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Old Sep 15, 2013, 08:54 AM
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Help!
A few questions about a DC motor

Hey guys

I'm intending to make a little 30cm boat and was considering this as a motor for it. I just have a few questions about it.
http://www.hobbyking.com/hobbyking/s...erCooled_.html

Would this be a suitable motor for this size boat? Has anyone used one of these before? Would a 30A ESC be suitable for this motor? What sized mount would i need? And what prop size would be appropriate and with how many blades?

Thanks =)
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Old Sep 15, 2013, 01:59 PM
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It seems a LOT of motor for a very small boat. With the almost total lack of information in the link, I would be strongly tempted to look elsewhere. Preferably somewhere where they are prepared to give clues over and above size and weight and vague mentions of "standard mounts". BTW, strictly speaking, its not a DC motor, but a 3 phase AC type, the ESC chopping the DC to supply the "phases".
What type of boat? How much performance? Which bit of water do you intend to go on? (Fleetwood, Fairhaven and St Annes lifeboat station are all salt, Stanley Park isn't, but involves a lot of walking).
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Old Sep 15, 2013, 02:03 PM
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Ah right, I see. Probably a mono hull and it doesn't need massive performance, just a good speed and handling. I'll probably use it on the canal mostly.
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Old Sep 16, 2013, 02:32 AM
Did you check the FAQ already?
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A Speed 280 brushed motor will be power enough, even when run on 4.8 volts.

Here's a vid of my 40 cm boat running on that motor on 6 volts.

Second testrun of my small SAR boat Vegesack (1 min 52 sec)
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Old Sep 16, 2013, 02:50 AM
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Your boat seems to have a fair speed on it. Would a 3.2kg AS-16 servo be strong enough for that?
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Old Sep 16, 2013, 03:52 AM
Did you check the FAQ already?
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Thanks. I'm pretty happy with the performance as well.

3.2 kg is the pull force I assume? Is that a 9 gram servo (servo weight)? If so, it should be ok, in the Vitality FT007 speedboat, where more forces are acting on the rudder, a small, similar size servo does the job just fine.

In my boat there is actually a full size servo, so 40 grams, 5 kg pull force, but that's only because micro servos were not available so easily back in the days when it was built.
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Old Sep 16, 2013, 04:58 AM
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Quote:
And what prop size would be appropriate and with how many blades?
12-15mm prop, 2 blade for a 280 on 4.8-6 volts.
If running on a canal, beware the reeds on the opposite bank. Traditionally, always there, also strangely attractive to model boats, especially new ones.
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Old Sep 16, 2013, 06:36 AM
Did you check the FAQ already?
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I have a 3-blade 20 mm on, if my memory serves me well.
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Old Sep 16, 2013, 12:03 PM
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Near enough, but on a higher voltage a 280 would probably be happier (ie run cooler) with a slightly smaller prop.
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Old Sep 16, 2013, 12:55 PM
Did you check the FAQ already?
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Could be. Perhaps on my boat it helps that it's a wave piercing design, so the hull has less drag than for instance a tug boat, as I am running it on 6 volts (5 cell NiMh) and it doesn't even get warm to the touch. The prop used also has a fairly shallow angle on the blades, so it doesn't create a lot of drag when rotating.
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Old Sep 17, 2013, 02:54 AM
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Ok. Thanks for all the help guys =)
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Old Sep 17, 2013, 07:50 AM
Did you check the FAQ already?
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Looking forward to pics of the final result.
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Old Sep 17, 2013, 09:17 AM
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I'll be sure to start a thread up in the following weeks
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Old Sep 17, 2013, 03:05 PM
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If you happen to be in the area, a visit to the show at the Norbreck (Oct 19, 20) might give you some useful insights.
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Old Sep 18, 2013, 03:55 AM
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I'm not sure if i'll be around that weekend but i'll see if i can make it. Thanks for the info.
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