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[mistasam]

The motor hasn't changed between 2016 and 2017, but since the controller was upgraded, it's able to pump out a bit more power.  So!

Does anyone know what the absolute limit of this motor is?  Say there was a controller with 1000amps and batteries that could discharge quickly enough.  And say there wasn't a limit on the motor's rpm at 6500.  Does anyone know how much power it could potentially put out, and how high the rpm could go?

[Lenny]

I'm pretty sure you could easily tweak the torque and the power further, question is how long it's able to take that. Sustained power is the key, and that is pretty much limited by the thermal capacity of the motor. That didn't change with the new controller, it just offers more peak power. Although the new gearing might have improved it slightly as rpms are lower at the same speeds in 2017 compared to 2016. Zero claims about 22kW of sustained power, but I don't know at what temps that was measured. It's probably less on hot days. Tesla does the same, peak is above 500kW, whereas sustained is less than 90 kW. That's the reason why Tesla's and Zero's are not ready for the track yet.

The rpm are limited by mechanical forces, which will destroy the rotor once rpm get to high. Some say it might do up to 7000 rpm, but apparently Zero considers 6000 as a safe limit.

[MrDude_1]

Has anyone done a liquid cooling mod with a in-out circuit on the motor (not just filling it with liquid)?

[Doug S]

RPM is primarily limited by the inductance of the motor windings. At low RPM, under full throttle, the current through the driven phase(s) of the motor ramps up from 0 to the maximum allowed by the controller pretty quickly, and you get full torque because you've got full current. But the faster the motor turns, the faster the motor controller has to cycle the phases of the motor on and off, and eventually, you reach a point where there's not enough time (because of the inductance of the motor windings) for the current to ramp up to maximum before that phase has to be turned off and the next phase cycled on. At that point, power starts to drop off, so very shortly after that, the motor won't have enough torque or power left to drive the load. The mechanics of the motor could easily have been designed for higher RPM, but there's no point since you'll be current-limited anyhow.

[mistasam]

Ahh, that makes a lot of sense!  So then, I wonder how much current the motor could handle if the only thing limiting it is the controller and batteries.. or am I misunderstanding how electric motors work?

[Doug S]

Well, I didn't say the only limiting thing was the controller and batteries. There are a LOT of limiting factors, including what I said above: the inductance of the motor windings limits the speed with which current can ramp up in them.

The easiest way to get more torque, and thereby more power (since power is proportional to torque times RPM), is to pump more current through the motor. Several things can bottleneck that effort. First, the motor windings have a DC resistance because they're copper wires with fixed gauges and lengths. The bike's wiring external to the motor also has some DC resistance in it. If you apply more voltage to a fixed DC resistance, you'll get more current, but the batteries only give you ~110VDC to play with....and of course, the battery has a current limit of its own. You'll need to be sure the controller can handle the current as well; you won't go very fast once you smoke the controller. Since the motor rotates and therefore the windings have to be commutated (driven on and off in the proper sequence and speed), the motor's inductance also comes into play as we've already discussed.

You could change some of this stuff fairly easily (higher-gauge wiring is pretty simple, though might be tough to fit in some of the tight confines the Zero's wiring is routed through), but other things are more difficult. To reduce the motor winding's DC resistance, you'd want to use heavier wire...but you wouldn't be able to get as many turns onto the same coil form. Fewer turns would create less inductance, which also helps allow higher current levels, but fewer turns also results in a weaker magnetic field for the same current, so you might actually reduce the torque the motor puts out. Then you'd also need to be sure you don't over-current the controller, or the batteries.....and we haven't even talked about keeping everything cool.

It's kind of like asking what's the highest VO2 max an athlete can put out. It's not just about his lungs, it's about his heart, his muscles, his metabolism at a microscopic level, even about his mental attitude. Tweak any one thing and the system's whole balance shifts. That's why us engineers make the medium-sized bucks.

[mistasam]

Doug!  Holy cow man, thanks for such an in-depth response.  Since I have you here, I'll branch out a bit.

Gearing seems to play a big part in the acceleration.  Imagine I didn't care about top speed at all.. strictly the launch.  Is there a formula to find the optimal gear ratio for that?  All the stunt bike guys use huge rear sprockets to pop wheelies, but is there a certain size that would work best with the Zero's motor?  Like, too big and it doesn't have enough torque to drive it quick enough, but just right to match it perfectly?

[Doug S]

As I understand it, there's no limit to the torque multiplication factor. Gear it lower, lose top speed, but get more torque. I know some of the earth movers use compound low gears to achieve ridiculously low gears to move insane loads. It's a sign of the limitations of ICEs that they NEED gears -- you can't find a good compromise between low-speed and high-speed capability with a single gear on an ICE. Gear it too low, it can't give you any speed. Gear it too high, there's no torque multiplication to help out at low speeds. You'll need multiple gears, maybe six or seven, and a clutch, to make an ICE motorcycle work well. To move a mountain at 900 rpm, you'll need a very, very low gear, and a lot of time to get it done at 1 mph. It's a tribute to the electric vehicle motor that it can give adequate power at high rpm, and plenty of torque all the way down to (literally) 0 rpm.

But gear it lower if you want. You'll get a better launch, but I bet you'll miss the higher top speed and comfortable freeway cruising. I would.

BTW, there's no "power multiplication" associated with gearing. The motor's power output is what it is, and it isn't affected by the gearing. That means the bike has one "top speed", which depends on the bike's power output vs. drag, which require matching with the proper final drive ratio. Again, it's a tribute to the electric motor that proper top-speed gearing still gives plenty of torque to launch well.

