you in all situations" so maybe a gearbox could be useful but only if it's pretty lightweight and honestly I would try it without first and see if you can use that much more added low end torque anyway, you can't really apply that much power into dirt anyway and on the street you probably want to be going at the higher gear speeds anyway.

You have to remember also that watt-sipping cruising also has a lot of other variables, a slightly different gear ratio may make the motor slightly more efficient but compared to even some very basic aero, tire choice, tire pressure, driveline efficiency, motor design. I'm not so sure if it's worth the time and weight compared to looking into some of those.

 

[larsb]

If you’ve ever ridden a mtb you know that on a lot of trails going fast is not an option. This is what i mean.

And.. I didn’t get any surprises in the justin video. no need to explain about tire pressure, aero etc

 

[scianiac]

If you’ve ever ridden a mtb you know that on a lot of trails going fast is not an option. This is what i mean.

And.. I didn’t get any surprises in the justin video. no need to explain about tire pressure, aero etc

Sorry I got lost halfway through my post and switched to talking about owhite's build so most of that was about his QS165 + BESC build.