Model Boat Mayhem - Forum

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: Brushless motors in parallel  (Read 2981 times)

john44

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,388
  • member of the Potteries Model boat club
Brushless motors in parallel
« on: March 23, 2013, 07:15:33 PM »

Hi guys,
I have just been reading some interesting views regarding
wiring up 2 or more identical brushless motors wired in parallel
controlled by 1 esc.
1 chap ran 2 -4074,s on 1 -120amp esc.
Has anyone on the forum tried this?

john
Logged

Martin [Admin]

  • Administrator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 19,052
  • Location: Peterborough, UK
    • Model Boat Mayhem
Re: Brushless motors in parallel
« Reply #1 on: March 23, 2013, 07:25:27 PM »


I thought this couldn't / shouldn't be done as any difference in shaft speed will blow up the controller....

Logged
"This is my firm opinion, but what do I know?!"    -   Mayhem FaceBook Group!

john44

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,388
  • member of the Potteries Model boat club
Re: Brushless motors in parallel
« Reply #2 on: March 23, 2013, 07:32:14 PM »

That,s what I thought as well Martin, but some chaps on rc world rc universe
have other thoughts.

john
Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,563
  • Location: Blackpool, Lancs, UK
Re: Brushless motors in parallel
« Reply #3 on: March 24, 2013, 10:57:39 AM »

That,s what I thought as well Martin, but some chaps on rc world rc universe
have other thoughts.

john
Just had a look there - http://www.rcuniverse.com/forum/m_5276285/anchors_5276285/mpage_1/key_/anchor/tm.htm#5276285
The consensus is that each motor needs its own ESC, 2 ESCs can be connected to one channel using a Y lead.  This makes sense as the electronics in the ESC performs the job of the brushes and commutator in a brushed motor.
I would imagine that to run two motors off one ESC they would not only need to be identical in every respect (probably beyond the bounds of normal quality control limits) but identically loaded, and very lightly at that.  Either that, or mechanically linked so that they were locked in phase.  Is there a link?
Logged
"With the right tool, you can break anything" - Garfield

john44

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,388
  • member of the Potteries Model boat club
Re: Brushless motors in parallel
« Reply #4 on: March 24, 2013, 12:01:04 PM »

I watched this demmo and others on Youtube.
www.youtube.com/watch?v=zeYAWqt2rlE

I have just tried to watch the link from the forum but it says it is not available
so you will have to google it.

regards
john
Logged

john44

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,388
  • member of the Potteries Model boat club
Re: Brushless motors in parallel
« Reply #5 on: March 24, 2013, 12:16:20 PM »

Hi guys I have tried the link it does not work for me .
I had to google  2 brushless motors and 1 esc
and the video is on the drop down list.
I dont think I will be trying it but some may find it interesting.

john
Logged

Martin [Admin]

  • Administrator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 19,052
  • Location: Peterborough, UK
    • Model Boat Mayhem
Re: Brushless motors in parallel
« Reply #6 on: March 24, 2013, 08:26:11 PM »

 
Found this on Utube!   :o

http://youtu.be/zeYAWqt2rIE
Logged
"This is my firm opinion, but what do I know?!"    -   Mayhem FaceBook Group!

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,563
  • Location: Blackpool, Lancs, UK
Re: Brushless motors in parallel
« Reply #7 on: March 25, 2013, 10:33:48 AM »

Like the man said "It's a no-load test".  Even then, there appeared to be little or no low speed control. 
I suspect that the cost of 2 ESCs appropriate to the motors being driven would be less that the cost of one capable of the current for two, plus the cost of replacing it with the two appropriate ones and possibly the motors when they stall themselves and fry.
2 motors geared to the same shaft so that they are phase locked to effectively give a larger motor of a different shape, maybe.
Another link  http://www.rcgroups.com/forums/showthread.php?t=1435626  and scroll down to #5.
Logged
"With the right tool, you can break anything" - Garfield

Mad_Mike

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,597
  • Lincolnshire
  • Location: Lincolnshire
Re: Brushless motors in parallel
« Reply #8 on: March 25, 2013, 11:11:33 AM »

For sensorless brushless motors the esc times the comutation of the motor by measuring the back emf of each coil winding. Back emf is the voltage generated by the magnets the in motor rotating passed the coils like a generator. This voltage works against the imput voltage from the esc.

EG:

12v put into motor by esc

minus;

3v back emf generated in reverse direction by motor

equals;

9v actually then going into motor.

If we were to take an example of a 3 pole brushless motor, to make the make the motor turn only 2 of the 3 poles are given current at any one time. The esc changes which 2 of the 3 poles is powered up as the motor revolves through 360 degrees. When the motor is turning all the poles are creating an equal amount of back emf voltage towards the esc. The esc reads all the back emf voltages from all the poles. When the esc applies input voltage to 2 of the 3 poles to make the motor turn, the back emf voltage readings of those poles is lower than the back emf voltage of the single pole that isnt being inputted. Because one pole has a different reading to the others the esc from this feedback can tell where the rotor position is in the 360 degree revolution.
By using 2 motors on one esc, It would only work if both motors and back emf readings were perfectly insinc all the time. If just 1 of the 2 motors was slowed down by load, then the back emf readings from the motors would get all crossed and say anything. The esc then would get a jumble of readings and lose the position of the motors, get all the sink wrong and throw a paddy.

Something like that %%
Logged

sparkey

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,228
  • I think I am as mad as I think I am then I am mad
  • Location: wandsworth
Re: Brushless motors in parallel
« Reply #9 on: March 25, 2013, 03:34:29 PM »

 %% Sounds like the wife! >>:-( >>:-(
Logged
My boats are all wood like my head fluctuat nec mergitur

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless motors in parallel
« Reply #10 on: March 26, 2013, 10:42:52 AM »

Gents,
It is fairly normal (or was) to run two brushlesses on a single ESC.  This was a fairly normal set-up for a Twin star (aircraft)
The thing that matters is that the loads on both are very close to identical, so that they rotate at the same speed and produce the return pulses more or less together
andrew
Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,563
  • Location: Blackpool, Lancs, UK
Re: Brushless motors in parallel
« Reply #11 on: March 26, 2013, 02:20:46 PM »

Maybe true, but airscrews are not running in water.  Screws in water will get differential loading when the boat rocks, and very differential loading if one hits a bit of weed or a feather or a plastic bag.  In the resulting confusion, it will be anybody's guess which goes first - wiring, motor(s) or ESC, but it is probable that one will before sync is re-established.
Logged
"With the right tool, you can break anything" - Garfield
Pages: [1]   Go Up