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Author Topic: Mtroniks 15a esc and motor.... in a 28'' grp?  (Read 6190 times)

Bluechrisp

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Mtroniks 15a esc and motor.... in a 28'' grp?
« on: July 04, 2009, 12:10:29 PM »

Hello all,

I just opened up my new Mtroniks 15a combo 900KV and it's small, I wanted it for my 28'' launch which has a graupner 500 on it plus 7.2V batt. Has anybody got any thoughts on this, I don't want to set it up and then find its to small or under powered.

The 500 was ok but lacked speed and endurance and got hot....  with 32.5mm two bladed race prop {:-{

So if not what sort of set up should I go for? any help would be grateful  :-))

CP
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Martin [Admin]

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #1 on: July 04, 2009, 12:38:41 PM »


Any chance of a photo of the launch please?

I've heard good things about the Mtronics brushless package, have you tried a bench run of
the motor to see what kind of revs you get 'dry' and what kind of power consumption?

BTW: I can't find that set on the Mtronics website but it's still advertised in the mags.? - http://www.mtroniks.net/
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Bluechrisp

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #2 on: July 04, 2009, 12:54:13 PM »

Hi martin,

 By setting up the motor I will not be able to return the motor and esc, the launch weights in just under 2 pound, so according to the small print it's to small, by over a pound, wonder what it would do on the converted seven?


will send in a pic of the launch later, 28 '' by 10''

C P
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Umi_Ryuzuki

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #3 on: July 04, 2009, 06:26:00 PM »

I have run an old Mtroniks ECO 20 in a 56" destroyer weighing 15 lbs, running
 two pittman 14volt motors for about 10 years.

It will depend on the amp draw of  your motor propeller combination in the boat.
Knowing the amp draw of your loaded, or stalled motor would tell you whether the
ESC could handle the load.
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Bluechrisp

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #4 on: July 06, 2009, 01:30:30 PM »

Hi,

The motor is the mtroniks 12mm 900kv and 15 amp brushless, in at the moment is a  graupner 500 with a 15 amp which runs well but after 5 minutes runs down on a 7.5v 3700. on a 7'' 4mm shaft with a 35mm x prop

Am I right that a small brushless such as above, would in the same league ish, would it be like for like.... as you can guess I have very little idea.  %)

Chris
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malcolmfrary

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #5 on: July 06, 2009, 07:52:56 PM »

5 minutes from a 3700 via a 15 amp controller seems a bit short - in the region of 40 amps being pulled unless I am missing something about LIPOs.  Even if the ESC stops the action at 50%, that gives 20 amps, a bit much for the ESC.
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Proteus

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #6 on: July 06, 2009, 09:13:02 PM »

is this the speed controler and I cannot find a 900kv listed have you got the product numbers n?


http://www.mtroniks.net/details1.asp/ProductID/194/sid/1/Genesis-hydra15.htm
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Bluechrisp

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #7 on: July 12, 2009, 03:29:49 PM »

Hello

I sorrry I don't have them, I've returned them, I have a Hydra 30 amp ESC now and looking to put a lower amp brushless inrunner in, maybe a Black Mantis? it all very black magic still.  {:-{



Black Mantis BM2435 2700kv Inrunner Motor

Dimension: ¢24X35(mm)
Shaft: ¢3.0X12.0(mm)
Weight: 64
KV:2700
Lipo:2S-3S
Idle Current: 0.5A
Internal Resistance: 0.099
Max Amps: 11amps

Cheers  ChrisP
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Bluechrisp

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #9 on: July 13, 2009, 01:11:56 PM »

Afternoon all,

Maybe I've been going about this the wrong way.... if I have..?  :-X  So am I right in thinking ( yes somewhat dangerous) with this 28'' patrol craft / launch, with a 35mm x prop with a Mtroniks 30 amp ESC, I should be looking at a engine below 30amps..? I am using a 6 volt lead acid battery.

Now if using a brushless unit and it starts to hesitates ie starts and stops ( after 10 metres away) what happening here?

Any brushless surgaries nearby.... :embarrassed:

Chris P

What started as a hobby ! is now a mere.......
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malcolmfrary

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #10 on: July 13, 2009, 07:05:12 PM »

