Model Boat Mayhem - Forum

Please login or register.

Login with username, password and session length.
Pages: 1 [2] 3 4 5   Go Down

Author Topic: Brushless Basics  (Read 77737 times)

Garabaldy

  • Guest
Re: Brushless Basics
« Reply #25 on: November 18, 2008, 03:31:48 PM »

I understand that for converting a tug to brushless requires a motor with a lower kv rating to lower keep the revs low and also to produce the required torque.  My question is - Is it possible to do this as economicly as with brushed motors?  For instance i could buy 2 graupner 900bb torques and a action twin speed controller (P94?) for £110 or there abouts.  All the lower KV motors seem to be really expensive.  Or much more than £30-£40.  Do you think a motor with a 600KV running on 6v swinging a say 100mm would be suitable?
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #26 on: November 18, 2008, 04:59:58 PM »

Garabaldy

I don't know the exact answer to your question, but am happy to give it some thought:

Do we know what revs you would like, or any more information about the prop?
I know (qualititively ) that tugs need low revs, big props, etc, but do we know any numbers?

Generally the lowest KV motors are the biggest in diameter and power, hence the most expensive.  Within a given size of outrunner the lowest KV motor is the easiest to make (easiest winding) and the most efficient (most copper on the poles)

900BB Torque
Eureka - I recognise that motor - and so does anyone with a high-class 12V electric drill (not DeWalt)  it has a KV of 6500/12 or 541RPM/volt
(which is very similar to the  Roy's geared inrunner at 527 KV)

I will have a scout round and see what seems like a good bet in outrunners. 
I'm working on the assumption that we are aiming at a direct drive to the prop, and it may be that the right direct drive motor might be an LRK type.

If gearing is a possible thought, then using say a MFA Olympus belt drive (3.3 to 1) and a 1500KV outrunner around

Looking through an ebay range of direct drive motors I came across this one.  Not sure why you say the Low KV motors are expensive - even though this is a Oz site,  71$Au is pretty cheap - the KV is 800, on 3 Lipo cells, so running this around 7 to 10 Volts (or 12) would, I think, memorably overpower your tug

Please don't dive in with the possibility of me beng wrong, and you being broke - have a look at the specs of the 900BBtorque and this motor

more tomorrw
andrew

http://cgi.ebay.com.au/RC-EP-850rpm-v-518W-Outrunner-Brushless-Motor-AU_W0QQitemZ290266988983QQihZ019QQcategoryZ34055QQtcZphotoQQcmdZViewItemQQ_trksidZp1742.m153.l1262





Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #27 on: November 20, 2008, 01:09:54 PM »

Sorry, Chaps; I lost a complete post yesterday - it must be somewhere in virtual space :}

While researching i have found some good resources (or at least better than nowt)

First up a motocalc listing of very large numbers of motors - brushed and brushless
http://www.motocalc.com/data/motor.html

This is very useful as it includes hundreds of the familiar Graupner and Robbe motors, and lot of Mabuchi standard winds and sizes - and gives the essential KV and efficiency information.  Hundreds of BL motors are listed, too, so it might be a help in finding good replacements.

While hunting for low KV tug motors I found a goldmine, as well as what I was seeking :}
http://www.micronradiocontrol.co.uk/scorpion_data/comparison.html
This is a table of the Scorpion range of BL motors.  They folllow the size numbering convention we discovered earlier, but this is a comparison table with many other manufacturers BL motors - including AXI which are very good, but only their mother can work anything out from their model numbers
Scorpion motors are offered as kits (so are GoBrushless and Komodo) - suggest you have a look at that page, too

betterer and betterer - there is a complete BL power/performance calculator
http://www.micronradiocontrol.co.uk/scorpion_calc.html

No doubt this works best for scorpion motors, but would probably give a fairly close answer for another of the same dimensions and wind

These two are both on the Micron RC site - they are card-carrying good guys (no relationship - just satisfied customer) - yopu might like the have a look at the micro-motors, too, and imagine a micro-hydroplane with a 4gm brushless going like micro-stink :}

More soon including more practival ansrws for Garabaldy and the Tug

I have started a thread nearby on my brushless demonstrator - and made the boat this morning (30 mins so far)

This is my (new) cutting mat with 540 buggy motor (for scale) with my homemade brushless motor (blue cylinder), ESC and a CDROM motor as salvaged out of a computer CD drive.

