R/C Tech Forums

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

Reply
 
Thread Tools Search this Thread
Old 03-21-2011, 06:22 AM   #1
Tech Addict
 
ground-round's Avatar
 
Join Date: Jul 2004
Posts: 708
Trader Rating: 18 (100%+)
Default What causes brushless motors to fade?

Here's the setup: Running 17.5 Duo 2 (about 5 weekends on this motor) with Tekin RS boosted in an X-ray. Same speedo settings as the fast guys at the track. Batteries decent, but nothing special.

In my first qualifier I cooked the motor. It came off close to 220 degrees. I took it apart, and nothing was melted, deformed or shorted. So I cleaned it, oiled the bearings, put it back together and thought it'd be fine.

Second qualifier, went down a tooth and backed off some timing but 2 minutes in and it felt like my batts were dumping. Everything went soft. Finished the race, but got progressively softer and slower. Motor came off at 171 degrees.

Third qualifier, changed the battery, but again went really soft on the track.

Main, pit mate says my motor is done, may as well crank up the timing and see if I can finish. Less than a lap in, and I was a moving target for all the other cars. It felt like I was running un-boosted.

So the question is why did this happen? Is this just how B/L motors are? If you overheat it once, its done even if the internal components seem OK? Anything I can do to revive the current motor or is it now trash?
ground-round is offline   Reply With Quote
Old 03-21-2011, 06:38 AM   #2
Tech Addict
 
chubbspeterson's Avatar
 
Join Date: Jun 2005
Location: Ridgemont
Posts: 518
Default

I think once you get it that hot, it's all but over... 220 on a Duo=paperweight...
__________________
Mike Demone
7-Eleven, National Accounts Manager
Ridgemont, CA, 90026
"I vowed to never let this happen.."
chubbspeterson is offline   Reply With Quote
Old 03-21-2011, 08:00 AM   #3
Tech Addict
 
Join Date: Apr 2010
Location: Berkeley, IL
Posts: 646
Trader Rating: 23 (100%+)
Default

Quote:
Originally Posted by chubbspeterson View Post
I think once you get it that hot, it's all but over... 220 on a Duo=paperweight...
But what happens AT 200+? What part of the motor is failing that is keeping it from being effective? My guess is the rotor loses its magnatism at high heat. I would also think a new rotor is all you need.
ChiMiniRC is offline   Reply With Quote
Old 03-21-2011, 08:13 AM   #4
Tech Addict
 
chubbspeterson's Avatar
 
Join Date: Jun 2005
Location: Ridgemont
Posts: 518
Default

Quote:
Originally Posted by ChiMiniRC View Post
But what happens AT 200+? What part of the motor is failing that is keeping it from being effective? My guess is the rotor loses its magnatism at high heat. I would also think a new rotor is all you need.
Yes, and no, you are correct that high temps do effect the magnatism, I think the bigger issue is what it does (the heat) the the epoxy and windings inside the can.

I know from running the LRP x series motors thay are just as fast as the DUO 3's and you can run them in the 200-220 range, they seem to be built very hefty. But they fade over the run, Personaly I know that I can run faster up front with an LRP motor, but the DUO holds up over the run=faster. (again for me)

All these motors need to be kept cool, I think what all of us realy have to look at is after we get the gearing right, is our driving style and our chassis heating up the motors unnessarly. (do you run fans?)

I have never tried to put in a new rotor into a overheated motor, I am not sure if this will correct your problem. I have a feeling from my own past experiences that once you overheat the motor once, it is only a matter of time till it lets go, and in my experience it is the epoxy that finaly melts...

Again I stress, if you are gearing correctly, and fring motors, someting else is wrong...(Driving style, Chassis)
__________________
Mike Demone
7-Eleven, National Accounts Manager
Ridgemont, CA, 90026
"I vowed to never let this happen.."
chubbspeterson is offline   Reply With Quote
Old 03-21-2011, 08:17 AM   #5
Tech Master
 
Join Date: Feb 2009
Posts: 1,920
Trader Rating: 1 (100%+)
Default

i think inside the motor whare you cannot see the windings get melted and then you get either a short in the windings making the motor less efficient and imbalanced , also maybe the rotor will loose some magnetism too

i had a Tekin motor and it got over 140 degrees C and i looked in and saw nothing , stripped it and it was all melted ,

If the out casing is 200+ dergees then the inner is a lot hotter trust me , the GM120 speedo and GM motors have a temp sensor in the sensor pack and my race mate was looking and the outer case temp was 65 degrees and the inner was 120 degrees
sidecarphil1 is offline   Reply With Quote
Old 03-21-2011, 08:22 AM   #6
Tech Addict
 
chubbspeterson's Avatar
 
Join Date: Jun 2005
Location: Ridgemont
Posts: 518
Default

Quote:
Originally Posted by sidecarphil1 View Post
i think inside the motor whare you cannot see the windings get melted and then you get either a short in the windings making the motor less efficient and imbalanced , also maybe the rotor will loose some magnetism too

i had a Tekin motor and it got over 140 degrees C and i looked in and saw nothing , stripped it and it was all melted ,

If the out casing is 200+ dergees then the inner is a lot hotter trust me , the GM120 speedo and GM motors have a temp sensor in the sensor pack and my race mate was looking and the outer case temp was 65 degrees and the inner was 120 degrees
+1

very solid, when we temp the outside of the can, it has become the basis for what we "gear" with, and guess what, everyone checks in diffrent places, uses diffrent temp guns.

I like the pratice of gearing low and working up to the correct gear. It's safer, and if you start lower and you cant get to the "gear" that everyone is saying you need to run because you are nuking your motor already, it might make you look at the rest of the package. (Chassis, Driving)
__________________
Mike Demone
7-Eleven, National Accounts Manager
Ridgemont, CA, 90026
"I vowed to never let this happen.."
chubbspeterson is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
MurfDogg Synergy Brushless Motors The MurfDogg Electric On-Road 357 11-30-2011 01:15 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 09:35 PM.


Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net