Hot motor

[NoelParticipant @noel26080]

 

I have got a speedboat that I adapted from a toysrus toy.

The motor is an MFA 380, and it is water cooled because the hull is sealed and has no venting at all. This has been fine so far and the cooling coil never gets significantly warm. It runs off a 7.4v lipo and the prop is 30mm.

After a brief session this morning there was a whiff of smoke from inside the boat when I opened the hatch to switch it off.

Nothing seemed to be that hot, but when I got it home and investigated properly I found that the motor end cover had melted a bit around the bearing:

I am pretty good at oiling stuff so was surprised about this. Am I just toasting the motor and expecting too much from it, or do I need to maybe introduce a bit of air cooling here? Should I perhaps just whack a 540 into it?

Thank you for any suggestions.

Edited By Noel on 03/09/2017 22:34:12

[NoelParticipant @noel26080]

[Dodgy Geezer 1Participant @dodgygeezer1]

Presumably the bearing has melted because the armature has heated up and conducted heat along the shaft.

Several points spring to mind. The motor brushgear could be badly damaged as well, so I expect it will need replacing. Was the motor stalled, or might the water cooling be blocked?

If you replace the motor, consider going brushless. They are more powerful and at the same time more efficient, so you would run faster and cooler with a longer b?ttery life…

[Malcolm FraryParticipant @malcolmfrary95515]

If the plastic end cap has been melted even just a bit, it is likely that the bearing is not in quite the same place. If it hasn't already done so, this will have a bad effect on everything else. The motor will need "mending with a new one". Another 380 or a speed 400 will be a drop-in but might suffer the same fate if it is driving too much prop.

Even in an enclosed space, unless it is being worked very hard, the right size motor shouldn't need extra cooling.

[ashley needhamParticipant @ashleyneedham69188]

Noel. I have had several boats with 380 motors in them on 30 or even 35mm props and they have been ok.

The ruined motor needs binning. A speed 400will be a bit more pokey, or even a speed 480 (a J. Perkins one). The speed 480 will provide a considerable power increase and should be working less hard. Obviously changing to a brushless could be the way forward but this might make it a bit too fast for your little oiks to handle (a consideration!!)

Ashley

[NoelParticipant @noel26080]

Thanks for all the suggestions.

Posted by Dodgy Geezer on 04/09/2017 05:30:21:
Presumably the bearing has melted because the armature has heated up and conducted heat along the shaft.

Several points spring to mind. The motor brushgear could be badly damaged as well, so I expect it will need replacing. Was the motor stalled, or might the water cooling be blocked?

If you replace the motor, consider going brushless. They are more powerful and at the same time more efficient, so you would run faster and cooler with a longer b?ttery life…

Sounds about the sum of it. I think the heating is probably due to the fact that its quite a hot motor that I am overloading a bit with a prop that is a tad larger than the can size. According to spec sheet the non-load speed at 7.2v is supposed to be 26000rpm, which is huge, and it probably would be better off in an application where it can be geared. Whoops.

I'm not going brushless though as this whole boat has been a project in getting something that was otherwise scrap into a useable machine at low cost.

I think Malcolm is right in that the next application for this motor will be the bin. Although it does seem to run OK now ironically.

Ashley you suggests a speed 480 – where's a good source of these please so I don't end up with something duff?

The young ones are happy with tug boats, plus they've got their crazy fast ones to play with too, once the younger wildlife vacates Bushey later in the year.

Thank you!

Noel.

[NoelParticipant @noel26080]

Just noticed the 400/480 is the same can size and shaft diameter, so it will fit straight in!

[Dodgy Geezer 1Participant @dodgygeezer1]

Posted by Noel on 04/09/2017 10:46:05:

……………………

I'm not going brushless though as this whole boat has been a project in getting something that was otherwise scrap into a useable machine at low cost.

 

……………………

 

Motor – £3.09 – **LINK**

ESC – £ 2.85 – **LINK**

Total £5.94. That price includes postage delivered to your door.  I'm running this in an 18" Marinecraft model, and it goes like a rocket (though the balsa boat IS very light,,,

Edited By Dodgy Geezer on 04/09/2017 11:26:14

[Dave MilbournParticipant @davemilbourn48782]

Noel

I've run one of these in a small balsa launch (20" long) and it goes a treat with a 7.2v battery and 25mm 2-blade brass prop. **LINK** Like all 380/385/400/480 motors, the can size and mounting holes are identical.

The common wisdom is never to exceed 10A with these motors. A cheap watt-meter on board will indicate the maximum current drawn. I use this one **LINK** but there are cheaper types around.

Dave M

[NoelParticipant @noel26080]

Brushless for under £6!!! do you think that'll be ok turning a 30mm two blade prop in an unvented hull?
Will keep that in mind for future project.

Might try the 400 as it will be a straight swap in with no changes in mounting or wiring!

Thanks

[NoelParticipant @noel26080]

Just found a Jperkins 400 on ebay, so have bought that and will see how it goes.

[ashley needhamParticipant @ashleyneedham69188]

What prop is it???? An X30 will not be good for this. An S30 will be ok. Props marked on blade….X30 or just 30 for the lesser pitched variety.

​A vent will be an easy thing to arrange, does not need to me massive, just let some fresh air in and hot air out.

​Ashley

[Dodgy Geezer 1Participant @dodgygeezer1]

Posted by Noel on 04/09/2017 11:51:06:

Brushless for under £6!!! do you think that'll be ok turning a 30mm two blade prop in an unvented hull?
Will keep that in mind for future project.

Brushless PLUS a speed controller for under £6. You can probably get things cheaper if you try… It has no problems turning a 40mm 3 blade in my unvented hulls. There are several KVs for you to choose from. And brushless motors, according to another thread on here, use about a third of the electricity for the same or better performance.

Just don't expect any back-up service from China.

[NoelParticipant @noel26080]

Re the prop, its not a "normal" X or S.
It's the prop and shaft as fitted in ToysRus's high technology production facility, thus:

30mm across. Do you think the profile is OK?

[Dave MilbournParticipant @davemilbourn48782]

Noel

That doesn't look anything like as coarse as an X prop – you should be OK with the earlier caveat about keeping below 10A.

Dave M

[NoelParticipant @noel26080]

Thanks Ashley and Dave for checking this.

I think the root cause of this is that I have used a motor better suited to running at high speed with a moderate load, whereas I am expecting it to do work at a much lower rpm with this direct-drive prop. Which it doesn't like.

[ashley needhamParticipant @ashleyneedham69188]

Noel that is a lowish pitch prop which your 380 should have had no probs in turning.

Get the sp400 on it and we could use my wattmeter to see what is going wrong (if anything).

​Ashley

[NoelParticipant @noel26080]

Hmm, your right it does seem to have given up prematurely.

Maybe it was just a duff motor. I must say it was never a particularly smooth runner, it had a terrible buzz to it when it was running at high rpm – maybe that contributed to the bearing getting hot?

Or maybe it's nominal 7.2v rating was getting fried by the 7.4+ lipo? Maybe it was all a bit close to its limits?

[NoelParticipant @noel26080]

Let's see if this one fairs better!

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