Model Boat Mayhem - Forum

Please login or register.

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

Author Topic: Recommendation for SMALL brushless....  (Read 10346 times)

dodgy geezer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,920
  • Location: London
Recommendation for SMALL brushless....
« on: August 02, 2009, 08:46:44 AM »

All the advice here seems to cover large and powerful motors (and why not!).

I am putting together a trial 'starter' boat for children out of balsa in the old EeZeBilt style - you can see it under the Pictures section of http://modelboats.hobby-site.com . It is 20" long - the frame you see weighs 1 1/4oz at the moment, and I suspect it will end up at about 4-6oz.

These boats used to potter sedately around with a 4.5v flat battery and a small Mabuchi brushed motor, however I suspect that modern technology might improve matters a bit. I am looking to keep the build very low-cost, but I thought there might be a lightweight aircraft brushless and ESC for perhaps 10-15 which would make it plane on 4 cells. Has anyone got any advice....
Logged

monarch

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #1 on: August 02, 2009, 09:28:13 AM »

Hi
Not an easy question to answer, so many types - Outrunner tend to be large low revs high torque, Inrunner tend to be faster revs less torque.
If you want the boat to reverse watch what ESC you get most a/c and fast electric are forward only.
Hope someone can help a bit more on suitable recommendations.

Monarch
Logged

dodgy geezer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,920
  • Location: London
Re: Recommendation for SMALL brushless....
« Reply #2 on: August 02, 2009, 11:14:33 AM »

Hmm....

I've never used a brushless, but the impression I get is that they rev very fast. I suspect that, for a 'sports' boat, low revs/high torque is better. No reverse would not be a killer, but I would need the ability to go full, half, dead slow and stop. Do cheap brushless motors (probably intended for aircraft) have throttling issues when used on light boat loads?
Logged

stallspeed

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #3 on: August 02, 2009, 03:06:00 PM »

Quote from: dodgy geezer
Do cheap brushless motors (probably intended for aircraft) have throttling issues when used on light boat loads?
The motors don't.The cheap controllers can't give low revs without gearing.

The cheap controllers get hot on two lipo cells(thats ~ 7 volts).It is down to the choice of P-ch transistors used.
Logged

Mi Amigo

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #5 on: August 02, 2009, 03:37:04 PM »

My friend has one of these, it works well, (in an aeroplane), never had a problem yet, he's had it about 6 months now.

http://www.brchobbies.co.uk/?page=shop&action=additem&item=184

12 is good value for a motor with esc.

Neil

Logged

dodgy geezer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,920
  • Location: London
Re: Recommendation for SMALL brushless....
« Reply #6 on: August 02, 2009, 04:43:35 PM »

That IS good value - worth getting (as I just have) purely to experiment with these motors! This looks like a shop which will go in my bookmarks...
Logged

jimtrellis

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #7 on: August 02, 2009, 04:52:45 PM »

The cheap controllers get hot on two lipo cells(thats ~ 7 volts).It is down to the choice of P-ch transistors used.

I've been following this thread with some interest, but then you threw this in and you have confused me completely.
What is a P-ch transistor? Do the adverts tell you which type of P-ch transistor is fitted, and what are the types to avoid? If the type fitted isn't stated then how do we know whether or not a speed controller is going to get hot, and does it matter?
Logged

dodgy geezer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,920
  • Location: London
Re: Recommendation for SMALL brushless....
« Reply #8 on: August 02, 2009, 05:46:45 PM »

Do the adverts tell you which type of P-ch transistor is fitted, and what are the types to avoid? If the type fitted isn't stated then how do we know whether or not a speed controller is going to get hot, and does it matter?


Without knowing anything whatsoever about brushless motor controllers, I can state categorically that, in common with all other advertising, the adverts will:

- only tell you about the 'good' things their product has
- avoid mentioning anything about the downsides of what they offer
- indicate that their product is the peak of desireability, and that no other product can match it.

I am constantly surprised by the way companies generally manage to provide a product line of several grades of product at different prices, and yet each one is the absolute best....
Logged

Captain Povey

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #9 on: August 02, 2009, 07:16:38 PM »

H Dodgy, I have posted some stuff on here of my experiences of fitting a small brushless motor, Fusion 1100rpm/volt, in the Mantua Mincio. Whilst the motors are a good price the cheap controllers are not good value. In the end I had to buy the proper job which was programmed for a boat and had reverse. Cheers, Graham.
Logged

andrewh

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,064
  • Location: Melbourne, Australia
Re: Recommendation for SMALL brushless....
« Reply #10 on: August 02, 2009, 07:27:29 PM »

