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Author Topic: Overheating motor/ESC  (Read 756 times)

mudway

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Re: Overheating motor/ESC
« Reply #25 on: May 30, 2019, 10:36:26 AM »

Do you know the amps that you are pulling?


Damn, a typo > Well a Graupner 600 eco on the same prop and 9.6 V NIMH came out at 5,700 rpm and 6.4 amps.
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Tug Fanatic

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Re: Overheating motor/ESC
« Reply #26 on: May 30, 2019, 11:11:53 AM »

I am constantly surprised at the mismatches of motors and props in scale or scaleish model boats which often result in either overheating, poor performance or both. Any significant heat in a scale model represents inefficiency somewhere in the propulsion setup.

My Fishery cruiser can be seen at way over scale speed in the video on the 2019 Mayhem page (55 seconds in). This boat is four feet long and weighs around 10lb (4.5kg). It is powered by two low drain 380 type motors geared down about 2:1 via belt drive to 11 inch M4 shafts with 35mm props on the end. Battery is a 7.2aH Nimh pack.

At full speed, using both motors the total current draw is just 2.5 amps in the bath, probably a bit less on the open pond. Nothing even gets slightly warm.I haven't measured current draw at cruising speed but it is probably under 1 amp per motor.

There are often huge efficiency advantages in gearing the shaft down as it helps motor revs to remain high while prop speeds stay relatively low. A win win situation.

Colin
Lovely model.
An MFA 385 is 975kv which with a 2:1 reduction (effectively a 487kv motor) is about the same as one of the low rpm 5 pole 500 (555) series motors. Whether it is better, has more power output/ torque or uses less power input???????
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SailorGreg

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Re: Overheating motor/ESC
« Reply #27 on: May 30, 2019, 11:34:59 AM »

Thanks to everyone who has pitched in on this. I (and, I hope, some others) have learnt a lot, not least that buying motors is a real minefield!

There are lots of gems of information on this thread that I for one will try and save somewhere.  But I am still rather confused - Colin says above that he has 2 380 motors in his Fishery Cruiser geared down 2:1.  Fine, but there is a plethora of 380s available, not all the same. Certainly a glance at e-bay shows lots, many without any technical data beyond the can size. How would I know what to buy to replicate Colin's setup?  (Sorry Colin, not having a go at you, just using your post as an example.) And his motors are low drain - what does that imply for turns, revs, torque...?  (Rhetorical question, just me musing!)

The more I find out, the more I realise I don't know. Yes, a real minefield!

Greg

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Re: Overheating motor/ESC
« Reply #28 on: May 30, 2019, 11:53:57 AM »

Thanks to everyone who has pitched in on this. I (and, I hope, some others) have learnt a lot, not least that buying motors is a real minefield!

There are lots of gems of information on this thread that I for one will try and save somewhere.  But I am still rather confused - Colin says above that he has 2 380 motors in his Fishery Cruiser geared down 2:1.  Fine, but there is a plethora of 380s available, not all the same. Certainly a glance at e-bay shows lots, many without any technical data beyond the can size. How would I know what to buy to replicate Colin's setup?  (Sorry Colin, not having a go at you, just using your post as an example.) And his motors are low drain - what does that imply for turns, revs, torque...?  (Rhetorical question, just me musing!)

The more I find out, the more I realise I don't know. Yes, a real minefield!

Greg
The MFA385 is the standard low drain 400 sized motor. As you say there are lots of much hotter motors that look the same (the Graupner 400's being the standard example).

Without meaning to critisize anyone there is a lot of partial information when it comes to model boat drive systems. You have highlighted motors but equal problems exist with propellers. Plastic props are generally designed differently to metal props & there are at least 3 very different plastic prop design - s type, x type and 3/4 blade scale. There are even more variations with metal props with 3, 4, & 5 blade props of numerous different designs. These can have vastly different performances.

So if someone tells you they (as an example) have a 540 motor driving a 40mm prop & it pulls 8 amps you have a lot to find out before that becomes useful information.

There is also the problem that things are often not linear. Going from a 40mm prop to a 45mm prop of the same design might well double the power required to drive it from the same motor etc. Going from 2S to 3S will not increase power in & out by 50% but by a much larger factor whilst going from 3S to 2S will often save a very overloaded motor at the expense of power. 

I would equally be wary of the often repeated old adages like "keep the prop diameter smaller than the motor diameter" for exactly the same reasons.

My rule of thumb is to be very motor kv aware and where possible fit a larger motor that will not be working as hard. Gearing does the same thing.
 
