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Author Topic: Which is positive?  (Read 3403 times)

oldflyer2

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Which is positive?
« on: December 12, 2016, 04:57:37 PM »

I just received two of these today. I need to know which side is positive?

Thanks

Tom
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Big Ada

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Re: Which is positive?
« Reply #1 on: December 12, 2016, 05:02:03 PM »

I do not think it matters, if the motor goes the wrong way round, swap the wires over.
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oldflyer2

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Re: Which is positive?
« Reply #2 on: December 12, 2016, 05:19:57 PM »

Thanks ... I will try them both ways and see if one way is faster than the other. They are going in a belt drive system for the Darby hull tug project.
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Stan

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Re: Which is positive?
« Reply #3 on: December 12, 2016, 05:38:06 PM »

Full spec  for the M F A RE 800 motor. Brushed motors always run slower in one direction. If you are not happy with the speed like the last post said just switch over the cables connecting the motor. Hope this helps if you have any further problems you can e/mail M F A Como they have a technical dept.

Stan
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John W E

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Re: Which is positive?
« Reply #4 on: December 12, 2016, 05:51:02 PM »

HI THERE

Sometimes I have seen a red dot on the nylon insulation, next to the electrical terminal - I have always taken that as the positive.

If everything else fails you can follow the advice of above.

John
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tugnut

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Re: Which is positive?
« Reply #5 on: December 12, 2016, 06:03:36 PM »

Hi Tom i have just fitted two into my new tug like the others said ether way :-)) .
My Mr Darby is the next  Build.
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tugmad

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Re: Which is positive?
« Reply #6 on: December 12, 2016, 06:23:25 PM »

That looks very neat Bro.👍👍
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oldflyer2

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Re: Which is positive?
« Reply #7 on: December 12, 2016, 07:42:09 PM »

Thanks for all the info. I double checked and there is no red dot on either of them, so I will try both ways and see which is the fastest.

Tugnut, do you have a complete Darby kit or just the hull?

Tom
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tugnut

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Re: Which is positive?
« Reply #8 on: December 12, 2016, 07:48:39 PM »

The Hull and the wood pack some of the fittings are missing so i will make my own.
I am finishing this one and then i will start on her.
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RAAArtyGunner

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Re: Which is positive? (Does it matter)
« Reply #9 on: December 12, 2016, 09:06:11 PM »

Full spec  for the M F A RE 800 motor. Brushed motors always run slower in on direction. If you are not happy with the speed like the last post said just switch over the cables connecting the motor. Hope this helps if you have any further problems you can e/mail M F A Como they have a technical dept.

Stan

Off on a tangent.
With the two motors, one clockwise the other anti clockwise, controlled by one ESC is the difference in speed discernable.
Would using two ESC's via one joystick be the same, whereas tank steering negates any differences as individual control/corrections can be applied.
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Peter Fitness

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Re: Which is positive?
« Reply #10 on: December 12, 2016, 09:11:28 PM »

It may depend on individual motors, but a couple of my boats have two motors on one ESC and I have not noticed any indication that one motor was running faster than the other. Even if that were to happen, an adjustment of the rudder trim should correct the problem.


Peter.
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RAAArtyGunner

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Re: Which is positive?
« Reply #11 on: December 12, 2016, 09:24:26 PM »

It may depend on individual motors, but a couple of my boats have two motors on one ESC and I have not noticed any indication that one motor was running faster than the other. Even if that were to happen, an adjustment of the rudder trim should correct the problem.


Peter.


Yes, was thinking about that as no boat would run straight and true without some control

My Billings Samson II has two motors on one ESC.
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oldflyer2

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Re: Which is positive? (Does it matter)
« Reply #12 on: December 12, 2016, 10:43:23 PM »

Off on a tangent.
With the two motors, one clockwise the other anti clockwise, controlled by one ESC is the difference in speed discernable.
Would using two ESC's via one joystick be the same, whereas tank steering negates any differences as individual control/corrections can be applied.

That is a good question. When I get this all set up I will be using an Action controler that will do both motors on one stick. I'll see what happens there when I get it running.

Tom
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oldflyer2

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Re: Which is positive?
« Reply #13 on: December 12, 2016, 10:45:03 PM »

Hi Tom i have just fitted two into my new tug like the others said ether way :-)) .
My Mr Darby is the next  Build.

Have you run the motors in yet?  Did you alter the belt tension at all and did the motors get warm. I have read several places where the belt tension had to be let off a bit.

Tom
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NFMike

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Re: Which is positive?
« Reply #14 on: December 12, 2016, 10:48:43 PM »

The way these small motors are built they should run the same speed either way. However, they often sound different in one direction from the other.
The coloured dot is probably more for production use, so that an assembler can get the wires the right way round and the testers don't have to change 50% of them.

derekwarner_decoy

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Re: Which is positive?
« Reply #15 on: December 12, 2016, 11:35:12 PM »

Tom......the pair of carbon brushes in these series of motors will bed in with a slight angle to the commutator irrespective of the initial direction & wiring setup.....so when each motor is reversed, both will provide light arcing and so make an apparent difference in audible signature

Irrespective of the change is sound, I would be surprised that any real differences in prop shat RPM would be evident

One of those $15.00 digital laser tachometers will confirm what is happening....[irrespective of any difference in motor sound] ....considering the total cost of motors ESC and the potential to trial different size/pitch propeller's....the $15.00 cost for the tachometer is the cheapest form of a diagnostic tool.......and take away any misconceptions of drive noise

Automotive air fan motors are a totally different proposition....they are designed to be used as singular direction and have a single ball [bearing ball] the armature shaft is pulled in by EMF in the intended singular direction to provide the air flow

When these motor are reversed, the armature floats in a longitudinal manner as the thrust is not contained against the ball

Derek




 
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Derek Warner

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oldflyer2

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Re: Which is positive?
« Reply #16 on: December 13, 2016, 02:00:07 AM »

Thanks Derek

I have been meaning to get one of those tachs for a while. I'll look for one around here.