As Neil says - good value

My friend has one of these, it works well, (in an aeroplane), never had a problem yet, he's had it about 6 months now.

http://www.brchobbies.co.uk/?page=shop&action=additem&item=184

12 is good value for a motor with esc.
Neil
This is a "bell" motor - the 21T version has a KV of 1200 and has been extensively used in by Brushless trial boats from 12 inches long (razor and White dwarf) to 18inches (hellkitten) and my 1/35th Higgins PT boat
Details and photos in http://www.modelboatmayhem.co.uk/forum/index.php?topic=14068.0
and http://www.modelboatmayhem.co.uk/forum/index.php?topic=13538.0

Dodgygeezer - your desire and quest are perfectly reasonable and possible - Brushlesses come from 1gram weight to hundreds of tonnes - there is one in there for you.  I would strongly reccommend a cheap aeor speed controller
 - can't possibly agree that their low speed is poor - they are designed and made to allow Andys to fly, hover and reverse in the air.  As always you get what you pay for (and weep for as long as it cost when the smoke comes out)  in my case at Wicksteed I wept for a few picoseconds while i found the fried FET

Please consider making your own motor :} :}
The "bell" motor is approx a 2209/XXT wheere XX is the KV.  For cheerful pottering  - with a prop like an EZbilt prop and a few cells (say 5 or 6 pencells for power) you should be looking for a KV from 1000 to 2000.
GOOD NEWS - this is what all the little motors are - unless they are inrunners (You don't need an inrunner)

Have a look at micronRC anyway - thy also do good deals with bell -motors but also sell  the GoBrushless kits you can wind these with any KV you like from  about 300 to 3000.  A CDrom motor taken straight from a disc drive will run with a cheap brushless ESC and is near-perfect for what you want.  With replacement magnets (which come in the Gobrushless kit) it is perfect - low current, fairly low KV (turns a sensible prop) and VERY cheap
http://www.micronradiocontrol.co.uk/gb.html

Go for it - I will help all I can
andrew

 


The Bellm otor
Logged

dodgy geezer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,920
  • Location: London
Re: Recommendation for SMALL brushless....
« Reply #11 on: August 02, 2009, 08:58:37 PM »




Please consider making your own motor :} :}
The "bell" motor is approx a 2209/XXT wheere XX is the KV.  For cheerful pottering  - with a prop like an EZbilt prop and a few cells (say 5 or 6 pencells for power) you should be looking for a KV from 1000 to 2000.
GOOD NEWS - this is what all the little motors are - unless they are inrunners (You don't need an inrunner)

Have a look at micronRC anyway - thy also do good deals with bell -motors but also sell  the GoBrushless kits you can wind these with any KV you like from  about 300 to 3000.  A CDrom motor taken straight from a disc drive will run with a cheap brushless ESC and is near-perfect for what you want.  With replacement magnets (which come in the Gobrushless kit) it is perfect - low current, fairly low KV (turns a sensible prop) and VERY cheap
http://www.micronradiocontrol.co.uk/gb.html
 

Hmm....a lot there!  I think buying a cheap brushless +ESC just to find out what all these acronyms mean is a starter for 10... Have you seen the aim of my site? I was looking to get kids interested in building - looks like they may be building motors as well! I have disk-drive motors coming out of my ears - I should be able to get 20 or 30 just by going into the attic... so that might be a good route to go...
Logged

dodgy geezer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,920
  • Location: London
Re: Recommendation for SMALL brushless....
« Reply #12 on: August 05, 2009, 02:54:48 PM »

I've picked up a cheap brushless now, a 2408-21T-3A, at 12 from BRC hobbies and here are my first impressions:

These things are complicated! With a brushed motor, as soon as I got it out of the packet I could connect a few volts to it and see how it ran, from any old batteries which were lying around, or a power supply if available.

With this, you must connect it to its ESC, then to a receiver, then get a transmitter. Your batteries must be fully charged, otherwise the Auto Detect will not work. Once connected, the transmitter throttle position, auto motor calibration (timing?), cell count (?), voltage cut-off and lost signal protection are set up automatically. Only then can you see how it turns. I have not done this yet -I don't know if the motor is safe to run with no load, and there are no instructions which might tell me...

The mount is intended for an aircraft, so will need modifying. I will have to mount it somewhere for testing. Unlike a brushed motor, I suspect you can't just hold this in your hand while test-running it with a few volts...

When I turn the motor it is very notchy, and requires much more of a 'hand twist' to turn than a brushed motor. The impression I get is that this is going to be very powerful...

There are warnings all over the instructions which tell me NOT to fit bigger props than specified, and to keep within Watt limits - use a wattmeter at all times. I had hoped to keep the speed within managable limits by fitting a suitably large prop - it looks like this is forbidden....

