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[Justin Andrews]

I'd imagine someone like Harlen, or Electric Cowboy, would know more about how much, if any, soft start is in the verious Zero's. As I believe they are both capable of programming the Sevcon controllers on the bikes.

[Doug S]

Wait, now I'm getting confused. I thought the secret sauce for Zero's new generation of motors was to essentially invert the usual construction by mounting the coils to the outside housing (the stator), where they can be cooled more easily, and mounting the magnets to the rotor. Doesn't "permanent magnet" mean "DC motor" in electric motor world? In other words, I thought Zero used PMDC motors?

Somebody please correct me if I'm wrong.

[Yon]

Zero does use DC motors.  Seems someone is/was confused.

[frodus]

Zero used to use PMDC motors (Motenergy and Agni motors) paired with Alltrax controllers. PMDC motors have coils on the Rotor and magnets on the stator. DC voltage goes to the motor. PMDC motors use mechanical commutation by using brushes to switch the magnetic fields.

All of the new generation Zero's (Sevcon-controlled motors) are PMAC, meaning Permanent Magnet AC, commonly referred to as Synchrounous AC motors. PMAC motors have magnets in the rotor and coils on the stator. These motors use an AC controller (or inverter) that converts the DC to AC. PMAC motors use Electronic commutation by using the controller to switch the magnetic fields, so no brushes.

[Doug S]

All of the new generation Zero's (Sevcon-controlled motors) are PMAC, meaning Permanent Magnet AC, commonly referred to as Synchrounous AC motors. PMAC motors have magnets in the rotor and coils on the stator. These motors use an AC controller (or inverter) that converts the DC to AC. PMAC motors use Electronic commutation by using the controller to switch the magnetic fields, so no brushes.

My understanding of electric motor configurations is pretty meager, but I thought what you're describing is referred to as a "brushless DC" motor. Whatever you call it, it doesn't seem like it should suffer from low torque at low rpm. The magnetic field from the magnets is fixed, and you can generate full-strength magnetic fields from the coils even when the motor's stalled out (or just starting to turn), so you should have maximum torque available at 0 rpm. I thought the reduced torque in AC motors was related to the field coils; a PM motor doesn't have any of those issues.

Then again, I could be completely HUA here. I'm an EE so I could probably build you a pretty decent controller, but I definitely don't qualify as a motor expert.

[teddillard]

Thanks for the link, Biff! 

On the specifics of AC motors, this is about the most informative page I've been able to find:
http://machinedesign.com/motorsdrives/difference-between-ac-induction-permanent-magnet-and-servomotor-technologies  Maybe that will help (though a lot of it is way over my little non-EE or E-anything brain).

As I learned in putting my post together, the starting torque is pretty important in your "launch" performance, and from the specs I've been able to compare the AC motors, whether with permanent magnets or not, do have lower numbers for that. 

[frodus]

All of the new generation Zero's (Sevcon-controlled motors) are PMAC, meaning Permanent Magnet AC, commonly referred to as Synchrounous AC motors. PMAC motors have magnets in the rotor and coils on the stator. These motors use an AC controller (or inverter) that converts the DC to AC. PMAC motors use Electronic commutation by using the controller to switch the magnetic fields, so no brushes.

My understanding of electric motor configurations is pretty meager, but I thought what you're describing is referred to as a "brushless DC" motor. Whatever you call it, it doesn't seem like it should suffer from low torque at low rpm. The magnetic field from the magnets is fixed, and you can generate full-strength magnetic fields from the coils even when the motor's stalled out (or just starting to turn), so you should have maximum torque available at 0 rpm. I thought the reduced torque in AC motors was related to the field coils; a PM motor doesn't have any of those issues.

Then again, I could be completely HUA here. I'm an EE so I could probably build you a pretty decent controller, but I definitely don't qualify as a motor expert.

I was more commenting as to the terminology, I appologize.

I wanted to illustrate the differences before starting to understand how the motors and controllers work. I've heard people use BLDC and PMAC interchangeably, but BLDC are actually slightly different. They're wound such that they have a Trapezoidal back-emf profile, and the poles stick out from the stator to concentrate the flux and the controller uses a pulsed DC waveform. I don't see BLDC used a lot in drive applications anymore, not with Sinusoidal drives widely available. In contrast, PMAC or Synchronous AC motors are wound such that the back-emf profile is sinusoidal and the controller uses a true Sinusoidal waveform.

More on BLDC and PMAC:
http://www.mpoweruk.com/motorsbrushless.htm

The reduced starting torque in AC motors mainly when using Induction motors, which require an electric field to induce a current (and in-turn a magnetic field) in the rotor. Both PMAC and AC Induction have "field coils" referred to as the "stator".

More on Induction (and Synchronous AC) here:
http://www.mpoweruk.com/motorsac.htm



Back to the original discussion about slow acceleration:
I know from looking at the Sevcon in the Brammo, that there are profiles inside the controller. I don't have a Zero to play with, but I assume that they're doing something similar with limiting the current a little at startup for safety reasons, as well as trying to stay below the force required to snap belts.