more as it happens - contributions welcome
andrew




Logged

muduck

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 46
  • Location: BRAIDWOOD Australia
Re: Brushless Basics
« Reply #28 on: November 26, 2008, 12:59:48 PM »

A thread in the nick "O" time...great stuff, waiting for more info to come.
I have a Mountfleet "Cruiser" with a Proteus steam plant. The combo is perfect, but I need the engine for another project, & was wondering how to go about utilizing brushless tech. I'ts still a bit of a mystery, & I keep re reading what you have written, but then it's probably why I love my Four Strokes on the planes, I know exactly what size I need for which plane...
Logged

muduck

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 46
  • Location: BRAIDWOOD Australia
Re: Brushless Basics
« Reply #29 on: November 27, 2008, 11:00:39 AM »

While you lot in the NH were shivering around the fire, I spent(not wasted) the 30C day looking for something that may power the Cruiser with her 4 bladed70 Rivabo prop.
Any thoughts?
http://cgi.ebay.com/RC-Ship-60A-Water-Cool-Brushless-Motor-Programmable-ESC_W0QQitemZ270305803396QQihZ017QQcategoryZ116074QQtcZphotoQQcmdZViewItem

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=290266988983&_trksid=p3907.m32&_trkparms=tab%3DWatching
Logged

Garabaldy

  • Guest
Re: Brushless Basics
« Reply #30 on: November 27, 2008, 12:39:43 PM »

i have the 35amp version of the seaking speed controller.  I have 2of them in my fireboat and they are good.  Once you get them set up.  The most iriitateing thing with them is when you want to reverse the motor you have to pull the throttle stick right back then set it back to zero then pull it back again to reverse the motor.  the manual calls it  "double click"

http://www.modelboatmayhem.co.uk/forum/index.php?topic=12668.msg126929#msg126929
Logged

lifeboatpaul

  • Guest
Re: Brushless Basics
« Reply #32 on: December 07, 2008, 01:37:01 PM »

I have just been reading this thread- Ohh I do love the part in Andrewh`s reply concerning the BL
Logged

lifeboatpaul

  • Guest
Re: Brushless Basics
« Reply #33 on: December 07, 2008, 01:43:29 PM »

this I was should have gone before the last post but it I hitthe enter key and posted halfway through


(I have taken as an example Lifeboatman Paul’s beautiful Arun so that we have something real to consider - hope that is OK with you , Paul, you are hero to us)
http://www.modelboatmayhem.co.uk/forum/index.php?topic=9830.0
P/s just to clarify I use the motors on 24v ( 2x 7ah lead acids) and both the ESC`S together on a Y lead ( the bec`s seem to be OK working together)

Paul - ( the hero?)
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #34 on: December 07, 2008, 04:01:13 PM »


Brushless speed controllers, or “How To Feed Your Brushless Motor”

Where to start?
I have been wondering where and how to get into this topic - and the obvious place seems to be at the beginning, with the basics :}

What the motor needs
We know that these are 3-phase AC motors, so we need to feed them a diet of just exactly that.  Speed comes from the frequency with which we feed the motor current in each phase (it is a variable-frequency alternating current)

I have failed to find any useful pictures of 3-phase supply, so I have generated some sketches using my CAD package (Pencildraffy1949).  I do not claim that these are perfect, or perfectly reflects what is actually happening – they are the way I visualise what is going on, and are, I hope helpful in imagining the process.


Fig 1 shows 3-phase AC - as it is generated for the mains - with each phase a nice smooth sine wave  I have called the phases 1 ,2 and 3,

Fig 2 shows the simplest and nastiest wave form which would rotate a BL motor - it is completely or nearly square and the sharp corners will make for noisy and rough running

Fig 3 is an attempt to show what is actually generated by the ESC - it approximates to a sine wave, but built from square, but narrow pulses.  The gapa and square enges are sufficiently narrow for the motor to run through them without much noise or mechanical stress.  There are, of course three phases, all generating the same kind of wave-form, but staggered by 1/3rd of a revolution

What I cannot show is the timing, which varies with speed and load, and the type of motor - depending on the speed Controller

More soon - reversing, and a BFO

andrew


Reversing
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #35 on: December 08, 2008, 12:57:41 PM »

While writing (indefatigably) late last night i managed to lose the entire spiel on reversing and reversability, so here is again.

