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Discussion Starter #1
Well Gentlemen,

The motors will arrive soon, I am told I do not need to run the Zilla2k series to parallel because the motors will put out enough torque in parallel settings. Hmmmmmn, not sure what route I will take, if i wire the Zilla2K series and use the hairball to switch to parallel that will creat an enormous amount of torque off the line. Two 11" motors at 2000amps, that is some serious torque! :eek: Might get better times if I go parallel? Must talk this over with George at Netgain. I can go either way. Any suggestions or calculations out there?

Remember the torque from two 11" motors is more than two 9" motors with the same amps/volts. ;)
 

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Discussion Starter #3
Honestly, I am not. Is it possible different size motors operating on the same volts and torque can achieve the same amounts of torque and horsepower? Hmmmmmn! I know one thing, it will take much more effort for a 9" to match an 11". :eek:

Are you sure about that? I would think that the only increase would be related to efficiency. Same amps/volts going in = same power coming out.

Keith
 

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from what I've read, power in = power out - losses. My understanding of torque is the 11" motor will produce more torque at a given RPM, HOWEVER it will take more voltage to get the 11" motor up to the same RPM as the 9" so lower torque of the 9" motor but at a higher RPM is roughly equal to the POWER the 11" motor is putting out since it is higher torque at a lower RPM for a given Voltage/Current combination.

It's a similar principal to the battery voltage/current is not equal to motor voltage/current but the power is roughly the same.

Torque and RPM of a 9" motor will not be equal to the 11" motor however power is roughly the same. So if you were to use a slightly higher gear ratio on the 9" motor the power to the wheels should be the same as the 11" motor until you reach the overload point where the motors size/mass start to play a big part in efficiency and power output.

That stupid law of conservation of energy states that power output cannot exceed power input. So an 85% efficient 9" motor is going to put out the same amount of power as an 85% efficient 11" motor. You may have to adjust gear ratios to get the same torque to the ground.

It's not untill you start to need the thermal mass of the larger motor that a larger motor will allow you to maintain a higher power level.
 

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That messes with my simplistic understanding that amps=torque. At zero rpm (stall), how can torque be different if amperage is the same? I realize the torque and hp curves will be different for the 9" and 11" motors, but I don't see how the peak torque can be higher through the 11".

Keith
 

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Discussion Starter #6
Very good explaination. I feel much safer with an 11". :eek:

from what I've read, power in = power out - losses. My understanding of torque is the 11" motor will produce more torque at a given RPM, HOWEVER it will take more voltage to get the 11" motor up to the same RPM as the 9" so lower torque of the 9" motor but at a higher RPM is roughly equal to the POWER the 11" motor is putting out since it is higher torque at a lower RPM for a given Voltage/Current combination.

It's a similar principal to the battery voltage/current is not equal to motor voltage/current but the power is roughly the same.

Torque and RPM of a 9" motor will not be equal to the 11" motor however power is roughly the same. So if you were to use a slightly higher gear ratio on the 9" motor the power to the wheels should be the same as the 11" motor until you reach the overload point where the motors size/mass start to play a big part in efficiency and power output.

That stupid law of conservation of energy states that power output cannot exceed power input. So an 85% efficient 9" motor is going to put out the same amount of power as an 85% efficient 11" motor. You may have to adjust gear ratios to get the same torque to the ground.

It's not untill you start to need the thermal mass of the larger motor that a larger motor will allow you to maintain a higher power level.
 

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That messes with my simplistic understanding that amps=torque. At zero rpm (stall), how can torque be different if amperage is the same? I realize the torque and hp curves will be different for the 9" and 11" motors, but I don't see how the peak torque can be higher through the 11".

Keith

Not really, since you aren't making any power. Power is torque x rpm, so at stall the 11" motor could easily have more torque, but power is the same either way ZERO.

