ElectricMotorcycleForum.com
Makes And Models => Zero Motorcycles Forum | 2013+ => Topic started by: steven_first on May 10, 2015, 08:01:32 PM
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So as I have gotten used to the acceleration of my FX 5.7 I have been noticing that the torque is not exactly 70F/lb from 0RPM as stated. I would say that the torque does not max out until about 20MPH or higher where you can get a noticeable increase in power. Because of this I am trying to decide if the batteries, motor, ESC, software, or Newtonian physics is to blame. On one hand, propelling a 460lb motorcycle (adding my weight) from 0 to X requires more force than from X to Y where X is any number greater than 0 and Y is the speed at which you poo your pants. How I can rule this out is because my GF has ridden with me and the 20ish mph for full torque does not change despite more mass. On the other hand you have a 5AH 100v battery with an unknown C rating. The ESC is something like 420 amps so to meet or exceed full ratted power of the ESC you would need to divide 420 amps by 5 amps (1C) and you get 84C. That means that the batteries need to be at least 84C to max out the ESC. Assuming they want the ESC to be maxed out not the batteries then we must assume that the batteries are at least 84C. Again, my GF's extra mass does slow down acceleration but does not change the apparent lag during takeoff. So that leaves me with the motor, software.
So if I take my bike and have it put on a dyno and there is a torque curve that is consistent rounded curve then that means that the software is what is doing the limiting right? If it is software then why is that there? For the belt? For battery, ESC, or Motor protection....or for liability? I guess that is the main question here... am I not getting 70 torques at take off because of limitations of the system or for liability....
End rant and questionable/incomplete math and reasoning.
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The shop near me won't dyno an electric bike. Might try again but they turned me down a year ago when they got the equipment.
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I agree with you. I have a 2015 SR and it does seem strange that I don't get my max acceleration until about 40mph. I thought it was software at first too but some others on here have pointed out that since there is no transmission it is basically like taking off in 3rd gear, which would make sense if this was an ICE but since we are dealing with an electric motor I would agree that most torque curves I have looked at on electric motors have full torque available at 0rpm. Maybe I am missing something too.
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Max torque does not come in until a certain RPM is reached.
This is controlled by software and is designed in.
The reasoning is that full torque off of a stop would most likely see people launching their bikes into garage doors and/or anything else in front of them.
As you have noted torque climbs quickly from about 20mph on.
If you give an FX full throttle (and hold it) from a stop you will see the front start getting real light (read wheelie) at about 20mph.
The (real) downside to this is when riding off road and wanting to loft the front end over an obstacle at a very low rate of speed. Cannot really do it. On an ICE dirt bike just feather the clutch, apply throttle and drop the clutch = wheelie.
Every Zero gets run on the Dyno before leaving the Zero factory.
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http://www.motorcycleconsumernews-digitalmagazine.com/mcnews/september_2014d?pg=20#pg20 (http://www.motorcycleconsumernews-digitalmagazine.com/mcnews/september_2014d?pg=20#pg20)
Dyno chart on the last page. It's annoying that it only goes down to 1000 rpm, but I'm sure they just left their usual setup in place, which of course is designed for ICE bikes.
Notice that the torque "peak" goes down at least to 1000 rpm. I used to believe the torque was limited at low rpm too, but I've become convinced it's not. It's just different from our expectations, which have been tuned by riding ICE bikes all our lives. We expect less and less torque as we shift up through the gears, not flat torque all the way from 0 rpm through where field-weakening sets in.
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Dyno chart only for paying customers...
@steven, it's a limitation of the ESC. Full current (full torque) at 0 rpm would induce great current ripple because the BEMF is too low. To have full current, you would have to increase ESC switching freq a LOT, but that means a lot of additional heat (=burned MOSFETs)
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We do have a thread somewhere discussing torque and how ICE bikes measure torque on the dyno in top gear, and you can't wheelie most bikes in 6th gear. Gears multiply the torque in lower gears so that you could have double the torque in 1st gear that you have in 6th..hence it is easier to wheelie with ICE bikes. Turns out 70 ft. lbs. of torque isn't a lot. While ICE bikes don't have max. torque at 0 rpms, you can rev the bike with the clutch engaged and as soon as you let out the clutch you get a lot of torque in a split second. The advantage for take offs and wheelies here goes to ICE bikes with gears.
