To gear or not to gear, that is the question.

Hey Guys,

Right now, I get more questions regarding gear changing on an E-system than any other single question. Shiftable transmission options are the hot topic right now. However, I want to throw some info out there for discussion;

My personal opinion on this is multiple ratios are only beneficial with low power systems as a way to optimize the relatively small amount of power available. However, for anything substantial (maybe 1kw or more?), multiple ratios are more of a novelty than anything.

Remember, the beauty of electric motors is 100% torque from 0 RPM (or relatively low RPM depending on the system).

I do not want to start an arguement over this. I have a huge amount of repsect for those who have implemented shifting transmissions. However, personally, I think multiple ratios for higher power systems are really not needed. They just add complexity and reduce efficiency due to the added rotating parts and the friction related to it.

Thoughts?

Matt

My two watts worth:

For some, efficiency becomes a factor; By having the ability to change gear ratio, shifting the gear ratio can show the minimum current draw at a given mph by staying always on the maximum efficiency. This increases range and could decrease battery size/cost.


This certrainly would not be a factor for quarter mile dragsters, but, if some one is trying to say go from Portland to Atlanta, the increase of effiency could mean a ~20% increase in range between charges, and possible carrying less battery, with no decrease in performance.

This becomes more important as the weight of the vehicle goes up, the terrain has larger variatons, along with headwinds.

Given a very high power to weight ratio over fairly constant terrain, you may be be spot on though.

It would take a sharper pencil than I to compare the cost differintial of an extra x watthours of hitech cells versus the cost of a stepdown 10 to transmission to handle ay 1.5 hp.

d

1969 RS 302 (205hp, 188ft lb) Camaro - POWERGLIDE 2 SPD.
1994 Camaro 305 (185hp, 190ft lb) - 4 spd Automatic with OD

If all you want is a bike which can run a single top speed efficiently - sure there is no problem with lack of gears.
If you want to have more torque when needed (either to climb hills, pull loads or rider) and higher top end speeds while maintaining efficient use of the electric motor - gearing of some form is the only answer I really know of.

My personal preference would be to keep operating at motors most efficient point for given speed / load, do you guys know some other way besides a transmission (multiple gears) to accomplish this?

As to how many gears we want... that's simple - as many as we can fit, as widely apart as possible.

Seriously though it depends on 5 factors:
1.) Maximum Desired Speed
2.) Minimum Desired Speed
3.) Average Desired Speed
4.) Motor Efficiency @ RPM
5.) Load or Weight being driven.

It seems most people have been designing alternate drive systems by figuring out reduction required to get maximum desired speed at perhaps nominal pack voltage - this is fitting with the exemplar of going a specific speed really efficiently and not worrying about the inbetweens.

In my location (and many others) this simply doesn't work out - this area is not flat by far and the top speeds I need to operate within vary from 5mph (pedestrian paths, big ass hills) to 45mph - getting that range out of a single speed system is possible but not very efficient...

Assuming I need to have the following top speeds:
5mph
15mph
25mph
35mph
55mph

A 3 speed transmission would suffice (overlap between 25-35 and 5-15) but a 5 spd would keep me in the sweet spot while operating in my environment at the various speeds required for safe transit.

I think the perception that we don't need to shift a powerful bike are because of the type of terrain, riding style and expectations various people have.

In the end I loved both my camaros but... the 94 was much more efficient while being "gentle" than the powerglide was regardless of speed (in the range above actually) and when needed, the power was available to accellerate and go really FAST (at a nominal hit to potential - note I say potential, performance).

I can say this much... a street legal (US) ebike of 746w nominal power (capable of more but limited) backed up with a 5spd transmission would make everything possible... limited for "legal" use but capable of soo much more - while still being "legal" (yes this would pass muster with appropriate electronic limits set).
-Mike

I have to agree with the general idea that if you're looking at huge potential power and you're limiting your top speed that doesn't even begin to maximize that potential, than a single gear does just fine. The reason being is that the "power curve" of the motor is SO steep in that condition, that a drop in speed of 3 mph may cause the motor power output to more than double while retaining just about the same motor efficiency. Thus, heavily loaded or not, the system as a whole is still efficient.

But, for lower power inputs where your top speed does tap the max potential of your system or is close to it(i.e., a 1000 watt output system maxes at about 30-35 mph - if you gear for 30 mph, you have a lot to benefit from multiple gears. If you gear it for 15 mph, gears won't make much noticeable difference under varying conditions.), gears are useful for varying conditions.

