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Author Topic: Kv and volts (Brushless Motors)  (Read 8909 times)

The Wizard

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Re: Kv and volts (Brushless Motors)
« Reply #25 on: January 28, 2016, 10:56:22 PM »

Perhaps I should read through these posts from start to finish to make sure I sort of understand.
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tsenecal

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Re: Kv and volts (Brushless Motors)
« Reply #26 on: January 28, 2016, 10:59:41 PM »

Its really kind of complex, but the simplest way to put it is you have 4 variables for a specific boat.


prop
motor
speed control
battery


all four of these inter-relate on how much run-time a boat will have.  change any one of them, and you change the run-time.  depending on what you change, and how you change it, run-time might increase, or it might decrease.
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derekwarner

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Re: Kv and volts (Brushless Motors)
« Reply #27 on: January 29, 2016, 12:22:53 AM »

1. I take all of this on-board DM,...... O0...but I think it would be near impossible to metricate or convert Roman Sundials into prime units of 10+

2. Force of habit has me writing something like .......see you @ the track @1400 %)...the response is sometimes.....'do you mean today or is that tomorrow?' {-)

3. My dear old father in law was named Kelvin...however he was a Bank manager so the temperature probably didn't bother him too much........

Derek
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Derek Warner

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Tug Fanatic

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Re: Kv and volts (Brushless Motors)
« Reply #28 on: January 29, 2016, 11:20:48 AM »

Well my simple question certainly got a discussion going and a heap of information.
So after all that am I right in saying more volts and lower kv will give me more run time on the pond.


Wizard

Bigger capacity batteries (eg 4400mah instead of 2200mah but the same number of cells) will give you a longer run time provided your hull is capable of carrying the extra weight - about double the run time in my example.

More volts & lower kv where the two give an equal rpm (eg 12 volts 1000kv = 12000rpm as opposed to 24 volts 500kv which also equals 12000rpm) are likely to give you very similar run times although your 12v batteries would need double the capacity say 4400mah 12v instead of 2200mah 24v. Your motors at 12v would be using twice the amps (but the same watts - volts x amps) than they would be at 24v.

Actual real world results depend on the componets used, their efficiency and how near their limits you are using those components,

This is very simplistic but I hope that it helps and assumes that you use the model in the same way for both examples.
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canabus

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Re: Kv and volts (Brushless Motors)
« Reply #29 on: January 29, 2016, 11:33:36 AM »

Depends on the speed you  are driving the boat at, the faster ewe go the faster ewe use up the battery!!!!!
I only go fast or go home!!!
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nick_75au

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Re: Kv and volts (Brushless Motors)
« Reply #30 on: February 28, 2016, 02:00:35 AM »


Multiple things use versions of KV etc


https://en.https://en.wikipedia.org/wiki/Motor_constantswikipedia.org/wiki/KV


Down to motor constantshttps://en.wikipedia.org/wiki/Motor_constants




Nick

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TomHugill

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Re: Kv and volts (Brushless Motors)
« Reply #31 on: February 28, 2016, 07:44:52 AM »

The problem is that I am very familiar with electrics/electronics terms, which is why this whole theme was so confusing.  It should read rpm/V  to equate to descriptions given subsequently.  Using the letter "k" is daft IMHO as it means something totally different to anyone familiar with accepted terminology.  Might just as well have indicated degrees Kelvin.

I only asked a very reasonable question. 
Some of the replies were less than we expect from experienced Mayhemer's.

I thought I was a pretty good explanation, plenty of instances in science/engineering where term aren't totally logical and you just have to accept what they mean rather than break it down to first principles. The motor constant description pretty much nailed it.
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warspite

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Re: Kv and volts (Brushless Motors)
« Reply #32 on: February 28, 2016, 02:37:02 PM »

When I see KV - I thing of thousands of volts, i.e. power line amounts like the national grid uses, 420KV is 42000 volts, or local supply 145KV is 145000 volts, not mv millivolts or parts of a volt, so I am confused by the brushless motor terminology, I do know that static voltage is in thousands of volts say 12000v but has virtually no amperage so is not as dangerous (though that is not to say it cannot be).
So I stay away from it - I struggle with getting a 6/9/12v set up in those boats i do have running.
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dreadnought72

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Re: Kv and volts (Brushless Motors)
« Reply #33 on: February 29, 2016, 12:07:14 AM »

An aside:

I work in a petrol station. Yesterday, a customer came in, having fuelled up his brand-new Mercedes.

"Do you know anything about tyre pressures?" he asked.

I nodded.

"The plate on the door says '200', front and rear", he said, "I haven't a clue what that means."

200?! Our machine does PSI or atm. Go much above 60 in the former or 4.0 in the latter and you'll cover the forecourt in tiny bits of rubber.

I went out to his car.

"200 kPa."

Ah! Now I don't know whether this is a New Thing, but it seems like the Germans, at least, are using SI units for tyre pressures.

Much more sensible, from an engineering point of view, but utterly unworldy, given the tyre pressure machines you'll tend to find on UK forecourts.

Andy

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Re: Kv and volts (Brushless Motors)
« Reply #34 on: February 29, 2016, 08:21:33 AM »

An aside:

I work in a petrol station. Yesterday, a customer came in, having fuelled up his brand-new Mercedes.

"Do you know anything about tyre pressures?" he asked.

I nodded.

"The plate on the door says '200', front and rear", he said, "I haven't a clue what that means."

200?! Our machine does PSI or atm. Go much above 60 in the former or 4.0 in the latter and you'll cover the forecourt in tiny bits of rubber.

I went out to his car.

"200 kPa."