Tom
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tugnut

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Re: Which is positive?
« Reply #17 on: December 13, 2016, 08:01:41 AM »

Have you run the motors in yet?  Did you alter the belt tension at all and did the motors get warm. I have read several places where the belt tension had to be let off a bit.



Hi Tom i have run them slack if they are to tight they are noisy

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Colin Bishop

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Re: Which is positive?
« Reply #18 on: December 13, 2016, 11:16:09 AM »

If the motors are identical and they do have a tendency to run better in one direction than the other then surely the only way you will get equal performance is to have both props of the same hand and that will cause other problems. (unless of course you could take the drive off the other end of one of the motors which I don't think is possible with these.)

I doubt very much that it will have any noticeable effect at all in practice.

Colin
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derekwarner_decoy

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Re: Which is positive?
« Reply #19 on: December 13, 2016, 11:58:55 AM »

Tom...so as not to confuse.........could I suggest  %)

1. get both new motors mounted down to a temporary bench board
2. mark the motors respectively port & stdb
3. wire the motors with your preferred counter rotating orientation set for FWD movement
4. run the motors for a few hours on a regulated power supply at a nominal 1/4 to 1/3 of the planned final voltage

This will bed in each set of carbon brushes in the respective motors which now have a preferred rotation direction for FWD movement, however with each motor rotating in opposite directions

As an alternate to this, use the digital tachometer to check shaft speed of both motors  in both directions  ...if you have an amp meter of sorts, this could be used to better understand the motors performance and efficiency

The data sheet suggests these motors have a 6.35 mm diameter output shaft, however with an equal length output shaft at either end. From this you could consider mounting the motors with the commutator at opposite ends and using the opposite output shafts as the connection for the prop shafts 

This will have no effect or impact if you do decide to later install belt drive reductions to the build

Derek
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g6swj

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Re: Which is positive?
« Reply #20 on: December 13, 2016, 02:07:19 PM »


This will bed in each set of carbon brushes in the respective motors which now have a preferred rotation direction for FWD movement, however with each motor rotating in opposite directions

Derek

Is not the reason a brushed motor may run faster in one direction than the other simply due to the relative positioning of the fixed magnets and the commutator? Without moving the relative positions (magnet vs. commutator) the motor will always have the same characteristics regarding preferred direction of rotation as the time of manufacture unless modified simply due to the time the electro magnetic field is activated and the position of the magnets to that electroc magnetic field?


Quote
It's due to the timing of the commutator (which on a DC motor affects the timing of the magnetic field generated on the rotor).
 
 It's usually advanced on one side by a certain angle to cause the motor output to be higher for a certain rotation direction. That's most likely what you're seeing here.
 
 The motor in reverse would see a retarded timing - which translates to lower output.
 
 In RC car racing back when brush motors were the common motor racers would adjust the timing on some of the motors to get even higher output than previously possible without changing anything else. (and in some racing classes this was considered cheating)
 
 You will also notice this on some (most?) drills - usually unscrewing is slower by a reasonably noticeable amount - although the difference in the noise is usually the big give away.

Regards
Jonathan
 
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oldflyer2

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Re: Which is positive?
« Reply #21 on: December 13, 2016, 02:49:53 PM »

Hi Derek

My digital tach is "in the mail" and will be here just after christmas.

These motors are going to be in belt drive assemblies. On first assembly, the belts in these units are too tight so I am going to put the bearing blocks in the mill and skim off a thou or two and reassemble them. Once they are to my liking, I will set up as you suggest and run them in for a few hours. That should loosen up the belts a wee bit as well.

Tom
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boatmadman

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Re: Which is positive?
« Reply #22 on: December 13, 2016, 05:31:16 PM »

Blimey, bit of overkill going on here!
These motors, if indeed they do run at different speeds depending on direction, are not exactly highly specified and high tolerance units!
Does it matter if there is a slight difference in speed? I say not.
Running in? waste of time, just fit them and use them, for this kind of service they should outlast your lifespan.
Belt tension? Not too critical on those type of belts, all you need is to be able to move the belt towards the motor centre line a couple of mm when pressed halfway between the two belt wheels.
Alignment? Always critical, take time to get it as close as you can.
Ian
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oldflyer2

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Re: Which is positive?
« Reply #23 on: December 13, 2016, 05:44:03 PM »

Ian, these belt drives as supplied have no slack whatsoever in them, and running one yesterday while holding it in my hand got quite warm after only 3 minutes. By shaving the bearing block just a whisker, it will give that 2mm or so that is required.

The rest of it is probably not required, but my batteries need cycling over the winter anyway so I may as well give them something to do.

Tom
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malcolmfrary

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Re: Which is positive?
« Reply #24 on: December 13, 2016, 09:28:22 PM »

Brushed "competition" moors have their brush timing tweaked or tweakable to optimize performance in one direction.  Ordinary everyday motors do not do this, they are designed to run equally either way.  Any differences are down to manufacturing tolerances - trueness of bearings, strength of magnets, all manner of stuff like that. 
The red dot is there to give you the required clue to enable the motors to be wired correctly, and give a reminder or act as a reference when rewiring or replacing a motor in a setup that has been known to work properly and still have the new motor rotate the same way as the old one.  The loading in one direction or the other by any external considerations probably has more effect than anything in the actual motor.
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