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Old 10-19-2010, 02:33 AM   #16
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Quote:
Originally Posted by ozace View Post
taken directly from manufacturers
Well i don't think Speed Passion gives 2700kv for the 17.5T.Actually Speed Passion doesn't give numbers for any motor.
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Old 10-19-2010, 03:11 AM   #17
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Originally Posted by Born2Run View Post
Well i don't think Speed Passion gives 2700kv for the 17.5T.Actually Speed Passion doesn't give numbers for any motor.
http://www.speedpassion.net/uploadfi...eb25th2010.pdf

this is where i got the numbers from, i could be mistaken but i assumed it was the official speed passion site
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Old 10-19-2010, 05:43 AM   #18
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Speaking for the SP v3 17.5T with 2700kv, looks overrated when all the other manufactures 17.5T motors are from 1990-2100kv.
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Old 10-19-2010, 05:52 AM   #19
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Are there any established standards for measuring Kv? Do they apply 1 volt and measure the RPM? Or do they apply 7.4 volts and divide by applied voltage? Are the measurements taken with nominal motor timing? Max motor timing?

Does an RPM reading at 1 volt with no load really tell you how fast the motor is? Don't things like torque, efficiency, etc matter as well? Rotor size, air gap, rotor strength all factor into the design of the motor. A small air gap generally gives you more torque and less RPM. Does that make a motor better? Depends on your ESC settings, gearing, track size, driving style, 1s or 2s, etc.
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Old 10-19-2010, 06:16 AM   #20
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Originally Posted by CarbonJoe View Post
Are there any established standards for measuring Kv? Do they apply 1 volt and measure the RPM? Or do they apply 7.4 volts and divide by applied voltage? Are the measurements taken with nominal motor timing? Max motor timing?

Does an RPM reading at 1 volt with no load really tell you how fast the motor is? Don't things like torque, efficiency, etc matter as well? Rotor size, air gap, rotor strength all factor into the design of the motor. A small air gap generally gives you more torque and less RPM. Does that make a motor better? Depends on your ESC settings, gearing, track size, driving style, 1s or 2s, etc.
Good question, I've thought of that too!
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Old 10-19-2010, 03:22 PM   #21
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Most of the KV stats are tested at 7.2v for a total rpm figure, then they divide the total (for the methods i have managed to track down over the years.)

Considering pretty much all these motors are the same phisical size and weight the overall "performance" will be the same or very close, the decider is the KV. I think marketing and "fanboys" get in the way of the facts.

At the end of the day either we take the manufacturer figures as true and correct or we discount them all and wait for someone to purchase all the motors and test each one.

Choosing the "right motor" for the task at hand is not always about the "fastest" motor in the pack, especially for racing on tighter tracks.
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Last edited by ozace; 10-19-2010 at 03:33 PM.
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Old 10-30-2010, 12:35 PM   #22
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Originally Posted by ozace View Post
I come from an Eflight background so i find the way car motors are sold a joke.

the number of "turns - winds" is pretty much garbage these days.

What makes sense is the "kv", rpm per volt.

Take any motor you like in the 540 can size (36mm) and the motor with the highest kv will be the fastest, the lowest kv should have the most torque.

When i started playing with cars i measured some motors and found there is a difference in the quoted kv of similar "turn" motors and the higher kv motors were the "fast" ones.

I hope in the near future the "car" companies wake up and realise not all car enthusiasts are stupid and they start labeling with meaningful real information.



speed passion 17.5 comp3 = 2700kv
speed passion 17.5 ultra sprotsman = 2100kv
epic d3 17.5 = 2300kv
losi 17.5 sensored = 1820kv
tekin redline 17.5 = 2500kv
lrpvector x-12 17.5 = 2200kv
novak ballisic 17.5 = 2200kv
orion vortex 17.5 = 2280kv
Fastest? Because it turns more RPM? RPM without torque is pointless.
And by your analysis, the SP V3 17.5 is hands down nearly 50% better than any other motor out ther...LOL.

Being that all these motors are built to very strict specs from ROAR, there is not 17.5 motor with ROAR approval that is 50% better than anything.

Using KV to determine the fastest motor is silly, because there is no standard method used by all. Let me bump the timing up to 50 degrees, and run an 11mm rotor in a 17.5 and come on here boasting 3300kv... will you then run out and buy that motor? It would be fastest right?

Ill tell you that it would be the worst motor you ever ran, but by your method of rating the "best" motor, it would be far superior. KV rating is a great tool for Multi cell applications, where you need to calculate gear ratios for proper speed, or prop size and pitch for proper flight of a plane...

RC cars need a combo of Torque, RPM, and efficiency. In a limited power class, a motor making more watts is uaually better. KV takes only one of these factors into account.

Quote:
Originally Posted by CarbonJoe View Post
Are there any established standards for measuring Kv? Do they apply 1 volt and measure the RPM? Or do they apply 7.4 volts and divide by applied voltage? Are the measurements taken with nominal motor timing? Max motor timing?

