Conclusive proof gearboxes are awesome.

[Punx0r]

With the evolution of high-powered race and production electric motorcycles it will be interesting to see when/if any start shifting towards hubmotors.

I do wonder at what point the penalty of extra unspring mass with be outweighed by not having a chain drive consuming 2-3%(?) of motor output.

We should also remember that a hubmotor still has a transmission loss in the tyre!

 

[speedmd]

For something like rail or smooth road transport I can see it, but any thing that wants its wheels to follow the contours of more natural undulating terrain, it will be some time and many material break through's to get the hub motors weight down low enough to avoid rather large penalties in suspension drawbacks.

 

[Doctorbass]

and if you ever visit Santa Cruz I will let you ride deathbike and you will immediately gain awareness that all the transmission related BS was just noisey parts grinding around on each other in a box rather than something to be desired in an EV drivetrain.

I totally agree with that Luke! 8)

I did it and if someone can do the same don't miss your chance! :wink:

The death bike is awesome and Lukes home road is too short!! :lol:

Doc

 

[Tommy L]

and if you ever visit Santa Cruz I will let you ride deathbike and you will immediately gain awareness that all the transmission related BS was just noisey parts grinding around on each other in a box rather than something to be desired in an EV drivetrain.

I totally agree with that Luke! 8)

I did it and if someone can do the same don't miss your chance! :wink:

The death bike is awesome and Lukes home road is too short!! :lol:

Doc

Are you both Doc and Luke, saying NO to gear boxes on electrics? The Brammo has a 6 spd box on one of their models.
Here's a quote from their website:

"Fully 10lbs of weight is removed from the Empulse, further improving performance, handling, and range. With the ground-breaking IET integrated 6-speed transmission, the Empulse is able to translate its 90Nm (66 lb-ft) of electric motor torque to over 880Nm (650 ft-lbs) at the rear wheel*. That’s enough forward thrust to relegate direct-drive competitors to the rear view mirrors and compel the motorcycling press to compare the substantial performance to that of 650cc twin class motorcycles.
*In first gear."

Is this a bad thing? Will it give out because of the torque of the Electric Motor? Or do you think that the controller soft starts in every gear change to protect the
gear box?


Tommy L sends.....

 

[Arlo1]

My Zero with a 75-5 has 400ft lbs at the rear wheel with just 1 size four running it. My next bike is a 75-7 with 2 size 4s Luke has all the motor torque numbers maybe he will post them.

I don't see a need for a gearbox its just a marketing thin. My old Motorcycle mechanics instructor told me before trying my bike he likes shifting and the noise etc... Well needless to say after just 15 min on my bike he was blown away and loves the powertrain (just a 75-5 with a size 4) and he liked the fact he was always in the right gear! My bike does 0-60 mph with me on it in 3.8 seconds and tops out at 88 mph. So I don't think I see a need to add something else to have to maintain and wear out while robbing power from the motor. Gears can multiply torque but not increase HP. I can pull wheelies at 60 mph so how much more do I need???? Especially when the next bike will have 2x the torque! BTW there is Zeros with more then 650 ft/lbs at the wheel!

 

[speedmd]

I can pull wheelies at 60 mph so how much more do I need????

Sounds like it has the power to easily top 110 MPH, so why not keep up with the 500- 600cc gasers down the long straights? It also is not a hub motor which I am certain is clearly perceived as a benefit in the suspension and handling department. It seems that most high performing ev's are all using some sort of reduction gearing and using higher voltages to get to higher rev ranges. I bet it is a blast!

Wondering how your zeros motor efficiency is in the 10 - 20 mph range.

 

[Arlo1]

I can pull wheelies at 60 mph so how much more do I need????

Sounds like it has the power to easily top 110 MPH, so why not keep up with the 500- 600cc gasers down the long straights? It also is not a hub motor which I am certain is clearly perceived as a benefit in the suspension and handling department. It seems that most high performing ev's are all using some sort of reduction gearing and using higher voltages to get to higher rev ranges. I bet it is a blast!

Wondering how your zeros motor efficiency is in the 10 - 20 mph range.

Its a motard bike its not safe past 88 in fact its not safe at 88 I built it my self.

And If I wanted what you sugest all I need is the bigger motor and bigger controller with higher gearing like oh IDK the SR??? Which does 0-60 in 3.3 and tops at ~105 mph.

 

[speedmd]

I guess your missing the point. 105 mph is still a dog compared to a fast gaser with a gear box. Agree, you don't need to be that fast, but it is just a fact.

I am not suggesting a electric motor would be best suited mated to a mechanical gear box/ changer, but very interested in a controller / electrical side "changer". For example, if you had two separate battery packs on the bike, each 50 volts (just to make things simple). For low speed, you had them connected in parallel. You would have more current, lower motor RPM, and generally better efficiency at lower speeds.

Now when you get closer to highway cruising speed, you switched the connections some way to series and ran 100 volts to the controller /motor. Half the current, yes, but she will rev like a banshee and should continue to climb in speed if the torque is there with the same motor. Am I missing something?

