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[evtricity]

Over the last few weeks I've been trying to eke out some extra performance improvements from my 2014 Zero SR for use on both the road and the track.

Having recently acquired the Sevcon software and CAN adapter to modify the Sevcon Gen 4 Size 6 motor controller, a multitude of options have opened up to tweak the bike's performance. While many Zero owners have trodden this path before me I thought I would post some of the changes to:
- give everyone some more insight into the out of the box torque settings of a Zero SR;
- highlight opportunities to improve performance; and
- compare notes with those who have made similar tweaks to improve on what is already a high performance naked bike

Torque curves:

The diagram at the end of the post shows the standard Zero SR 2014 torque curves as set on the Sevcon controller.

The key highlights are 100% torque from 0 rpm and a tapering of that torque beyond 2350rpm (default motor max is 6,000rpm). I asked some forum members about what would happen if I increased these settings and was told to watch out for two things - motor cutouts and to stay within the 6,000rpm limit. I was also told that field weakening limits motor performance as rpm increases and so I can't be like a kid playing with his Dad's graphic equaliser and put everything up to the max!

While I don't have a torque curve diagram for the actual Zero SR motor, I think the one for a Remy 250-90 (see bottom of past) is a good example of how a similar motor's torque would reduce as rpm's increase (presumably suffering the same field weakening as my SR). The gradual reduction for the Remy made me think that the Zero could handle a gradual reduction rather than the steep reduction set on the stock motor.

Looking at the two curves together it seemed to me that there was an opportunity to increase the SR's torque at higher rpm without reaching the motor's limits which would result in motor cutouts. After some trial and error on the road and recent testing on the track, I have been able to successfully increase torque by 30Nm @ 4680 rpm and by 45Nm @ 5320 rpm as shown in the updated torque curve at the bottom of this post.

In my trials I also tried to increase the mid-range torque @ 3,590 rpm but when I moved from 155Nm to 165Nm I got cutouts so left it at the 155Nm.

I think I've made some small but important performance improvements and the bike now accelerates much better at high rpm (which was particularly useful when I'd lowered the gearing in the successful search for wheelies and reduced the max speed to 135kph). I think there may be a few more Nm I could eke out in the higher rpm range and I'll try that in the coming weeks and update this thread accordingly.

On the opposite end of the spectrum, I've also learnt a lot about improving the stopping performance of my SR and you read more on that in my "powerful regen" post.

Keen to hear others success in tweaking their Zero's performance and any questions you may have around the changes I have made.

[Nuts n Volts]

Thats pretty interesting.  I have a SR powertrain in my R6, while already fast, it would be cool to see how the limits may be pushed.  I'll look into giving this a try.

Also the Remy motor is not a good comparison for field weakening.  The Remy is an IPM (internal permanent magnet) motor and the Zero is a SMPM (surface mount permanent magnet).  Basically the remy as more reluctance torque capabilities which allows the field weakening capabilities to be greatly enhanced from my understanding. 

[lolachampcar]

Would you care to share the weight of your R6 with SR drive combination and the size battery you are using?

[Nuts n Volts]

Somewhere between 370-390lbs plus rider.  6kWh of Nissan Leaf cells.

[Francois]

well done

[CScalpeL]

First of all, props for putting out all this info dgh853!

Interesting that the stock torque settings are 100% from 0 RPM. There have been numerous posts relating to the lack of off-the-line (until ~20-30 mph) pull for a bike that puts out 106 ft lbs of torque, some have purported that the sevcon settings must have been detuned to prevent snapping of the belt and/or unwanted wheelies. This seems to put that to rest but still leaves open the question as to why the SR can't wheelie with all that torque... (motor design, battery discharge limitation, weight distribution???)

Have you found any settings in the controller that would allow for traction control? That and the variable regen lever you posted would be great aftermarket features!

I'd love to start modding my bike (I just got a 15 SR) but I don't want to void the warranty so I've got a couple of years, in the meanwhile learning and accumulating the tools that I'll need.

[Doug S]

There have been numerous posts relating to the lack of off-the-line (until ~20-30 mph) pull for a bike that puts out 106 ft lbs of torque, some have purported that the sevcon settings must have been detuned to prevent snapping of the belt and/or unwanted wheelies. This seems to put that to rest but still leaves open the question as to why the SR can't wheelie with all that torque... (motor design, battery discharge limitation, weight distribution???)

I was one of the chief instigators of that discussion, and I think I've finally figured it out, at least to my satisfaction. The key is torque multiplication, which is why ICE vehicles have gearboxes in the first place.

When an ICE vehicle is run on a dyno, they rarely run torque and horsepower curves in all gears. It would just be repetitive and give no new information. Instead, they typically put the vehicle in top gear, and run the curves only once. That doesn't matter for horsepower, but it DOES matter for torque, because a lower gear gives higher torque multiplication. So when, for instance, they say that a Hayabusa peaks at 100 ft-lbs of torque, that's in top gear. I looked up the gear ratios for the Hayabusa, and first gear on that bike is 2.6 times higher numerically than top gear. So when a Hayabusa is in first gear, it's not putting 100 ft-lbs of torque on the pavement, it's putting down 260 ft-lbs. The SR has no gearbox, so its 106 ft-lbs of torque is what you get, period. That explains why other bikes may have wheelie and  wheelspin issues our bikes don't have, even though many other bikes use much wider tires.

Of course, there are other issues involved -- smoothness of power delivery on the EV, instant throttle response, no time lost to shifting, etc., but the upshot is that the gearbox on the ICE vehicle does exactly what it's supposed to do, it multiplies the torque available at low road speeds.

[Richard230]

That is a great explanation and analysis, Doug.   