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Dyno chart only for paying customers...
It gives you that message, but it works anyhow...at least it does for me, and I've never given them a dime.
We do have a thread somewhere discussing torque and how ICE bikes measure torque on the dyno in top gear, and you can't wheelie most bikes in 6th gear. Gears multiply the torque in lower gears so that you could have double the torque in 1st gear that you have in 6th..hence it is easier to wheelie with ICE bikes. Turns out 70 ft. lbs. of torque isn't a lot. While ICE bikes don't have max. torque at 0 rpms, you can rev the bike with the clutch engaged and as soon as you let out the clutch you get a lot of torque in a split second. The advantage for take offs and wheelies here goes to ICE bikes with gears.
Yep. That's a very good synopsis of that discussion. The reason ICE vehicles have gearboxes is because they need them. They don't put out any torque at 0 rpm and very little at low rpm, so a single gear can't possibly cover the whole range of road speeds necessary. EVs can often get by without them, although we do lose the torque multiplication effect. I'd imagine that's why Brammo decided to go with a transmission in spite of not really "needing" one.
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I think what I may do is contact some places with bike dynos in my area and see if any of them can record from 0RPM.
I would be surprised if the "BEMF" is great enough to warrant effectively a throttle cut up till 20 mph. Any initial current spikes would end after the initial voltage was applied to the motor and would be almost gone by even 10 RPM. As a matter of fact (I think) the lowest speed you can get the speed controller to spin the motor is probably high enough to rule out inrush current and locked rotor forces. There may be other forces I am not aware of but I am doubting that they are the reason for the full lack of power down low.
I keep coming back to the liability issue more than anything on this. A bike as light as this with as much torque as it has should be not be so delayed on taking off. I am not unhappy about it but if anything it gives me hope that there are some room for tuning!
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Steven
BEMF, or back electromagnetic force is proportional to rpm. So, as you can imagine, at 10 rpm in a 5000 rpm motor, the BEMF is very low. (I don't max rpm of the FX motor, but you guys get the picture)
On the FX, 17 mph is 1/5 of 85mph, so 1/5 of rpm (1000rpm) is very different from 10 rpm.
For more "punch", put a Size 6 ;)
My 2 cents.
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Sorry, you are right, I was thinking in rush; my bad please forgive me!
My point with the 10 rpm isn't anything more than saying you have already overcome the "in rush" current from a stationary rotor thus a large amount of the current spike, from that, would be gone. I won't try to pretend I know a lot about motors here so if I am wrong I am wrong. That being said, I can't see such a big lack of torque being necessary up to such a relatively high speed.
If I could get my hands on a Size 6 dirt cheep I would but I don't see me getting that lucky... Crap, I wouldn't mind putting in a whole SR setup for that matter! I have seen Cortezdtv's videos and that would be a blast!
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See the article that Ted wrote up here, and pay close attention to the comments.
https://evmc2.wordpress.com/2014/07/07/motor-starting-torque-stall-torque-and-motor-types/ (https://evmc2.wordpress.com/2014/07/07/motor-starting-torque-stall-torque-and-motor-types/)
The Dyno chart from motorcycle consumer news (linked above and here for reference) shows that the motorcycle has relatively constant torque from 1000 RPM (their dyno lower limit) up to 3200 RPM (that is from 17mph up to 55mph) .. the flatness of the torque curve remains even at lower RPM.
http://www.motorcycleconsumernews-digitalmagazine.com/mcnews/september_2014d?pg=20#pg22 (http://www.motorcycleconsumernews-digitalmagazine.com/mcnews/september_2014d?pg=20#pg22)
The "slow" acceleration at lower speeds is purely a human perception, not an imposed limitation on the vehicle.
-ryan
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The "slow" acceleration at lower speeds is purely a human perception, not an imposed limitation on the vehicle.
Human perception is force that the vehicle makes, which is directly related to wheel torque.
This is why we feel stronger accel in 1st gear then on 2nd, on a ICE bike, and engine power is the same.
So, if torque was constant from 0 rpm, we would feel the exact same pull from 0 to 3200rpm.
What we don't perceive is power.
Since the dyno chart only presents from ~800 rpm up, we cannot infer anything on this topic (very low rpm's).