 

[Punx0r]

Yes: The controller already controls voltage and current to the motor, you don't need to attempt to do so by varying the pack voltage presented to the controller.

Functionally there's no difference between a direct-drive hub motor and a single-speed non-hub motor - they have the same torque characteristic: max at 0rpm and zero at no load speed.

I suspect that the future of EVs is single-speed. The advantages described by Luke et al, above, are persuasive. However, I can't shake the suspicion that it's the best compromise rather than being ideal. The decaying torque and power on an electric motor as road speed increases is the opposite of what you want, considering the disproportionate increase in air resistance as speed increases. I suspect this is why we tend to see very limited top speeds for EVs.

I get the argument that you just have an oversized, over-geared motor and feed it a ton of phase current, but isn't this resulting in poor efficiency and wasted battery power at low speeds?

Likewise, if Luke's Deathbike has more torque than is useable at the highest manageable road speed, isn't the motor too big for the job, incurring a weight and cost penalty?

Is there something that can be done to the motor or controller design to increase low-speed efficiency and render this point moot?

 

[gwhy!1]

I can pull wheelies at 60 mph so how much more do I need????

Sounds like it has the power to easily top 110 MPH, so why not keep up with the 500- 600cc gasers down the long straights? It also is not a hub motor which I am certain is clearly perceived as a benefit in the suspension and handling department. It seems that most high performing ev's are all using some sort of reduction gearing and using higher voltages to get to higher rev ranges. I bet it is a blast!

Wondering how your zeros motor efficiency is in the 10 - 20 mph range.

Its a motard bike its not safe past 88 in fact its not safe at 88 I built it my self.

And If I wanted what you sugest all I need is the bigger motor and bigger controller with higher gearing like oh IDK the SR??? Which does 0-60 in 3.3 and tops at ~105 mph.

what if you don't have the room to fit a bigger motor and controller.. thats the problem I have ..

 

[gwhy!1]

Think of your small motor and a 10:1 reduction stage. Now think of your small motor simply grown in radius to give you the 10:1 torque increase you desired (which only needs to grow to ~3.2x radius), and now you have your same small motor + gearing stage system performance, but with more area to shed heat from active motor materials and none of the losses of the gearing stage.

There is not the space on my bike to go 2 or 3x bigger with the radius and then there is all that extra weight... My bike is a single speed but it do have a reduction .. but the size/weight of that reduction could also be 2 speeds , yes it may not be ideal but if you cant fit a big motor into the space and keep under the weight limit target with also keeping the same battery capacity then I cant see any other solution.

 

[speedmd]

Yes: The controller already controls voltage and current to the motor, you don't need to attempt to do so by varying the pack voltage presented to the controller.

Understood, but the battery can supply twice the current when in parallel and not sag as much if your controller is calling for more current to drive from a stop or near that.

With the same 100 volt capable controller (removing the low voltage cutoff circuit), the motor will drive twice the rpm at 100v than it does at 50v. Lots of other relationships certainly, but were are looking for extending rev/speed range in the smallest lightest package.

 

[liveforphysics]

So much misinformation in this thread.

SpeedMD- Learn how a buck converter works my friend. The motor winding is the inductor in the circuit.

There is no practical efficiency penalty in bucking 100v at 5A off the battery to 5v on the phase leads at 100A (only some tiny FET switching losses).

Gwhy- Why do you think direct drive needs a larger battery? It doesn't. You have never had any EV that makes so much torque for so little from the battery as deathbike. With a stalled rotor it takes something like 7A at 116v to send 660A RMS phase current into my motor to make 650ft-lbs of torque. Let's stop propagating BS about using a tiny motor and a bunch of gearing having an efficiency advantage, it can't. The most efficient solution for making torque will be the one designed around natively being a high torque producer rather than adding stages of loss.

Likewise, it does not need to be heavy.

The current state of motors is stuff made to be as cheap as humanly possible to manufacture, largely all for the Chinese domestic ebike market. This is why they are generally heavy and have shit efficiency. It is not an intrinsic property of the drive topology to be made of shitty materials and be badly designed and heavy etc. Miles motor has shown us it can be done with efficiency and very low mass if done right.

Punxor- Feeding a big motor (that has crazy low phase resistance) huge currents isn't inefficient at all. It's not wasting that current, it's turning every bit of it into torque that is rocketing you forward, and it's doing it with better efficiency than any small motor setup could do if you were trying to make identical performance.

It's not until you get to very light cruising loads at high RPM that having a large motor becomes an efficiency penalty through the core loss. For everything happening at low speeds, big motors are the cats pajamas.

ATB,
-Luke

 

[speedmd]

Hi Luke

I respect what your saying, and yes I have much to learn. Your still not answering how to get more RPMs / speed out of the motor besides gearing them taller. They top out where they top out at a given voltage. There is certainly an efficiency variation in the motor, not the controller that is RPM dependent, correct? So I just need to run higher voltage /higher kv? It is like talking to Currier's riding fixies claiming they don't need no stinking gears.

