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Author Topic: Recommendation for SMALL brushless....  (Read 10324 times)

dodgy geezer

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Re: Recommendation for SMALL brushless....
« Reply #25 on: August 06, 2009, 02:43:18 PM »

How about Li-Po's instead? I have a suitable one for sale.

I'm looking for a cheap, simple build, suitable for kids. The boat so far has £3 worth of balsa - probably needs another £1. Propshaft and rudder will be a few quid, and I was expecting a £50 radio. If I went for a conventional brushed motor that would be perhaps £4, with not much for batteries - I assume every house has a charger and 4 AA nicads. A speed controller, though, would be about £20-30?

A brushless motor, on the other hand, might be free if we use a CD-Rom, with £8 for a cheap ESC. I got a motor+ESC for £12. If this could be run off 4 nicads, we could have a very cheap system. Cheap LiPos would cost about £15, plus a charger?
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andyn

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malcolmfrary

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Re: Recommendation for SMALL brushless....
« Reply #27 on: August 06, 2009, 11:21:13 PM »

The CD motors that I have used in the past have all been brushed types, running on a fairly conventional ESC.  There may be a change in motor technology that I haven't run into yet.  I haven't taken one apart yet, but it could well be that floppy and hard drives may well contain brushless motors.  What their performance would be, who knows?
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jimtrellis

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Re: Recommendation for SMALL brushless....
« Reply #28 on: August 07, 2009, 09:46:50 AM »

So if I can try to pull all of this together -
•   Brushless motors and/or speed controllers aren’t very good at slow speeds without having a gearbox
•   Brushless speed controllers only work in one direction, so you can’t reverse the boat
•   If you just happen to have a spare CDROM drive then if the motor still works it might just be the right sort of motor (three “ifs” here)
•   The DIY kits from Micron all seem to be out of stock
•   You must avoid speed controllers with the wrong type of P-Ch transistors but you won’t necessarily know what type is fitted when you buy one
•   Lipo batteries are dangerous if they are allowed to go too flat and cheap speed controllers won’t stop that from happening
This does seem like a lot of different people all beating their own drums in different rhythms at the moment – very jumbled and confusing. If it’s all largely fact then there’s not much here that would encourage me to try a brushless motor yet. For those people who don’t make fast electric boats simplicity and reliability are important, as are slow-speed control and reverse.
I also wondered about the figures quoted, so I’ve looked at one popular website and found that a 7.4v 2200 mah Lipo and mains charger costs £35 while a 2400mah Nimh battery and mains charger is £13. That gives a price advantage of £22 in favour of the brushed motor when it comes to buying a speed controller. Also the Micron kit to make a small brushless motor is £6.60 while a 360 brushed motor can be bought for £3.50. I might not be the world’s best model boat builder but I can count.
I have seen models go with brushless motors and it is impressive if speed is your main concern. They do seem very limited in other ways, though. Perhaps when there’s more collective experience and therefore more agreed wisdom on this technology then a more even balance may be achieved.
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nick_75au

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Re: Recommendation for SMALL brushless....
« Reply #29 on: August 07, 2009, 11:29:51 AM »

No drum beating on my part or at least I dont think I have {:-{
Dodgy, any of the three wires can go in any combination, if the rotation is wrong swap two of the three wires :-))


I have a total of 2 brushless motors so I'm not an expert (drip under pressure?) but I have taken the time to understand what the different numbers mean.
 1 motor is high speed 3200Kv  and the other is low speed 1000 Kv, both outrunners same diameter as the CD style motor but longer which improves torque.
I use the 1000 kv on 6 volt gel cells in a Springer tug which achieves a massive 4.6 Kph the other motor was in a GG Miami crashboat on a 2.3:1 gearbox and 25 Kph on 10 Nimh cells. Not a Lipo in site

(well actualyIi do have 1 lipo which..... I happen to use on a brushed motor set up :o) I use it because its light not because its Lipo ;)

Im not sure about the overheating thing, for P12 (Aussie Keyboard, never found that pound symbol :D) why not suck it and see. work out the cutout so its the minimum and on Nixx. My bets are it will work on 4 cells. As far as I know most ESCs brushed or brushless need 6 volts or greater anyway so the BEC can work with some exceptions of course. On the Hobbycity website there are tiny brushless escs that will work on a single 3.7 lipo cell so will be happy on 3 Nixx cells as well

