Racing and efficiency

[thepronghorn]

Another perfect example of no one reading the op.....

Does any one here think the KTM in that video is anything other than weak sauce? (or remotely competitive with a modern 4-stroke 250cc ice on a real course?)

You can spout off about single speed all day & be right.....but no one can produce a list of parts to assemble a real Moto crosser that could compete heads up. there isn't a motor/battery/controller combo that will get the job done.....even for a 15 minute moto.

This is why Kim abandoned this thread....too much theory & no data that supports his(& mine) specific interests or constraints.

I tried to address this with the Emrax motor. I don't know much about motocross so it's hard. Maybe you could say how much power a modern 4-stroke 250cc ice makes? And how much it weighs so we know how much weight we have to work with?

The overall idea of this thread may have been seeking a battery/motor/controller combo that will support his (&yours) specific interests and constraints, but the first post (and many subsequent posts) contained a lot of numbers and ideas that just aren't true. If we can understand/accept the basic motor theory that promotes a single motor going through a single speed drivetrain as the ideal drivetrain, then we can move to the practical limitations of motor/controller availability/cost and stuff like that.

Edit: also your KTM comparison is lame because the E-ride isn't really designed to be competitive with 250cc bikes. It has way less power and weighs a lot less. For a more competitive bike maybe look at the Alta Motors Redshift?

 

[tangentdave]

What if we were limited in the amount of power the system was able to produce? There would be many causes of this- thermal, battery capacity, weight and size, desired range, etc. In this case, would a transmission be a viable option to optimize vehicle performance for different situations?

 

[liveforphysics]

What if we were limited in the amount of power the system was able to produce? There would be many causes of this- thermal, battery capacity, weight and size, desired range, etc. In this case, would a transmission be a viable option to optimize vehicle performance for different situations?

If your vehicle is battery power limited, and you add a transmission, you just added a series power transfer loss ontop of the identical battery power limitation, meaning a net reduction in possible output and efficiency.

The misconception that causes confusion in this matter is lacking the awareness that making torque directly at the motor is some kind of penalty to the battery. If the motor winding is say 2mOhm phase resistance, and you want to put say 650A through this winding, it requires 1.3v of winding voltage drop to accomplish this. 1.3V*650A is 845W of power going into copper loss to make this torque. From a say ~116vdc battery this means ~7.2A of current from the pack to make full output torque.

If you make a motor with better copper fill, this copper loss penalty to make the torque becomes even less. When you compare this 845W of total copper losses to make full torque VS any kind of series power transfer using gears churning oil, you find its an energy bargain.

 

[induna]

OK, so is there a fixed gear solution that will climb 1100 meters in 5 kilometers without a. destroying the motor/controller by overheating, or b. which requires that I carry a massive motor/controller/battery combo? I'm planning to do this with a Bafang mid drive and a 13s6p 18650 GA pack. Are there other more efficient and equally economical options? High speed is neither required nor wanted. Sorry if this is too off topic since it isn't about racing, but I am interested in whether the efficiencies of keeping all of the torque conversion duties in the motor as outlined by LFP have a practical application to more pedestrian needs.

 

[liveforphysics]

Perhaps this will help.

If you have say a 70hp system that to make the full torque at peak acceleration has 845W of total peak copper losses, even if you magically swapped to some solution that magically has NO copper loss, from a total system performance perspective, it's hardly impactful from a battery or performance perspective (a potential maximum system efficiency improvement of a couple percent). If the system you use to reduce copper loss adds more than just say 2% drivetrain frictional losses to magically reduce ALL copper loss, you're at a net efficiency and performance loss, ontop of having a more fragile system with more moving parts and associated failure modes.

 

[liveforphysics]

OK, so is there a fixed gear solution that will climb 1100 meters in 5 kilometers without a. destroying the motor/controller by overheating, or b. which requires that I carry a massive motor/controller/battery combo? I'm planning to do this with a Bafang mid drive and a 13s6p 18650 GA pack. Are there other more efficient and equally economical options? High speed is neither required nor wanted.

If you don't care about power and only torque, then you have a few options. You can make a tiny motor, and then run it through a series of mechanical toothed levers (gears) to try to simulate as though it were a motor with a larger radius, OR you can just have a motor with the appropriate radius natively, and skip the leverage stages in trade for having all the leverage you need in the motors radius. If you put the leverage you need in the motors radius itself, then for a given mass of motor, you can always achieve highest continuous power, because more of the system mass is iron and copper doing the actual conversion from the packs energy to the mechanical work output you wanted. Any portion of vehicle weight that isn't storing the electrical energy or making the electrical to mechanical power transformation is your vehicles performance burden to be minimized or removed if possible.

 

[Hillhater]

........ If we can understand/accept the basic motor theory that promotes a single motor going through a single speed drivetrain as the ideal drivetrain, .."........