Does an RPM reading at 1 volt with no load really tell you how fast the motor is? Don't things like torque, efficiency, etc matter as well? Rotor size, air gap, rotor strength all factor into the design of the motor. A small air gap generally gives you more torque and less RPM. Does that make a motor better? Depends on your ESC settings, gearing, track size, driving style, 1s or 2s, etc.
Exactly....Im glad there is someone questioning things.... KV and C ratings.... two things RUINING the RC electric world. Both are arbitrary numbers that can ultimately be made up by the manufacturer to sell products. AND IT WORKS!!! Question the numbers being forced down your throats... again, like in each of these "BEST" threads that pops up.... Kudos to Novak for explaining their method of rating KV.

Quote:
Originally Posted by ozace View Post
Most of the KV stats are tested at 7.2v for a total rpm figure, then they divide the total (for the methods i have managed to track down over the years.)

Considering pretty much all these motors are the same phisical size and weight the overall "performance" will be the same or very close, the decider is the KV. I think marketing and "fanboys" get in the way of the facts.

At the end of the day either we take the manufacturer figures as true and correct or we discount them all and wait for someone to purchase all the motors and test each one.

Choosing the "right motor" for the task at hand is not always about the "fastest" motor in the pack, especially for racing on tighter tracks.
The big picture is this... Keep purchasing motors based on KV rating, and their marketing ploys have earned your money.

I suggest you go out to your local track and see what motor is going fastest. Buy that one. Better yet, find the fastest guy at your local track who is willing to share info and help you out.... buy whatever he runs! Then he can get you right into the ballpark on gearing and you can be fast.

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Old 10-30-2010, 06:27 PM   #23
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I find the values quoted by manufacturers to be no value to me. I'm sure someone here has the equipment, like a brushless analyzer/motor checker to see what motor produces whatever KV, rpm, watt.

up to a few months ago, I was running one of the oldest brushless motors around.....novak 17.5 ss pro, and it was running head to head with all the latest brushless motors.

by the way, how do you measure the output of watts?
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Old 10-30-2010, 09:12 PM   #24
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Originally Posted by captain stacker View Post
I find the values quoted by manufacturers to be no value to me. I'm sure someone here has the equipment, like a brushless analyzer/motor checker to see what motor produces whatever KV, rpm, watt.

up to a few months ago, I was running one of the oldest brushless motors around.....novak 17.5 ss pro, and it was running head to head with all the latest brushless motors.

by the way, how do you measure the output of watts?
according to Novak your "old" motor is 2200kv, right in the ball park so it should be right in there.

As i posted above the numbers i printed are from the manufacturers, i dont claim them to be right only as put forward from the source. If they are misleading then we are all being taken for a ride.

As to measuring watts, the only way i know if is to put a data logger of some sort in the mix. This will measure how many watts the battery is putting out for the powertrain (esc, motors and gearing drag). Watts is not really a great measure unless it is the exact same setup used each time for testing.

There are motor dynos out there that can actually measure the motors output but i have not come accross any that are practical for the hobbiest, and the owners of such devices usually wont publish the data as it can effect their business.
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Old 02-25-2011, 10:45 AM   #25
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Hi all

I just thought I would bump this thread instead of making a new similar one. I'm planning to race in the local club's 1/10 on road TC stock (17.5) class, and looking for the fastest motor as well as the best bang for the buck motor. I think I have my speed controller choice done, what do you think for the motor. Someone has recommended the Speed Passion V3 17.5 motor, now I can get that but I want some second opinions really. I can get the bossrcmotorsports version if enough people say its better (it's not that much more cost after all).

Opinions welcome. I will probably be running a schumacher mi4 or a xray t2/t3 (hopefully lol). Thanks
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Old 02-26-2011, 11:29 AM   #26
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Originally Posted by Zoea View Post
Hi all

I just thought I would bump this thread instead of making a new similar one. I'm planning to race in the local club's 1/10 on road TC stock (17.5) class, and looking for the fastest motor as well as the best bang for the buck motor. I think I have my speed controller choice done, what do you think for the motor. Someone has recommended the Speed Passion V3 17.5 motor, now I can get that but I want some second opinions really. I can get the bossrcmotorsports version if enough people say its better (it's not that much more cost after all).

Opinions welcome. I will probably be running a schumacher mi4 or a xray t2/t3 (hopefully lol). Thanks
What esc will you be using? this can make a difference.
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Old 02-26-2011, 12:06 PM   #27
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I've been recommended this one from hobbywing;

Xerun XTREME STOCK Brushless 60A
But if I get a good deal on a used one I can always get something else. Your suggestions here would be great also.
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Old 02-26-2011, 09:36 PM   #28
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Originally Posted by Zoea View Post
Hi all

I just thought I would bump this thread instead of making a new similar one. I'm planning to race in the local club's 1/10 on road TC stock (17.5) class, and looking for the fastest motor as well as the best bang for the buck motor. I think I have my speed controller choice done, what do you think for the motor. Someone has recommended the Speed Passion V3 17.5 motor, now I can get that but I want some second opinions really. I can get the bossrcmotorsports version if enough people say its better (it's not that much more cost after all).

Opinions welcome. I will probably be running a schumacher mi4 or a xray t2/t3 (hopefully lol). Thanks
Have a look at what the fastest drivers at your local club are useing,this should be good starting point. Thats what I did. SP V3 + Tekin RS = 1st place in 17.5 unlimiited timeing class
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