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Human perception is force that the vehicle makes, which is directly related to torque. So, if torque was constant from 0 rpm, we would feel the exact same pull from 0 to 3200rpm.
What we don't perceive is power.
Not trying to put words in anybody's mouth, but I believe what Biff is saying is that we're all used to ICE vehicles, which have more rear-wheel torque at very low speeds because they have a comparatively low first gear, which multiplies the torque available from a dead start. We're all used to that feeling, from having driven ICE vehicles all our lives, so an EV with no gears and therefore constant torque available all the way down to 0 rpm can actually feel somewhat weak on bottom because it doesn't have any torque multiplication going on.
I'm pretty sure that's why Brammo put a gearbox on the Empulse. It just plays better to our pre-programmed feel for vehicle acceleration.
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Note the 10mph minimum on the chart ;)
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Human perception is force that the vehicle makes, which is directly related to torque. So, if torque was constant from 0 rpm, we would feel the exact same pull from 0 to 3200rpm.
What we don't perceive is power.
Not trying to put words in anybody's mouth, but I believe what Biff is saying is that we're all used to ICE vehicles, which have more rear-wheel torque at very low speeds because they have a comparatively low first gear, which multiplies the torque available from a dead start. We're all used to that feeling, from having driven ICE vehicles all our lives, so an EV with no gears and therefore constant torque available all the way down to 0 rpm can actually feel somewhat weak on bottom because it doesn't have any torque multiplication going on.
I'm pretty sure that's why Brammo put a gearbox on the Empulse. It just plays better to our pre-programmed feel for vehicle acceleration.
Yes, that is what I am proposing, I also think that dropping the clutch to give a sudden jolt at 0mph in an ICE vehicle also sets our expectations for "quick" acceleration.
I know 2 tings for fact ..
1) prettymuch everyone who rides a modern Zero says "it feels slow below 20mph, but then above that it really pulls hard"
2) the torque (and hence acceleration neglecting air resistance) from around 400RPM (7mph) up to 3000rpm 50mph is pretty-much constant, Instrumentation from Motor Speed, GPS, accelerometers and dynamometer all agree on that, the dyno charts show that there is about a 7% increase in torque between around 40 and 60mph (depending on model)
everything else I say on the subject is just theory, and I try and present it as such.
-ryan
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I have started contacting places with bike dynos in my area. I only called one so far and it was a HD dealer. They said they will not dyno anything that is not a HD ::). The main question I couldn't get an answer on from the guy was if the dyno 250i can read from 0 rpm or 0 mph wheel speed. It does no good to dyno the bike if it can't read below 1000rpm. That being said, I have been working on a side project for about a year now that will log GPS, accel, angle, rotation, pressure etc at 50 times a second in a small form-factor . This may be a good test for it.
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Before 20 mph everyone says its "slow" but people after a year of riding my fx I thought it was slow too....
What is your very first impression I know it's not "o well damn that thing was slow 0-20". No it was holy crap that thing started pulling like a mother....
No I think that zero should make a tune that can be loaded into the bike via app that would give experienced electric riders more power lower etc, it's just not something you can have on every bike, it is already much easier to whiskey throttle an electric than a gas bike, so the de tuning is to protect the end user
If you really want to go faster fork out the money buy a size six and find someone crazy enough to put it on, and be mindful of the batteries. You will loose some "waterproofing" because the size six is so much bigger, it ends up hanging out the bottom.
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@ Cortezdtv
You have a size 6 in one of your FX bikes don't you? Do you have any pictures of the install? I have to agree with you that when you first ride the bike 0-20 does not feel slow but then again there is so much going on that you don't even know what to think. I asked Harlan at Hollywood Electrics and he feels that it is perception.
I think what I am going to do is work on getting some hard numbers be it via dyno or accelerometer. It may take a few weeks but I will post my findings in as objective a way as I can.
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do you have also the curve of the zero SR?
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Francois are you asking if I have a sr tune on my fx?
Yes Steven I have a size six on a fx, and it has that "snap" or quickness that everyone commonly compares to dropping the clutch on a gas bike where you get a sudden jolt
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do you have also the curve of the zero SR?
http://www.motorcycleconsumernews-digitalmagazine.com/mcnews/september_2014d?pg=20#pg22 (http://www.motorcycleconsumernews-digitalmagazine.com/mcnews/september_2014d?pg=20#pg22)