In the case of a 30A ESC, thats as much as it can ever handle without letting the smoke out.  If your motor is liable to draw anything like that off your chosen voltage, you need a bigger ESC or a motor that draws less current (and therefore delivers less power).
To produce a high level of performance, forget SLA.  They are good for displacement hulls that need ballasting for stability and a moderate amount of current for a long run, not for tearabouts.
Ampere-hours are the electric equivalent of gallons, the bigger the number, the more juice in the tank.
Amperes equates to the rate at which the fuel is delivered.  The bigger the pipe, the more fuel you can get through it in a given length of time.
Volts is like the pressure of the fuel pump - the harder it pumps the higher the pressure (voltage) and the more fuel can be pushed through the pipe.
Some batteries can deliver huge currents for a short time without damage.  SLAs are not amongst them.  The plates tend to heat unevenly, go curly, touch, short the battery out, and kill it.
If the brushless unit takes more current than the supply can deliver, the voltage will drop.  If this is supplying the control circuitry, this will stop, causing the motor to stop.  If the voltage then comes back up, the cycle might restart.
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nick_75au

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #11 on: July 15, 2009, 11:22:12 AM »

Hi,
I think the 2700 kv motor may be too hot unlless you use gear reduction, the max amps spec doesn't mean the motor will only draw 11 amps it means don't exceed 11 amps, if you over load it it can draw more and likely to fry.

I would suggest upping the voltage and using a lower Kv motor say 1000-1500 on 8 or 10 NiMH (max for the Mtronics)

The hesitation your seeing is most likely the low voltage cut-off activating due to the gel battery not being able to supply sufficient current.

Ive used a 3200 kv Heli motor on 3:1 reduction and 12 cells and achieved 25 Kph in a Miami crashboat by Glynn Guest which is slightly smaller, 35 mm racing 2 blade prop submerged drive, A lower Kv motor direct drive will be a better solution as the reduction wastes power and is noisy. the motor Im using is 22 mm in diameter outrunner style and looks almost half the size of a 500.

Regards
Nick
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Bluechrisp

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #12 on: July 17, 2009, 04:09:52 PM »

Hi all,

Good news, I have tried out my boat fitted with a 2200kv 18 amp with a 30 amp Mtroniks esc, on a 7.2 volt 3700 battery, goes very well indeed some good speeds, and last twice as long as the graupner 500, goes well on 6V sla aswell.  O0

I have noticed that it gets quite hot to the touch is this the norm, if not, what might be causing this..?

many thanks for your help so far. :-))

CP
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malcolmfrary

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #13 on: July 17, 2009, 05:09:32 PM »

Lots of energy = heat in proportion
As long as nothing actually SMELLS hot - that is a precursor to the magic smoke making its bit for freedom.
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Bluechrisp

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #14 on: July 17, 2009, 07:55:05 PM »

Hello,

So are we saying to stop it getting to hot, go for a lower KV ie 1000 to 1500.. and add a large heat sink..

using a 40mm instead of 35mm prop will it improve it and speed..  %)

cheers

CP
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malcolmfrary

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #15 on: July 17, 2009, 10:10:54 PM »

Quote
So are we saying to stop it getting to hot, go for a lower KV ie 1000 to 1500.. and add a large heat sink..
Depends on whether it is actually getting too hot.  A real brushless expert needed here.  I just go on general principles.
Quote
using a 40mm instead of 35mm prop will it improve it and speed
As a general principle, a smaller prop is often better than a large one overloading the motor.   Its part of the black art thing with powering boats.
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stallspeed

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #16 on: July 18, 2009, 08:11:21 AM »

Don't be worried if it reaches 100 Celcius as the current conducting copper wire (armature) of a brushless inrunner is the stator (case) and not on the rotor.That makes inrunners good candidates for heatsinking and forced cooling.
A lower kv motor with the same power has greater torque (Power Output = Torque x Rotatinal Speed) so its torque is inversely increased
So ,yes, a lower kv motor will reduce power loss as does a reduction gear or reduced size and pitch of prop.

Quote
...using a 40mm instead of 35mm prop will it improve it and speed..  %) ...
No.Using a larger prop will increase losses and it may actually reduce the output power and model speed.If your full throttle revs with the 35mm prop are < half the kv value then you should go smaller.

Half the endurance with the Graupner 500 time would suggest it was overpropped.
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Bluechrisp

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #17 on: July 26, 2009, 12:55:49 AM »

Hi all,


I have replaced the 35mm x prop with a 32.5mm it does go faster and last some what longer, will look at seting in a aluminium plate for the heatsink, so in short i've been converted.  :}

many thanks all.  :-))

CP
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stallspeed

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Re: Mtroniks 15a esc and motor.... in a 28'' grp?
« Reply #18 on: July 26, 2009, 03:13:48 PM »

Chris,I meant only that,unlike a brush magnet motor where the rotor is hot,brushless inrunners are easier to cool.Yes the motor runs more efficiently when cooler (copper losses are 30% higher when 750 hotter) but it may not be neccessary.

With the 35 mm prop, the motor was < 50% efficient.You have cut your current,power loss,temperature & increased power output with a 32.5 so why not continue the process? A 2200 kv motor on 7.2 should give 8000 rpm at maximum power.
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