Another thing, is that you've got a gear ratio that must suit all speeds between 0 and 100mph (or whatever the Zero is). While you may produce the most torque at 0RPM, your gearing is set up such that you can reach 100mph. If you had a small gear ratio, the acceleration will be terrible until you hit the power band of the motor (max HP). If you had a high gear ratio, you'll accelerate like a bat out of hell, but you may not ever be able to hit 100mph because the max RPM of the motor might occur before then.

I'm thinking its a combination of the two. Because zero chose transmissionless, they're limited to some degree as far as gear ratios. I think some of it is also safety and trying not to break belts/pull the bike out from under you.

[Doug S]

Another thing, is that you've got a gear ratio that must suit all speeds between 0 and 100mph (or whatever the Zero is). While you may produce the most torque at 0RPM, your gearing is set up such that you can reach 100mph. If you had a small gear ratio, the acceleration will be terrible until you hit the power band of the motor (max HP). If you had a high gear ratio, you'll accelerate like a bat out of hell, but you may not ever be able to hit 100mph because the max RPM of the motor might occur before then.

Agreed. Lower (numerically higher) gearing gives you a higher torque multiplication factor, so more torque, but only at lower speeds since the motor will spin out faster. At the high end, the top gear should allow the motor to wind to its highest-horsepower rpm just as the aerodynamic/rolling resistance equals that horsepower output.

On the Zero SR (my bike), the single gear is arranged so the motor spins out just as it's hitting the highest speed at which it can push air aside...around 105 mph. That gear doesn't provide much torque multiplication on the low end, but who needs it? The bike already does 0-60 in 3.3 seconds.

That's why I think this conversation is important. If it was a motor of a variety which has lower torque at 0 rpm than at higher speeds, a single gear might not work very well -- gearing for top speed might leave a pretty big hole at low speeds. My point is that I don't think that's what's happening. I think Zero actually had to REDUCE the torque available at very low speeds in software, to avoid snapping belts, shredding rear tires and getting newbie riders into serious trouble.

[Doctorbass]

I can add some explanation from Richard320 observation.

On my 2012 S I have recently installed the 2013  75-7 motor ( same as the 2013 S). the battery is still the original 66V and the controller is still the stock controller as the 2012 S and 2013 S have.... and same sprocket ratio

My previous acceleration with the ME0913 Motonergy motor  was 7.8 sec.
With the new 75-7 motor it is now between 5 and 6 sec.

From my understanding the torque is related to the phase AMP available from the controller and the torque per amp of the motor. The 2012 and 2013 S have the same exact controller  capable of 420Amp per phase so in this situation the only difference that can affect the torque is the motor. I clarely see that with 7.8sec to 5 sec drop 

On my previous stock 2012 S setting the torque curve is set at 66Nm max
On my new setting with the new 2013 motor it is set to 115Nm wich is not double but close too.

The 75-7 motor make a huge difference on torque but I lost a bit of max speed starting from 90km/h and up wich translate by reduction of the powerband. The field weakening feature of teh controller wich boost the max speed of the motor is enable but reduce efficiency too so I can not go as fast as with my stock 2012 motor was.

I also agree that the torque curve of the 2013 S is damped at low speed. On my modified 2012 S with 2013 motor I have maxed all torque from 0 to 4000rpm to 115Nm and it make also a great difference. The low speed acceleration is more brutal than before.

With the Size 6 controller I should  get about 180Nm torque according to the 55% more phase current available.... all that on a 2012 S =))))

I expect to get the 0-100kmh in less than 5 sec  with the weight of a ZF9 battery wich is about 50 pounds heavier than a ZF6.

Doc

[teddillard]

That's why I think this conversation is important. If it was a motor of a variety which has lower torque at 0 rpm than at higher speeds, a single gear might not work very well -- gearing for top speed might leave a pretty big hole at low speeds. My point is that I don't think that's what's happening. I think Zero actually had to REDUCE the torque available at very low speeds in software, to avoid snapping belts, shredding rear tires and getting newbie riders into serious trouble.

I'd love to know for sure.  I can say, from personal experience, I have a friend with a bike running the AC20 and a big RC lipo pack.  He has it geared for around 100+, and it pulls just like the ZeroSR I rode a month or so ago.  I know he's not done any de-tuning, and once you're rolling at around 20mph it's all hell breaking loose. 

(edit: Just cross-posted with the good Dr., and I'll take that for what I was looking for.  Thank you sir!)

[Doug S]

My previous acceleration with the ME0913 Motonergy motor  was 7.8 sec.
With the new 75-7 motor it is now between 5 and 6 sec.

It definitely sounds like there's a pretty big difference in the motors. Probably the main reason Zero designed their own -- they recognized there were big gains to be made.

On my modified 2012 S with 2013 motor I have maxed all torque from 0 to 4000rpm to 115Nm and it make also a great difference. The low speed acceleration is more brutal than before.

THIS! How did you do that? I'm assuming you need some sort of programming device to communicate with the controller? I'm an EE so I should be able to figure it out if you'd outline the process for me.

It's not that I WANT to snap drive belts, shred rear tires or even point the front wheel at the sky, but it'd be nice to have the ability if I do decide I want to! ;-)