For 1000 output watts, I'd say somewhere in the 15-20 mph range for designed TOP SPEED, variable gears aren't that useful.
For 2000 output watts, I'd say somewhere near 20-30 mph.
For 4000 output watts, I'd say somewhere near 35-40.
For 6000 output watts, somewhere near 40-50.

Thus, multiple gearing wouldn't benefit matt's 10+ kW creations since they're typically limited to 40-50 mph.

To simplify, if you plan on getting close to the max output power for your system to go as fast as possible, you probably have quite a bit to gain from variable gears under varying loads and conditions. If you're actually maxing your top speed to be well below the peak output power of your system, variable gears aren't nearly as useful.

I'd add that gearing can increase the rate of acceleration, but at the price of added complexity.

*If you can break traction at any speed in your range, you won't get better acceleration from variable gearing.

I agree, Matt. Only low-power systems that need to maximize performance need the benefits of a transmission enough, so that the added complexity and expense are worth it. A 48V/750W (or higher) light-weight bicycle that never goes over 30-MPH/45-kph doesn't need it.

But a 350-lb 48V motorcycle that needs to be able to achieve 65-MPH very much needs a 2-speed trans to help battery range and low-speed acceleration (especially if using affordable low C-rate batteries). A 750W/20-MPH cargo bike carrying a child and 4 bags of groceries in a hilly area could use a 2-speed (though the easiest and most affordable option might be a 3-speed Sturmey-Archer).

A tranny is about having your cake and eating it.

Even on my crazy built 2-stroke 380cc KTM 300MXC dirtbike, dropping a couple of teeth up front and adding a handful in the back helped the performance in technical riding.

Even when the stock gearing would let it lift or spin the tire at any crack of the throttle in first 4 gears, shortening up the gearing improved the feel and control in technical riding.

There is something about a granny gear that just feels great when torqueing your way up through a twisty very steep slope over logs and rocks and other obsticles. Even though 3rd or 4th gear is still able to supply all the power the tire can handle, having the control offered by the granny just feels fantastic IMHO.


But once out in an open field or something, of course you're never going to want anything but just pinning that throttle open in 6th and flying along.

Even with very powerful stuff, I always feel like in extreme techincal stuff, it's almost like 1st can't get short enough, and when out in the open, 6th can't get tall enough.

IMHO, a very wide ratio tranny (that is lightweight, and perhaps that incorporates the first stage reduction internally so it has no additional drivetrain loss), would be a helpful thing for any E-bike, from a 200w bike to a 20KW bike.
But, it's certianly not a critical thing, just an icing-on-the-cake sort of thing.

Matt,

I guess you may be right... it may be more useful in "low powered" ie: < 1000w setups but wouldn't a 2 speed with a hella wide range drastically (over 30%) increase your efficiency in various conditions (ie: pulling the kids to school vs tearing up the roads at 45mph)?

If you can tell me that you couldn't make a 30% increase in realized efficiency (ie: actual range in use) then forget it... it's for the little guys.

If you say 30% increase (knowing you are a very smart rider who knows how to "squeeze" every last wh out of your system) in range with gears even for your setup... then I have to stand by the gears argument.

What is your experience in terms of efficiency vs average terrain / speeds you travel at - not just the total wh per mile averaged for your best run but rather.... I imagine even though your rig is far more efficient than mine, you still see the same thing I do... at full theoretical speed (just below it really) on flat ground your running at peak efficiency / least wh per mile traveled. What's the efficiency like around 20mph? 10 mph (I personally won't take my son faster than 10 mi an hr - that's the point just below where I feel like I couldn't protect him with evasive actions).

It could just be that the math in theory doesn't work out to the results in the real world (red or blue pill neo) or that it just doesn't matter at some point (higher powered systems? {kicking the dirt - feeling simple}).

Regards,

-Mike

I've been promted to add to this post.
here is my take on the discusion.

Recumpence wrote:
My personal opinion on this is multiple ratios are only beneficial with low power systems as a way to optimize the relatively small amount of power available. However, for anything substantial (maybe 1kw or more?), multiple ratios are more of a novelty than anything.:

Click to expand...

Any time you can reduce the working load of any power unit there is a gain in efficancy. The gain is of course subject to losses associated to the method, but ultimatly it is a gain. You can measure it any way you like, lower amp draw & its bennifits, improved accelration, overall extension of the operating envelope of a machine.

Matt makes a valid point (specific to his latest batch of 20+ HP builds) top fuel dragsters operate in 1 gear.
but a NASCAR machine would be hamstrung with only 1 gear, I wouldnt consider that a "low power system"

Ultimatly it is a decision for the buyer of a powerd machine. Logicly, there is no argument. Different machines do different things.