Jim, in same order as your post
" see above , Springer, I can set the motor so I can see the bell rotating,  lower Kv motor if slower speed is required
"I have a reversing brushless  esc, Mtronics produce  a 15 and 25 amp version, there are a number of others available, expect to pay the same as a good quality brushed ESC with reverse.
"CD rom motors work but not nearly as much torque as a hobby motor due to only having fridge magnets rather than Neo" magnets(yes I've tried)
"dont Know
"IHNFI short for I have no idea what that's all about
" Lipos will be damaged (not usually dangerous) by over discharging, most brushless escs have protection regardless of price, electronics are available for any ESC that doesnt, Lipos do require more care than other battery types but all batteries have dangers if mistreated

It makes no difference what type of battery you use for brushed or brushless motors your battery price comparison has nothing to do with what motor you use.

The confusion is perhaps because the brushless esc's tend to be aimed with Lipo's in mind, this is possibly due to the fact that most brushless systems are aimed at electric aircraft which benefit from the light weight of Lipo batteries

The Brushless basics thread is an excellent read.  http://www.modelboatmayhem.co.uk/forum/index.php?topic=13538.0

Regards
Nick

 
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dodgy geezer

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Re: Recommendation for SMALL brushless....
« Reply #30 on: August 07, 2009, 12:09:56 PM »


So if I can try to pull all of this together -


With a nod also to nick_75au - thanks for the useful tip...


I wanted to find out if Brushless was a good way to go for a simple cheap 'small boat' motor. My understanding, gleaned from this thread and a bit of research, is as follows.

Short answer - at the moment, probably no.

Medium answer - probably yes, in the future. At the moment the cheap market is entirely for aircraft, so you have to pay a lot for anything which isn't hi-power/lightweight/LiPo

Longer answer - Brushless motors are probably the way ahead. They are much more efficient and can be optimised for hi-torque or hi-revs. There is no reason why a brushless motor should not outperform any equivalent brushed motor; they can come in any size, and can easily be rewound for any specific application. They should be cheaper than brushed motors - they are simple: I can probably get, or easily make, an ideal brushless motor at the moment.

What I can't get is an ideal cheap brushless ESC. I might want to use 2 Nicads or dry batteries for a small motor, or a gel pack for long duration. All the cheap ESCs assume you are using LiPo batteries, and they have LiPo safety features built in, which means they will detect the initial battery voltage at switch-on, and cut out when this has dropped to about 70%.  Typically, they do not have reverse (though I don't see this as a huge issue. Also, I suspect the current ESCs would not like the motor to be stalled if, for instance, weeds are hit.  There is no reason why an ESC should not be designed which has better marine characteristics, but they are complex beasts, and they are only cheap because of volume hobby aircraft production. Ours will probably always be expensive...

So, if you want a fast power boat with LiPo batteries, lucky you. You can get a high performance unit cheaply.  If you want a little motor for pottering around, you either buy a simple brushed system, or do complicated things with gears and expensive brushless EScs which have reverse, and can be programmed to use different battery types...
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dodgy geezer

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Re: Recommendation for SMALL brushless....
« Reply #31 on: August 07, 2009, 12:32:18 PM »

The CD motors that I have used in the past have all been brushed types, running on a fairly conventional ESC.  There may be a change in motor technology that I haven't run into yet.  I haven't taken one apart yet, but it could well be that floppy and hard drives may well contain brushless motors.  What their performance would be, who knows?

Some useful things you can get from a dead CDRom....

1 - flat sheet metal
2 - flat and curved plastic
3 - an assortment of bolts/nuts
4 - 4 anti-vibration mounting grommets
5 - various electronic components and connectors
6 - micro limit switches (see picture)
7 - various good quality gears
8 - an IR laser diode, a magnetically-suspended lens mount, and a powerful magnet embedded in the CD mount (see picture - red)
9 - two small 12v brushed motors (for opening the cd-slide and moving the laser reader) See picture - blue.
10 - one small brushless 12v motor for spinning the CD (see picture - yellow)


I would agree with nick_75au - the brushless motor looks as if it will be lower performance than the hobby ones - it's not notchy at all, but it will probably also be dead quiet?

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jimtrellis

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Re: Recommendation for SMALL brushless....
« Reply #32 on: August 07, 2009, 12:50:49 PM »

So, if you want a fast power boat with LiPo batteries, lucky you. You can get a high performance unit cheaply.  If you want a little motor for pottering around, you either buy a simple brushed system, or do complicated things with gears and expensive brushless EScs which have reverse, and can be programmed to use different battery types...

