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[Richard230]

Here is a pretty decent review by everyone's favorite reporter, Wes, writing for Ride Apart describing the 2014 Empulse RR race bike and what it is like to ride it:  http://www.brammo.com/media/ride-apart.php

[WindRider]

Nice review and amazing bike.   I like the 10/10 rating.   

[firepower]

"Without a gearbox, that 173 hp / 166 lb.-ft. of torque is instantly accessible"

No Gear Box, interesting maybe they do same as zero, not worth the extra weight, complex and friction.

[Justin Andrews]

Well Wes has done a bit of a U turn there hasn't he...

[WindRider]

I think that with the incredible power of that motor it probably became self evident that a gearbox was completely unnecessary.   

[firepower]

lol, I missed the first line didnt see hp 173, started reading from Whats New heading.
They have a hard time building a gear box to control that power, Tesla had same problem, gear boxes kept breaking, so they got rid of it.

[BrammoBrian]

I think that with the incredible power of that motor it probably became self evident that a gearbox was completely unnecessary.   

Actually, I've addressed this multiple times.  A gearbox is less necessary for high voltage systems as they have the voltage head room to both have very high torque AND high rpm.  Still, a gearbox would help as a race tuned 1000cc sport bike can still pull an advantage at the end of a long straight when we reach the limit of our gearing trade-off.  A single speed/direct drive solution will ALWAYS force you to make compromises that multiple ratios do not. 

We run a 6-speed transmission on the Empulse production street bike as this is a 104Vdc nominal system and we use the gearbox to give the rider what is truly important - REAR WHEEL TORQUE.  The Empulse can produce 880Nm at the rear wheel in first gear and provides for higher top speeds and more efficient operation of the motor than a direct drive solution.  Here's some food for thought - the Empulse achieves 880Nm rear wheel torque, 110 mph top speed, and can sustain continuous driving speeds over 90 mph - all with a  motor that weighs 35 lbs.  Yes - we have a gearbox, that adds weight, but it is 10 lbs lighter than the motor.

[NoiseBoy]

Interesting insight. Do you think that when production bikes start getting up to 400V+ to match their four wheeled counterparts there will be no need for gearboxes then? What is the maximum RPM limit on the latest batch of high voltage motors?

[protomech]

Depends on the motor. You can have a low-RPM high-voltage motor or a high-RPM low-voltage motor (think a battery-operated dremel).

Ex 1: AFM-140 is a 167 kW 40 kg motor that revs to 5000 RPM at 600+ VDC.
http://www.evo-electric.com/inc/files/AFM-140-Spec-Sheet-V1.1.pdf

Ex 2: Zero's 75-7 motor (50 kW 18 kg/40 lbs) revs to 7000 RPM at ~110 VDC. Zero's motor is a bigger motor than the Brammo Empulse's 16 kg/35 lbs motor, so perhaps it is not surprising that it makes more peak power with the same battery voltage and controller.

A gearbox/motor combination DOES have exactly this tradeoff vs direct-drive: for a fixed weight/packaging budget, you are giving up a larger motor in order to use a transmission. Brammo's gearbox weighs in at 11 kg/25 lbs, so the combination motor/gearbox is 27 kg/60 lbs or 9 kg/20 lbs more than Zero's 75-7 motor.

Now look at basic performance specs:

2014 Zero SR ZF14.2 is 452 pounds, 3.9s 0-60 (spec claim), 102 mph vmax (peak). Gearing is 30/132.

2013 Brammo Empulse R is 470 pounds, 4.8s 0-60 (as tested), 107 mph vmax (continuous).

Now run the Zero with 25/98 gearing. 0-60 time increases to 4.4s, gearing-limited vmax increases to 114 mph.

Granted we're looking at tested 0-60 acceleration vs claimed 0-60 acceleration, but it'll have to do until we get a true head-to-head comparison. With that said, it looks like a 40 pound direct-drive setup can offer both better acceleration and higher top speed than a 60 pound motor/gearbox setup.

Zero's passive cooling setup, even on the SR, is substantially weaker than the Empulse, and accordingly its sustained top speed is significantly lower. But presumably this could be solved with a well-sized liquid-cooling setup.

The other thing worth mentioning - and I recall Brian earlier citing this as a reason for selecting a gearbox - is that for a given power requirement, motor efficiency will typically improve when the motor is placed in its sweet spot rather than when operated at the RPM dictated by vehicle velocity.

As an example, look at the AFM-140 motor efficiency map.



At 5000 RPM and maximum continuous torque output (140 Nm), it is producing 73 kW at 92% efficiency. If the motor had a gearbox, then the same 73 kW power output could be instead produced at 3500 RPM / 200 Nm torque, which is 94.5% efficient. I guess the overwhelming majority of the efficiency loss is heat produced in the motor, so heat production at this output level would be reduced by around 30%.

The gearbox won't be 100% efficient, so it's likely that battery power draw would be similar between the two setups and heat would effectively "move" from the motor to the gearbox.

[WindRider]

Brammo Brian,

Thanks for participating here in the forum and expounding on the reasoning behind the Empulse transmission.

Great work on the Empulse RR.   Can I get a ride on it?     

[BrammoBrian]

Brammo Brian,

Thanks for participating here in the forum and expounding on the reasoning behind the Empulse transmission.

Great work on the Empulse RR.   Can I get a ride on it?     