If your going drag racing with an unlimited battery, motor, & tire budget, go for it & have a blast!

If you need utility get the "mini van" or pick "up truck" version to fit your style.

Having selectable ratios will give your utility vehicle extended utility, your sport vehicle more "sport"
your drag racer only needs more fuel.

If the opening post was a question, Do we need a shifting, multi range transmision? My answer is yes

Something that goes from 2:1 to 1:2 would be awesome, and could be made to be very compact due to the similar sprocket sizes (2r difference isn't too bad for a tranny.)

15mph top speed with excellent low speed control and tree climbing torque in first (great for technical stuff, climbing stairs etc), and 60mph top speed in 2nd.

Or, for my 100mph bike project, 25mph 1st gear, 100mph 2nd.

Really good discussion!

The primary reason I started this thread is because there is so much talk lately about shiftable trannys, that I am getting almost innundated with emails regarding this. The non-posting readers need some more accurate information about this. So, I started this thread.

One thing needs to be made clear, however, an ICE to electric drive comparison is not valid because an ICE engine makes power in a very narrow range. However, electric motors have a HUGELY W--I--D--E torque curve. So, it is truely apples and oranges. (And, yes, I do understand even electric motors have a sweet spot )

I do totally understand the issue of maximizing RPM for a given application for maximum torque. Right now I am setting up for my third monster KMX trike build using twin 2 turn motors running at 15,000 RPM geared way down for maximum torque and efficiency at my target performance range. I also understand that surplus power is making my personal need for gears neglegeable (non-existant). That is not what this thread is about, though.

I guess what I am looking at is something like this;

A single speed system with 1,000 watts. You can have motor, one or two stages of reduction to the rear wheel, a controller and a battery pack. Done, works great! Or you can add a transmission which can double or triple the complexity of the system, add weight and reduce mechanical efficiency due to the added moving parts as well as adding cost, all to gain a very small amount of added electrical efficiency.

I am totally blown away by the transmissions I have seen used in E-bike use and am 100% for them. I just want people to understand it is not needed for a good E-bike. Personally, I would LOVE two speeds, one for low range running and one for higher speed. Heck, it does not even need to be on-the-fly shiftable. But, it would be nice to configure a drive for torque or speed before each ride. But, being able to shift through multiple ratios while riding is not needed for 95% of users out there.

Thud, I love your tranny by the way. I am not knocking it at all. I just want people to understand the drawbacks outweight the benefits in many (but not all) situations. Shifting is fun, though!

Lastly, I have been looking into a shifting option myself. I just find other issues more pressing than a shifting transmission right now (in the E-bike community as a whole).

Matt

Great discussion on gearing very informative. That pretty much explains the motor side of the gearing, the other element is human. Most Ebikes are designed for an element of human input, more or less depending on the setups. I cannot peddle up a steep hill without gears, it is hard enough in a granny gear some times. Doing away with gears or even limiting them to 3 would seem like a step towards making the bike an e-moped with limited human power added to the equation. When the battery fails I would hope I could still peddle my ebike home to fix it; since these things are not light weight, gears would be essential as a get home safety feature. Just another 2 cents for the collective pot.

Gerard

Yup, I agree wholeheartedly. I like a minimum of 24 speeds on the pedal side.

With a few hundred watts of very RPM limited human power, many gears are needed.

Matt

recumpence said:

... you can add a transmission which can double or triple the complexity of the system, add weight and reduce mechanical efficiency due to the added moving parts as well as adding cost, all to gain a very small amount of added electrical efficiency.

Click to expand...

A little can be a lot:

liveforphysics said:

If a motor at 95% can handle 1000w,
that motor at 90% can only handle 500w,
that motor at 80% can only handle 250w,
that motor at 70% can only handle 166w.

So, for an example, if we have a 1,000w motor at 95% efficiency, if we wish to make a 1,000w motor with 70% efficiency (which would be typical brushed), then this motor needs to be scaled up to be 6 times larger to handle the same power without over heating.

Click to expand...

http://endless-sphere.com/forums/viewtopic.php?f=28&t=13977&p=212037&hilit=+efficiency#p212037

recumpence said:

I am totally blown away by the transmissions I have seen used in E-bike use and am 100% for them. I just want people to understand it is not needed for a good E-bike. ... But, being able to shift through multiple ratios while riding is not needed for 95% of users out there.

Click to expand...

Most comments would suggest the opposite: 95% of the users need/want gearing, 5% will have bikes designed for uses where gearing is superfluous.

Hello everyone,
Great thread, I was going to post this exact question when I came across this thread. I thought I'd share a prospective purchaser's viewpoint.

