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Author Topic: LONG RUNNING TIMES ON BRUSHLESS MOTORS  (Read 11041 times)

debssnal

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LONG RUNNING TIMES ON BRUSHLESS MOTORS
« on: October 12, 2008, 10:36:41 PM »

Hi everyone i have been playing around with brushless motors this year.I have had some good times with them and some bad.Now I feel I am going forwards very fast.I am getting bags of power and long running times.I have fitted them in small and large boats.I have fitted them in jet drive and prop boats.I have a Cygnus GM33 fishing boat 1:16 scale (24.5" long x 10.25" beam),and on a 6volt 7ahp gel cell battery runs for 4hours.It has a Tornado Thumper 3536 Brushless motor - 400 watt 1000 kv outrunner .The motor runs cold all the time so no power used to heat the lake.I have a 1:16 jet drive lifeboat (33" long x 9" beam).This has 2x 300watt 1700kv outrunner  brushless motors.It has 2x 2500 ma 11.1 volt lipo battery's,and runs for 3 hours.The motors also run cold in this boat.I have a 1:10 scale jet drive lifeboat (54" long x14" beam and coming in at 15kg).This has 2x Tornado Thumper 4250 Brushless motor - 720 watt 600kv outrunner.This boat runs for 1.5 hours on a 12 volt 12ahp gel cell battery.I have also tried the Tornado Thumper 4250 Brushless motor - 720 watt in my Speedline 1:12 Severn lifeboat.It went well ,at a bit over scale speed on 75 mm props,but they got a little warm.So i have two Tornado Thumper 5055 Brushless motors - 1280 watt 580kv outrunner on there way for it.The Tornado Thumper 4250 Brushless motor - 720 watt 600kv are going in a new 1:12 scale tyne class lifeboat.On the low rpm outrunner brushless motors it looks like you need 100watts of power per kg they work very well.I hope this is of some help to everyone.I will keep you posted on how the severn and tyne get on.

ALAN
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Stavros

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #1 on: October 12, 2008, 10:48:16 PM »

OK in laymans terms (if there is some) can you give the say Graupener equivalent size motor in a table so we can see what is what.It is so difficult to know what is an equivalent brushless to say a Graupener 700bb turbo or even a MFA 850.Thanks




Stavros
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debssnal

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #2 on: October 12, 2008, 11:19:53 PM »

Hi well a Tornado Thumper 4250 Brushless motor - 720 watt 600kv =4.58 MFA 850'S.It will run a model of up to 8kg with a four bladed prop up to 60mm with no probs.As for 700 bb turbo it is a high rpm motor so not the same.When i had my 1:10 Scale jet drive lifeboat first on the water i had 2 x 700bb turbo with 2:1 gear drives on the 40mm jet drives and it was slow and eat batterys.Have a look for yourself at how the 1:10 scale and the 1:16 scale lifeboat run on brushless.
The 1:16 scale http://uk.youtube.com/watch?v=yas3G4BQ-Fg
The 1:10 scale http://uk.youtube.com/watch?v=gLRKH9_MKfI
The 1:10 on 24volt http://uk.youtube.com/watch?v=Jn2QxbhaJUs

ALAN
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Garabaldy

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #3 on: October 12, 2008, 11:30:04 PM »

Ahh more brushless talk :-))

Sounds like you have a fari amount of experience in this are now debssnall?

In comparing the brushless motors to the 700bb it mite be easier to work out how much watts the 700bb produces.  So im sure thats just volts X amps?

I have just put 2 tornado thumper C3530 1100kv 340watt motors into my fireboat 39.  Hopefully they will be powerfull enough to give a good speed!

Debssnal what kind of speed controllers have you been using?  I have 2 35amp water cooled seakings.


Gary
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debssnal

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #4 on: October 12, 2008, 11:51:12 PM »

Hi Gary i am useing Programmable Brushless Car ESC XC60A Continue with BEC for the prop boats.I will have to get the XC100A ESC'S for the new motors for my 1:12 Severn.The ESC'S i use are fan cooled and they self program so no fuss.On the jet drive boat i only need forwards so i use plane ESC'S.