[mistasam]

Interesting.. I know a few people have swapped to chain and then changed the sprockets to allow for slightly higher top speed (or better launch but a top speed of 80mph) so it made me wonder if Zero set theirs to be the most efficient blend of the two.  Torque at the wheels should change depending on gearing, right?

I recently got to drive a converted electric VW Bug that just had the motor mounted straight to his transaxle, and the power delivery was definitely different in every gear.  Even though they say "you can start off in 3rd if ya want" it took a really long time to get up to speed if you did that.  What would be cooler is a single-speed like a Leaf or Tesla, but you'd still need to choose either epic launch or higher top speed, right?

Let's say.. I wanted to put a Zero motor in a car.. >__>.. and keep it having only one gear.  Do you know how to calculate what size gear to use to retain the crazy launching?

[BrianTRice@gmail.com]

I've added Doug's great explanation to the wiki manual:
http://zeromanual.com/index.php/Unofficial_Service_Manual#Motor_Limits

[Doug S]

Torque at the wheels should change depending on gearing, right?

Yes. I probably should explain exactly what "torque multiplication" is. The motor puts out what it puts out; it has maximum torque and power numbers. You can't do anything about the power output; the most power you're ever going to get to the rear wheel is the max the motor can put out. But torque is different; the Physics dictates that you CAN increase or decrease the torque to the rear wheel by changing the gearing. That's what gears are  for. ICEs turn far too fast to be directly geared to the wheels (although I know some drag racers have experimented with direct drive), so the gearing will always reduce the speed of the rear wheel with respect to the motor; that uses the high-speed capability of the motor to multiply the torque to the rear wheels to get the vehicle accelerating briskly. Even EVs do that...our Zero motors can spin in excess of 5000  rpm, which is far faster than you could ever spin the rear wheel.

I recently got to drive a converted electric VW Bug that just had the motor mounted straight to his transaxle, and the power delivery was definitely different in every gear.  Even though they say "you can start off in 3rd if ya want" it took a really long time to get up to speed if you did that.  What would be cooler is a single-speed like a Leaf or Tesla, but you'd still need to choose either epic launch or higher top speed, right?

Let's say.. I wanted to put a Zero motor in a car.. >__>.. and keep it having only one gear.  Do you know how to calculate what size gear to use to retain the crazy launching?

Torque multiplication works just as well for electric motors as it does for ICEs, so a gearbox with multiple gears will benefit an EV the same way. Generally speaking, the top gear ratio is chosen so the maximum motor power is just enough to counter the vehicle's drag at the motor's peak power rpm...that will give you the highest speed that motor can achieve in that vehicle. That's a tall gear, so it won't give you much torque multiplication to accelerate briskly at low rpm, so if you want better acceleration, you're going to need a multiple-speed gearbox. That's what's so astonishing about electric motors -- if properly designed, they can give you plenty of torque even with a tall gear, so you can just run a single gear with no need for a gearbox. Obviously the VW you drove wasn't all that torquey, and needed some help at launch because it couldn't really pull the tall gear well enough.

Putting a Zero motor in a car wouldn't be very satisfying. It just doesn't put out enough horsepower to attain any kind of top speed, so you'd wind up with a very short gear. That might make it might launch okay...but it sure wouldn't impress anybody. More (lower) gears could make it launch harder, but it would still run out of breath very early in the top gear.

[mistasam]

Thanks again for the amazing info!  The Bug had about the same power as the Zero, so I started wondering how much faster it'd be if he used Zero's lightweight components instead of the heavy AC50 and massive battery boxes.  It seems like using a gearbox would be a must for a motor with this little power (in a car, at least).  I'm still very tempted.  My car only weighs 1500lbs, but it's geared for an engine that revs to 9000rpm, so I probably wouldn't get a torquey boost when I shift up.  So far the Zero stuff seems to be the best option to keep the car light though.

Might be time to learn about Tesla swaps 

[BrianTRice@gmail.com]

FWIW there is a Porsche 911 conversion out there with two power packs and four Z-Force motors and the original gearbox. So, that's one way to multiply power, although absolutely impractical.

There are probably some very small and light cars that would move fine with a single Zero motor, but they'd either be like the Renault Twizzy or a 60s era mini car before the modern era.

[mistasam]

FOUR MOTORS???  How is that possible?  All the motors hooked up to the same throttle?  But even then, I can imagine all kinds of things going wrong if they weren't perfectly in sync.  Do you have any more info on this guy?

Two Z-Force motors and 2 monoliths would be pretty sweet.  Basically two complete Zeros in a car.  That'd be about the power of a Leaf.  Could even balance out the weight and make it AWD 

[BrianTRice@gmail.com]

FOUR MOTORS???  How is that possible?  All the motors hooked up to the same throttle?  But even then, I can imagine all kinds of things going wrong if they weren't perfectly in sync.  Do you have any more info on this guy?

Two Z-Force motors and 2 monoliths would be pretty sweet.  Basically two complete Zeros in a car.  That'd be about the power of a Leaf.  Could even balance out the weight and make it AWD 

I think this person is a Zero employee; their vehicle was at the Laguna Seca REFUEL 2017 track day. I suspect based on the results that it was Micah Bayless with a 1969 Porsche 912:
http://www.refuelraces.com/refueltt2017.php

Who... is a senior electric engineer at Zero: https://www.linkedin.com/in/micahbayless/

Maybe I'm getting too good at this gumshoe work for the wiki and need to just go take a long trip...