REVERSING - or GNISREVER

To reverse a Brushed (DC) motor you reverse the polarity of wires to the motor, and (ignoring differences of timing) it will run happily in the other direction. 
To do this under radio control requires an output on the ESC which works the other way round, electrically, usually arranged as an h-bridge.
FETs to run the opposite polarity are harder to come by and more expensive, which is why marine controllers are much more expensive per amp of output than aircraft controllers (where reverse is seldom called for, and when it is it isn't done that way :})

Reversing a BL motor is actually very much simpler - we just have to reverse the Sequence of the pulses in the three phases we are feeding it.  This is not a matter of polarity, since each of the phases is AC anyway.  Its really a software matter, since all (probably) of the BL ESCs are microprocessor controlled,  the output stages just have to "fire" in the reverse order and Bob will be your avuncular relative.

The phase sequence

I am going to call the phases (wires) A B and C
To rotate forwards the ESC needs to feed the phases with pulses of voltage in the order:
     A B C A B C A B C A B C A B C A B C A B C A B C A B C ........
If we want the motor to run in the other direction we need to send the phases in the reverse order
C B A C B A C B A C B A C B A C B A C B A C B A C B A.....

These are in fact the only two possible permutations of order with three phases , and if you compare them with hawk eyes (starting at any phase letter) you will see that one direction is ABC and the other ACB - in other words two of the wires are reversed.

Alleluia!  This is exactly the same switching that reverses a DC (brushed) motor! 
2 wires  - change them over to reverse
So I did

theory

Practice

Two small microswitches are glued side by side and wired as shown.  I use 2mm gold connectors, so they are designed to fit into my motor/ESC connections with appropriate male and female connectors.

Does it work?  Serpently it does - also works on a DC motor too.
The two microswitches are stuck on top of a servo and the plungers are operated together by a lump fitted to the servo arm so that they depress (together) at one end of the servo travel

You can do exactly the same thing with a DPST or DPDT switch operated by a servo (but do make sure that the toggle action can toggle freely)

Incidentally this little switcher is simple and suitable for a bowthruster made from a windscreen wash motor if anyone is interested.

I have used a another channel to operate this reversing switch, but it must be possible to do it elegantly with the same channel as the ESC - (or possibly brutally)  I am going to consult experts about this possibility, and will relay you anything interesting that comes out of it.
Why do this?  Well, 15A brushless ESCs are available for prices around a fiver :}

In case you missed it

certainly the fastest and silliest Razor in the world

Next chapter;  4-d flying and the boating community
andrew



 
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #36 on: December 08, 2008, 01:17:12 PM »

LifeboatmanPaul

Thanks for posting - your lifeboat is an impressive lesson to us all, and the detail you had included in telling us about it was so complete that it illustrated the whole type of large, planing boat beautifully.  Thanks

Thanks for the battery details, too - I had been rather concerned about the currents at 12V, and meant to ask you if those were interior running lights or the batteries glowing :}

Gentle readers  - you will have gathered by now that my (model) boating knowledge is not extensive.  You-all know much more that I do about the boats you specialise in.  Some of these emphasise performance, but length of run and the use of lead-acid batteries also seem to figure large in the design reqirements.

I still wish to set out a broad chart with first-cut Brushless motor suggestions for as wide a range of boat-types as possible
even Henry:

contributions welcome
andrew
Logged

roycv

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,318
  • Location: S.W. Herts
Re: Brushless Basics
« Reply #37 on: December 08, 2008, 03:06:12 PM »

Hi Andrew, very much enjoying the thread.
I expect that this is a very silly question, but here goes!
With a brushed motor if the load is increased generally the motor slows down.  What happens with a brushless motor?  I would expect that it would try to rotate to follow the variable AC input frequency.  If you start slowly and the motor follows, fine, but as the load increases with rpm what happens if the load is too great?  Does the motor stop, get hot or protest in some other way? 

many regards Roy
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #38 on: December 09, 2008, 08:40:51 AM »

Roy
andrew
I expect that this is a very silly question, but here goes!
With a brushed motor if the load is increased generally the motor slows down.  What happens with a brushless motor?  I would expect that it would try to rotate to follow the variable AC input frequency.  If you start slowly and the motor follows, fine, but as the load increases with rpm what happens if the load is too great?  Does the motor stop, get hot or protest in some other way? 

many regards Roy

There are no sillly questions, and this is a very wise one :}
I don't know the full answer, but am happy to explore it with you.

Some of the answer lies in the fact that a DC motor can run without the ESC, but it is not possible to consider a BL motor without its ESC. 