ALAN
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Stavros

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #5 on: October 13, 2008, 06:15:24 PM »

so an I right in thinking that the thumper 4520 produces 4 times the power of a 850???




Stavros
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debssnal

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #6 on: October 13, 2008, 07:01:18 PM »

Hi Stavros, yes that is wright.A mfa 850 out put is 157watts,were the Thumper 4250 out put is 720watts.
The mfa 850 is only 62.3% efficient (1/3 of its power is lost in heat and friction)so 1/3 of your battery power is wasted so making a shorter running time.
The Thumper 4250 is 96% efficient so giving more power and longer running time.
This is just over 200 meters the boat is doing in 8.5 seconds. http://uk.youtube.com/watch?v=Jn2QxbhaJUs
The boat is 54"long and comes in at 15kg.
2x mfa 850 will not do this.I know this as 2x 700bb turbo with 2:1 gear drives were no were near it.

ALAN
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Stavros

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #7 on: October 13, 2008, 07:31:49 PM »

Right then some sense at last with regards to theses brushless motors !!!




Stavros
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Weeds

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #8 on: October 13, 2008, 08:05:02 PM »

Wow, what a thread! Lots of primo information to digest here. Forgive me, but I couldn't quite figure out which motor you say is best.

Can you recommend the best brushless motor you tried and specify the motor, propeller (direct drive), boat size, battery and guesstimate the boat's speed and runtime?

I'd be able then to go and buy same stuff as you did and have similar success   {-)

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nick_75au

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #9 on: October 14, 2008, 08:08:52 AM »

Maybe Ive calculated it wrong , would that be 23.5 meters a second? or 80 odd KPH
What's your measured amp draw, say static in the water?

Ive got 2 Darke Horse (like what Pandan used to sell) motors per shaft with a total 4.5 :1  reduction, 20 amps per motor 40 amps per shaft or 960 watts per shaft as a comparison.

Regards
Nick
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Garabaldy

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #10 on: October 14, 2008, 08:35:52 AM »

can some one explain the brake function to me?  On a boat, is it better if its just turned off?
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Martin [Admin]

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #11 on: October 14, 2008, 08:41:46 AM »

yes!  :-))
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Proteus

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #12 on: October 14, 2008, 09:18:48 AM »

can I ask why its better turned off, if you leave it on a soft setting surely it help protect the speed controller from large amp surge if you slam it from forward to reverse, same as delay helps stop damage I thought. but I may be wrong  :-\  ???

Proteus

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malcolmfrary

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #13 on: October 14, 2008, 09:44:54 AM »

I assume that the brake function just removes the power and shorts the motor causing a sudden stop of the motor.  Being able to slam straight into reverse on a boat is your actual brakes.
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Garabaldy

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #14 on: October 14, 2008, 10:09:15 AM »

The user manual (http://www.hobbywing.com/upload/manual/SeaKing_080628_e.pdf) which came with my speed controller is not the clearest but the way i interprated it is the brake function is more for cars.  "when using brakes when steer" helps prevent the motor going into reverse when going round corners.  I am unsure though.  Ive read teh manual 4 or 5 times and its probably still going to take me a while to get the controller set up.  With or without break?  The "double click" function bothers me slightly, i hope when the break function is switched off that goes away......
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portside II

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #15 on: October 14, 2008, 10:18:51 AM »

I have allways admired the way brushless motors work ,and their efficency . So far all i have read is that they are good in high speed applications,jet drives etc, but what about tha other end of the scale brute power as in a tug application .
Just a thought.
daz
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Garabaldy

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #16 on: October 14, 2008, 10:43:37 AM »

on one of the other forums some one has fitted brushless motors to a dumas tug i think.  The torquer lower KV rated brushless motors tend to be more expensive though....
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andrewh

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #17 on: October 14, 2008, 11:57:52 AM »

Motor braking

Disclaimer - I have never been inside a hobby brushless speed controller and looked at what the software and hardware are arranged to do.
But I do design and make braking resistors and systems (up to about 20MW motors)

Any motor can be stopped by shorting the windings - try it if you are brave and confident! 
The currents flowing are huge and the torque released will break mountings and certainly any gears attached.