The data on power is designed for aircraft use, and compares prop size, number of cells and thrust. It expects you to use Li-Po - there are only two rows showing Ni-Cad, and both assume 8 cells. I had hoped to use 4 cells, or 2 if the motor turned out to be very powerful - it looks like this is forbidden... 

You are also warned to 'fly the motor until fully discharged' - probably something to do with the ESC automatic settings. If you are to do multiple flights you must make sure the battery is fully charged prior to each. For a small boat you might want to do a few runs, potter about a bit, pause for a sandwich, potter about some more.. it looks like this is also forbidden....

I suppose my first question to the Brushless experts is - can I use a small pack of 4 AA Nicads with this? And what will happen if the Nicads are not fully charged?

Logged

nick_75au

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #13 on: August 06, 2009, 09:19:45 AM »

Hi Dodgy Geezer

In answer to some of your points

"With this, you must connect it to its ESC, then to a receiver, then get a transmitter."
A servo tester will work equally well in place of the transmitter/receiver for testing, still need the esc though, it acts as the commutator.

"When I turn the motor it is very notchy"
Motor is notchy as they use Neo' magnets which are far stronger than the ferrite magnets found in most motors, gives more torque.

"There are warnings all over the instructions which tell me NOT to fit bigger props than specified, and to keep within Watt limits - use a wattmeter at all times"
Unfortunately with boats there is little detail on what prop is good with what motor, it would be nice if there was a table that matched air propellers with boat props that give similar watts. Fit a small prop to keep watts down. A good base line is a prop smaller diameter than the diameter of the motor.


Most esc's will run on 6 volts if its 2 cell lipo capable, I use mine on a 6 volt gel cell and just set the battery type to ni** and the cutoff to the minimum possible (0.4 V per cell) which gives a theoretical lowest voltage of 2.4 volts. Cutoff can be disabled on most esc's as well so it then will just want power and servo signal.

If using Lipo, this is important any other "usual" cells wont make any difference.

It may work with 4 cell nicad, I think you may need 6 though, good thing about brussless is a lower KV motor can be selected which will lower the rpm.

Regards
Nick

Of course you might have an ESC that is not overly programmable or sensitive to voltage
Logged

nick_75au

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #14 on: August 06, 2009, 10:29:16 AM »

Forgot to mention, no problem with running the motors unloaded
Nick
Logged

dodgy geezer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,920
  • Location: London
Re: Recommendation for SMALL brushless....
« Reply #15 on: August 06, 2009, 11:15:25 AM »

Nick,

Thanks very much - your responses give me a bit more confidence!

I understand the theory of why an ESC is needed, but I was reporting on the impressions that a 'standard' motor guy would have on seeing these things for the first time! Unlike a brushed motor, it's a non-trivial process to test-run a BL motor.

Your advice to use a small propeller is very helpful - the impression I have is that BL motors are high rpm, and noisy. The one I have makes quite a loud whine if I just twirl the rotor with no power applied! In a small scale boat I wanted to cut noise, so I thought over-propping the motor would slow it down and cut the noise, while running off 4 cells would limit the wattage.....

To get a motor running slowly, say, 3-4k rpm, on 4.8V I would need a KV of about 1000. I presume I would have to wind that myself - is there an easy calculator to indicate how to do this? I have lots of dead hard drives and CD-Roms available to me...

Why is there a voltage cut-off? Is it to protect the LiPo cells? Of course the ESC probably won't run with less than +5v, and you want to maintain control, but if you were feeding your motor from gel cells you could run flat with no problems. My ESC is cheap (12 for motor +ESC!) and it has an 'auto' cut-off - I wonder what that means, and how I can influence it? I probably can't disable it....

   
Logged

nick_75au

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #16 on: August 06, 2009, 11:59:05 AM »

Assuming your motor is the tower pro,

your motor is a 1400 Kv motor so is probably ok with a fine pitch prop and 6 Ni** cells, there is a tower pro 2410-12T-3Y which has a Kv of only 600 and quite a few in between

http://www.hobbyking.com/hobbyking/store/tp_motor.html

and the ESC is

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=656&Product_Name=TowerPro_n18A_Brushless_Speed_Controller

Bit of extra information if you read the reviews on setting up the ESC. You will want the Ni** setting which will reduce the cutoff voltage. The cutoff is to protect the batteries from over discharge, Lipos don't have anywhere near the slowdown like gels and Ni**. By the time a lipo powerd motor is slowing down the cells are damaged hence the requirement for a cutoff.