Both motors have the same characteristic of generating back EMF as they rotate - a DC motor has a VERY low resistance if you measure it statically - so it takes a huge current at rest (the start-up current). 
As soon as it is rotating  it also generates, and this has the effect of increasing the apparent resistance and reducing the running current.
All well and good, until you put your finger in the propellor!
(I (and my fingers) are more used to aircraft props, but the same applies to water props)
The motors slows down, the back EMF reduces, current increase and the second blade hits you a good one! - I have been cut by the 4" prop on a KP01 motor (2 volts, 4 Amps - an 8watt motor!)

This same process happens generally for both Brushed and brushless motors - now we need to consider what is happening with the BL and its ESC.
It is trying, as you say, to run at the speed commanded by the throttle stick - the ESC is feeding the motor a rate of rotation (of the phases) that does this, and the motor will, if it can, exactly follow this.
Now if the load increases suddenly - say picking up a nice length of fishing line in the prop :} - what happens?
Well several things at the same time - the "slowing down" habit described above will happen - current goes up to try and compensate for the slowing.
Also the ESC will detect the slowing (it listens as well as talking to the motor) and it will adjust its frequency to suit what the motor is actually doing - and try to restore the set speed.  So it will if it can.

So the basic answer to your question , Roy, is yes, pretty much!
The basic characteristics of "self regulation" will be similar, the second blade will still hurt badly, and even more - there is an ESC with its fast (but tiny) brain trying to do all it can to restore the motor to its original, set speed.  It should not overheat, since the ESC will not feed it more than the ESC can supply (most ESCs seem to be temperature -protected)

andrew
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #39 on: December 09, 2008, 01:43:34 PM »

I'm a (mature) mechanical engineer, and occasionally prone to bursts of the blindingly obvious.
 I'm also Scottish by birth and a little financially "aware"

I can tell that you-all  out there are electronic experts, but me, I just like to understand what is (or should be) going on in those boxes with electric strings going everywhere.

BLDriver
I am going to make, in the best Mayhem tradition, a brushless motor-driver
It will (OK, should) drive a BL motor, and in both directions.  Cost is expected to be approx GBP 6.00  if I buy the critical parts new
It will be visible, understandable and yes, fairly silly

BFO
I should occasionally listen to myself
I have thought, said and written that forwards-only BL ESCs are cheap and readily available - about a fiver
my reversing switch cost nowt - because I salvage microswitches from alll household gadgets before they are thrown away, but if you bought the microswitches and servo it would cost a lot more than a second ESC

Now all I need is a way to operate one ESC for forwards and the other for going astern, and both at once for the dramatic , but unique, fireboat impression :}

andrew

Logged

roycv

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,318
  • Location: S.W. Herts
Re: Brushless Basics
« Reply #40 on: December 09, 2008, 02:12:34 PM »

Hi Andrew thanks for taking the time to explain, please carry on with the information.  Look forward to seeing yourBL ESC, the commercial reversing esc's seem very expensive by comparison.
regards Roy
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #41 on: December 09, 2008, 02:34:23 PM »

Thanks, Roy

I hope I carefully didn't say ESC :}  I can't do E to this extent - thats what friends are for

But yes, motor driver and MSC it should be

My hope is that it will stimulate you or someone to say "Oh, I see now , all is need is a phase sequencer and deflocculator with an FET output"  and produce the ultimate marine reversing ESC

andrew
Logged

roycv

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,318
  • Location: S.W. Herts
Re: Brushless Basics
« Reply #42 on: December 09, 2008, 10:57:39 PM »

Hi Andrew  I used to know what a suppressor triggered phantastron was.
I found I could live life with little reference to it so it had to go.  I'm OK with FET's but I used to use emitter followers.
regards Roy
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #43 on: December 10, 2008, 07:37:05 AM »

I just try and avoid SED*s, unless they are free or very cheap

*Smoke emitting Diodes

andrew
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #44 on: December 19, 2008, 04:20:02 PM »

Nearly Christmas, so seasons greetings to all readers, or reader as the case may be.

I am fortunate that Amanda still puts my Zimmer frame through the carwash. 
If it helps you with visualisation she has a strong resemblance to Samantha the scorer on "I'm sorry I havn't a Clue"

Where are we?

A)      I threatened you with 4-D.  I hope you have done the homework (but at this season of goodwill I can overlook the claim that the dog ate your Google button.)

