December 11, 2017, 02:00:26 pm
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Author Topic: burning up brushless outrunners  (Read 826 times)

daggius

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burning up brushless outrunners
« on: October 21, 2016, 01:33:52 pm »
I was testing a new bot with a brushless outrunner and noticed some burning smell and black smoke from the motor after stalling it a bit.  I had connected it to a big weapon and the gear ratio wasn't enough so it was highly loaded

question is, is this a normal thing for outrunners or can i get some that are ok with being stalled?

i am more used to working with brushed motors like the silver sparks which dont burn up when stalled

2nd question.  is it possible to have too big of an ESC for the motor.  i.e. it lets the motor draw too much current when stalling and that is what burns the motor?  if i use smaller esc, then doesnt the esc burn up instead?

Jeff Gier

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Re: burning up brushless outrunners
« Reply #1 on: October 21, 2016, 03:00:34 pm »
Yes that will happen.  On a brushless motor, there are miliohms or less of resistance per coil.  So if they are stalled the amperage will go as high as the battery can source.

Some controllers have thermal protection and I am not too knowledgeable about what this entails but it might help.  You need to go with a more powerful motor or lower gear ratio.

2) Yes possibly.  Or they both burn up.

TeamAstroBot

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Re: burning up brushless outrunners
« Reply #2 on: October 21, 2016, 03:14:31 pm »
My understanding is that brushed or brushless motors will burn up if they are stalled for too long.

As Jeff says, there are ESC's that can protect the motor from being damaged by basically turn off power to the motor if it reaches a designated threshold.


daggius

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Re: burning up brushless outrunners
« Reply #3 on: October 21, 2016, 05:17:38 pm »
thanks guys.  i am reprinting my pulleys to increase gear ratio from 2:1 to 6:1.  I see guys using direct drive outrunners for their weapons all the time but they must be using really big motors (and light weapons).  my situation is the reverse.  but i may opt for a larger motor if this doesnt work. cheers

rcjunky

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Re: burning up brushless outrunners
« Reply #4 on: October 22, 2016, 09:59:20 pm »
How about we start with what motor, esc and weapon size/weight. If there's smoke out of the motor, it's toast. You can't really have too big of an ESC, the ESC will only give as much as the motor draws.
Andrew Burghgraef
Canadian Carnage Robotics

Great Hobbies- Canada's leading retailer of radio controlled models and related hobby supplies

zacodonnell

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Re: burning up brushless outrunners
« Reply #5 on: December 29, 2016, 11:01:45 pm »
When trying to size my motors I usually shoot for one that says it can fly a plane that weighs as much as my weapon.  They end up overkill that way and it improves the reliability.

A more scientific solution is to figure out how much KE you want to store in your weapon by using something like the Team Cosmos KE calculator (http://teamcosmos.com/ke/ke.shtml) and then dividing the energy in joules by 3 to figure out how many watts the motor would need to produce for 3 seconds to spin it up. In practice it will take more like 5-10 seconds to full speed because the motor won't produce peak power continuously and the system won't be 100% efficient. I've found that this usually produces a decent value for the output of the motor, which most manufacturers provide. If you want to be safer you could divide by 4 or 5 instead.

Happy building!

-Zac

Camo5

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Re: burning up brushless outrunners
« Reply #6 on: April 11, 2017, 11:42:29 pm »
shoot for a motor that has enough thrust to lift your entire robot off the ground when loaded, otherwise it's way undersized.