Much kinder and more controllable is to connect a braking resistor across the windings - so a DC motor needs only one, but ideally an AC motor (brushless) needs one per phase  - usually 3 in our world.  (you can  connect a brake resistor to just one (or two) phases but its a bit uneven and brutal)

How much is right? - well it depends on what you want.  My mental rule-of-thumb is that a resistor about equal to the resistance winding (in Ohms) gives a fairly "sharp" stop.   For aircraft brakes the resistor is usually set at this value approx (1 to 2 ohms), as usually it's required to fold the propellor.
The "sharp" stop (maybe 1/10 sec) won't do gearboxes any good at all - so a much higher resistance is used -  its best to start high and work down (if you ever have to do this use a length of hair-dryer wire, or car light-bulbs to find out what works and is safe)

So - the brushless ESCs may be switching in three resistors (one per phase) for the braking function, but these resistors would be quite large and visible, and would only be used for this function.
So I suspect that the designers use FETS as synthetic resistors (perhaps the same FETS used for the drive).  Although FETs have a VERY small resistance when they are fully "on" (and an infinite resistance when off) they can be driven so as to have any resistance, and would almost certainly  be pulsed so that the braking can be adjusted.

So in summary:
  • You can brake any motor by shorting it - its brutal, please don't
    switching in a resistor will give a kinder and controllable brake
    ESC manufacturers (probably) do exactly that, but use cunning electronics to create the resistor

Useful/interesting/shut up! andrew?

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Garabaldy

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #18 on: October 14, 2008, 12:35:53 PM »

very interesting....  So if its really bad for the motor  mountings etc why would the manufactuer have a mode where braking is turned off?
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andrewh

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #19 on: October 14, 2008, 12:47:49 PM »

Sorry, I've not quite understood.

When the brake is off - all the torque on the motor mounting is from the motor running (and largest at the start) - no problem 

I was just making the point that braking by shorting the motor windings WILL stop the motor, but it can apply huge forces to the mountings and any geartrain attached  - which is why it is not done much.

Not many users of ESCs want brakes - cars, trucks and rockcrawlers, and some aircraft, so the brake function, where it exists, is often switchable off, and adjustable.

andrew
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Garabaldy

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #20 on: October 14, 2008, 03:16:40 PM »

should i switch mine off?  Is it likely to break my 6mm ply mountings if i do? 
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johno 52-11

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #21 on: October 14, 2008, 03:19:14 PM »

Hi Stavros, yes that is wright.A mfa 850 out put is 157watts,were the Thumper 4250 out put is 720watts.
The mfa 850 is only 62.3% efficient (1/3 of its power is lost in heat and friction)so 1/3 of your battery power is wasted so making a shorter running time.
The Thumper 4250 is 96% efficient so giving more power and longer running time.
This is just over 200 meters the boat is doing in 8.5 seconds. http://uk.youtube.com/watch?v=Jn2QxbhaJUs
The boat is 54"long and comes in at 15kg.
2x mfa 850 will not do this.I know this as 2x 700bb turbo with 2:1 gear drives were no were near it.

ALAN

Alan

While I find the performance of your boat on the video  impressive I am a little concerned about your figures. If they are correct then your boat is doing 45+ knots which is 20 more that the real thing. Scale speed for 25 knots at 1/10 scale is about 8 knots or 4 Meters per second.
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andrewh

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #22 on: October 14, 2008, 03:56:02 PM »

Garabaldy

Switching the brake off cannot increase the load on the mounting device
If the brake is inside an ESC, it is not a short circuit - it will be much gentler
If it is "on" and works OK there isn't a problem whether its on or off

Have I been guilty of being confusing, or wrong or (far worse) giving you worry?
andrew
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debssnal

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #23 on: October 14, 2008, 10:59:21 PM »

Hi everyone ,one thing i forgot to say i have blown up a few couplings with brushless motors they have bags of torque.
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debssnal

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Re: LONG RUNNING TIMES ON BRUSHLESS MOTORS
« Reply #24 on: October 14, 2008, 11:23:26 PM »

Hi sorry everyone its just over 100meters not 200meters.
it has been run over a marked out 30 meters on 12volt.
ave on 4runs 5.3 sec.Could not do a 24volt run as i a coupling exploded into bits

ALAN
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