Why not use gear shifting on an emotorbike?

owhite

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Hear me out, and please just treat this as an instructive, hypothetical discussion.

If you go on ebay and amazon and search for "125cc transmission" you can find plenty of hits for the replacement gears that go into the gear box of lil pit bikes. You can also find gears for go-carts that would give you three gears and a reverse.

There are also some great videos on how motorcycle gearboxes work.

link
link

...being examples. There are also examples where you could get a whole 125cc engine, and what interests me about that is you could either use that to copy the shaft positions for the engine, or if you were ambitious you could possibly mill out the transmission side of the engine block.

So my point is this -- why not put a gearbox on an emotorcycle? The advantages would basically be the same as a gas engine: lowering the rpm in order to achieve the same speed or torque. In the case of an ebike, instead of using less gas, it would extend the battery usage.

I did my best to search ES to find posts on this, but they were swamped out by discussion of putting mid-drive motors on derailleur bikes.
 
Sure, can be done but overall less worth it due to the high efficiency of e-motors and high torque also at low rpm. I’ve looked at two gear systems for my bike purely as a hot rod item, if there was a good set i’d buy it.
 
owhite said:
Agree on the low torque point. This video goes into some detail about how changing the back sprocket of a surron by ten teeth really changed battery ride time. So maybe the best argument is that it would increase range of the bike and its top speed. It could basically create three modes:

  • hill climb
  • around town
  • long distance

At the cost of reduced output and efficiency during all of those activities.

Churning gears through oil causes a surprising amount of drag. If you're in the position to be adding that much mass and volume to your vehicle, using that mass to add series drag losses and friction rather than upsizing the motor iron/copper/magnet mass is irrational. Start with a motor that delivers the torque to loop you, up to the speed range you want to go. This means your system turns the least amount of your batteries energy into waste heat, and the most into your rear wheel. If each pound of steel gear was an extra pound of iron in your stator, and each pound of aluminum in the gearcase was another pound of copper in your winding, you would end up with a much higher continuous power motor that natively can sustain more torque at the wheels without the series friction and windage penalties.
 
liveforphysics said:
At the cost of reduced output and efficiency during all of those activities.

Churning gears through oil causes a surprising amount of drag. If you're in the position to be adding that much mass and volume to your vehicle, using that mass to add series drag losses and friction rather than upsizing the motor iron/copper/magnet mass is irrational. Start with a motor that delivers the torque to loop you, up to the speed range you want to go. This means your system turns the least amount of your batteries energy into waste heat, and the most into your rear wheel. If each pound of steel gear was an extra pound of iron in your stator, and each pound of aluminum in the gearcase was another pound of copper in your winding, you would end up with a much higher continuous power motor that natively can sustain more torque at the wheels without the series friction and windage penalties.

So I think see your point. Youre saying that for any additional weight represented by the gearbox, it's always a better proposition to put that weight into more motor.

I get that, but, I would wonder if that for any motor (that isnt a hub motor) no matter how ideally sized to the bike, you need to pick some gear ratio. And being able to choose from multiple gearings allows you more flexibility in terms of torque versus speed and distance performance.

and yes, I accept my last statement, ignores your point about oil and drag.
 
This is why I love more phase amps in a motor controller so much. It lets you make your wheelie torque with a lower winding count motor, enabling you to still reach high speeds (albeit up to the power limitations of your battery etc).

More phase amps and motor stator/rotor is how to adjust the gearing compromise between acceleration and top speed to be comfortable with a single ratio.
 
If you have enough motor to overpower the bike in every situation, then you would not need gears, but in reality, few situations make that practical .
Maybe, you can tolerate the size and weight of such a drive train on a bigger emotobike, but weight reduction would be a worthy objective.
The popularity of mid drives with deraillier gears on ebikes demonstrates the benefits of gearing to keep size , weight and cost down to realistic levels.
 
Some do,
https://endless-sphere.com/forums/viewtopic.php?t=111293
Oset is another emoto with gears.
What riders find is that they don't really need the gearbox much, a clutch might be more useful for technical riding..
 
X-Nitro said:
Some do,
https://endless-sphere.com/forums/viewtopic.php?t=111293
Oset is another emoto with gears.
What riders find is that they don't really need the gearbox much, a clutch might be more useful for technical riding..

Folks only ask for a clutch until you give them enough native shaft torque to violently lift the front wheel at a flick of the wrist, then they never ask about clutches again.
 