I am new to this forum and got quite excited about motorizing my bike, but then stumbled upon tadpole trikes. I love to cycle, but as the years accumulate, I find the hills, the sweat , sore wrists and the sore butt becoming more of an issue to my enjoyment. The trike screams out for the last two issues, electrifying the thing would help with the first two.

My first question on the forum was a 50/50 thing; 50 kph/50km? I still hold to this minimum and recumpence has answered with his 15kw monster, in aces! Alas, $6.5k + is not in my foreseeable future. I felt at this point maybe something smaller using the gears of the trike would help, which would extend the speed, distance and climbing with a modest motor 1~2kw. Cyclone is an option, though not sure of the reliability of it's components and I still have questions concerning the noise level (stealth) of a RC setup (riding back country roads with a buzzing RC doesn't excite me). This brought me back to hub motors, BMC's new 1000w (yet to satisfy Cycle 9, I'll wait) and AmpedBIkes new 400W geared hub (too small??), his video demonstration is very quiet indeed. Though, to install a hub motor doesn't utilize the transmission on the trike, which I believe is a waste, so I'm back to RC. Decisions, decisions :?

For those of us who can't afford the $$$ for 20hp at the wheel and still want the advantages, a transmission is the answer. I'm sure recumpence didn't ask this question without a motive :wink:

Guys,
I try to refrain from posting if I have nothing to add or point out in a topic. & I think most every one participating in this exchange are in total agreement regarding the application of power to bicycles. Sort of a non discusion as it were.
For the benifit of non-posters, mineing for information to make some decision with, I'll chime in again.

-FORUM BROWSERS-
You don't need a transmision on a twin motored Monster KMX rocket/bicycle
or even a "reasonably" powered one.

My $40 turnigy wouldn't last a week, starting from a dead stop & toping out at 30mph without the tranny.
That said,

recumpence:
-you can add a transmission which can double or triple the complexity of the system, add weight and reduce mechanical efficiency due to the added moving parts as well as adding cost, all to gain a very small amount of added electrical efficiency.

Click to expand...

Those are broad statments-and can be interpreted in many ways. I hope I am not too close to the subject to see it clearly.

Those issues are applicble in all reduction systems. An argument could be made that: If you are going to the trouble of building a high powered non hub bicycle & have the resources, Why not have every option to maximise the operational efficancys & performance envelope?
In the context of talking to a potential customer, it is fine to steer someone in a direction that is mutualy benifical. If Just posting opinions thats fine also.

The facts are: Muti range transmisions are not impossible & would extend the functionality range in every application. It Just would not be cost justifiable or practical if you have soooo much extra horspower that you are only using 30% of the system potential. Thats the point in the opening post.

The cost & complexity aren't valid conversation points when compairing "Monster Builds". Dual motors & tire smoking aside.
& yes I consider the tranny I made a MONSTER build.

Again, we are having a non conversation. I think we agree on all points.

I hope that clears up any confusion about putting transmisions on a bicycle.
Ive meant no offence in this reply & appoligise & retract in advance any percieved jabs( Ive been pm'ed about my tone in other threads)Nothing but respect to Matt & his contributions to this forum & e-bike comunity.I wouldn't be here if not for him.

OK, here is another point to argue (debate?) over.

Forgive the hypothetical here, but it illustrates a good point;

Someone has $1,000 to spend on motor, controller, other bits.......

Let's say a transmission is $200. I would rather see them put that extra $200 into a bigger motor than add a transmission (assuming their pack can handle it).

That being said, for someone looking to be right at the target 750 watt legal limit (or 200 watts in the UK), a multi ratio option is a must to achieve any kind of decent performance.

See what I mean?

Anyway, I am a terrible one to bring up this topic considering I am running way too much power and torque. So, I do not need gearing.

Also, bear in mind, I have been dying to build my own tranny for some time now. I am just exploring the benefits versus the drawbacks.

Matt

recumpence said:

Anyway, I am a terrible one to bring up this topic considering I am running way too much power and torque. So, I do not need gearing.
Matt

Click to expand...

A good rule of thumb might be:

If you have enough power to hold half your cruising speed in the most adverse conditions you want to meet, then you don't need gears!

JennyB said:

A good rule of thumb might be:

If you have enough power to hold half your cruising speed in the most adverse conditions you want to meet, then you don't need gears!

Click to expand...

That is a good simplification. The next bit of complication I would add:

If you have enough power to hold half your cruising speed without overheating in the most adverse conditions you want to meet, then you don't need gears!