It looks like we've arrived at the same point here. My thanks to the folk who've bothered to offer simple explanations. I'm still wondering about P-Ch transistors, half bridges and triple cascades, although I've concluded that they probably just cloud the issues and so are no business of mine.
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dodgy geezer

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Re: Recommendation for SMALL brushless....
« Reply #33 on: August 07, 2009, 01:34:52 PM »

It looks like we've arrived at the same point here. My thanks to the folk who've bothered to offer simple explanations. I'm still wondering about P-Ch transistors, half bridges and triple cascades, although I've concluded that they probably just cloud the issues and so are no business of mine.

The 'triple cascades' was me, was a tongue-in-cheek comment about audio amplifiers, and has absolutely nothing to do with ESC electronics.

Nick_75au's comments make a lot of sense to me. I am sure brushless are the way ahead - the issue at the moment is that the cheap ESCs are optimised for LIPo flyers.

The ESC is the equivalent of the commutator. Cheap motors just have a couple of brass strips touching three segments of copper. Once a multi-phase ESC becomes cheaper than two strips of brass all motors will go brushless - that probably means that we have to wait for a single-chip ESC. At modern speeds of development, that will probably be next month.....

I will continue trialling a cheap brushless with 4 cells, and perhaps rewind the CD-Rom motor, if I can find a wiring calculator... 
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dodgy geezer

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Re: Recommendation for SMALL brushless....
« Reply #34 on: August 09, 2009, 07:01:20 PM »

Well, I can report the first (short) trial of this brushless motor I am trialling to see if they will work for small models...

I first tried it with 4 NiCads. Stallspeed had commented that it probably wouldn't work with these, so I was not surprised to find that the ESC beeped, but otherwise did nothing. (Later I found that one of the NiCads was dud, so that was even less surprising)

Then I tried 6 Nicads. The ESC woke up and beeped a lot more at me. It beeped once, then once again. Then it beeped twice, then twice again. Then a pair of three beeps, and back to one again. I believe this is a standard feature of brushless ESCs - you're supposed to move the transmitter throttle at some point to program it. But there were no instructions with the item I bought, so I just moved the throttle at random. Suddenly, there was a single low beep, and the motor started.

The throttle response was, unsurprisingly, odd, given I did not know how to program it. One half of the throttle throw did nothing at all, then at half way the motor started and accelerated up to full when the stick was fully forward. Compared to a little brushed motor the power was phenomenal, and being delivered at higher revs. I was interested in the low speed regime, so tried to run it slowly, and found that I could. It would run at what I would call a medium tick-over - not a crawl, but quite slow, certainly lower than planing speed.

Getting this low speed was a bit tricky. It was only available at one or two click positions on my throttle, and the motor rapidly accelerated if I upped it a notch. If I put an excessive load on the motor with my fingers when running slowly it would stop, and then I had to return the throttle to zero before bringing the motor back up to speed again. Setting up the ESC is definitely a critical point for brushless operation.

I noted that my cheap ESC was specified as 'between 6 and 10 Nicads'. I could have bought one for 'between 4 and 8 Nicads' but at three times the price.

The noise was not high - it was quiet and vibration-free at low speeds, while a medium-pitched whine developed when I ran it fast. It was probably quieter than a comparable speed brushed motor.


So I am wondering whether to install this motor/esc pair at the moment. The motor will be fine for about half its range (when I have worked out how to set it up, but the boat will probably be grossly overpowered at the top half of the range, and there will be a need to strengthen the prop shaft mounting...
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stallspeed

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Re: Recommendation for SMALL brushless....
« Reply #35 on: August 09, 2009, 10:03:10 PM »

Did you switch on the boat with the throttle at the half way point?

However hard you try with transmitter settings you can't get down to a crawl with a cheap 3-wire brushless.
To do that you can gear down and yet still maintain the top range with a larger prop.

If slow speed is required something similar to the robotbirds gearbox is out your budget then you could purchase gears and make one.

If budget and weight is a priority you could chose a brushed 385 or 360 and six to eight high capacity pencells.
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dodgy geezer

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Re: Recommendation for SMALL brushless....
« Reply #36 on: August 10, 2009, 12:59:04 AM »

Yup - now I understand the basic programming set-up - had to find it on the net, though - nothing in the instructions...