No problem!  Those new to the e-moto scene may not realize that Brammo (and myself) spent a lot of time testing our first attempt at the Empulse with a direct drive (i.e. no transmission) drivetrain.  There was nothing inherently "wrong" with the design, it just didn't provide the low-end acceleration, engagement, and overall experience that we were after with our premium product. For reference, the motor in the concept vehicle below was water cooled, 80Nm/40kW, and weighed in at about 55lbs ready to install into the bike.  I would be extremely impressed if the Zero motor only weighed 40lbs with its physical size and performance spec. 






You can ride the Empulse RR if you're faster than EBoz or Shane Turpin...

[BrammoBrian]

Here's a nice wrap-up from our last race of last season with the RR and coincidentally, a showdown between the Empulse TTX bike and the "fastest Zero in the West" - Kenyon Kluge's modified Zero S. 

https://www.brammo.com/blogs/?p=1916

[BrammoBrian]

Interesting insight. Do you think that when production bikes start getting up to 400V+ to match their four wheeled counterparts there will be no need for gearboxes then? What is the maximum RPM limit on the latest batch of high voltage motors?

I think using a gearbox still provides an advantage at these higher voltages, but it is diminished.  It really all comes down to what you want.  If you want maximum range as the top priority, then using the packaging space and weight for battery may be the better solution.  If you have performance as a priority, then surely a more optimized drivetrain with a transmission needs to be considered.  The RPM limit on a permanent magnet AC motor is determined by 1. the maximum commutation frequency supported by the inverter and the number of poles of the motor and 2. the mechanical limit of the rotor design itself.  For our race motors, the theoretical maximum is about 12,000 rpm, but we do not typically spin it past 10,000.   AC induction machines tend to spin faster, but also make their power later in the rpm range, so need to spin faster anyway.  In general, I do not view this characteristic of ACIM as being beneficial on an EV motorcycle. 

[C. Dolan]

Depends on the motor. You can have a low-RPM high-voltage motor or a high-RPM low-voltage motor (think a battery-operated dremel).

Ex 1: AFM-140 is a 167 kW 40 kg motor that revs to 5000 RPM at 600+ VDC.
http://www.evo-electric.com/inc/files/AFM-140-Spec-Sheet-V1.1.pdf

Ex 2: Zero's 75-7 motor (50 kW 18 kg/40 lbs) revs to 7000 RPM at ~110 VDC. Zero's motor is a bigger motor than the Brammo Empulse's 16 kg/35 lbs motor, so perhaps it is not surprising that it makes more peak power with the same battery voltage and controller.

A gearbox/motor combination DOES have exactly this tradeoff vs direct-drive: for a fixed weight/packaging budget, you are giving up a larger motor in order to use a transmission. Brammo's gearbox weighs in at 11 kg/25 lbs, so the combination motor/gearbox is 27 kg/60 lbs or 9 kg/20 lbs more than Zero's 75-7 motor.

Now look at basic performance specs:

2014 Zero SR ZF14.2 is 452 pounds, 3.9s 0-60 (spec claim), 102 mph vmax (peak). Gearing is 30/132.

2013 Brammo Empulse R is 470 pounds, 4.8s 0-60 (as tested), 107 mph vmax (continuous).

Now run the Zero with 25/98 gearing. 0-60 time increases to 4.4s, gearing-limited vmax increases to 114 mph.

Granted we're looking at tested 0-60 acceleration vs claimed 0-60 acceleration, but it'll have to do until we get a true head-to-head comparison. With that said, it looks like a 40 pound direct-drive setup can offer both better acceleration and higher top speed than a 60 pound motor/gearbox setup.

Zero's passive cooling setup, even on the SR, is substantially weaker than the Empulse, and accordingly its sustained top speed is significantly lower. But presumably this could be solved with a well-sized liquid-cooling setup.

The other thing worth mentioning - and I recall Brian earlier citing this as a reason for selecting a gearbox - is that for a given power requirement, motor efficiency will typically improve when the motor is placed in its sweet spot rather than when operated at the RPM dictated by vehicle velocity.

As an example, look at the AFM-140 motor efficiency map.



At 5000 RPM and maximum continuous torque output (140 Nm), it is producing 73 kW at 92% efficiency. If the motor had a gearbox, then the same 73 kW power output could be instead produced at 3500 RPM / 200 Nm torque, which is 94.5% efficient. I guess the overwhelming majority of the efficiency loss is heat produced in the motor, so heat production at this output level would be reduced by around 30%.

The gearbox won't be 100% efficient, so it's likely that battery power draw would be similar between the two setups and heat would effectively "move" from the motor to the gearbox.

Interesting, but I would have rather seen the numbers done with a Zero SR 11.4, which is a more common and 40 Lb lighter version.

The Zero SR 14.2 is with the so-called Power Tank ( 40 Lb more battery added. )

My 11.4 comes in at 417 Lbs with the changes I made to the suspension and wheels.

I may be getting a deal on an Empulse R in the near future.

Stay tuned. 

[Doug S]

If you have performance as a priority, then surely a more optimized drivetrain with a transmission needs to be considered.

I think that's generally a valid statement, but it becomes less so as the motor performance increases. If the motor is capable of enough torque to break the rear wheel loose during a hard launch, while being geared for an acceptably high top speed, I don't see that the transmission buys you anything at (or past) that point. I think the Zero SR is very close to that point, for most street riders. More torque at 0 rpm would just result in tire smoke, and it's a general purpose street bike, not a race bike, so I think a top speed of 100+ mph is very adequate.

Of course, the equation balances very differently for different situations: a TT bike with the same motor, but a much wider, stickier tire, and the need for a much higher top speed, would still benefit greatly from a transmission. If you gear the bike for a top speed that matches the highest power output of the motor, you're going to have very inadequate torque on the bottom end.