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Old Feb 05, 2015, 02:12 AM
Bri.T is offline
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Help!
Brushed to brushless replacements

Hi all,

My current build/refit is in need of replacing the two motors, they are 545's with maximum rpm of 4500 turning 60mm props in a displacement hull. The boat itself is of the anchor handling type and is 41in long with a 10 in beam.

As I have seen many articles about brushless I thought I'd give them a go. However I can't find any help at all with working out what sizes of brushless to replace the brushed ones with. There seems to be plenty of stuff out there on the interweb to recommend them but hardly anything to help the new user.

Can anyone offer advice/ recommend which type/size or should I stick with what I know?
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Old Feb 05, 2015, 04:06 AM
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If the 4500 rpm gives the required performance, I would take that as a starting clue to narrow the search down to motors with the right sort of Kv figure for the voltage intended. The ones that I have seen so far seem to start a bit suddenly, not a big problem with a fast boat, but can be if close handling is needed. A common answer seems to be a gearbox or belt drive to gear it down. This could result in a smaller, cheaper, higher Kv motor.
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Old Feb 05, 2015, 04:07 AM
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That depend on do you have a gear box on existing config and what expectation with a new brushless motor, higher speed, higher torque? If you have a 60mm props 4 blade without a gear box you should have LC700 type or 3740 motor, <120A ESC and 11.1 lipo and water cooling. But it will run like a speed boat and 5000mah battery run out within 5-7 mins.

Normally a 3126 or LC500 type outrunner >1000kv with 90A ESC direct drive under 35 props or with 2-3: 1 gear box around 60 -70 props will running well and a 5000 battery on full speed lasting around 15-25 min
On the above setup you must have a water cooling on motor mount and ESC and the motor mount should be 25mm and motor shaft are 5 or 6 mm

If you not mention on speed just want to enjoy the efficiency on the brushless you can have a high radio gear box with 2216 900kv, 40-60A ESC, you can without any water colling but the speed like a normal brush motor. On my case I play around 3-4 hours each time but never require replace the battery before I leave. But the motor mount are 19mm and shaft are 3-2.3 mm
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Old Feb 05, 2015, 06:26 AM
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Assuming your running 12 volts and are looking for 4500 rpm at the prop direct drive, Id look for an outrunner around 400kv.

Brent
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Old Feb 05, 2015, 06:51 AM
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I don't understand your present setup. For maximum efficiency these small motors are high revving - a 5 pole 545 will do 11000 to 17000 rpm off load at 6 to 8.4 volts. They will turn props 30 to 45 mm in direct drive.
Here is a typical performance chart for 540 motors - see how the efficiency drops with increasing load and decreasing speed - that means it is producing heat not doing work. http://www.mabuchi-motor.co.jp/en_US...s/rs_540sh.pdf
In a tug boat they might be better with say a 2:1 reduction at least.

Are you using gears to get your 6000 rpm or loading the motor and using lower voltage?


My thoughts rather than recommendations follow.

Rather than looking at brushless motors it might be worth looking at specialist motors as used for low speed applications - RC trucks and rock crawlers. such as this which runs at about one third of the speed of the common 540/545 boat motors
http://www.amain.com/rc4wd-540-crawl...or-80t/p260759
There are faster versions that run at about half the speed of the 540/545 boat motors..

Brushless motors come in two types, inrunners and outrunners

- inrunners look a bit like like a brushed motor with a third wire. They run high speed, low torque and can be easily water cooled - or there is an air cooled rock crawler motor here
http://www.hobbypartz.com/96m12-car-2858-1200.html
Note this example is a sort of 380 size motor brought up to 540 size by its cooling fins - the smaller motor size is possible because of the higher efficiency and higher energy of the brushless design.

- outrunners have a larger diameter and it is the can that turns. They may have lower speed but more torque than a similar weight inrunner. They are more difficult to cool so need to be run conservatively in a boat. The larger diameter may make installation difficult.

It seems generally accepted that brushless motors have there uses in aircraft and in racing cars and boats where low weight and high efficiency (hence endurance) are essential considerations. Displacement boats (except for very small scales or where stability is delicate) do not have problems with heavy motors or batteries so can tolerate low efficiency or running a big motor at a fraction of its maximum power.

A final consideration is whether during manoeuvres you want precision at low speeds. I imagine that rock crawler motors and controllers are good at that.
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Old Feb 05, 2015, 07:37 AM
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You don't say why the current motors need replacement but if your boat is an anchor handling tug I would think you would want handling at lower speed over faster motors. I would definitely rule out inrunner brushless for such a boat. Why not just drop in a pair of 55 turn 500 size motors that will not require any mods to your mounts and can be had for about $15 ea.. If you go brushless you will also need to replace the esc's. They won't require cooling either. I have a 39" Seguin tug with a 55t brushed rock crawler and with a cheap esc you can almost count the prop turns by eye at lowest throttle and I set the throttle at 60% top for not wanting it any faster.
Currently brushed motors are still better for SOME scale boats such as tugs in my opinion.
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Old Feb 05, 2015, 01:28 PM
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Thanks all for your input. I am replacing them as they have been in this grp hull for 20 years albeit not used for the last 16 or so years, just in storage. They turn by hand but the bearings are very tight.

I was looking at brushless because it seems everyone in europe is converting to them, but as pointed out I would need to replace much of the electronics I have recently bought- putting the cart before the horse as the old saying goes! I think I'll go with sound sailors option of just replacing the 545's new ones.
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Old Feb 05, 2015, 04:42 PM
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Just put a very small drop of oil on each bearing on the motor, usually this is all that is needed on old motors, 30w motor oil or similar will work.

Steve
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