Amps = torque, and Volts = rpm. However the 9 and 11" motors will have different torque/amp and rpm/volt constants. If torque per amp is higher than motor X, then rpm per volt must be lower than motor X. It's all power in = power out - losses, there is no magical properties. Think of it like a gas engine, there is a good chance a 5L motor will have more power than a 2.5L motor but that's simply because it is able to transform more fuel into power. Since fuel for the electric car isn't quite so easy to ramp up, then a pair of 9" motors off a Zilla 2K with proper gearing should be similar in performance to a pair of 11" motors off a zilla 2k again with the proper gearing. For drag racing the limiting factor is most likely the Zilla 2k, (and/or the batteries) not the motor size. White Zombie beats up on those siamese IMPULSE 9's, not even regular Warp 9's with a Zilla 2k and they seem to do just fine. Until you up the current and/or voltage you do not have more power than White Zombie, you just have a heavier car.

Looks like you might be in the market for a Zilla 4K, there's already one custom unit out there, perhaps with enough money you could have one too.

I hope this doesn't come across negative, I'm just trying to clear up some myths.
Crodriver mentioned that short super high power runs don't seem to heat the motor the same way a much longer but low power drive does. This was mentioned when he had to disconnect the external blower that cools his motor when he had dc/dc converter problems. He estimated total power output was similar, but the short drag run didn't cause the same temperature rise in the motor.
 

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Discussion Starter #9
There must be some reason why large trucks, buses and trains operate on much larger motors. The larger the motor the less stress on parts. I would believe it takes more energy for a smaller motor to match a larger motor when weight comes into the factor. If motor size did not matter, then all electric vehicles would operate on a small motor. Larger is better when matching vehicle weight to movement. Sounds good! :D

That messes with my simplistic understanding that amps=torque. At zero rpm (stall), how can torque be different if amperage is the same? I realize the torque and hp curves will be different for the 9" and 11" motors, but I don't see how the peak torque can be higher through the 11".

Keith
 

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Discussion Starter #10
Netgain stats:

Warp 11"
135 Ft. pounds torque
43.7 HP
______________________

Warp 9"
70 Ft. pounds torque
32.3 HP
______________________

Warp 13"
130 ft. pounds torque
35.5 HP
______________________

Impulse 9"
60 Ft pounds torque
38.6 HP
______________________

All specs are based on 72 volts.
 

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Discussion Starter #11 (Edited)
I totally understand your explanation. There are other facters in drag racing to add into the equation, tire traction is a huge factor. While WZ is getting great times in the 1/4 mile, he still is losing traction on launches. Our Camaro has some HUGE slicks on the rear and will get plenty of traction. We are installing the wheelie bars today. Like you mention total weight is another huge issue, even though our motors are heavier, the car will be very light. We have ordered fiberglass one piece nose, doors and trunk lid, these reduces the weight hundreds of pounds. Most of the car is aluminum to keep our weight close to 2000lbs. My Camaro is not street legal though, oh well. I will take her down the strip in front of my office, should be a sight to see. lucky I have many officer friends in our local gym. ;)

Not really, since you aren't making any power. Power is torque x rpm, so at stall the 11" motor could easily have more torque, but power is the same either way ZERO.

Amps = torque, and Volts = rpm. However the 9 and 11" motors will have different torque/amp and rpm/volt constants. If torque per amp is higher than motor X, then rpm per volt must be lower than motor X. It's all power in = power out - losses, there is no magical properties. Think of it like a gas engine, there is a good chance a 5L motor will have more power than a 2.5L motor but that's simply because it is able to transform more fuel into power. Since fuel for the electric car isn't quite so easy to ramp up, then a pair of 9" motors off a Zilla 2K with proper gearing should be similar in performance to a pair of 11" motors off a zilla 2k again with the proper gearing. For drag racing the limiting factor is most likely the Zilla 2k, (and/or the batteries) not the motor size. White Zombie beats up on those siamese IMPULSE 9's, not even regular Warp 9's with a Zilla 2k and they seem to do just fine. Until you up the current and/or voltage you do not have more power than White Zombie, you just have a heavier car.

Looks like you might be in the market for a Zilla 4K, there's already one custom unit out there, perhaps with enough money you could have one too.

I hope this doesn't come across negative, I'm just trying to clear up some myths.
Crodriver mentioned that short super high power runs don't seem to heat the motor the same way a much longer but low power drive does. This was mentioned when he had to disconnect the external blower that cools his motor when he had dc/dc converter problems. He estimated total power output was similar, but the short drag run didn't cause the same temperature rise in the motor.
 