Why would a "single speed drive train" be considered any more "ideal" than a 2/3 speed drive train ?
In terms of transmission efficiency, if thats the goal, then The "Ideal" drive train is direct 1:1 motor to wheel (hub motor , or direct shaft drive ?) , any other transmission components add weight and losses to the system.
However, few, if any, seem to have achieved this in a practical package due to the limitations of available technology.
Single speed reduction systems have become the compromise that even the best designers resort to.

 

[tangentdave]

Now I'm curious why all EVs aren't direct drive. From the sounds of it, I should use a hub motor and be happy that I'm being as efficient as possible. Why is this not the case? Why don't I have direct drive a motor on my ebike that will give enough torque for wheelies and 40mph? Why does a Tesla Model S use a 10:1 reduction before the differential?

 

[thepronghorn]

........ If we can understand/accept the basic motor theory that promotes a single motor going through a single speed drivetrain as the ideal drivetrain, .."........

Why would a "single speed drive train" be considered any more "ideal" than a 2/3 speed drive train ?
In terms of transmission efficiency, if thats the goal, then The "Ideal" drive train is direct 1:1 motor to wheel (hub motor , or direct shaft drive ?) , any other transmission components add weight and losses to the system.
However, few, if any, seem to have achieved this in a practical package due to the limitations of available technology.
Single speed reduction systems have become the compromise that even the best designers resort to.

Okay yeah hub motor is the best but as the application is motocross I assumed at least one stage would be necessary to get the motor weight out of the wheel. With regard to the 2/3 speed drive train, maybe shifting time, extra weight for extra gears, clutch, etc. would make it worse than single speed?

Now I'm curious why all EVs aren't direct drive. From the sounds of it, I should use a hub motor and be happy that I'm being as efficient as possible. Why is this not the case? Why don't I have direct drive a motor on my ebike that will give enough torque for wheelies and 40mph? Why does a Tesla Model S use a 10:1 reduction before the differential?

We're moving more and more into the realm of the "Conclusive Proof Gearboxes are Awesome" thread which I think is rather offtopic for this thread. There is also the "The limits of torque production for a given weight of motor" thread. Links below. Basically there's a fair bit of debate about this, but the Model S is discussed in addition to high torque hubmotors and stuff like that.

https://endless-sphere.com/forums/viewtopic.php?f=30&t=47930&start=700

https://endless-sphere.com/forums/viewtopic.php?f=30&t=78923

 

[liveforphysics]

Now I'm curious why all EVs aren't direct drive. From the sounds of it, I should use a hub motor and be happy that I'm being as efficient as possible. Why is this not the case? Why don't I have direct drive a motor on my ebike that will give enough torque for wheelies and 40mph? Why does a Tesla Model S use a 10:1 reduction before the differential?

Existing hubmotors are largely designed around being the cheapest path to making the cheapest Chinese scooter roll forward with no performance or efficiency concerns.

Hubmotors designed around being efficient have been made, and had measured system efficiencies beyond 98% (CISRO solar car motor etc).

Essentially we have a controller current control speed limitation driving our motor designs to remain in the shitty-ish range to be functionally controllable with existing tech.

 

[Hillhater]

Now I'm curious why all EVs aren't direct drive.....
..... Why does a Tesla Model S use a 10:1 reduction before the differential?

There is a long thread on that a few months back...Two threads actually
Bottom line is, because a motor to give the same torque at the wheels in 1:1 drive would be too big to package into the available space, and most likely much heavier than the current motor and reduction box.
..because theory is not reality !

 

[motomoto]

So this is what a 250 race is like at 40+ hp

I suggest you watch it in 1080p if you can

[youtube]7f6QyCMqxTQ[/youtube]

 

[motomoto]

This is the same track with 60+ hp 450s

I only need enough battery to do this for 6 minutes. The length of a supercross heat race.

[youtube]-hfxm0M_SvQ[/youtube]

 

[liveforphysics]

This is the same track with 60+ hp 450s

I only need enough battery to do this for 6 minutes. The length of a supercross heat race.

Great riders and great chassis, the powertrain aspect looks very mellow to replicate in electric power.

 

[motomoto]

If you can't win the race to the first turn, you might as well not show up.

An Alta electric bike would get smoked even though they claim 40+ hp and 34 ft/lbs of torque.
That's why you don't see it drag racing ICE bikes on Youtube. It gets smoked off the line.
They are also 50 lbs overweight compared to a 450 at 270 lbs vs 220 lbs
http://www.altamotors.co/machine/redshift-mx/

A 450 makes 30 ft/lbs of torque. A 250 makes 20 ft/lbs of torque

This video by Doctorbass got me thinking. He is at 141 lbs in this video.
One of the dual size 4 setups maybe? You would have to add better suspension and
more battery. Under 200 lbs would be sweet.

[youtube]OMgZHCrv7r0[/youtube]

 

[motomoto]

Luke wrote:

Great riders and great chassis, the powertrain aspect looks very mellow to replicate in electric power.

If I got the motor, controller, and battery who could I get to program the controller(s) ??

It would take some talent to beat a bunch of billion dollar factories.