I have still got a few things to try with brushless motors before going brushed...

Without a tach, I estimate that I can run this motor at 1000-2000 rpm on slow (no load). It will go slower with a load, but then I would probably want to up the speed a bit for safety. Unlike Brushed motors, the ESC will stop the motor if it's overloaded, and you have to drop to zero throttle to start it again. But 1500 rpm is quite slow...

I see quite a few 5-cell brushless escs advertised, and some 4-cells, though these are usually not at rock-bottom prices. Then there is always the option of rewinding a motor for a lower kv - I might try that with the cd motor I have. At the moment I would be happy with the slow speed I have, if only it weren't quite so damned powerful at top speed!

Budget, space and weight are the drivers - ideally I want to run on 4 cheap NiCad pencells. The original EeZeBilts ran on a 3 cell dry battery of 4.5v...
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stallspeed

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Re: Recommendation for SMALL brushless....
« Reply #37 on: August 10, 2009, 02:12:06 AM »

By a crawl I was meaning about 60 rpm with no load,That is possible with a brushed motor.

Rewinding will only effectively change the motor voltage.The same effect would be be more easily obtained by reducing the supply voltage.....that's if you can get hold of a controller.

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sunworksco

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Re: Recommendation for SMALL brushless....
« Reply #38 on: August 10, 2009, 05:51:19 AM »

Here is what I am using in my www.scaleshipyard.com 1/32nd Type IX-C Submarine.Runs cool,silent,slow scale speed,instant reverse/forward,battery miser,no gear reduction required,no bec required or noise cancellation resisters.
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nick_75au

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Re: Recommendation for SMALL brushless....
« Reply #39 on: August 10, 2009, 06:23:36 AM »

My Springer motor spins at 600 rpm with load, the boat barely moves at this speed so Im happy with my slow speed performance. Granted a sensored system will be better and will go slower, great for cars but not the cheap setup wanted for this project. Who runs props at 60 RPM?, maybe a paddle wheel perhaps
Nick
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stallspeed

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Re: Recommendation for SMALL brushless....
« Reply #40 on: August 10, 2009, 12:26:16 PM »

[
Who runs props at 60 RPM?, maybe a paddle wheel perhaps
Who runs props at 60 RPM?
model tugs when they have no tow line.
In relation to their size they have greater power which needs to be throttled back on occasion in relation to their size.
Quote
My Springer motor spins at 600 rpm with load, the boat barely moves at this speed
That is a factor of two improvement which could be achieved with a lower kv motor with more poles than dodgy's one.
Aye,just like a cdrom brushless. ok2

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andrewh

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Re: Recommendation for SMALL brushless....
« Reply #41 on: August 10, 2009, 12:54:48 PM »

DG

Rewinding CD-ROM motor - near infinite information in both the Gobrushless forums and on
http://www.rcgroups.com/electric-motor-design-and-construction-361/

If you need specific help - PM me and I will try and help.

Basically there are levels of mods to a CDROM as howked out of a computer:
  • Use as is - I find the same as you  - uncertain starting and poor low speed control
    Replace the magnets - you probably need 5x5x1 replacement rare earth magnets - easy and takes care of power and starting!
    Rewind to different KV - most CDROM motors arewound, I think for 12V so they have lots of turns and maidenhair wire.  For flying I rewind mine for 11 turns of fencewire, then use them in silly fast boats (not what you want)
    Replace the bushes with ballraces - not needed for your needs

So I think your best option is to change the magnets - let me know if you need help or would like to borrow a bell with hot magnets on to try.
andrew
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andrewh

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Re: Recommendation for SMALL brushless....
« Reply #42 on: August 10, 2009, 01:05:20 PM »

<<The Brushless basics thread is an excellent read.  http://www.modelboatmayhem.co.uk/forum/index.php?topic=13538.0>>

I would have to agree, wouldn't I :}

Any merit it has came from the wonderful Do-How contributions from Nick and others :}

THIS thread is interesting, too - you are asking a new and good question, DG - and doing the trials to get some foundations installed on the subject.  Thanks and well done!

Could you please post where you found the programming instructions for your ESC - I can see that being helpful to me and others

BTW - I mounted my bell-motor on an SHG 380 motor mount using self-tappers to hold the bulkhead mount to the upright bit, and the bell clears the base easily - its a straight drop-in replacement at least on my PT boat.