What on earth, I hear you ask, is 4-D?  well its a branch of indoor RC flying  which involves the plane not only flying and hovering forwards - but flying and hovering BACKWARDS and nose-down :} as well
http://www.youtube.com/watch?v=LGWNHzaSGE0
http://www.youtube.com/watch?v=GPUb6CW1iJs&feature=related
So?
Well its a hobby for a young, rich person since  the walls, floor and roof approach from both ahead and behind the plane, but it may have some interest to boat-builders and users because the trick is done, not by reversing the motor (always brushless) but by reversing the prop blades!

So all 4-D motors have hollow shafts, and you can buy hollow shafts for most of the smaller brushless motors. 
This leads me to think about reversible pitch props for brushless boats. 
What we generally want is efficient progress forwards and some sort of reverse.  Not the same speed and power, but just some reverse motion
Thinks:  4-D props - helicopter tail rotors, swashplates - there is a lot of hardware out there that could make the linkages work easily. 
All we need is a strong, reliable variable (and reversible) pitch prop

B)  BL twins

The written wisdom is that you need one brushless ESC per motor. 
There are many recorded and successful cases where that is not essential and twin motors are run off one BL ESC.
While I'm not sure if anybody knows the whole answer, it is certain that for this to happen:
The motors must be identical (same model, same manufacturer)
The propellors must be identical - in each case I have heard of these have been Gunther props
The ESCs have been of several sorts, both cheap and Castle type.

None of the flyers (they were all flyers) had any problem with getting it to happen, or changed the program of the ESC to suit.
 
Flyers are generally using equipment MUCH harder than boat modellers (we have to to get into the air) so the motors and ESC were running close to their rated power.   
It should be very much easier for boat modellers to get two motors to run off one ESC since the speeds and loads are generally lighter, and its not too difficult to get near-identical props.

DISCLAIMER - I can see no way in which trying this could damage either the motors or ESC, but I have not done it myself (home-made motors - none identical). 
If you try it do so carefully, it may well not work and you do so at your risk
(I have subsequently done a search which confiirms basically what I said above - it often works .  There was one mention from an owner that he ruined two motors and damaged the ESC)

That's it for now - I am going to update the BL test boat thread now
I aim in the near future to go back over the thread and pick up any loose ends and try and tie them off (or encourage them to slip BL motors into boats and tell us about it)

andrew
 



Logged

Bluechrisp

  • Guest
Re: Brushless Basics
« Reply #45 on: December 28, 2008, 11:03:12 PM »

Hello Andrew,

A great thread, now my heads hurting, I fairly new to model boating, I would like to update a Sea commander from a Graupner 600 on a 6v/7.2 batt to a brushless set up, the boat is 34 in long weighting up to 6 kilos. speed about 2-3 mph.

I had a look at a few but not sure where to go for, on a old woodern boat.  any ideas.  :-))

Cheers

ChrisP
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #46 on: January 06, 2009, 04:04:39 PM »

Hi, Chris
Sorry for the delay in replying - family things over Christmas and the New Year have got in the way
Reply very soon

CALLING ALLLL MAYHEMERS
Ths back cover of the UK comics  carry adverts from Mtronics which include the Hydra 15  brushless motor and ESC package for about GBP50. 
This combo doesn't appear visibly on their website, altho the ESC does (with its big brother the Hydra30) so we don't know what the BL motor is - it LOOKS like a 28/20 and they do say it fits onto a 480 (from memory) mounting. The 15 and 30 BTW refer to Amps continuous but there is very little further info
 http://www.mtroniks.net/products.asp/SubCatID/1/brushless-speed-controllers.htm

Here is the question - has anyone ever seen the combo, or bought one, or seen one in a boat or on the water?
I have enquired of Mtronics for more details, and will pass them on as received
If offered a unit to test I might hesitate for picoseconds before replying :}
andrew
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Brushless Basics
« Reply #47 on: January 07, 2009, 01:28:33 PM »

Chris,

Thanks for your query - Sea Commander, eh?
I don't know the answer, but let's see if we can work towards it :}
We have a tree-wood boat, quite heavy (6KG) 34inches by 10+inches and a good planing shape
You are powering it with a a Speed 600 , buggy pack, unknown prop and get 2-3mph

First some questions
  • What do you want your SC to do?  (similar performance/plane smoothly/go ment'l)
    Prop size and type (photo too, please)
    Direct or geared?
    more motor info - I'm guessing its either the S600 7.2 or s600 7.2 eco
    nicad pack capacity?
TIA for answers

