Racing and efficiency

Thanks Luke. I have just never seen a zero beat a 450. I thought that whatever voltage the battery was, was what
went to the motor and I didn't know that the voltage changes.

I will build a bike with the latest Zero drivetrain.
 
thepronghorn said:
There's nothing to concede. The math isn't very hard. It's just ohms law and basic motor theory.

Say we have a motor that spins 10k rpm no load at 100V which means its Kv is 100 rpm/V and its Kt is 0.0954 Nm/A. Suppose its internal resistance is 0.01 ohm.

Now say we're in 3rd gear, our motor is spinning at 1000 rpm, so our BEMF is 10V.
To make 9.5 Nm of torque from our motor, we need 9.5Nm / 0.0954Nm/A = 10A which requires 10V + 10A*0.01ohm = 10.1V into the windings.

Now say we have the same motor in 1st gear which has a ratio 3x lower than 3rd gear. Now our motor is spinning at 3000 rpm to get the same rear wheel rpm, so our BEMF is 30V.
Since our ratio is 3x lower, now we only need 3.16 Nm of torque, which is 3.16Nm / 0.0954Nm/A = 3.33A which requires 30V + 3.33A*0.01ohm = 30.0333V into the windings.

Our two different scenarios result in the same torque and rpm to the rear wheel, but one requires 10.1V into the motor windings while the other requires 30.0333V into the windings. Guess which one needs a higher duty cycle in the controller? Guess which one results in more power being drawn from the battery?

That's right, it's the one needing ~3x higher voltage into the windings and the one in low gear.
Click to expand...

Maby the math isn't very hard, and sure there's more to it than this nice simplified example, but you got it wrong.

Turns out the example here of producing 1kw requires 100A to the phases in 3rd gear and results in 100w of winding loss, and 33.3A in 1st gear results in only 11w of loss.

9 times less total motor winding losses (and lower controller losses) from a 3 times lower gear ratio.

And Luke i believe, is making the same point here:

liveforphysics said:
Some folks still don't get that it's less burden on your battery.

If you had a lower ratio gear you could shift into, this would get the motor BEMF higher and draw more power off the pack.

If you have an EV with gears, and you want to pull the most current from your pack, then start in 1st gear. If you want to pull the least current start in 4th gear (or whatever you have ).
Click to expand...

If we are talking about the same starting acceleration here (and its a pointless comparison if we are not) then you Luke are also are flat out wrong.

Nice to have spotted this one pop up somewhere new again though. :)

On the original topic of racing and efficiency though motomoto, the bikes ive built with a ca120 or colossus type motors do benefit from a 2 speed gearbox (that adds 385 grams and 13w of loss vs single speed) but the Joby powered bike doesnt really need it, however the sprockets can be changed from 8:1 through to 12.4:1 and we dial the gearing in to the track.
There are noticeable benefits from getting the gearing dialed in for the conditions, even if we can get the acceleration we need with taller gearing on an open speedway track in 450cc class by using more phase amps, these losses build so not surprisingly if we are talking gear ratio for a machine in the real world there is compromise required and theres no way any simple philosophical or blanket statement about taller gearing for best efficiency in all occasions can be correct.

Put simply there is a price to pay for additional motor torque, the winding losses for ALL these motors at ANY torque level rise by the additional amps, squared.

You also have likely observed this in action Dave, with your sweet Tangentdrive climbing a steep hill in a low gear using 1000w vs a taller gear using 3000w, most hub motor setups on 26" wheels that are clearly making use of all the "greatness" of direct drive and tall gearing are claiming (consuming) 5000w may not even get up the hill.
If we enter an otherwise identical machine to the Joby bike but with a cro motor it gets lapped twice in a 6 lap race haveing used around 1.5 times more power off the battery and now with a stinky motor, a while back with an x5 motor and a decent ride the sideplates were still to hot to touch after 2 hours rest. -I dont mind leaving hub motored bikes outside because of the smell, its really the wasted battery power that bothers me. :wink:
 
Yeah there are a lot of things wrong with that post. I realized I was wrong yesterday, that's why I had him delete that part from the post, I also tried to correct my original statement on page 1 although looking at it again I don't really like its conclusion. Here's an example with winding losses and drag losses included. I can delete all this stuff about a hypothetical scenario if it's too made up to be useful.