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I totally understand your explanation. There are other facters in drag racing to add into the equation, tire traction is a huge factor. While WZ is getting great times in the 1/4 mile, he still is losing traction on launches. Our Camaro has some HUGE slicks on the rear and will get plenty of traction. We are installing the wheelie bars today. Like you mention total weight is another huge issue, even though our motors are heavier, the car will be very light. We have ordered fiberglass one piece nose, doors and trunk lid, these reduces the weight hundreds of pounds. Most of the car is aluminum to keep our weight close to 2000lbs. My Camaro is not street legal though, oh well. I will take here down the strip in front of my office, should be a sight to see. lucky I have many officer friends in our local gym. ;)
I agree, and I can't wait to see your car launch. Especially if you can get it to hook up with the motors in series and you have a big enough pack to keep the voltage up the whole race.

You probably said it somewhere, but are they Warp 11's or 11HV's?
Your Zilla turned out to be an HV?
 

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There must be some reason why large trucks, buses and trains operate on much larger motors. The larger the motor the less stress on parts. I would believe it takes more energy for a smaller motor to match a larger motor when weight comes into the factor. If motor size did not matter, then all electric vehicles would operate on a small motor. Larger is better when matching vehicle weight to movement. Sounds good! :D
Main thing is longevity at a desired power level. Sure you run an 11" at a few hundred KW, but you won't be able to do it for very long before you start to melt stuff because of soo much heat/arcing. If you have say 15% of inefficiency heat that needs to be dissipated, a bigger motor will do it better since it has more thermal mass. Now if you had 100% efficient motor and assuming that the mechanical parts (i.e shaft, bearings, etc) could take the mechanical force then you are correct, we could use a very small motor, 200kw through something the size of a can of soda anyone. But unfortunately physics ruins our fun.
 

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Netgain stats:

Warp 11"
135 Ft. pounds torque
43.7 HP
______________________

Warp 9"
70 Ft. pounds torque
32.3 HP
______________________

Warp 13"
130 ft. pounds torque
35.5 HP
______________________

Impulse 9"
60 Ft pounds torque
38.6 HP
______________________

All specs are based on 72 volts.
These specs are just one point on the torque curve. In fact the specs shown here for the 13" and 11" would disprove your theory of the larger motor having greater torque.

If you compare the Netgain chart for the Impulse 9" and the Warp 8" you will find them very close (when taking efficiency into account).

Warp 8" - 70 ft-lbs - 2744rpm - 463amps - 81.8% efficiency

Impulse 9" - 70 ft-lbs - 2754rpm - 449amps - 84.7% efficiency

I still think that your max torque is related more to your available amperage than your motor size.

Later,
Keith
 

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Discussion Starter #15
Our motors are not HV, but they have a little something special from George at Netgain. ;) So the Zilla 2KHV will work just fine. We are running the controller series to parallel. We are counting on huge jump off the line with all that torque and when she kicks into parallel the 200V to each 11" to finish the job. I could have ordered HV motors and build a larger pack with a heavier car (more batteries) and counted on higher rpm's to win a race, but we are going the lighter weight more torque route. We will test with many rear end gear ratio's to maximize our launch from high torque, lower ratio, lower rpm, aaaaaallll torque. Example, ever drive a car and start of in 2nd? If your motor can pull enough torque you will launch much quicker. Yes, it will be a strain on the drivetrain, but we have the strongest axles money can buy. I might need a good chiropractor after a few races! :p

I agree, and I can't wait to see your car launch. Especially if you can get it to hook up with the motors in series and you have a big enough pack to keep the voltage up the whole race.

You probably said it somewhere, but are they Warp 11's or 11HV's?
Your Zilla turned out to be an HV?
 

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These specs are just one point on the torque curve. In fact the specs shown here for the 13" and 11" would disprove your theory of the larger motor having greater torque.
The 11" was pulling 450 amps to generate that 135 ft/lbs
The 13" was pulling 375 amps to generate 130. ... also at a lower rpm.

Get the amps on the 13" inch up to 450 and see what your torque is....
 

