R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Reply
 
Thread Tools Search this Thread
Old 01-19-2014, 06:09 PM   #1
Tech Regular
 
reracer's Avatar
 
Join Date: Aug 2009
Location: Socal
Posts: 382
Trader Rating: 4 (100%+)
Default Why aren't all 17.5s the same KV?

I'm looking to get into on-road racing, and I was comparing stock motors. It seems like even the same manufacture offers several different 17.5 540 can motors all with different KVs. What's the deal?
reracer is offline   Reply With Quote
Old 01-19-2014, 06:39 PM   #2
Tech Addict
 
rc car guy's Avatar
 
Join Date: Sep 2013
Posts: 647
Default

Quote:
Originally Posted by reracer View Post
I'm looking to get into on-road racing, and I was comparing stock motors. It seems like even the same manufacture offers several different 17.5 540 can motors all with different KVs. What's the deal?
Each motor can be made slightly different within the roar rules and specs id suggest the orca 17.5 it comes with a ht rotor and is FANTASTIC
rc car guy is offline   Reply With Quote
Old 01-19-2014, 07:30 PM   #3
Tech Fanatic
 
Join Date: Jan 2012
Location: Carrollton, TX
Posts: 902
Trader Rating: 27 (100%+)
Default

Kv rating is basically useless. There's no standard whatsoever between companies so there's no standard of measurement.

+1 to the orca 17.5. I'd also recommend a Team Powers Plutonium.
__________________
Xray | Airtronics | R1Wurks LiPo | Hobbywing
hyujmn is offline   Reply With Quote
Old 01-19-2014, 08:08 PM   #4
Regional Moderator
 
CarbonJoe's Avatar
 
Join Date: Jul 2006
Posts: 2,661
Default

Different rotor strengths, rotor diameters, air gaps, etc.
__________________
*** The Gate - Celebrating 8 years at the same location ***
The difference between genius and stupidity is that genius has its limits. - Albert Einstein
Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car
CarbonJoe is offline   Reply With Quote
Old 01-20-2014, 12:42 AM   #5
Tech Fanatic
 
daleburr's Avatar
 
Join Date: May 2010
Location: Oxfordshire, UK
Posts: 861
Default

Its measured unloaded. Turn the timing up, fit a smaller rotor, and the revs will increase.

Its a useless measurement
daleburr is offline   Reply With Quote
Old 01-20-2014, 01:46 AM   #6
Tech Regular
 
Join Date: Jun 2011
Posts: 290
Default

OK, so KV rating is useless for a camparison, can watts be used as a standard measurements?

Bb
bucketboy is offline   Reply With Quote
Old 01-20-2014, 09:02 AM   #7
Tech Fanatic
 
daleburr's Avatar
 
Join Date: May 2010
Location: Oxfordshire, UK
Posts: 861
Default

Quote:
Originally Posted by bucketboy View Post
OK, so KV rating is useless for a camparison, can watts be used as a standard measurements?

Bb
No, as the same issues apply. Crank the timing up and you'll get more peak watts, but at the expense of low-end power and current draw. That's if the watt numbers are even from a dyno and not just invented.

The cheapest and simplest way for most people to find out if a motor is decent is to ask the people who are winning at the tracks you race at, in the class you race. In reality there's not much between any of the top motors, which is why you see all of them up in the A final at some point or another.

If you want a true comparison "number", you'll have to build a dyno and buy/borrow a lot of motors, and even then you end up comparing power curves which isn't always simple.
__________________
Team Xray
RC-Timing Software - http://www.rc-timing.com
Mercedes AMG F1 - http://www.mercedes-amg-f1.com/
daleburr is offline   Reply With Quote
Old 01-20-2014, 09:09 AM   #8
Tech Regular
 
Join Date: Jun 2011
Posts: 290
Default

Thanks Dale

Bb
bucketboy is offline   Reply With Quote
Old 01-20-2014, 09:12 AM   #9
Tech Addict
 
rc car guy's Avatar
 
Join Date: Sep 2013
Posts: 647
Default

Quote:
Originally Posted by daleburr View Post
No, as the same issues apply. Crank the timing up and you'll get more peak watts, but at the expense of low-end power and current draw. That's if the watt numbers are even from a dyno and not just invented.

The cheapest and simplest way for most people to find out if a motor is decent is to ask the people who are winning at the tracks you race at, in the class you race. In reality there's not much between any of the top motors, which is why you see all of them up in the A final at some point or another.

If you want a true comparison "number", you'll have to build a dyno and buy/borrow a lot of motors, and even then you end up comparing power curves which isn't always simple.
there are certain companies that build motor dynos my buddy has one, and when he sets the motor to be the most efficient it IS the most efficient because the motors are always good the trail and error method however its not always the best he messes with the motor timing and rotor placement i give him the rotor i want to use ( i run the orca 17.5 tx with stock rotor (a ht rotor)). He sets it to where its the best and it is its like a rocket for each motor he sets
rc car guy is offline   Reply With Quote
Reply



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 04:16 AM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net