Say we have a motor that spins 10k rpm no load at 100V which means its Kv is 100 rpm/V and its Kt is 0.0954 Nm/A. Suppose its internal resistance is 0.01 ohm. Finally, suppose that at 10k rpm we have 400W of no load (hysteresis + eddy current) losses and that these iron losses rise linearly with rpm.

Scenario 1:
We're in 3rd gear, our motor is spinning at 1000 rpm, so our BEMF is 10V.
To make 9.5 Nm of torque from our motor, we need 9.5Nm / 0.0954Nm/A = 100A which requires 10V + 100A*0.01ohm = 11V into the windings. Our copper loss is 100A^2*0.01ohm = 100W. Our no load loss is 0.1*400W = 40W.

Scenario 2:
Now we have the same motor in 1st gear which has a ratio 3x lower than 3rd gear. Now our motor is spinning at 3000 rpm to get the same rear wheel rpm, so our BEMF is 30V.
Since our ratio is 3x lower, now we only need 3.16 Nm of torque, which is 3.16Nm / 0.0954Nm/A = 3.33A which requires 30V + 33.3A*0.01ohm = 30.333V into the windings. Our copper loss is 33.3A^2*0.01ohm = 11.1 W. Our no load loss is 0.3*400W = 120W.

Total loss in scenario 1: 140W
Total loss in scenario 2: 131.1W

The loss is pretty similar with scenario 2 in the lower gear being slightly worse since our iron losses more than make up for the reduced copper loss. These are all made up numbers, but I guess it just goes to show that you have to account for everything, and trading copper losses for iron losses may help your controller a bit but may heat your motor up more...

Your data from your experiences with the CA120, Joby, and Cromotor is greatly appreciated. It's cool to see how jumping to a far more expensive motor and the associated increase in efficiency from better design and materials allows you to ditch the gearbox and improve efficiency.
 
Thanks you guys for getting me to see what is going on. I was under the impression that the voltage to the motor was always
the same and that the waveform was just segmented more at lower throttle settings.

Hey Toolman, is that 8:1 to 12.4:1 the motor to the rear wheel? I am designing a downhill suspended bike with the RV-160 short
and have been off on my gearing calculation. The thing is geared for about 100 km/hr. I should have it adjustable between 60-80 km/hr
or it wouldn't climb or accelerate well.

Another thing that keeps tripping me up on this supercross bike thing is that I add up the weight of the 38 lb zero motor and the 10 lb controller
and the 20+ lbs of batteries I will need to go 6 minute and the weight is more than the ICE engines. If I look at 5 Astroflight motors and hardware
and controllers (HV160) I get about 20 lbs less weight for the motor and controller.
 
Miles said:
thepronghorn said:
Finally, suppose that at 10k rpm we have 400W of no load (hysteresis + eddy current) losses and that these iron losses rise linearly with rpm.
Click to expand...
Why would one suppose that?
Click to expand...

Simplicity? idk? I saw Joby's graph and this graph of the rv160 short and they were pretty linear. Is the 400W not very realistic for a 0.01 ohm motor? Is it just too simplistic? Please correct me if I'm wrong - I'm just trying to understand motors a little better and maybe help some other people understand as well.

http://www.jobymotors.com/public/img/products/JM1S/JM1S_data_sheet.pdf
JM1S idle power.PNG

https://endless-sphere.com/forums/viewtopic.php?f=30&t=75494&start=0#p1177299
RV160s idle.PNG
 
I didn't know where to put this interview with the Alta creators....& some good footage of the bike in action...I still say it needs to lose 50#s but its looking better every time i see it in action.
[youtube]MORcWFtWJbM[/youtube]
 
I used to email with Mark Fenigstein about the bike launching off the line. At that time and presently I think it takes a big hit of
enertia or horsepower to get the weight of the rear wheel and drive train spinning instantly. He seemed to think they could figure
it out electrically. I don't see videos of the Alta bikes starting against ICE bike. He says they lose about 10 feet off the line.
 
I ordered a 75-7 motor. I don't know if that is the motor, but I have been thinking about the possibilities of making
new sideplates and using the motor as a structural part of the frame. I don't have a problem with doing that. Whatever works.

This morning I was thinking about a 8 inch ring gear to an automatic transmission with 5 planetary gears attached to 5 Astroflight motor
with 5 HV-160s. When there's a will there's a way.
 
