Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[teddillard]

I've read you comment on Teds page twice now and it really doesn't answer any question for me. The things that im discussing aren't quite as subjective as how it feels to me. Its does the wheel lift or tire break loose.

Exactly how I feel about the comment as well.  Very true, but missing the point.  There's a lot of keyboard smarts here, and not a whole bunch of real-world experience.  There's also some basic understanding that's AWOL.  Forgive me for being frank.  Just callin' it as I see it.

And ditto on the exhaustion.  Gonna get off the forum again and go back to the shop now...     ..hopefully it's a little warmer than 20º by now.   

[tyskmoped]

Believe what you like but the same vehicle with more horsepower will accelerate faster. Even if the motor has only 10% of the torque, because at same wheel speed you will have more wheel torque if geared for same top speed.

Um, again, no. I'm not trying to argue with you, or make you feel bad, I'm just correcting you. You persist in denying what any Physics 101 class in any college could teach you has been known and accepted for literally 500 years now: Force = mass times acceleration, F = ma. Isaac Newton formulated the law and everyone from high school Physics teachers to every engineer around to NASA understands and agrees that it's true. It's not power that accelerates an object such as a vehicle, it's force, or its rotational analog, torque. High power only becomes necessary as energy is drained from the system at a high rate of speed (such as aerodynamic drag becoming very large at high vehicle speeds), and has to be replaced. That's why power is so important to racing vehicles, which need to attain the highest speeds possible, but torque is far more useful at lower (street-legal) speeds.

Hit up wikipedia or Google and learn some facts. Reality is a pretty nice place to live.

Maybe I did write something wrong in my first post as English is not my home language. I know the physics, it is very kind of you to teach me, thank you. For me it seems as you want to read something I did not try to say.

I try again. Motor torque alone isn't the only/main indicator for acceleration. It depends on the curve how it is delivered and at which speeds. To make it more clear what I mean, here an example. Which bike accelerates faster? Zero Fx 2.8 with 94nm torque and 27hp or an 250 KTM with 35nm/40hp?

I did share two diagrams with you, both are from dynos I did myself. The first (red) shows the torque curve of a Fx 5.7. In my world it shows that the torque is not limited, it's constantly at maximum till other things than the setup let it decrease.

[chdfarl]

I refer to it as pushing down rather than "lifting" like you do on a fx

Chd where are you from?

I don't quite understand what your saying there. When I say lifting im referring to the front wheel not with my arms and yanking. The FX was throttle alone but I could see how you'd be pushing down or leaning over the front of your bike and still popping a wheelie  .

I live in a place called New Bedford Ma. ( from Moby Dick ) between Rhode Island and Cape Cod.

[Cortezdtv]

To me if you try to wheelie in an aggressive riding position (leaning. Forward elbows up) from 0 mph.  The fx won't really pick it up until 20 30 I mean yes if you give a little tug up or lean back a little it will come up, but it doesn't have enough to pull you up if you were leaning as far forward as you can


Mine is like push down as hard as you can from 0mph and half to 1/4 throttle.   Climb on the front of the bike feet hugged around the front controller area.   And ride that wheelie to 70, first time I tried drag it I wheeleid the whole street far from what the fx can do all in a power wheelie

   First few times I tried to "drag" some big 650 enduros I just weelied toying with them then I relized I need 600 street bikes and up to stoplight to stoplight; depending on the rider than can be pretty even, put a professional on one and I'm sure I'd probably get left racing is all in the rider

[tyskmoped]

Mine is like push down as hard as you can from 0mph and half to 1/4 throttle.   Climb on the front of the bike feet hugged around the front controller area.   And ride that wheelie to 70, first time I tried drag it I wheeleid the whole street far from what the fx can do all in a power

How did you realize this improvement?

[Cortezdtv]

Mine is like push down as hard as you can from 0mph and half to 1/4 throttle.   Climb on the front of the bike feet hugged around the front controller area.   And ride that wheelie to 70, first time I tried drag it I wheeleid the whole street far from what the fx can do all in a power

How did you realize this improvement?

Not sure I understand?
What do you mean how do I know it's faster?

[tyskmoped]

How did you make it faster?

[Cortezdtv]

Spent way to much money and time 



I upgraded the motor and controller for basically what's in the SR with a "limited tune" because unlike the sr I only have 2 batts compared to its "4."

