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Old Dec 09, 2013, 07:06 AM
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rk295's Avatar
United Kingdom, England, Ruislip
Joined Mar 2007
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Motor selection

Hi guys, I'm looking for some advice, hopefully somebody can guide me!

I've only built a little Sea Nymph before so I don't have a lot of experience with model boats. However I've just picked up a second hand Aerokits Sea Rover, which I'm in the middle of restoring. It is currently bare wood with no equipment beyond the prop shaft and rudder. I'm hoping somebody can help me choosing a motor, ESC and battery.

I'd like it to have a fair turn of speed, but I don't want it to be a powerboat, if that makes sense!

I have a standard sized servo for the rudder and a receiver, but I need to buy the rest. Any help gratefully received!

If there is any interest, I'll post some pics of the restoration.

r.
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Old Dec 09, 2013, 10:06 AM
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United Kingdom, London
Joined Oct 2006
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I presume that you're thinking of electric?

In that case, the first choice is: "Do you want to go brushed, or brushless?" Are you aware of the differences? If not, research those first.

I have an old Sea Rover in the shed waiting for restoration, so I would certainly be interested in looking at your pictures. In the meantime, the Vintage Model Boat Company sell a Sea Scout (slightly smaller than your Rover) and they have several pages of motor suitability details.

http://www.vintagemodelboats.com/page13.html


http://www.vintagemodelboats.com/page19.html

Vintage Model Boat Company Aerokits Sea Scout (5 min 12 sec)
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Old Dec 09, 2013, 10:20 AM
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rk295's Avatar
United Kingdom, England, Ruislip
Joined Mar 2007
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Hi dodgy, thanks for the reply.

Yes, sorry it is to be electric, silly of me to assume readers would know that!

I fly a lot of aircraft, so amfamiliar with brushless, however is there anything specific relating to model boats I ought to consider before making the decision of which to use?

r
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Old Dec 09, 2013, 02:01 PM
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United Kingdom, London
Joined Oct 2006
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Hmmm....

Well, brushless motors are associated with high-speed and shortish runs - much like aircraft. Usually using LiPos. Which means LiPo battery care...

Brushed motors are associated with lower speed, longer runs, and better speed control at low speeds. You can use NiMh batteries - lead-acid or Gell batteries are more suitable for tugs...

Brushless motors really need careful matching to their props to get best results without burning the motor out. You often have a water jacket for an inrunner, or a water-cooled mount for an outrunner. But because boats are not as common as aircraft, there will usually be very little advice or recommendation about prop size, and you will need to try things out yourself.

Because the Sea Rover is quite a heavy boat, I suspect that the light weight of LiPos won't really be noticed, so you might as well use NiMh packs. I would tend to leave a window unglazed or arrange airflow in some way if you are looking for high performance. The Graupner Speed range of motors are very good, but cost a fair bit...

You can get really cheap Chinese ESCs, but remember that they rarely have good quality control. Sometimes they work very well - sometimes they blow up when 5v is put into them... You probably don't need a reversing ESC - unless you were looking forward to going backwards, as it were. The motor needs to be connected to the prop-shaft with little or no deviation, and I have found that the universal joints with a bit of silicone tube in the middle are better for cutting noise than the jointed ones...

There - that's about all I know about model boating....
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Old Dec 10, 2013, 02:32 PM
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United Kingdom, England, Ruislip
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Thanks for the information dodgy and taking the time to reply, it is all very useful.

I was hoping to go with NiMH packs because I've a few kicking around from buggies and the Sea Nymph, so that is good news that there will be no problem with them.

I had a browse of the vintage model boat company website, those setups are interesting. I actually called them to discuss the Sea Rover and they informed me that they are now selling laser cut kits of the rover, although the website has not been updated. The power train they are suggesting for the Rover is this one. It looks like it would have more than enough power. Hopefully with their suggested ESC and Motor then I'll get reasonable runs from the 4500mah packs I have at the moment.

I will remember to experiment with different props when I get that far! I'm assuming that the existing prop shaft is imperial so I'll need to find some props with the correct thread on them though.

I'll start up a new thread with pics of the restoration when I get going, hopefully they'll be of interest to some.

r.
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Old Dec 10, 2013, 04:12 PM
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Australia, QLD, Regents Park
Joined Mar 2007
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Go Brushless if you are already familiar with them. I use brushless almost exclusively now for all my boats and I don't have any fast stuff.

I also like Lipos even for heavy boats because of the high energy density and better run time from smaller packs.

On anything up to 40 mm props a 28 mm diameter out-runner works well, 1000 Kv on 2 cell Lipo or 6 volt Gel for sedate stuff or 3 cell for good planing hull performance. The Ni mh are OK to, if you are going with 6 cell packs then fore spritley performance a 1200-1500 Kv would be better, though 2 packs of the same capacity In series and a 900-1000 Kv would be my preference.

I don't bother watercooling, haven't needed to as I size the motor so usually only at half its capability so little heat is generated.

The ESC on that site is pretty good, I've used a few of the 30 amp ones, I get them from Hobby King.

Nick
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