Toorbough ULL-Zeveigh wrote
Luke has no knowledge of the weight issue... it's like he has a complete blind spot to that topic and always scales his motor up so that it's 20 times bigger than needed and says:

"See... big motors are the answer."

Well, yeah, if you accept the weight penalty.
Click to expand...

Yeah, there are a lot of things to consider on my motocross project. I cancelled the Zero motor and am going back to Astroflight motors. Even with astroflight motors
I have to watch weight on every part to make it work. I know the clutch idea isn't popular with some as it's 'just a waste of energy and weight'. I want to get to the first turn
first so the motors will be at their maximum RPM and hopefully launch the bike like a speedway bike.
[youtube]9tCHCrxTuwk[/youtube]
 
Toorbough ULL-Zeveigh said:
Luke has no knowledge of the weight issue... it's like he has a complete blind spot to that topic and always scales his motor up so that it's 20 times bigger than needed and says:

"See... big motors are the answer."

Well, yeah, if you accept the weight penalty.
Click to expand...

http://visforvoltage.org/forum/14118-concepts-ebike-propulsion-2?page=2
Click to expand...
This guy was on ES since 2006. Has he practically done 1 useful thing, discovery, achievement or whatever? He moved to VV because of some reason, bunch of more competent people getting all the attention because they archived something maybe? I do not know, but I know a lot of users disappearing that I really miss here, they did more then just moving air with their lungs or sharing their thoughts all over again. I still think anyone should prove it better before barking at someone (at least in 1 of 100 ways).

BTW. Astroflights will kick ass if you have enough of them :D
 
There is nothing happening with the motor at maximum rpm except for some kinetic energy which might help get
the drivetrain spinning when the clutch is engaged. The motor will drop down into the horsepower area with some
skill from the rider and stay there until all the accelerating is done. I think of electric motors differently. I have a
shop full of belt sanders, grinders, lathes etc. They all sit there at the rpm they run at and when you apply a load to
them they slow down, if too much load is applied they slip. I have thought about just having the throttle wide open
all the time and have some kind of device that engages the motor the desired amount like a clutch. I need something
that doesn't create heat like a clutch does. A magnetic clutch might work but I haven't worked out the details, like how
to disengage it.
 
motomoto said:
There is nothing happening with the motor at maximum rpm except for some kinetic energy which might help get
the drivetrain spinning when the clutch is engaged. The motor will drop down into the horsepower area with some
skill from the rider and stay there until all the accelerating is done. I think of electric motors differently. I have a
shop full of belt sanders, grinders, lathes etc. They all sit there at the rpm they run at and when you apply a load to
them they slow down, if too much load is applied they slip. I have thought about just having the throttle wide open
all the time and have some kind of device that engages the motor the desired amount like a clutch. I need something
that doesn't create heat like a clutch does. A magnetic clutch might work but I haven't worked out the details, like how
to disengage it.
Click to expand...

you mean something like a torque based throttle? :|
 
motomoto said:
There is nothing happening with the motor at maximum rpm except for some kinetic energy which might help get
the drivetrain spinning when the clutch is engaged. The motor will drop down into the horsepower area with some
skill from the rider and stay there until all the accelerating is done. I think of electric motors differently. I have a
shop full of belt sanders, grinders, lathes etc. They all sit there at the rpm they run at and when you apply a load to
them they slow down, if too much load is applied they slip. I have thought about just having the throttle wide open
all the time and have some kind of device that engages the motor the desired amount like a clutch. I need something
that doesn't create heat like a clutch does. A magnetic clutch might work but I haven't worked out the details, like how
to disengage it.
Click to expand...


You think you need something like this only due to not yet experiencing good motor control with an adequate torque motor. That's the real solution.

At pikes peak this year, Zero FX-S finished in the same time ranges as the pack of unlimited class 1000cc+ gas bikes.

So much misconception and confusion in this thread. At some point if you continue building performance EVs you will gain awareness there is no replacement for having more copper and iron and magnet. This is ultimately what determines how effectively a vehicle is able to convert the energy in its battery to useful thrust. You are more than welcome to get there the hard way as I also had needed to do myself. Spend enough time on the dyno making pulls with little motors and you quickly learn to appreciate big motors.