Hello,
I have a two speed transmission on my bike and it works quite well. My bike is relatively low powered compared to other bikes on this forum and having the two speeds keeps the power use low. If I start off in high range from a stand still then I can see a spike of over 80 amps, but if i start in low range and then shift to high I will get to max speed faster and not pull more than about 35 amps. The bike is a lot more torquey in low range which makes the bike much more fun to ride. I can see how a more powerful system may not need multiple gears, like the Tesla roadster now uses a singe speed.

I certainly see mulitple speeds as being useful, especially on low power builds. On high power builds, it would make the vehicle more flexible. I want to go 40mph, but I also want to go downtown (20mph limit) and offroad. I can use a smaller motor for the task if I have a two speed tranny with 1:1 and 1:2 ratio. This way I can cruise to town at top speed, and downshift to first when I hit the lower speed limit. This would allow me to sit on full throttle and not speed, allowing peak motor controller efficiency. As long as the motor is not outside of the efficient range, everything will be happy.


Add in an amp limited controller and you can have more flexibility than an asian gymnast.

Ah, the conversation is turning to semantics,
We are all in agreement. there are just application & style varients that are the sticky points.
:lol:
To add to the "debate" I would allways recomend buying more or better batteries over rarley used horsepower

If transmisions were cheap & easy every one would already have them. (especialy Matt, I suspect just for the cool factor)If I thought I could make a turnkey solution I would. A read through the High power rc reduction thread & then the 2 speed tranmision thread will show the folks how many factors come into play regarding the actual implimentation of such a system.

I took a lot of shortcuts on the final version of my little 2 speed that will all affect long term durability. Nothing I am comfortable selling (there have been tempting offers)to any one without the ability to perform any nessisary repairs.

Yup, I think we are all in agreement. It is merely an application debate, more than anything.

Thud,

No need to handle me with a velvet glove. I can take criticizm.

Matt

Hi,

recumpence said:

My personal opinion on this is multiple ratios are only beneficial with low power systems as a way to optimize the relatively small amount of power available. However, for anything substantial (maybe 1kw or more?), multiple ratios are more of a novelty than anything.

Remember, the beauty of electric motors is 100% torque from 0 RPM (or relatively low RPM depending on the system).

Click to expand...

http://endless-sphere.com/forums/viewtopic.php?f=28&t=7220&p=153367

recumpence said:

I found that the fun really opens up when you hit 3kw. The bike goes from "Pedal Assist" to "Scooter" mode at that kind of power.

Click to expand...

I think any setup under about 3kw will get a huge boost from gears. Gary stated that his Cyclone system driving through a Nexus 3 speed with 2.5kw had better performance than a 5kw DD hub.

recumpence said:

However, personally, I think multiple ratios for higher power systems are really not needed. They just add complexity and reduce efficiency due to the added rotating parts and the friction related to it.

Click to expand...

I think we all agree with that. The issue is defining "higher power systems". How about anything over 12kw ?

recumpence said:

Forgive the hypothetical here, but it illustrates a good point;

Someone has $1,000 to spend on motor, controller, other bits.......

Let's say a transmission is $200. I would rather see them put that extra $200 into a bigger motor than add a transmission (assuming their pack can handle it).

That being said, for someone looking to be right at the target 750 watt legal limit (or 200 watts in the UK), a multi ratio option is a must to achieve any kind of decent performance.

Click to expand...

One big potential advantage of a non-hub system is the ability to use the bikes gearing. One of your belt drive single stage units in a configuration like Gary's parallel drive to a 3 speed geared hub will give a big performance and efficiency boost. This setup would add very little (if any) cost or complexity, mainly just run the chain on the right rather than the left. An additional benefit is this makes it easier to use rear disc brakes. OTOH difficulty (which can be overcome) is getting as wide a range of pedal gearing as a left side drive.

Obtaining performance via gearing rather than higher wattage also means you are much less likely to blow an esc.

Another factor is terrain, obviously if you do a big percentage of your riding in very steep terrain you will benefit more from gears.

Isn't it nice to realize were all saying the same thing.... just from different perspectives, even if as Thud points out ... it's a non-discussion atleast were all on the same page and ... there are the trawlers looking for help/answers.

I suppose since my first RC build will likely use the Tower Pro 5330 with a Kv of 235 and a max power of 2900w @ 60sec - I want to ensure efficient operation at my various top end speeds.. Also compared to many (most) the 2100w maximum I would be running (to attempt to keep the motor alive) is peanuts and so... I would want a bit more mechanical assistance at the low end (more torque/reduction) and less at the top.

So Matt, Thud? When is the race - it would make a great video.

-Mike