Not sure about the whine bit, should be silent if your spinning it by hand, something loose/rubbing or dry bearing?

Regards
Nick

Logged

stallspeed

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #17 on: August 06, 2009, 12:05:46 PM »


Why is there a voltage cut-off? Is it to protect the LiPo cells? Of course the ESC probably won't run with less than +5v, and you want to maintain control, but if you were feeding your motor from gel cells you could run flat with no problems. My ESC is cheap (12 for motor +ESC!) and it has an 'auto' cut-off - I wonder what that means, and how I can influence it? I probably can't disable it....

   
You couldn't run a simple hobby brushless controller with 4 NiXX without a voltage cut-off.It would overheat to destruction.
Logged

dodgy geezer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,920
  • Location: London
Re: Recommendation for SMALL brushless....
« Reply #18 on: August 06, 2009, 12:24:11 PM »

Hmm... not sure about that. I simply bought this combination, as advised above:

http://www.brchobbies.co.uk/?page=shop&action=additem&item=184

This is advertised as a 15A ESC, and a 2408-21T-3A motor. There is no information provided on 'setting up' the esc - I was going to connect it to an old 27Mhz futaba receiver and drive it from that, so there will be no 'computer' input from the transmitter. I will look for more info on this requirement. I will try it on 4 NiCads initially, unless you think that will damage anything...?

If you spin a small brushed motor you will typically hear a faint 'clicking' sound, as the brushgear slides over the commutator. When I rotate the BL, instead of complete silence, or slight ball-bearing noise, I hear a low 'thrum' of vibration as the magnets notch round the stator. If I spin the shaft between finger and thumb, that noise increases in pitch to a whine - about the same volume as a brushed motor, but I had been expecting a dead hush...

I have one immediate question - how do you connect the ESC wires to the motor? The motor has a red, blue and white set of wires, the ESC just has three black wires. No wiring diagram was provided - does this mean you can connect any wire to any other wire? I enclose a shot to show what I mean...

Logged

dodgy geezer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,920
  • Location: London
Re: Recommendation for SMALL brushless....
« Reply #19 on: August 06, 2009, 12:32:06 PM »

You couldn't run a simple hobby brushless controller with 4 NiXX without a voltage cut-off.It would overheat to destruction.

How does that work? The cut-off is for LOW voltage, isn't it? Are you saying that a motor will be OK on 6volts, but will overheat if given 2v?

The only way I coulod see that happening is if the ESC stopped working at some low voltage, and this left one phase energised continuously (though that would be a poor ESC design).

Logged

stallspeed

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #20 on: August 06, 2009, 12:33:58 PM »

How does an audio amplifier work?
2v would need an N-channel bridge.

Simple brushless controllers have got the equivalent of three half bridges.
Top of page 1 shows the connection and the table shows how at 2.5 volt the resistance increases.
Logged

stallspeed

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #21 on: August 06, 2009, 12:43:25 PM »

that's three complementary half bridges with N and P
Logged

dodgy geezer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,920
  • Location: London
Re: Recommendation for SMALL brushless....
« Reply #22 on: August 06, 2009, 01:08:17 PM »

How does an audio amplifier work?

Um...lots of different ways? They tell me my Quad uses a clever triple cascade design. But I still have valve amplifiers here... :)


Simple brushless controllers have got the equivalent of three half bridges.
Top of page 1 shows the connection and the table shows how at 2.5 volt the resistance increases.

Yes, but the amperage has gone down. Aren't we talking about I2R heating here? I had hoped to save weight by using 4 cells, but if 6 is really essential I suppose I can squeeze them in...
Logged

OMK

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #23 on: August 06, 2009, 01:19:44 PM »

And so good that it had to be said twice.

Don't you just love repetition?
Don't you just love repetition?

Quote
Do the adverts tell you which type of P-ch transistor is fitted, and what are the types to avoid?

No, and BC109s.
Maybe better still, elbow the P-ch transistor and bung in a P-ch FET instead?

How does an audio amplifier work? Easy. It works in the same way as a radio. You start off with two wires, bung one of the wires away, then you end up with a wireless.
To make the audio louder you connect two loudspeakers in parallel; negative to negative and positive to positive, then connect both neg's and pos's to 240 a.c. and holler into loudspeaker #1, then wrap the green wire around your Tx antenna, about five or six turns. Don't worry about the inductive foldback loop issues because the yellow wire takes care of that.
Logged

andyn

  • Guest
Re: Recommendation for SMALL brushless....
« Reply #24 on: August 06, 2009, 01:25:52 PM »

How about Li-Po's instead? I have a suitable one for sale.
Logged
Pages: [1] 2 3   Go Up