It seems like there is an area at low weights and powers where it makes sense but a lot of that is just because derailleur systems are very efficient and lightweight but once you start to add power you quickly start losing that battle and honestly a lot of why it works in middrive ebikes is because you're running that system right at the edge of what it can take. You probably could make a tiny gearbox that was very light with small gears that can barely take the torque your dumping into it but this really brings us back into the other advantage of a single speed, simplicity and reliability. Also using trying to ride that edge of weight means you can't take advantage of dumping stator saturating amounts of current in for short bursts of extreme torque.
 
Thank you people for the very thoughtful comments here. What I'm taking from this is:

  • keep it light or dont bother. no one is particularly convinced that the weight-to-added complexity is really worth the trouble for an emoto.
  • some of us really like doing wheel stands :)

I like doing wheelies too -- or said another way the collective mind likes the emotor advantage of bikes being optimized for high torque. I think all of us place a premium on muscle/performance. When most of us think about riding any motorcycle on thing on their mind is the ability scoot like hell out of a dead stop at an intersection.

Fair. I think I'm after making a dent in improving distance and run time. soOOOOooo here's a system that is (probably) lightweight, low drag (no oil) and "simple". Meet, the moped variator: [VIDEO].

Basically the variator changes gear ratios over a range, by changing in diameter of the pulley as it increases in speed. This is rather impressive engineering, in that pulley diameters change based on the centrifugal force the rotating pulley.

What is intriguing here is they are mass produced (so, accessible), lightweight, dry (no gearbox oil), and are entertaining AF to watch. The other thing that intrigues me is I wonder if instead of using a centrifugal system you could just have a mechanical control to kick it in when you want more distance. So, default would be wheelstand mode, engaged would be for long hauls.

Where would it be placed? How bout substituting it in right between the output sprocket of the motor, and the right pulley of the jackshaft used by surron bikes: [IMAGE]?

Thoughts?

Thanks for this discussion, this is fun.
 
I don't have any hard numbers but I think variators and most belt type CVTs (excluding maybe metal belt versions) are pretty inefficient so factoring in weight and complexity you'll probably waste more energy they you would save by changing the ratio for cruising.

Depending on how one is using the bike I think one way that may work is to just have a belt or chain drive with double sprockets that you can manually move the belt or chain over easily. The added weight would be minimal and no additional drag loss. If you were for instances going to drive the bike on the road at high speeds somewhere and then do some slower trail riding this could have some advantages but really only if those average speeds are pretty far apart or you are limited by motor, controller, or battery power for cost reasons for instance.

For a motorcycle I think the real advantage to using a gearbox is cost, if you already have a gearbox from your donor bike you can get away with a smaller motor, cheaper controller and cheaper battery but it will be a worse bike and this assumes your time is valued cheaply.
 
liveforphysics said:
At the cost of reduced output and efficiency during all of those activities.

Churning gears through oil causes a surprising amount of drag. If you're in the position to be adding that much mass and volume to your vehicle, using that mass to add series drag losses and friction rather than upsizing the motor iron/copper/magnet mass is irrational. Start with a motor that delivers the torque to loop you, up to the speed range you want to go. This means your system turns the least amount of your batteries energy into waste heat, and the most into your rear wheel. If each pound of steel gear was an extra pound of iron in your stator, and each pound of aluminum in the gearcase was another pound of copper in your winding, you would end up with a much higher continuous power motor that natively can sustain more torque at the wheels without the series friction and windage penalties.

It’s probably on a splitting hair scale for efficiency but for the possible use range i think gears are hard to beat.

A two gear system with a simple dog box like thud designed could get climbing AND speed with a mid sized motor. Pinions and rohloffs with 16 gears weigh about 2kg so an optimised two gear system should get to about 500g or so. Add 500g to the motor - I don’t think it will equal the geared system speed and torque range.
 
larsb said:
A two gear system with a simple dog box like thud designed could get climbing AND speed with a mid sized motor.

I was curious so I dug around to find this reference. Time has not been kind to pictures of Thuds 2 speed shifter. I found a pdf: ES page1. There are some images that appear to have survived photobucket's normal shelf life here: ES page2. Which also includes some vintage praise from livefromphysics for the transmission idea. :) I mean hey if it seemed like a good idea 12 years ago -- where's the love?

There is also this fantastic video from 2010. This box went into the build shown here...which DEFINITELY possesses enough screaming gear noise to convince me from seriously thinking about this at all. :confused: I am so not riding around the streets of baltimore on something that sounds like a hideous mechanical mosquito.
 
owhite said:
larsb said:
A two gear system with a simple dog box like thud designed could get climbing AND speed with a mid sized motor.

