Model Boat Mayhem - Forum

Please login or register.

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

Author Topic: Another thread on motor choice!  (Read 1236 times)

moley

  • Guest
Another thread on motor choice!
« on: June 21, 2011, 09:09:25 PM »

Right,  I've got a baitboat which I'm in the process of stripping down and rebuilding.  Here are some pics - it is 55cm long and 35cm wide,  and it will weight about 8kg when fully loaded.  As you can see,  it's not the most aerodynamic!










Obviously it is never going to be a speed merchant,  but I'd like get it running at 5 knots minimum.  It used to run a 55mm prop on an MFA torpedo 850,  maximum speed 5000rpm on 6v,  which made it pretty slow.  I tried running it at 12v which made the speed OK,  but it then suffered overheating problems!

I'd like to go brushless if I can!  I'm limited on prop size to 70mm,  and motor diameter to 50mm.  I want to get a reasonable speed along with the lowest current drain possible.  

Am I better off with higher rpm and a smaller prop,  or lower rpm and a larger prop?  I'd be grateful for any recommendations on a motor / ESC combo  :)
Logged

moley

  • Guest
Re: Another thread on motor choice!
« Reply #1 on: June 21, 2011, 09:45:41 PM »

Just to add,  I'd like to use 7.4v Lipo's,  probably 2x 10Ah 5C in parallel,  will these cause any limitations?
Logged

nick_75au

  • Guest
Re: Another thread on motor choice!
« Reply #2 on: June 23, 2011, 10:31:26 AM »

Your current drain is related to the prop and the speed you spin it at, so regardless of the motor you use, to get it going faster you will draw more amps. In general a bigger prop going slower is better

If you pick a brush-less motor with similar spec's as the MFA and run it on 2 cell Li-po you will get better performance.

So the MFA is approx. 850 Kv, look for a similar Kv, a 36 mm or 42 mm out-runner will have sufficient power to drive a 70 mm prop at 7.4 volts.

Those batteries will have sufficient C rating to run the set-up as I've described.

Nick
Logged
Pages: [1]   Go Up