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It's rather simplistic but I think of motors like drive shafts, if you aren't breaking your drive shaft then putting in a bigger one won't give you more power. Similarly, if your motor isn't melting from the battery pack output, putting in a bigger one won't give you more power. The optimal setup would probably be the smallest motor that can barely survive the power from the pack for the duration of the run. Same concept of dragster motors that get rebuilt after each race, run them right on the edge.
 

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Discussion Starter #18
Good point. In my personal situation (Camaro Huge Slicks) I would be nervous trusting a 9" to handle the pressure from massive amounts of torque "gripping" the track all at once. When you have that amount of stress on the drivetrain you need the strongest parts available, that includes the motor. ;)

It's rather simplistic but I think of motors like drive shafts, if you aren't breaking your drive shaft then putting in a bigger one won't give you more power. Similarly, if your motor isn't melting from the battery pack output, putting in a bigger one won't give you more power. The optimal setup would probably be the smallest motor that can barely survive the power from the pack for the duration of the run. Same concept of dragster motors that get rebuilt after each race, run them right on the edge.
 

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Good point. In my personal situation (Camaro Huge Slicks) I would be nervous trusting a 9" to handle the pressure from massive amounts of torque "gripping" the track all at once. When you have that amount of stress on the drivetrain you need the strongest parts available, that includes the motor. ;)
Correct me if I'm wrong but the shaft of both motors is 1 1/8" so the 11" is not "stronger" when you compare them that way. If anything the 9" would be a bit easier on itself and the rest of the drive train because the same torque comes at a little higher RPM.

Did you read about the White Zombie runs where the controller was wired wrong and they estimate the Zilla was putting out 3000A to a pair of series Impulse 9's? They didn't break! I would think your coupler/drive train will need to be up to the task of handling the torque from the motor. Not the motor handling the "grip" from your tires.

What you need to work on is getting everything else up to the level to actually justify the need for a pair of 11's....
 

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I'm going to post this in both threads:

Disclaimer - I am not attacking you! Anything I say is constructive criticism, and the only reason I am even replying is I would really like to see you have some measure of success.

You really should consider just stopping for a minute. Before you spend more, cut more, build more, you really should try to get your head aroundthe concept of drag racing with an electric powertrain. You're thinking almost entirely in terms of ICE technology and procedures - many of them are pretty much opposite with electric.

  • Bigger electric motors don't necessarily mean more power, or stronger.
  • I like the idea of siamese 11s but until you reach the point of melting a pair of 9s, they're probably costing you more than you're getting from them. Two cars, one with 9s, one with 11s, otherwise identical, the smaller motored car is probably going to fo faster - unless it reaches the point of zorching.
  • Theoretically, the biggest advantage of your 11s is more copper and more steel - you need to be focused on taking advantage of that or they will be nothing more than a weight penalty and bragging rights.
  • The best way I know to take advantage of them is to have so much power - i.e. a MONSTER battery pack - combined with enough chassis to push them to the ragged edge in a matter of seconds.
  • Personally, I think two Warp 11s are going to laugh at 2000 amps for a few seconds. (You only pull max amps long enough to get the car off the line and up to a certain velocity) You have the chassis and rear tire to push them, but your current pack won't have the power to test that limit.
  • You're pushing that pack to the ragged edge. One way or another, I can't see how it won't let you down. I think you should have a pack that can handle 2500-3000 amps within its "safe" limits. When I built my A123 packs on paper, I never counted on pushing the cells more than 50c, even though they are supposedly good for up to 60c. Also, the numbers I had at 50c were beyond what I think my chassis could get to the ground effectively, so it would probably be pulling more like 40c. Likewise, my voltage estimates were way over what I needed, to account for sag and for making multiple passes back-to-back (I am also planning to autocross).
  • I agree 100% with the guys about running the whole race in series. If you can push that Z2K-HV to 350 volts that would give you enough to stay near your motor's rated max voltage. Eventually you need an EHV version to have maybe a couple hundred volts ready for each motor. Remember you set the limits going to the motors with the controller, not the pack. Maybe Otmar will talk to you about how much voltage you can actually get away with in the pack with your controller. I wonder if he would upgrade it for you???
Again, this was all meant to be constructive criticism. If you see it any other way, but disregard the post and I'll shut up. ;)
 
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