ATB,
-Luke
 
Hello,

My name is Sebastian and I am from Germany. We do racing Motocross with our own prototype bikes. We race with gasoline bikes (open) in mx races and in an electric class in enduro races.
Through the years of experimenting, developing and testing, I would say I have good knowledge on this specific type of racing. One thing should be clear for everybody, you cannot save energy with using a gearbox, a given acceleration takes always the same amount of energy, if you use 1 or 10 gears. But the amount of losses will increase with every stage of the gearbox. That's you decision, use a motor that's suits your needs (easier in motocross because of the relative small speed range) or you use a gearbox with several speeds to achieve same rear wheel torque.
To make it a bit more less theoretical, we tested 5speed gearbox, with and without clutch. We tested 2speed gearbox with and without clutch. But we keep the single stage design. With 5 speed you as a rider are not able to shift fast enough as you need, you completely need to redesign the gearbox as no motocross gearbox will take the instant torque very long. You add weight and also you spend a lot of space on your bike. 2 Speed was much better than 5 speed but when we were on the tracks every ride only started in first and took the whole ride 2nd gear. Ok it depends on the track but why you should carry a gearbox around the track when it only has an advantage in 5% of track time and in the rest a disadvantage? I have so much data from datalogging, lap times and so on and I can tell you it other things that count to make a competitive motocross bike than a gearbox. It's the cooling, the weight distribution, the suspension, it's the whole package. The electric bike will be completely different and so it's not only putting a motor and battery in..
Our bike is 100% competitive with 250-4, it outperform it. But the problem is the battery capacity. We have to turn down the power (battery current) a lot to achieve our 20-24min race time and swap batteries once on 50min enduro runs.

If someone has question regarding electric motocross, feel free to ask.

If you are interested in our bike, just go to http://e-mxm.com, the site is not up to date as we change always a lot on the bike..
 
Thank you for sharing your experiences Sebastian!

Nice looking bike and nice website!
 
parabellum said:
Cool bikes Sebastian! How is it working out without mechanical brake assist in the rear? Was it difficult to get working?
Click to expand...

Thanks. Yes and no. It is only possible with coaxial lineup of sprocket and swing arm, the hard part was to make the brake lever feel like real brake with pressure point feeling. At this point there is only one downside, you cannot stall the rear wheel, as the controller wants prevent wheel lock scenarios. Also you add a little bit of heat. The advantage is simplification and less unsprung mass.
 
motomoto said:
There is nothing happening with the motor at maximum rpm except for some kinetic energy which might help get
the drivetrain spinning when the clutch is engaged. The motor will drop down into the horsepower area with some
skill from the rider and stay there until all the accelerating is done. I think of electric motors differently. I have a
shop full of belt sanders, grinders, lathes etc. They all sit there at the rpm they run at and when you apply a load to
them they slow down, if too much load is applied they slip. I have thought about just having the throttle wide open
all the time and have some kind of device that engages the motor the desired amount like a clutch. I need something
that doesn't create heat like a clutch does. A magnetic clutch might work but I haven't worked out the details, like how
to disengage it.
Click to expand...
Wheelspining , speedway type starts is all about keepint the ICE motor in its max power range at the expence of traction at the wheel.Drag racers know that wheelspin is a lose
Some testing is likely needed on dirt to confirm if there is more traction and launch speed with a electric drive when you keep the tyre slip to a minimum but with maximum torque from the motor.
It might just be a advantage for EV dirt bikes.
 
Peak traction actually happens at ~10-15% wheel spin on a good track surface. It does not peak at its static traction coefficient like a highschool physics teacher would try to tell you.

Dirt behaves similarly, but peak thrust occurs at some point of wheel spin rate highly variable on the dirt conditions.
 
You must log in or register to reply here.

Similar threads

D
Twin brush controllers
Replies
12
Views
677
dumbass
D
TheBeastie
AKM-100H 350W motor configs 48V-328RPM vs 36V-201/260RPM
Replies
6
Views
956
Aloles
Aloles
J
Attempt to achieve torque control of an induction motor via a tachometer and off the shelf vfd
Replies
1
Views
361
Jrbe
J
Skyler
Wheel building for hub motors.
2
Replies
31
Views
2,799
D Alan Stewart
D
W
Electric Wakeboard Winch Motor
Replies
7
Views
1,067
siml
S
Back
Top