[liveforphysics]

Stall torque and it's effect on 0 RPM performance is not a theory, just to be clear.  Given that, you're talking about two different things - acceleration from 0 RPM, and acceleration from well onto the torque/power band to a higher RPM. Seems like it'd be hard to measure, but if it's the case, it would certainly suggest throttle mapping, which it sounds like we've confirmed is what Zero is doing. 

My suspicion is that they're concerned with riders who are unaccustomed to riding without a clutch.  Most experienced riders will use the clutch to feather power off the line, even during hard acceleration on the power band, and in some cases use it for low-speed control of power.  You don't have that kind of option with an electric motor. 

Please stop proliferating this rumour, It is not true.  ...

I'm not "proliferating" anything, and certainly not what you call a rumor.  I think it's fairly clear if you read my comment that I have nothing but a suspicion and suggestions.  I'd certainly like someone with credentials and evidence to get on and put it to rest, and I'm certain there are more than a few who read this who could. 

The only dog I have in this fight is the fact that different types of motors have different stall torque characteristics, period.  Does the Energica motor have lower stall torque than a similar (100kw or so) PMDC motor?  Yes.  Is that why I couldn't wheelie it?  No clue.  I have no idea if it was mapped or not, and I really don't care. 

Believe what you like but the same vehicle with more horsepower will accelerate faster. Even if the motor has only 10% of the torque, because at same wheel speed you will have more wheel torque if geared for same top speed.

As far as horsepower goes, you need to have a really basic understanding.  Horsepower = (Torque x RPMs) / 5252.  End of discussion.  http://danielmiessler.com/study/horsepower/  So explain to me how you can have a vehicle with 10% of the torque and more horsepower.

Ted- You are mistaken.  Biff is trying to set you straight.  Biff knows this better than any other human on earth I have awareness of, you would be wise to listen rather than continue spreading falsehood.

[teddillard]

Please be specific.  What precisely am I mistaken about? 

I ask because it seems we have about 3 discussions going on here.  Correction - 4.  One about the characteristics of motors, one about riders perceptions of performance, and one about Zero's tuning of their controllers, and finally about what makes acceleration. 

As far as I understand it, different motor designs have different stall torque characteristics, by their design.  Is that correct?  (...and that's the only point I'm trying to make, as I've said.  Since I've talked about it with motor designers and thought they confirmed this, I'd love to know what I got wrong. Sincerely.)

I think I have a firm grip on perceived performance vs. actual numbers, since I've been building motors and bikes for a few decades now. 

I don't particularly care whether Zero is mapping their response or not.  As I've said a few times now, my comments were simply guesses and discussion.  If someone reads those comments as perpetuating rumors, that's an issue with their reading comprehension.

On what makes a machine accelerate, I really don't think I'm mistaken about basic physics, am I?

[teddillard]

So I've been scratching my head about this, and the comments above, and went back and re-read Biff's comments as well as his comments on my blog post.  Here's the point that was interesting:

3) Many DC motor controllers have the current sensor on the input to the controller, on the battery side. When the motor is stalled or spinning slowly the battery current will be very low even though the motor current (torque) is really high, once the motor is spinning more quickly and the power increases, the battery side current also increases bringing the current into the range that the sensor is more accurate and the controller will then have a better time controlling the motor current based on the battery current. Also Many DC controllers are speed control, so when you change the throttle position it tries to give everything it has to get you to the new commanded speed, so they give you a big punch initially until you get closer to the desired speed.

So that's what I missed, but that begs the question, are you saying that this behavior of a DC controller is completely responsible for the different response of the two types of motors, or are there measurable differences (as I've been told there are)?

[chdfarl]

Can you find the TTXGP crash and show specifically where it was a bearing failure of the motor? I am sure there must have been a huge write up about this somewhere. That stated I am not racing my bike but it does have ceramic bearings in the motor.

I didn't find the video but it is one of the missing you tube videos on one of the articles. I knew it wasn't a dream!

http://plugbike.com/2009/10/26/2010-ttxgp-rules-published/
http://electricmotorcycleforum.com/boards/index.php?topic=420.0
http://green.autoblog.com/2009/06/10/ttxgp-complete-wrap-up-of-first-day-of-qualifying-w-video/
http://www.motorcyclenews.com/sport/tt-road-races/2009/june/jun1009-ttxgp-story-behind-first-crash/

Ironically the eRocket bike had a six speed gear box but no clutch so an emergency disconnect was mandated by the TTXGP.