R/C Tech Forums

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

Reply
 
Thread Tools Search this Thread
Old 06-19-2012, 05:30 PM   #1
Tech Regular
 
SMR 510RR's Avatar
 
Join Date: May 2011
Posts: 318
Trader Rating: 2 (100%+)
Default Motor Turn Vs. KV What To Choose?

Ok, I apologize in advance if this has been covered before...I am having a hard time finding anything related to my question here or anywhere.

So I am in the process of buying all the parts for my new drifter and I have everything ordered except for the motor. From the information I have found (there isnt much anywhere it seems) most people recommend 4000kv or less for a drifter because they generally have a smoother powerband with more mid range control (again from what I have read). Now here comes the part where I am getting confused. If you look at a motor from a US brand like Trinity or most "high end" brands to get ~4000kv you are looking at a 10.5t motor. Now if you compare that to some of the import brands like HobbyWing you are looking at a 8.5t motor.

So what would be the difference between the two? Obviously the rated top speed would be similar but how about torque, efficiency, etc.?

Anyone have any recommendations on what would work best? I was going to buy a HobbyWing motor but then I figured I would check out some used motors from US based companies or maybe even pony up the extra money if the benefit was worth the extra cost. And then, I got so confused I am not sure what I should buy anymore of if I should just go by turn or by KV or a little of both.

Any help is gladly appreciated.
SMR 510RR is offline   Reply With Quote
Old 06-19-2012, 05:44 PM   #2
Tech Adept
 
Spawne32's Avatar
 
Join Date: Jun 2012
Location: South Jersey
Posts: 108
Default

Im kind of a newbie at the whole thing but here is what i have learned so far.

Start with the can size that you are going to use...280, 380, 540, 550, etc. Once you have determined that, calculate whether or not you are going to need lots of accel with a lower top speed or a high top speed with less accel. I found that a easy way to determine what KV will be required vs gearing is to use the rollout calculator. Rollout is basically a measurement of how many inches the car will roll per revolution of the motor.

dhrc.rchomepage.com/RolloutCalc.htm

Then last but not least, i look at the turn rating, because turn rating seems to only be a theoretical thing in brushless that is basically an estimate of torque. Finally, you have your motor timing which is done through the programmable ESC. Of course, you need to make sure your ESC can support your motor, thats why sticking with the combo kits is good for beginners.

Then you can throw 2S and 3S lipo into the mix and shit gets crazy.
Spawne32 is offline   Reply With Quote
Old 06-19-2012, 05:52 PM   #3
Tech Fanatic
 
Join Date: Nov 2010
Posts: 972
Trader Rating: 5 (100%+)
Default

Kv is really not a useful indicator of performance. I'm not sure why it suddenly became vogue to publish it. At most it might give you a ballpark idea of where to start with gearing, but even then I would ask someone who had the motor before paying any attention to the Kv rating.

I don't know much about drifting, but I would think something like a 13.5T would be plenty unless there is some benefit to spinning your wheels even faster? Different manufacturers are reasonably similar for equal number of turns. I think the differences will only be apparent in non-drift racing.
Steve S is offline   Reply With Quote
Old 06-19-2012, 05:53 PM   #4
Tech Adept
 
Spawne32's Avatar
 
Join Date: Jun 2012
Location: South Jersey
Posts: 108
Default

Quote:
Originally Posted by Steve S View Post
Kv is really not a useful indicator of performance. I'm not sure why it suddenly became vogue to publish it. At most it might give you a ballpark idea of where to start with gearing, but even then I would ask someone who had the motor before paying any attention to the Kv rating.

I don't know much about drifting, but I would think something like a 13.5T would be plenty unless there is some benefit to spinning your wheels even faster? Different manufacturers are reasonably similar for equal number of turns. I think the differences will only be apparent in non-drift racing.
KV is RPM X VOLT so its a pretty big indicator of how the motor performs.
Spawne32 is offline   Reply With Quote
Old 06-19-2012, 07:03 PM   #5
Tech Fanatic
 
Join Date: Nov 2010
Posts: 972
Trader Rating: 5 (100%+)
Default

That only tells you what RPM range it operates in, hence it may be marginally useful for a gearing starting point. It tells you nothing about torque, power, or efficiency.
Steve S is offline   Reply With Quote
Old 06-19-2012, 07:07 PM   #6
Tech Adept
 
Spawne32's Avatar
 
Join Date: Jun 2012
Location: South Jersey
Posts: 108
Default

Quote:
Originally Posted by Steve S View Post
That only tells you what RPM range it operates in, hence it may be marginally useful for a gearing starting point. It tells you nothing about torque, power, or efficiency.
Theres so many unnecessary stats thrown on these brushless motors, i hardly ever know what to go by.
Spawne32 is offline   Reply With Quote
Old 06-19-2012, 07:47 PM   #7
Tech Regular
 
SMR 510RR's Avatar
 
Join Date: May 2011
Posts: 318
Trader Rating: 2 (100%+)
Default

This is my first drifter so I honestly have no idea I just thought it was odd that there was such a discrepancy between the import and "domestic" motors. We are talking 50% more kv when looking at something like a revtech, D3, or the like compared to a Hobbywing or Tacon, etc. That is not a small difference and there must be some power, efficiency, etc. gains and/or losses attributed to gaining 2000kv.

From what I could find a faster motor would come in handy more on something like a long sweeper where you may pick up speed through the corner requiring even more wheel speed to maintain the drift.

I think a quality 10.5 should do the trick, even a 13.5 would probably be ok. Decisions, decisions...

Thanks for your input everyone.
SMR 510RR is offline   Reply With Quote
Old 06-20-2012, 09:21 AM   #8
Super Moderator
 
Cpt.America's Avatar
R/C Tech Elite Subscriber
 
Join Date: Mar 2009
Location: Washington State
Posts: 11,081
Trader Rating: 52 (100%+)
Default

Quote:
Originally Posted by Steve S View Post
That only tells you what RPM range it operates in, hence it may be marginally useful for a gearing starting point. It tells you nothing about torque, power, or efficiency.
But the number of turns tells you everything about torque, power, and efficiency?

The answer is pretty simple: Drifting? = it doesn't matter. Racing? = use turns.
__________________
A big thanks to my sponsors:
- Fantom Racing - www.fantomracing.com -
- Fusion Graphix- www.fusiongraphix.com -
- RCSpecialties -
Cpt.America is offline   Reply With Quote
Old 06-20-2012, 09:57 AM   #9
Tech Fanatic
 
Join Date: Nov 2010
Posts: 972
Trader Rating: 5 (100%+)
Default

Quote:
Originally Posted by Cpt.America View Post
But the number of turns tells you everything about torque, power, and efficiency?

The answer is pretty simple: Drifting? = it doesn't matter. Racing? = use turns.
Wow, you sure burned me on that thing I never said.
Steve S is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
New track near Peoria,Il lcjhobbyworld Wisconsin & Illinois Racing 1231 08-01-2014 01:00 PM



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 09:09 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