 

[zEEz]

interesting! so to summarize a zero S is more or less power limited in its top speed and a gear
could not help to achieve better top, just wasted power. If I want a 'busa style rocket to do 300 kmph
I need to increase the diameter of the motor and its power to accomodate required top speed power.
straightforward :wink:

have fun!

 

[gwhy!1]

Gwhy- Why do you think direct drive needs a larger battery? It doesn't. You have never had any EV that makes so much torque for so little from the battery as deathbike. With a stalled rotor it takes something like 7A at 116v to send 660A RMS phase current into my motor to make 650ft-lbs of torque. Let's stop propagating BS about using a tiny motor and a bunch of gearing having an efficiency advantage, it can't. The most efficient solution for making torque will be the one designed around natively being a high torque producer rather than adding stages of loss.

Likewise, it does not need to be heavy.

I did not say i would need a bigger battery :? ... But I would need the same capacity battery as I have now and if I was to use a bigger motor/controller then I would have to reduce my battery capacity and that is not a compromise I do not want also a bigger motor/controller will not physically fit . Of course my bike has a efficiency advantage over other bikes in its class which all have physically bigger motor/controller , mine has more power and is much lighter ( and it has a higher top speed :wink: ) , there is no BS here... Im sure a motor can be custom made to for fill my requirements , but there again why bother when what I already have would take some beating for cost.

 

[Arlo1]

OK... So let me get this strait you have room for a transmission but not a few mm more motor diameter or length???

 

[gwhy!1]

OK... So let me get this strait you have room for a transmission but not a few mm more motor diameter or length???

Yes

 

[Arlo1]

Weird. I would be inclined to redesign or run 2 motors.

One thing I think people don't understand is when a transmission is used in a ICE vehicle a transmission will help with efficiency by keeping the rpm low but with a electric it will only hurt efficiency because the efficiency losses of higher rpm is fairly low with a well designed electric motor.

 

[gwhy!1]

I do run 2 motors yes if I built a frame from the ground up I could have double the power that I have now and still come in lighter than a off the shelf same class bike .

 

[speedmd]

Thread is getting a bit fragmented and confused with off topic scenarios. Lots of good information and experienced folks here can help nail some stuff down and help bring the group to better understand some of the tradeoffs.

Can we keep it to one motor size and discuss for a bit. Understood, that the better or bigger the motor the better results you should get.

Looking at the ebikes.ca simulator quite a bit and using the same motors and controllers, but changing out the 36v 20ah ping for a 52v 20ah ping you can overlay and see the difference in motor efficiencies. In every case I went through, clearly the lower voltage was more efficient at lower speeds /rpm. Most in the 3-4% range but some more than 10%. This reverses as the speed increases past the upper ranges of the lower voltage setup. We also see a major drop off of the efficiency trace when going above the rev range. At this point, even going down hill will not help you at all. You either go up in voltage, or gearing to get more speed assuming you have the motor torque/power to make it happen.

Question is, is it better to keep it simple and take the efficiency hit at a higher voltage setup at the lower speeds and give up maximum top speeds or better to some how change the system voltage setup to improve the efficiency/ rpm range and effectively out perform the simple setup at both the low speeds and extend the top speed range.

 

[Punx0r]

Thanks for the clarification, Luke.

Am I right in thinking that with proper motor design it's not a problem to run a motor at high load at low speeds, with regards efficiency? We're used to ebike motors accompanied with warnings about not running them hard at less than a certain fraction of their no-load speed because the efficiency sucks and they burn up. "reduce wheel speed, volt up" we're told. Is this just a limitation of those cheap motors and not intrinsic of motors generally?

gwhy!, this may be a bit over-simplistic, but if we boil it down then the only weight we should have in a motor/drive is active material that makes torque. So copper and stator iron in most cases (but I guess just copper ideally). The rest is necessary to the structurally support the copper and transmit drive, but produces no work and so is wasted at best, parasitic (gearing) at worst.

I appreciate that variable gearing may allow someone to make the best of the available (inappropriate) motors.

 

[Arlo1]

With a proper controller you will be just as well running at low rpm vs higher rpm.

The phase amps (motor amps or the amps flowing in the windings) will determine the torque. So if you want a flat torque curve you will have smooth and consistent acceleration and the same amps in the motor at all motor speeds. This will make roughly the same heat in the motor at all speeds.
There is a bit more are higher rpm from eddy losses etc. but as a rule of thumb your heat in the motor is from the resistance in the windings when running close to its limits which is what I'm thinking we are discussing.

IN other words for the same torque at say 1000 rpm and the same torque at 4000 rpm you will make the motor basically heat up the same amount.

 

[speedmd]

Hi Arlo

It would be great if we could get some of the more advanced motors/ controllers / batteries loaded on the simulator just for comparison to the basic ebike stuff.

 

[liveforphysics]

I would say yesterday's most excellent electric vehicle race event at Pacific Raceway called Silent Thunder was a strong demonstration of vehicles with gearboxes and vehicles without them racing head to head.

You can decide for yourself what makes more sense.

ATB,
-Luke