sizing motors? - Page 2

sunnybob · 28-01-2008

I've been advised against seperate speed controllers, I am told that if one one engine is cut while the other is running, the cut engine will still turn from the prop, and generate a back feed and hurt the battery and controller. Is that true? At this stage I'm trying hard to learn who to trust for advice.

The boat has loads of room inside, Space is not an issue, so I will most likely go with twin engines (once I am sure of the size I need) and a single controller, as
I'm also trying not to spend huge amounts on this boat. Its a 50 year old project that I want to see completed, but I just cant afford another big time hobby (lol).

jankers · 31-01-2008

A single controller will be easier to set up, just make sure you get one that will handle the stall current of two motors.

Damage to batteries/ controllers? the controller will be effected by any stalled prop on a two controller system, the battery should escape any problem. With the modern controllers i would guess that they would be protected from any damage, but i cannot say i have tested them out.

J.

sunnybob · 31-01-2008

well, I've just ordered the motors and controller, so its just a case of waiting now, and getting on with painting the hull

IainM · 31-01-2008

Co-incidentally we had a tutorial the other night in the Club on ESC's and here, to the best of my recollection, is what was said:
There is really no difference between motors and generators. If you rotate the stator of a motor you will generate a voltage at the terminals.
ESC's work by feeding pulses of power to the motor.
In between the power pulse the motor is still turning and so it generates what is termed a back EMF.
ESC's don't like back EMF's and so are protected by the installation of a suitable size diode at the design stage.

So I guess, having an prop drive the motor would not be a problem and should certainly not damage the ESC. If the back EMF can't get through the ESC it can't reach the battery so allus gud so to speak.

Any more and I've got to see the man that knows

sunnybob · 31-01-2008

Thanks Ian, yes thats right regarding a motor being a generator, but I did not know that the esc was protected from back emf. I have some electrical and electronic knowledge, but this radio control stuff is completely new to me, so I'm on a huge learning curve (G).

IainM · 31-01-2008

I know what you mean!!
I console myself with the thought that the day I stop learning ..... I'm dead

Iain