No mater what the starting torque is, your typical street EV rider has a good chance of beating an IC rider off of the line.  While your EV might have less starting torque, not having to rev the motor and slowly let out the clutch to prevent a scary wheel spin or a wheelie, really makes a difference. Anyone riding an EV can just open up the throttle and take off as fast as the bike will go, without needing the experience and skill of feathering the clutch properly.  That is a real plus for any rider, especially a new rider.    The gearbox-loving crowd might complain that takes away the challenge of owning a motorcycle and being a real motorcyclist, but I say that direct-drive is more likely to interest and increase motorcycle sales to new riders and I base my claim on the number of automatic transmission cars sales, compared with manual-transmission car sales.

[protomech]

It's actually putting down more than that; besides the transmission gearing, you also have the ratio between the output sprocket and the rear wheel sprocket, assuming chain or belt drive.

The Zero SR has a 30 tooth front, 132 tooth rear sprocket. That means the motor is turning 4.4x as fast as the rear wheel, and also wheel torque is 4.4x as high as motor torque. So 106 ft-lb at the motor will be 466 ft-lb at the rear wheel. Of course, as vehicle speed and wheel RPM increases, motor RPM will increase as well; and around 2350 RPM (motor) = 39.2 mph the torque will start to fall off.

Compare that to a conventional motorcycle, which has a primary drive ratio, transmission gear ratio, and final drive ratio which all amplify torque. A Hayabusa has a 1.596 primary drive ratio, 2.352 final drive ratio, and in 1st gear has a 2.615 ratio. Multiply all of those up for a 9.82x multiplier.

At a 10 mph roll, for example, the Hayabusa rear wheel will be turning at about 137 RPM and the motor will be turning at about 1345 RPM. Most dyno plots for the motor don't go down that low, but the trend indicates it will be producing about 60 ft-lb at the motor at that RPM. With all of the multiplicative effects of the transmission, it should then produce about 590 ft-lb at the rear wheel.

Brammo Empulse R for reference has about 650 ft-lb in 1st gear.

All of that is ignoring the drag effects of the transmission and drive systems (gearbox will be higher drag), vehicle mass, clutch and flywheel effects, etc.

[Doug S]

@protomech: You're right, of course, that all gearing ratios between the motor and drive (rear) wheel count. I was really just pointing out that there's a CHANGE in gear ratio possible on ICE bikes that never happens on our direct-geared bikes. Effectively, I was assuming that the top-gear ratios were about the same, and discussing why that means more low-road-speed torque for the ICE bike. In reality, I'd be willing to bet that's not too far off -- the SR tops out about 6000 rpm just over 100 mph, where the Hayabusa is geared for considerably higher top speed but turns a lot faster too.

[frodus]

Some reference on those numbers, not here to fight, just giving some additional information on the different torque numbers. Both with transmission and without have their benefits... I just wanted to share my calculations for you guys to use as needed.

Brammo Empulse R:
http://electricmotorcycleforum.com/boards/index.php?topic=3871.0
Torque at rear axle:
1st: 882.09 N-m or 650.60 ft-lbs
2nd:721.33 N-m or 532.03 ft-lbs
3rd: 597.68 N-m or 440.83 ft-lbs
4th: 507.00 N-m or 373.94 ft-lbs
5th: 428.68 N-m or 316.18 ft-lbs
6th: 391.58 N-m or 288.81 ft-lbs

Rear tire peak force at rubber:
1st:  2760 N or 620.47 lbf
2nd: 2258 N or 507.62 lbf
3rd: 1871 N or 420.62 lbf
4th: 1587 N or 356.77 lbf
5th: 1342 N or 301.69 lbf
6th: 1226 N or 275.62 lbf


Zero SR:
http://electricmotorcycleforum.com/boards/index.php?topic=3872.0
Torque at rear axle: 633.6 N-m or 467.32 ft-lbs
Rear tire peak force at rubber: 1983 N or 445.80 lbf

[MichaelJohn]

There have been numerous posts relating to the lack of off-the-line (until ~20-30 mph) pull for a bike that puts out 106 ft lbs of torque, some have purported that the sevcon settings must have been detuned to prevent snapping of the belt and/or unwanted wheelies. This seems to put that to rest but still leaves open the question as to why the SR can't wheelie with all that torque... (motor design, battery discharge limitation, weight distribution???)

I was one of the chief instigators of that discussion, and I think I've finally figured it out, at least to my satisfaction. The key is torque multiplication, which is why ICE vehicles have gearboxes in the first place.

I also posted that I thought the power was dialed down when starting. I was even told that by a Zero tech so I wonder where he got his info. We get so locked in to the 106 ft lb number that a simple concept like gear reduction and torque at the rear wheel gets forgotten. So, I need a gearbox to wheelie? Darn!

[Doug S]

So, I need a gearbox to wheelie? Darn!

Nope, you just need MORE TORQUE! If you want to wheelie or create wheelspin, you just need torque, whether you get it from lower gearing or however.

[evtricity]

The SR will wheelie if you run lower gearing - my 15 tooth front and 80 tooth rear sprockets will lift the front wheel on uphill grades sitting back on the seat!

Unfortunately the Sevcon controller does not support traction control although there are some settings about ramp rates for acceleration.

[dkw12002]

Yes, good information. Remember too, ICE bikes don't have max. torque at 0 rpms, but they can have max torque at 0 mph by reving the engine and popping the clutch, so really ICE bikes have all their torque potentially available from takeoff just like an electric bike. With a clutch wheelie, you can even be moving in 1st or 2nd gear typically, then briefly pull the clutch to get the revs higher and pop the clutch again for a second or 3rd wheelie. The revs increase so rapidly when you do this that it might as well be instantaneous.