 

[Hillhater]

It would take some talent to beat a bunch of billion dollar factories.

Yes, the road race bikes are realising this also..
Even with some big resources behind then like Mugen, Polaris , etc, the Zero TT bikes are far from competitive with the ICE bikes

 

[motomoto]

That is just a duration thing. Two years ago the Lightning electric bike beat the Ducati factory team at Pikes Peak by 20 seconds.

It was a 10 minute race. As long as the duration is short electric is more than competitive with gas.

Electric rules Pikes Peak with the cars now for the overall win.

 

[Hillhater]

Oh, and thats not an altitude thing ?
But since then a Kawasaki has been up faster.
EV cars are still a minute off the Outright record at PP

 

[induna]

OK, so is there a fixed gear solution that will climb 1100 meters in 5 kilometers without a. destroying the motor/controller by overheating, or b. which requires that I carry a massive motor/controller/battery combo? I'm planning to do this with a Bafang mid drive and a 13s6p 18650 GA pack. Are there other more efficient and equally economical options? High speed is neither required nor wanted.

If you don't care about power and only torque, then you have a few options. You can make a tiny motor, and then run it through a series of mechanical toothed levers (gears) to try to simulate as though it were a motor with a larger radius, OR you can just have a motor with the appropriate radius natively, and skip the leverage stages in trade for having all the leverage you need in the motors radius. If you put the leverage you need in the motors radius itself, then for a given mass of motor, you can always achieve highest continuous power, because more of the system mass is iron and copper doing the actual conversion from the packs energy to the mechanical work output you wanted. Any portion of vehicle weight that isn't storing the electrical energy or making the electrical to mechanical power transformation is your vehicles performance burden to be minimized or removed if possible.

Thanks for the reply. That's where I thought you were going with your earlier posts. So now it's for me to dig in and see if such a motor/controller combination exists in my price range and design constraints.

 

[motomoto]

Hillhater wrote:

Oh, and thats not an altitude thing ?
But since then a Kawasaki has been up faster.
EV cars are still a minute off the Outright record at PP

2 electric cars won top times last year and the top car only had front wheel drive for half the race
and he beat the first gas car by 29 seconds?

Sure, gas sucks at altitude, but it's likely that it's game over for gas at PP.

We will see in a few weeks how the 2016 event ends up.

 

[motomoto]

So Luke, looks like you watched some of the motocross videos. What motor/controller combination would you go with
to beat these guys to the first turn?

 

[Hillhater]

2 electric cars won top times last year and the top car only had front wheel drive for half the race
and he beat the first gas car by 29 seconds?
Sure, gas sucks at altitude, but it's likely that it's game over for gas at PP.
We will see in a few weeks how the 2016 event ends up.

And what happened in the bike class's then ?
I think last years results says more about the standard of competition than EV vs ICE, since no one got near the record.
PP has lost much of its attraction since it became a surfaced road. Its just another road sprint now with HP and tires dictating the times.

 

[motomoto]

And what happened in the bike class's then ?

Lightning or any serious electric wasn't there.

 

[liveforphysics]

So Luke, looks like you watched some of the motocross videos. What motor/controller combination would you go with
to beat these guys to the first turn?

To beat them to the first turn seems like a Zero SR powertrain running high-c-rate cells to be as light as possible for the power if you really only need to run for 6minutes. I've watched a SR powered Zero XU holeshot the entire line of 450cc class professional class supermoto 450-550cc race bikes and make turn 1 first every start. This is a very high traction environment of a kart track, I don't know if mud has some special vastly different power requirements to go fast on, but from what I've seen of just stock FX power at the enduros I race on them, I've never felt like I was an acceleration disadvantage to anything from any size 2/4stroke. I will give you that a supercross track is more power hungry than the technical enduros I race, and that's why I recomend the SR powertrain.

On high c-rate cells (to not require carrying extra battery mass for a race that's only 6 minutes total), the SR drivetrain may dyno >~70hp at the rear wheel (gas engines with transmissions need to make ~77-82fwhp to match performance at the rear wheel through a tranny.) Having 106ft-lbs of torque on tap for dirt (even on a DS-R weight bike) means ability to violently break traction and roost at will for the entire speed range I saw people traveling in that video. I don't know how much more power is even useful to have racing on dirt.

Your torque won't have interruptions in it's delivery anymore for shifting, and you will never fall out of the powerband or exit a turn in a gear low or whatever.

To accomplish a powerband for that low speed range that simply delivers enough torque to always and predictably break traction or wheelie at any point on the track from say 0-75mph or whatever they are reaching is effortless to do in a single drive stage (belt or chain to rear wheel sprocket) or directly like a hubmotor. However the hubmotor approach would require a fair amount of work to design suspension that would work for that extreme suspension motion racing environment with so much mass in the wheel.

Beating a tuned 450cc single cylinder bike ICE powerplant is really not difficult with electric. Lightning already showed beating a 1,000cc 4 cylinder at everything acceleration/power related is also easily possible for sub 15-20minute races.