It may be worth bearing in mind - all of us that power produced by a prop is NOT proportional to the revs at all (probably a cubic function) - there may be little point in achieving VERY low revs, only low enough to reduce the resultant power to the low level you want.
andrew

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dodgy geezer

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Re: Recommendation for SMALL brushless....
« Reply #43 on: August 10, 2009, 05:55:06 PM »


Could you please post where you found the programming instructions for your ESC - I can see that being helpful to me and others



No problems - I just googled on 'Brushless esc Beep' to get quite a lot of data - here are some example instructions:

http://www.2dogrc.com/ecommerce/os/catalog/Documents/Xcontroller.pdf
http://www.beatyourtruck.com/bytstore/index.php?main_page=product_info&products_id=232&zenid=502a01688fc65ac9728a3dc1e94a3219
http://www.bphobbies.com/pdf/bp/BP-60A-ESC.pdf
http://www.horizonhobby.com/ProdInfo/Files/20

It ought to be easy to make a brushless motor creep - they are pretty similar to stepper motors, which can go very slowly. I suppose the most common escs are just designed for high revs. Perhaps if we treated them like a stepper motor and used a stepper driver....
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dodgy geezer

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Re: Recommendation for SMALL brushless....
« Reply #44 on: August 10, 2009, 06:04:47 PM »

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stallspeed

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Re: Recommendation for SMALL brushless....
« Reply #45 on: August 10, 2009, 06:54:40 PM »

It ought to be easy to make a brushless motor creep - they are pretty similar to stepper motors, which can go very slowly. I suppose the most common escs are just designed for high revs. Perhaps if we treated them like a stepper motor and used a stepper driver....
It is impossible to make your 3-wire brushless motor creep.There is no back emf feedback at low revs.If you want creep with brushless you have to use a sensored motor/controller combo.

You couldn't use a stepper motor driver as brushless windings are too low a resistance and the windings are in threes.Cdrom motors have three hall sensors.You could use a sensored brushless controller chip but there are complications there too.

How many pencells do you want to use in total?
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andrewh

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Re: Recommendation for SMALL brushless....
« Reply #46 on: August 10, 2009, 07:41:46 PM »

I'm only a simple mechanical engineer, but it seems to me that if you feed the beast slow pulses you will get slow rotation to follow the pulses - exactly the same as a stepping motor.  there is no need for locking or position holding - there is a strong magnetic "notch" which will hold the position between pulses

Worth a try, anyway.

The Hall sensors are there for speed control, because the CDROM duty is quite different to our DG's requirement and. for that matter, mine.
andrew
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stallspeed

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Re: Recommendation for SMALL brushless....
« Reply #47 on: August 10, 2009, 09:41:13 PM »

I'm only a simple mechanical engineer, but it seems to me that if you feed the beast slow pulses you will get slow rotation to follow the pulses - exactly the same as a stepping motor.
Despite some physical similarities in the motors,the controllers don't work the same way.

If dg wants slow speed brushless control and willing to consider stepper motor circuits then sensored cdrom drive,using the hall sensors and the IC's meant for the purpose, is the logical path for future experiments.
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dodgy geezer

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Re: Recommendation for SMALL brushless....
« Reply #48 on: August 10, 2009, 10:48:16 PM »


If dg wants slow speed brushless control and willing to consider stepper motor circuits....


I drive one of the axes of my telescope using an L293D driven by a PIC16Fnnn - I supose all I need to do is code that up to go faster (though that is a bi-polar driver..).  There is probably a practical speed limit on the top speed for the telescope stepper driver circuit based on the clock speed of the PIC. I wonder what the limiting factor is which determines the slow speed for these three-phase drivers? You would think it was quite possible to put out a pulse every 1/10th sec or so...?
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stallspeed

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Re: Recommendation for SMALL brushless....
« Reply #49 on: August 10, 2009, 11:21:18 PM »

I meant if you are going to the bother of rigging up your own controller you may as well use the correct chips when they exist.
You wanted two pencells for the motor and  I presume you have four for a receiver so why not just use six on a brushed bec esc with a 360 or 385?

Your present brushless controller works at a fixed frequency of 8kHz but changes the duty cycle
The limiting factor is the driver or controller cannot pick up back emf at low brushless rpm.

For low speed control,you need feedback sensors,whether hall effect or optical encoder, for the controller to perform the commutation electronically.The coloured cables on the Novak rock crawler motor are the sensor wires.




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