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DaveM

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Re: Overheating motor/ESC
« Reply #29 on: May 30, 2019, 12:04:30 PM »

Greg
What Colin omitted to say is that a 380 and 385 are as alike as chalk and cheese, despite their physical similarities.

A 380 is a 3-pole motor which is very fast-revving (about 26000), usually runs on a maximum of 7.2v and should never exceed 10A. They are the ones which are often sold as Speed 400 motors. I've only ever used them in a Glynn Guest-designed airscrew-driven swamp boat and a 20" all-balsa semi-scale Swordsman. With a 25mm 2-blade bronze prop that thing went like greased weasel pooh!

A 385 is a 5-pole motor which can be run up to 15v, strangely has slightly less torque and is much slower. However at its maximum efficiency it draws only 1A c/w over 5A for the 380.

MFA's website has excellent data sheets on all of their motors, which include their "stock" 540/1 as well as what they term "noise attenuated" versions of the 540 and 385. Here's the link https://mfacomodrills.com/motors/motors.html  Just click on the motor you're interested in and it will download a datasheet in PDF format.
Dave M
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Colin Bishop

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Re: Overheating motor/ESC
« Reply #30 on: May 30, 2019, 01:13:27 PM »

Quite right Dave & Greg, I should have made myself clearer, the motors are 380 size and fitted a long time ago so I can't recall where they came from which is why I described them as 380 type. They are definitely low drain and presumably 5 pole. They work very well in my setup. Props are 35mm standard scale 3 blade brass Raboesch.

Colin
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SailorGreg

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Re: Overheating motor/ESC
« Reply #31 on: June 07, 2019, 05:41:41 PM »

If anyone wants to know the outcome of my new motor fit, read on -

I purchased one of these and left everything else the same - 40mm kort prop, Mtroniks 20A Viper ESC, 6V SLA.  I ran the boat today (in between the rain) and kept it at full power for about 20-25 minutes.  Previously this would have resulted in a very hot motor and intermittent losses of power.  Not this time.  The motor was certainly warm/hot to the touch, but not as hot as previous motors, and there was no interruption of service.  I do believe the problem has been solved!  :} :}

Thanks again to all who offered advice and information.  I am slightly better informed on motor technology and much more aware what to look for when buying anything new.

Happy sailing

Greg

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Re: Overheating motor/ESC
« Reply #32 on: June 08, 2019, 08:36:27 AM »

Greg
That is great. Do you know how any amps your are using?
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SailorGreg

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Re: Overheating motor/ESC
« Reply #33 on: June 08, 2019, 10:41:36 AM »

No.  I am not sure how to measure that under load.  The 20A ESC didn't get even a little warm so I guess it is operating well within its capability.

DaveM

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Re: Overheating motor/ESC
« Reply #34 on: June 08, 2019, 11:20:38 AM »

No.  I am not sure how to measure that under load.  The 20A ESC didn't get even a little warm so I guess it is operating well within its capability.
I have one of these for that purpose. It's small enough to be carried on-board. No doubt there are others available e.g. from our inscrutable little friends...  http://www.4-max.co.uk/wattmeter-budget.htm

DaveM
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roycv

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Re: Overheating motor/ESC
« Reply #35 on: June 08, 2019, 12:30:22 PM »

Hi all, many years ago i built a 16 inch loa Swordsman.  Power was a MFA 380 with 1 :2 gear reduction onto a 30 mm S series black prop running on 5 nicads (ex camera). 

The power consumption was about 40 watts so current over 6 amps.  The speed was dramatic and at full speed just 2 or 3 inches of hull in the water.
regards

Roy
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chas

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Re: Overheating motor/ESC
« Reply #36 on: June 08, 2019, 12:37:15 PM »

IF your SLA is the popular 4 or 4.5 ah 6 volt battery, you can estimate the current to be around the 5 to 6 amp area.
 A lighter 7.2 volt NiMH battery would make a dramatic difference.

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Tug Fanatic

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Re: Overheating motor/ESC
« Reply #37 on: June 08, 2019, 02:34:41 PM »

I really like to know the current (amps) consumption of my motor/prop combination before I put the controller into the circuit - it is much cheaper that way! Battery to ammeter/ wattmeter to motor (which is attached to shaft & prop & in the water).

If you have the controller in circuit you can always start at low throttle which is also low amps & gradually ramp it up to full throttle keeping an eye on the readings. This is only a really bad idea if you dramatically overloaded the motor.

 
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