Brushless Motors

[ManxmanParticipant @manxman]

Hi Folks,

Looking through Graupners catalogue came across their section of brush-less motors, beautiful piece of kit,  Have to admit I’ve never read up on these before and my question is – why do they have three electrical connections ? –  

Cheers – Kenny

[TelstarParticipant @telstar]

Hi Manxman

Not sure how technical to do this.  A brushless motor has 3 coils(windings) nominally connected together at one end like a "Y" , the other end of each coil comes out to give 3 wires.   To make them work, you need to feed them with a pulse of electricity in rotation, ie 1,2,3,1,2,3 etc. the permenant magnet of the rotor( the moving bit) then chases the magnetic field produced by these coils which a arranged physically(mechanically) at an angle to each other(for 3 field coils 120 deg apart). 

The clever bit of a brushless motor set up is the controller, it converts the dc battery voltage to 3 continious sets of pulses each out of step with each other, and can change the speed (repatition rate) of the pulses to give speed control of the motor. You can reverse these motors by swapping any 2 of the 3 connections over, but some controllers do that for you.

I have tried to stay away from ‘3 phase’ and ‘phase rotation’ analogies  . and this explanation is rather simplistic for the technophiles, but I hope it answers your question

Cheers Tom

[ManxmanParticipant @manxman]

Hi Tom,

Your going to regret replying to this query ….

Basically its like a three cylinder car engine, the three wires being the equivalent to the ht leads each taking a positive pulse to each "cylinder" in turn.  Ok that part makes sense, but on a standard motor V+ enters via red and returns via black V- to the battery (a circuit) and on a car it returns via the chassis – but where do the three pulses return ? – the only way I can think of is a pulse enters the motor and returns via one of the other two in sequence again back to the battery,  makes sense to me but is probably wrong.

The motors look very good, small, reasonable cost and loads of torque for the size

Cheers – Ken

[TelstarParticipant @telstar]

 Hi Ken

I regret it all ready

As mentioned  it is the controller that is the clever bit. If you take the ‘Y’ connection bit (we use the same in elect. eng. but call it star connection) and say if a connection to the motor is +ve that coil is a north pole N, and because they are connected any current going in must come out then in the following chart (simplified) for three coils equally spaced around a circle :- 

 wire 1    +   +   –   –   –   +   + 
 wire 2    –   +   +   +   –   –   –
 wire 3    –   –   –   +   +   +   – 

coil 1      N   n   s   S   s   n   N  

coil 2      s   n   N   n   s   S   s  

coil 3      s   S   s   n   N   n   s    

The magnetic field shown is N =full strength north    n = half strength north

same for south s

if you mark these out round a circle at 120 deg spacing you will see the magnetic field does go round and round  the rotor with it permenant magnet N and S will try to aligne with this  and as such chase it round and round

hope this helps  i would do drawings but I cant get the system to accept these as inserts

Cheers Tom

[Paul TParticipant @pault84577]

Hi Tom and Ken

Good answer Tom. I have been scratching my head for a couple of days trying to figure out how to write down what you did without going round in circles (pardon the pun) 

Ken these motors are very powerfull with huge ammounts of torque and would be great for your latest matchstick creation

[ManxmanParticipant @manxman]

Hi Tom,  Paul

Finally got the hang of it now – two wires working together as +/- and moving around all three – cheers Tom.

Already have the motors for Pacific Light (my currant) using Graupners Power 1000s – big babies – and expensive at £37 a throw – could have got them cheaper though as they are the ones fitted into starters for the nitro users. Some would say overkill, but she’s a heavy beast and is going to need lots of power to push her through the water.

again thanks Tom, Paul

Cheers – Ken

[ManxmanParticipant @manxman]

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