I was curious so I dug around to find this reference. Time has not been kind to pictures of Thuds 2 speed shifter. I found a pdf: ES page1. There are some images that appear to have survived photobucket's normal shelf life here: ES page2. Which also includes some vintage praise from livefromphysics for the transmission idea. :) I mean hey if it seemed like a good idea 12 years ago -- where's the love?

There is also this fantastic video from 2010. This box went into the build shown here...which DEFINITELY possesses enough screaming gear noise to convince me from seriously thinking about this at all. :confused: I am so not riding around the streets of baltimore on something that sounds like a hideous mechanical mosquito.
I’m sorry to let you down but that noise is mostly from the motor :D

I agree that straight cut spur gears can have a nice whining to them though, better suited for hot rodding 😉
 
larsb said:
It’s probably on a splitting hair scale for efficiency but for the possible use range i think gears are hard to beat.

At a high enough power level, traction or wheelies limit low speed torque, and gross power limits top speed. So there's little you can do by shifting gears.

When power is small compared to gross weight, as when I rode a BBS02, it's possible to dramatically improve some elements of performance by changing gears. My BBS02 bike climbed steeper grades and had a higher top speed than either of my hub motor bikes that have 1.5 times as much power.
 
Chalo said:
When power is small compared to gross weight, as when I rode a BBS02, it's possible to dramatically improve some elements of performance by changing gears.

Thanks! In my case I'm thinking about using it for the QS165 -- which is a QS drop in replacement for the surron. Building a custom trail bike but will probably use the two stage gearing approach used by the stock surron's. I got into thinking about this whole thread because no matter what I have to use some kind of gearing, and I'm thinking about how to extend my range.
 
owhite said:
larsb said:
A two gear system with a simple dog box like thud designed could get climbing AND speed with a mid sized motor.

I was curious so I dug around to find this reference. Time has not been kind to pictures of Thuds 2 speed shifter. I found a pdf: ES page1. There are some images that appear to have survived photobucket's normal shelf life here: ES page2. Which also includes some vintage praise from livefromphysics for the transmission idea. :) I mean hey if it seemed like a good idea 12 years ago -- where's the love?

There is also this fantastic video from 2010. This box went into the build shown here...which DEFINITELY possesses enough screaming gear noise to convince me from seriously thinking about this at all. :confused: I am so not riding around the streets of baltimore on something that sounds like a hideous mechanical mosquito.


I think Thuds 2 speed is a perfect example. He made the gearbox and it worked he brought it to the race, and ended up just racing in 2nd gear.
 
Thuds 2-speed gearbox. I believe he used #35 chain. #415 uses smaller links and is very strong, but they don't use master links.

https://endless-sphere.com/forums/viewtopic.php?f=28&t=48731

thud-system.jpg


Thud2Speed.jpg
 
spinningmagnets said:
Thuds 2-speed gearbox.

thud-system.jpg

preserved on the es server for when external link dies ;)

(copy url of external image, click attachments tab, click add, paste url in "file location" box, click open)
 

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Formula electric racing series is another prime example.

They started with 6spd gearboxes in Formula E. The winner of the series removed 5 of the 6 gearsets and won as a single speed. The 2nd place car ran 2spd of the 6spd box.
 
True, but there could be some different categories of users out there :D
I must refer to Chalos (well stated) post above. e-motor + gearbox has its' uses
Race=large enough motor and overpowered controller -might be fine
Everyday rider=average motor and average controller. Possibly even caring about electric shock risks and legality of their diy system :wink: - Could be an improvement with a geared system.

I think also for technical riding a lower gear can be nice. A loss of traction with an ungeared high kV motor that powers through at low rpm is worse than same slip with a downgeared motor.
 
True, but there could be some different categories of users out there

I agree. Respectfully, I feel like liveforphysics creates a false dichotomy in his examples. Yes, if you have the performance you need for racing with a single gear ratio, that's great. But vehicles that are optimized for racing (ebike or F1) are by definition not optimized to save amps or gasoline.

I agree with him in the sense that if I can use a fixed gear ratio if I'm after pulse-raising performance on my bike I'll stick with it. But if I want both aggressive riding AND want to flip into amp-saving mode, it still seems to me there is a reasonable case for a two-speed box with dog gears.

Maybe I should have started this thread by saying: "Duel use, duel gear ratios?"
 
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