Ways to size a BL motor:
1)   Go to the Mayhem BL database and find the closest to boat and performance option (still lies in the future!)
2)   See what we can calculate from the existing power system
3)   Ask stavros
4)   see if there is anything similar in Weeds spreadsheet

We can't yet do (1), so lets have a go at the rest
2) existing power system
S600 with bugggy pack.  I will assume direct drive.  2 to 3 mph is displacement speed (not planing).  I have no information on current draw, duration or prop so let's  assume about 35mm prop, current draw of 5A (this is a 20 to 30 Amp motor in aircraft).  If the battery pack is 2000maH (guess) thats 2Amp for an hour, or 4 amps for 1/2 hour so 5 amps would run for about 25 minutes
5 amps at 6 V is 30 watts (assuming 6-cell pack)
If the prop is 35mm diameter with a pitch of about 40mm it travels 40mm per rev (ignoring slip)
3mph is close to 1.5m/sec or 1500mm/sec
it takes 37.5 (1500/40) revs to move this far, and this is per sec
37.5 revs/sec is 2250 revs/min - which seems to be FAR too low  - under light load I would expect even the ECO motor to be turning about 10Krevs
BUT - I have also found an SC which is powered by an OS30 or 35, and the action pics show it resolutely ploughing through the water (not over it).  This is what I call a stunt motor - long-stroke workhorse which would probably be running 7 to 8000 rpm under load
This boat has a 55mm prop
if the OS produces maybe 1/4 HP (187watts) (it is a slogging motor with a long, small diameter  exhaust) the boat appears to be moving at jogging pace - maybe 5 to 8 Mph, but certainly not near the plane.

3) Stavros, I know has a large aeroKits boat (prolly Huntsman), and a cunning plan to give it a surprise, large brushless and blinding performance
When last we spoke he was plotting a 800watt motor and 75mm prop.  It seems likely therefore that Lllllyn Padarn will be crossed with the boat only touching the water a couple of times
We reckoned that the power train out of half a 1/10 lifeboat sounded about right (for blinding performance)

4) Weed's spreadsheet
http://spreadsheets.google.com/pub?key=p9c1CESjtjA7ZkLJHEz5XDQ
I'm going to have a look when I can get it to load - we will come back to that

So here we are - what have we learned?
Power aim is more than 30Watts , more than 180watts if we want her up on the plane (once planing the power requirement comes right down, but you need raw power to get the hull out of the watter)
We don't know how much room there is for prop diameter, but the bigger the diameter the more "grip" it has on the water, and the less slip and wastage of power
The two probable S600 motors have KVs of 2526 (S600 7.2V) and 1583 (S600 7.2V Eco) so we need to match this IF THE PROP HAS TO REMAIN.  It would be better to aim for a larger prop and BL motor with medium KV (say 1000 to 1500)

So before Chris replies my thoughts are going down the lines of
http://www.overlander.co.uk/product.asp?cid=10&scid=83&pid=2593
 - this is 350 watts and would need feeding with up to 12 cells - could be 2 cheap buggy packs.  KV is 1100 so it would need or like a bigger prop.  Max current is 30 A so a 30 to 50 A brushless ESC would be needed

Contributions welcome
I have not been able to open the Weeds spreadsheet today

andrew
 




Logged

Bluechrisp

  • Guest
Re: Brushless Basics
« Reply #48 on: January 10, 2009, 12:30:26 AM »

Hi Andrew,
The SC does plane for the first 5 minutes, even on a 6V SLA then reverts to  normal as the power goes, I have a 37.5mm P prop 2 blade plastic, could take a 50mm prop, the 600 engine is 6V. I would like it to go faster, even leap out of the water maybe  :o well nearly, did see a 700 series water cooled, to big mmmm   %% any help would be great, I'm still trying to get to grips how great these brushless motors are....  :-))

CP
Logged

EJL

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 110
  • Model Boat Mayhem is Great!
Re: Brushless Basics
« Reply #49 on: January 11, 2009, 01:58:02 PM »

If I can offer any help ask away. I run high power racing boats/ scale racing boats and all my boatss have brushlkess motors in them.(except the gas turbine)

I own Mega's and  Aveox to name but two.........  Numerous makes of speed controllers.

Some of you will remember me from my days writing about fast electrics and related boats for Marine Modelling Magazine (12 years).

Andrew has covered the technology I can cover the application.  I am a little out of touch with Lipo technology having stuck with Sub C cells but will be catching up soon.

Ernie Lazenby
Logged
Pages: 1 [2] 3 4 5   Go Up