Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[narrowboater]

Hi all,
I am currently building a 1:24 scale Vosper MTB and was going to use 3 x brushed 600 size motors. However, on trying the hull in the test tank (bath!) It is really too heavy. I need to reduce weight and am considering using brushless motors and lipo batteries but am a complete novice where these are concerned. The boat is 36 inches long with 3 x 4mm shafts and 30mm 3 bladed props. I know I will need special speed controllers and a charger for the lipo batteries but which brushless motors should I use? Outrunner/Inrunner (whatever that means), Size, Type?????

I also want to be able to control the two outer motors with a mixer (W Tail or similar) but can I still do this with brushless motors?

Any info will be gratefully received.

[Time Bandit]

Considering your weight problems and the fact that outrunners are 20-30% lighter compared to inrunners I´d use some 28mm outrunners.
A 2830 outrunner will probably beat a standard 600 size motor in power output and weighs just something around 60g.
The other question will be necessary kv (rpm/V).
So if we suppose you are going to use 3S lipo (11,1V) and brass 30mm props with a pitch of around 30mm you would need around 1700kv to reach 15 mph (which will probably already look "too fast").

I always buy the cheapo chinese outrunners since most "branded products" are just the same with different color.
Hobbyking or ebay would be a good address to buy them.
As ESC I use the Robbe Roxxy 9xx series only, they are expensive but the best brushless esc I know. You would need 3 Roxxy 930 for your boat.
For sure you can use mixers.

edit:
I just saw most 2830 motors just have max 1300 kv. So you should use 4S or props with higher pitch to reach 15 mph.

[Calimero]

Scale speed should be around 15kph. A 1300kv motor should do the job hooked to a 3s battery.

There are 'faster' 28mm outrunners but I think they'd be too fast.

HK has various suitable ESCs.

[canabus]

Calimero is on the right track for motors.
As for W/V mixers go for Y connectors for the ESC's(kept it simple).
As for ESC's on 3S batteries with 3 motors the Hobbyking 45A car ones(69grams each)with fan on top will save space and no plumbing required.
The scale 30mm 3 blade props will handle higher kv motors but your scale speed will be over the top.
Slow down you are pasting the torpedos, skipper!!!

[spearfish99]

If you are looking for a mixer, have a look at this one. I bought one for an brushless twin motor catamaran. It works quite well

http://mr-rcworld.co.uk/index.php?productID=1019

[Unsinkable 2]

Hi narrowboater, does your radio have mixing capabilities? If so you could plug the motors into separate channels and then mix with rudder if that's what you wish to achieve. Although that would require 3 ESCs. If you have exponentional I think you can even control the amount of power to each motor depending on how much you move the rudder........... Or have I got the wrong end of the stick?  U2

[Calimero]

Although that would require 3 ESCs. If you have exponentional I think you can even control the amount of power to each motor depending on how much you move the rudder........... Or have I got the wrong end of the stick?  U2

If he goes the brushless route, he'll have to get three ESCs anyway. You can't hook multiple motors to a single ESC. And yes, using three channels is IMHO the way to go. You can then use mixes to control throttle of the side motors when turning as you said.

[spearfish99]

He will need 3 ESC's if using brushless motors, but I would only use one channel to control them.  If he were to use two Y leads and the Mr RC World switcher, it is quite a simple set up.

1) One output of the Y lead on the steering channel directly to the rudder servo. The other output goes to the steering input on the switcher.

2) One output on the throttle channel Y lead goes directly to the ESC on the centre motor. The other goes to the speed input on the switcher to control the two outer motors with the steering effect given by the switcher.

  In fact using the above set up, you can get pretty good control from the most basic 2 channel radio set. If you look at the multichannel stuff with % settings on channels, etc  they are really meant for aircraft/helicopters and the manuals for setting up the features can be a nightmare.

The simple approach to the control set up means that the relationship between all three motors is maintained as a constant , multiple channel control usually leads to "fiddling" and loss of balance between the motors.

[Calimero]

He will need 3 ESC's if using brushless motors, but I would only use one channel to control them

I would not. Less clutter in the boat, more flexiblity on the TX, more reliability. Being able to change the settings on the fly. Being able to have different modes of operation.

[spearfish99]

Calimero,

 I am sorry but I wouldn't class 2 Y leads extra as clutter. Nor can I see that using Tx mixing actually adds any reliability.

From experience with a lot of modern Tx's, I not sure that any degree of reprogramming on the fly is possible or even desirable. 

I am not really sure that on the model suggested you need that much changeability. I am a believer in KISS

[Tugtower]

Just a reminder if using 3 ESc's through a set of Y leads, to disconnect the BEC wire from 2 of the ESC's or your gonna blow up the receiver

[spearfish99]

Just a reminder if using 3 ESc's through a set of Y leads, to disconnect the BEC wire from 2 of the ESC's or your gonna blow up the receiver