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Author Topic: Vosper RTTL  (Read 14709 times)

Steven.T

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Re: Vosper RTTL
« Reply #75 on: November 17, 2013, 12:31:40 PM »

Haha, only just then  :-))
Just got back from the lake again, took my dad through to show him it running. The motor ended up getting very hot again, and partially deforming the motor mount, which is of course just plastic...
At a bit of a loss of what to do now, as either way I'm getting a warm running motor... The ESC is just fine, no problems there.
Looks like I might have to butcher the motor mount and make another with enough room to add water-cooling. It won't be easy mind, infact, I don't know if it can be done...

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Steven.T

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Re: Vosper RTTL
« Reply #76 on: November 17, 2013, 01:04:29 PM »

Just had the boat in the bath to see how much current its pulling. With just the motor, me holding it in my hand, no prop or anything, it pulls half an amp at full speed, which is what the motor spec says it will, with the motor just getting luke warm. With the prop connected via the uni joint and the motor in the boat, the consumption goes up to 7.5A, and the motor becomes very hot.  I think I might try it with the old rubber coupling, just to see what sort of current it pulls with that on...
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Netleyned

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Re: Vosper RTTL
« Reply #77 on: November 17, 2013, 03:30:50 PM »

Is the prop the right type/size/pitch for the motor?

Ned
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Steven.T

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Re: Vosper RTTL
« Reply #78 on: November 17, 2013, 03:43:04 PM »

To be honest Ned, I don't really know. The prop is the same one that was supplied with the kit for the 385 motor, which I have changed to a 400 now. Anyway to tell if it is suitable?
Cheers,
Steven
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Netleyned

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Re: Vosper RTTL
« Reply #79 on: November 17, 2013, 03:59:22 PM »

Not sure.
But someone on here will know. :-)) :-))

Ned
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Steven.T

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Re: Vosper RTTL
« Reply #80 on: November 17, 2013, 04:46:50 PM »

Just had the original 385 motor in the boat with the same uni joint and prop, it only pulls around 1.5A at full speed, although the full speed is no where near that of the 400 motor, maybe it is the propeller?
Steven
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StuartL

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Re: Vosper RTTL
« Reply #81 on: November 17, 2013, 05:57:09 PM »

I was once told that unless you're racing water cooling is the fallback for a badly matched prop and that's something I try to live by.

Can you measure the prop and put some photos up?  Measure the diameter and try to guess the pitch of the blade.  It's a large boat to move at any speed with a single 400 size motor so picking a small prop or one with a less aggressive pitch will probably help the current consumption and therefore heat.  If your motor runs about 15krpm unloaded a 25mm prop with 1:1 ratio (pitch also of 25mm, blade angle 45 degree at the tip) would probably be about right.  It's certainly a place to start.  Be aware that water doesn't scale like props do, so a scale-looking brass prop is relatively inefficient compared to an efficient design at this size and you may need to compromise between scale-look and performance/efficiency.

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Steven.T

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Re: Vosper RTTL
« Reply #82 on: November 17, 2013, 06:43:46 PM »

If I'm measuring the diameter right, I think it's a 30mm prop, how would I measure/guess the pitch? What am I looking for?



Like I say it's just the prop that was supplied with the kit, for the 385 motor.


I have spoke to Robert (rem2007) who I got the idea of changing the motor from and he has kept the original prop. He says his gets warm, and that he lined the motor mount with modelling clay. Might have to give the clay a try, will probably act as a heatsink...
Cheers,
Steven





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pompebled

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Re: Vosper RTTL
« Reply #83 on: November 17, 2013, 07:35:39 PM »

Assuming you got this motor for your boat: http://www.graupner.de/en/products/1794/product.aspx I think I know why the motor got hot.
In the video the motor didn't sound like it was revving at 15000 rpm, half that is more likely, meaning you're bogging down the motor severely.
It'll still do it's best to get up to the rpm dictated by the Voltage applied and will draw quite a lot of current, heating things up.
As no brushtab or cancooling was installed, the heat build up has nowhere to go.

Another point (literally) is breaking in a brushed motor; new brushes have just two tiny contactpoints to the commuter.
When you apply full throttle, all current has to flow through these minute points, the brushes will arch badly and possible burn into the copper of the commuter, damaging it for the rest of its working life.
The arching also causes a lot of heat.

A new brushed motor should be broken in, running submerged in a glass of water, on an as low Voltage as possible (1,5 - 3V) to avoid arching.
When the water starts to get dark, check if the brushes have assumed the curve of the commuter, if so, dry out the motor (compressed air work well) in a warm place, put a tiny(!) drop of oil on the bushings and you're good to go.
Hi Steven,

Sorry to hear the motor keeps overheating, I quoted my earlier message about why this may happen, if the motor is the one from the link, it may be toast by now...

You 'upgraded' to a hotter motor, didn't brake it in and kept the same prop as supplied for the stock motor.

I was once told that unless you're racing water cooling is the fallback for a badly matched prop and that's something I try to live by.
As mentioned above, the prop is too large and the motor can't rev out and runs (very) hot.

Watercooling is rarely necessary in scale boats, only the occasional over powered ones (like my MAS) may require some cooling assistance, but as StuartL correctly stated, it's not a bandaid for a poor setup.

Modeling clay will absorb some heat, but if the setup isn't sound, the motor will keep overheating until the magnets get demagnetized and the motor looses all power.

A Speed 400 revs too high for this application; a smaller prop will help a little, but the performance will suffer, as the mismatch remains.

Regards, Jan.
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