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I know that motors burn out but what i want to learn is the reasons why. What are the main causes and the science behind it. I know for instance if a motor is stalled its not good for it and can burn out. But understanding the burnout bit is what i want to know and also long term burn out. Any cleverclogs that can give indepth explanation most welcome.
Volts * Amps = Watts ( power )
In an electric motor most of the Watts is converted into rotational energy and some goes into warming the motor windings.
A stalled motor however has no rotational component and becomes the equivalent of an electric fire.
cut and paste:-
Temperature Rise
Excessive heat shortens the life of a motor. Motor losses dissipate as heat and are removed from the motor by the motor cooling system. The motor cooling system includes internal or external fans, fins, and even coolant-based systems for special application motors. While losses increase with the load, the cooling ability of the motor does not; therefore, the temperature of the motor increases with load. When a motor application overloads the motor or restricts air flow over the motor, inhibiting the fans and fins most commonly used to cool the motor, the motor temperature can rise over the designed limit shortening the life of the motor.
Overloading the motor, improper supply voltage (high/low), frequent start/stops, poor input power quality, restricting the cooling system and using variable frequency drives increase temperature rise. This heat destroys motors in two main ways:
Heat reduces the expected life of lubricants and seals. At higher temperatures, the soap component of lubricants that time-releases oil becomes sticky increasing friction losses, reducing the life of the bearing and leaking the released oil onto the motor windings. Lubricating oils deteriorate winding insulation causing premature winding insulation failure.
Winding insulation in motors is classified by its life expectancy at various temperatures. When the rated temperature is exceeded, the insulation breaks down at a faster rate resulting in premature failure.
Excellent. Thanks Woody
A low gear ratio will also cause a motor to run hot.................
Trev :lame:
I thought that was a high gear ratio... e.g. a low gear ratio being one where the input speed is reduced by the gearing to provide a low output speed but much greater torque (so the motor would be doing less work)?
yeah trev :crazy:
Trevs right Kane - High ratio is the bigger the ratio. 15:1 being a higher ratio than 5:1.
so in a waty running a higher voltage is ok if you have a higher gear ratio?
Alex - no, if you exceed the wottys input voltage it will expire, rapidly.
A high gear ratio ie; 15:1, will load the motor less than a low gear ratio ie 5:1. A low gear ratio does not allow the motor to reach its peak revs as quickly as a high ratio therefore generating heat from the excess current it will draw..........yeah Swanny :lame:
Tut. Trev i want to have a good chat with you soon about gears and stuff me old pal. Might even pop round for some of them there chips your good lady does.
LOW is SLOW :)
http://www.weirdrichard.com/gears.htmhttp://www.weirdrichard.com/gears.htm
So ...as I see it...and Kane.
A LOW gear ratio ie; 15:1, will load the motor less than a HIGH gear ratio ie 5:1
(Message edited by woody on January 14, 2009)
Edit to above ..
15:1 means.. to me..15 Turns of the motor one turn of the wheel.
5:1 means 5 turns of the motor and one turn of the wheel.
GEAR DOWN
To adjust gears in such a way that the DRIVER ( OUTPUT ) gear goes slower than the DRIVING ( INPUT ) gear. MORE POWER!
Considering that statement came from the same page i wouldnt trust it too much. Its states in my Uni handbooks a higher ratio is the higher the actual ratio as trev said.
Edit ...
(Message edited by woody on January 15, 2009)
What have I started - it was only a long running joke between Swanny and me.
You are welcome round any time bud, and the spuds are ready for peeling. :talker:yum yum
I think this disagreement / misunderstanding is based on the terms used / misused ....
Ratio and gearing are two different things.
Low ratio = High gearing
High ratio = Low gearing
Trev said A low gear ratio will also cause a motor to run hot
When it should perhaps have been written thus ...A low ratio / high gear will also cause a motor to run hot.
and I should have written.
A LOW gear / High ratio ie; 15:1, will load the motor less than a HIGH gear / Low ratio ie 5:1
So we are all saying the same thing but have been using incorrect terminology.
A couple of other things to consider regarding motor heating:
The ESC - if the esc has a low switching frequency, it will tend to heat the motor more. A Vantec has a standard switching frequency of only 300 Hz, which will result is more heat than necessary being generated by the motor at part throttle. The new Wottys are around 12 kHz IIRC, which results in a resonably smooth output current at part throttle. Much better. The IFI Victor/Thor is especially bad in this respect - only 75 Hz.
Another thing that has a big effect, of course, is how much throttle you use. With reasonably powerful motors (e.g. Bosch or better), you should be able to get wheelspin at low speeds at half throttle or less. Using more than this generates substantially more heat in the motors, without any significant increase in thrust. Learn to be gentle with that throttle.
Ive being trying to get myself to back off the throttle in the last couple of fights (Boschs at 33V are a little marginal), and its surprising how little you need.
Also note that gyros can give the motors a hard time, especially if the gain is turned up, as they can send frequent large bursts of power to the motors to maintain course.