Ah! Now I don't know whether this is a New Thing, but it seems like the Germans, at least, are using SI units for tyre pressures.

Much more sensible, from an engineering point of view, but utterly unworldy, given the tyre pressure machines you'll tend to find on UK forecourts.

Andy

29psi I think.

If this is to be a world standard I support it. There is no reason that we cannot all use the same. All it takes is a few weeks to get used to the different measures. My local market still use lbs pricing with kg in very small numbers. I now find this extremely unhelpful. I have forgotten Fahrenheit.

If it isn't a world standard why use a measure that few understand?
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malcolmfrary

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Re: Kv and volts (Brushless Motors)
« Reply #35 on: February 29, 2016, 09:38:34 PM »

Never having heard of kPa  thought i'd research google it. 
https://en.wikipedia.org/wiki/Pascal_(unit
Seems it is named for some guy called Pascal, who thought a lot about such stuff.  The article claims that it is a "world standard", except where either it isn't used, or it is used, but with local variations, often involving moving the decimal point a few notches either way.

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Norseman

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Re: Kv and volts (Brushless Motors)
« Reply #36 on: February 29, 2016, 10:00:01 PM »

. I have forgotten Fahrenheit.

I and my skin understand the weather only in Farenheit; any mention of Celsius and my wife translates for me. But you are right about mixing standards. In work linear lengths are given in  miles, chains, and yards but the tamping computer has metres as its standard for length. Track gauge and heights are in mm. Rail weight is in pounds. Oh my  %%
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TomHugill

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Re: Kv and volts (Brushless Motors)
« Reply #37 on: February 29, 2016, 10:28:20 PM »

I and my skin understand the weather only in Farenheit; any mention of Celsius and my wife translates for me. But you are right about mixing standards. In work linear lengths are given in  miles, chains, and yards but the tamping computer has metres as its standard for length. Track gauge and heights are in mm. Rail weight is in pounds. Oh my  %%

Good old ALC, although gauge was always 4 foot 8 and a half, its 1435 is just the metric conversion. Are you on the tamper operator side or the pway side?
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Norseman

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Re: Kv and volts (Brushless Motors)
« Reply #38 on: March 01, 2016, 01:52:47 AM »

A TQS for my sins so PWay. I am looking forward to my retirement in a couple of years. Forty years of ballast walking  <:( ooh my poor feet!
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derekwarner

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Re: Kv and volts (Brushless Motors)
« Reply #39 on: March 01, 2016, 02:37:19 AM »

It is rumoured that the relevant Government Official  :embarrassed: signing off on that countries use of the unit of pressure being kPa..was indeed an Accountant and not indeed an Engineer

Probably went to the same dingbat school where earlier graduate's invented hands, leagues, chains, cubits & other demonstrably confusing units of measurement  %%............

Now, we all know that cubit was not a singular unit of measurement.....as the following will explain........Derek {-)

http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0ahUKEwimxpbguZ7LAhXClZQKHWQXCL4QFghBMAY&url=http%3A%2F%2Fwww.convert-me.com%2Fen%2Fconvert%2Fhistory_length%2Fbibcubit.html&usg=AFQjCNGUNDoX_LDK4JIE5EJ9OgqUZm8N_g
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Netleyned

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Re: Kv and volts (Brushless Motors)
« Reply #40 on: March 01, 2016, 08:10:15 AM »

I have a cheapo digital tyre pressure gauge bought
from Netto, about 10 years ago that can measure
in PSI, Bar, or KPa.
Obviously in use in the rest of EU for some time. %)


Ned
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BarryM

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Re: Kv and volts (Brushless Motors)
« Reply #41 on: March 01, 2016, 09:32:20 AM »

....BTW why is the SI symbol for current I when its unit is A (amp) .....?
I blame the French...
DM

Out of curiosity - alright I had nothing better to do - I tried to pin down the use of "I" for Amps and all I could find was the suggestion that it stood for 'Intensity'. I suspect it was just the choice of some theoretical scientist who had never worked in very close proximity to a live 440V switchboard with insulating gloves filling with sweat while praying that all the 'I's' didn't shoot up his arm and fry his innards.

Personally, as long as our village blacksmith still produces steam-propelled velocipedes, I shall insist on the velocimeter being calibrated in barleycorns per bat-wink as understood by our ancestors.
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Steve Dean

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Re: Kv and volts (Brushless Motors)
« Reply #42 on: March 01, 2016, 05:37:22 PM »

I've just read all of this thread and it put a smile on my face. Sorry for going slightly off topic but have you all noticed that many of the modelling and model engineering magazines we all read now produce articles with mixed imperial and metric measurements in the same sentence. i.e. take a piece of 0.5mm brass sheet and cut to 3 inches long. etc, etc.

For all your amusement I was chastised by a teacher last year when I was doing the commentary on a very large model of the Titanic. For historic reasons I gave the dimensions of the full size ship in Feet. The teacher told me I was damaging children's education. When I responded that they will have problems when they learn to drive and encounter distances in miles and speed limits in miles per hour he huffed and puffed and walked away.

Never forget the old joke, 'Britain is going metric - inch by inch'.
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Subculture

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Re: Kv and volts (Brushless Motors)
« Reply #43 on: March 01, 2016, 05:50:56 PM »

Funny how we don't use imperial capacity for car engine size though. They do in the states.

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Re: Kv and volts (Brushless Motors)
« Reply #44 on: March 01, 2016, 06:40:47 PM »

Metrication is something the Americans have steadfastly resisted - along with democracy, good manners and eating green vegetables. Of course, you can always take that with 1/10 cup of salt...
DM
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