# Question concerning Brushless motor

Discussion in 'The Projects Forum' started by destiny98, Aug 6, 2014.

1. ### destiny98 Thread Starter New Member

Aug 6, 2014
1
0
Hello everybody,

I have some questions about an experiment test that i made with my propulsion system. The test was to test the propulsion force that the motor can make and the power consumption. I this test I have used:
1- DC brushless motor: Alien 6374 Outrunner brushless motor 170KV 3200W ( http://alienpowersystem.com/shop/63mm/alien-6374-outrunner-brushless-motor-170kv-3200wa/ )
2- XERUN-150A-SD Sensored Brushless ESC for 1/8 Car (http://www.hobbywing.com/product_show.asp?id=238)
3- Voltage and Current Sense - 180A (https://www.sparkfun.com/products/10644)
4- 2 Gens Ace 5300 3S 30C Lipo Battery
(http://www.hobbypartz.com/98p-30c-5300-3s1p.html)

I am running the motor underwater with a propeller ( I took safety measurments for that ).

I know that voltage and current consumed by the motor are independant from each other and that current is the image of the load on the motor and voltage is the image of the speed. I am changing the rotation speed of the motor by sending different commands to the ESC. When I increase the rotation speed, I see that the current is going up exponentially.Can somebody help me explain that?

2. ### Alec_t AAC Fanatic!

Sep 17, 2013
7,015
1,451
At higher revs you're moving a greater mass of water per sec. The water's kinetic energy is proportional to both mass and the square of its speed. Hence the motor energy/current needed to provide that kinetic energy is a very non-linear function of the revs.

3. ### THE_RB AAC Fanatic!

Feb 11, 2008
5,435
1,309
It's amusing the way they claim "3200W" for those little motors. Like they think no one will catch them out.

4. ### Experimentonomen Member

Feb 16, 2011
331
46
Yeh, considering a properly rated 1.35kW bldc motor is this big and also uses NdFeB magnets, just like those rc ones: http://i.imgur.com/brNIisD.jpg