Dragged my old RC Boats out of the loft, what now.

[wakadoo]

they have been in the loft for a while and i would like to refresh them with brushless.

 

one is the MFA piranha, seems a good place to start as it is the 540 motor size and lots about, just need to work out what power to go for.

 

the other 2 are going to be a tad harder for me to get my head around, they have the bigger 850 torpedo motors in and how that would work

with brushless is over my head. they are the MFA Spearfish and MFA Seahawk.

 

How do i choose a brushless motor, back in the day i chose the motor turns and for me it was around a 10 turn, matched up the speed controller

and chose what Mah pack to use and that was it.

 

thank you for any help

 

 

[dhutch]

Anyone?

[dhutch]

Anyone?

[Nitroholic]

Brushless motors are rated in KV ..... the KV basically is a measure of RPM per volt.

The motor should have a max amp draw...which you use to gauge the ESC you need to have. Quite easy to buy a motor/ESC combo ready to go, which saves the hassle.

Then you choose a battery that is able to supply the current... use the formuls Mah value/1000 x C rating. So a 5000mAh 30c pack ... 5000/1000 = 5  ... 5x30=150, so you can power a 150A ESC. Just.

 

Also look at the number of poles. Generally, a 4 pole motor will be smoother than a 2 pole.

Higher KV rated motors spin faster, but have less torque.

 

In broad terms, a 3300KV motor is around a 13.5T equivalent, with 4300KV being around 9T.  Can;t recommend a setup though, as I am not a boat guy. You can't play with the gearing, and prop size and rpm matter. Thats all I know

 

[Redback]

I would look at the current brushless boats, then look at the spares and see how they work the brushless systems. you can get a nice 3660 water cooled hobbywing motor these are usally low kv due to the need for high torque not rpm with boats and usally no gear down.

Other brushless boats use outrunner motors (the outside of the motor spins), these are good as they are usally 14 pole meaning exceptionally smooth start up and enough torque were the motor wont cog and stutter, this means you could go slightly higher kv as they are torque dense they lack the rpm and power of inrunner motors at top end.
A 540 motor would work out to be about a 3660 (36mm can, 60mm long), just watch the shaft size most are 5mm bore ensure your propshaft connector can take it, or you will be limited to 3mm bore brushless motors and that limits the can length quite a bit.
A nice crawler setup might work well in a boat, like if you can find a cheap hobbywing axe v1 or v2 unit they are designed for low rpm high torque situations and can not stall out like non sensored setups.