Adding hall sensors to outrunners

[olaf-lampe]

Ysterday I had my first problem with fitting Hall sensors to an outrunner. So far I've done several low Kv wound, wye connected motors, with internal Hall sensors fitted in every fourth slot (so 120 degree spacing - these were 12 slot stator, 7 pole pair rotor, motors). All have worked very smoothly with masses of low speed torque.


You can just see the three Hall sensors set into slightly widened stator slots and glued in with epoxy.

Where exactly did you place the halls? Between the two Aa Bb Cc teeth? Would it help to place them 2 teeth further back ( or forth?) Would be 60 dgree difference


After a bit of playing around, I found that the roughness and cutting out problem was indeed caused by the Hall timing being out. This motor doesn't like running on internal sensors at the neutral position, as I needed to shift the timing by around 10 degrees from neutral (physical, ~ 70 degrees electrical) to find a point where the motor would run smoothly and accelerate cleanly .

Jeremy

[Jeremy Harris]

Where exactly did you place the halls? Between the two Aa Bb Cc teeth? Would it help to place them 2 teeth further back ( or forth?) Would be 60 dgree difference

I can't see why it should make a difference as to which slot the Halls are in, as their placement is relative to the edges of the magnet passing any stator slot, isn't it?

In the past I've just picked any random set of three slots at 120 deg to each other and it's worked fine.

Jeremy

[olaf-lampe]

Where exactly did you place the halls? Between the two Aa Bb Cc teeth? Would it help to place them 2 teeth further back ( or forth?) Would be 60 dgree difference

I can't see why it should make a difference as to which slot the Halls are in, as their placement is relative to the edges of the magnet passing any stator slot, isn't it?

In the past I've just picked any random set of three slots at 120 deg to each other and it's worked fine.

Jeremy

You're right Jeremy,
it isn't that important, but doesn't it make it easier to determine which hall corresponds to which phase?
For you it's not the first motor to mount halls on, so I guess you have a certain wiring-pattern, that always works?

-Olaf

[Burtie]

I cant quite work this out

Assertions (please correct me if wrong), Assuming 14 magnet, 12 slot motor driven by a 6 step controller:

1) The hall sensors respond to the position of the 14 magnets on the can.
2) Consider the symmetry of the magnets around the can. If we rotate the hall group by 51.4 mech deg (360 electrical deg), we would expect everything to work the same.
3) going a bit further, If we rotate the hall group by any multiple of 60 electrical deg (then sort out the wiring), everything should still work the same. (Because we use a 6 state controller.)
4) However, if we rotate the hall group by 1 slot, that is 30 mech degrees = 210 electrical degrees

Problem is that 210 is not a multiple of 60, so the timing must have changed by + or - 30 electrical degrees ??

Burtie

[gtadmin]

One's moving 1/7 of 360, the other 1/12 (stuffed that twice ), so the second will almost always be out of step with what's required.

[Jeremy Harris]

I cant quite work this out

Assertions (please correct me if wrong), Assuming 14 magnet, 12 slot motor driven by a 6 step controller:

1) The hall sensors respond to the position of the 14 magnets on the can.
2) Consider the symmetry of the magnets around the can. If we rotate the hall group by 51.4 mech deg (360 electrical deg), we would expect everything to work the same.
3) going a bit further, If we rotate the hall group by any multiple of 60 electrical deg (then sort out the wiring), everything should still work the same. (Because we use a 6 state controller.)
4) However, if we rotate the hall group by 1 slot, that is 30 mech degrees = 210 electrical degrees

Problem is that 210 is not a multiple of 60, so the timing must have changed by + or - 30 electrical degrees ??

Burtie

Glad it's not just me that finds the concept of 7 magnet pole pairs and 12 slots mildly confusing at times!

The Hall angular position datum is relative to the stator, as the Halls trigger commutation. The timing is relative to the magnet position. This means that the Hall sensors need to provide either 120 electrical degree or 60 electrical degree (relative to the stator) outputs. Because all slots are the same, in effect, the three Halls can be placed (at the correct angular spacing) relative to any of the 12 slots.

Timing variation is relative to the magnet pole passing position, so is angularly related to 360/7 per cycle, rather than 360/12 per cycle.

Jeremy

[gtadmin]

Glad it's not just me that finds the concept of 7 magnet pole pairs and 12 slots mildly confusing at times!

The Hall angular position datum is relative to the stator, as the Halls trigger commutation. The timing is relative to the magnet position. This means that the Hall sensors need to provide either 120 electrical degree or 60 electrical degree (relative to the stator) outputs. Because all slots are the same, in effect, the three Halls can be placed (at the correct angular spacing) relative to any of the 12 slots.

Timing variation is relative to the magnet pole passing position, so is angularly related to 360/7 per cycle, rather than 360/12 per cycle.

Jeremy

Yes, that's what I meant, but much more eloquently expressed by Jeremy

[Jeremy Harris]

You're right Jeremy,
it isn't that important, but doesn't it make it easier to determine which hall corresponds to which phase?
For you it's not the first motor to mount halls on, so I guess you have a certain wiring-pattern, that always works?

-Olaf

I always use a 'scope and a sensorless controller to find which wire is which, after I've wired up the motor. I don't bother to try and trace the windings and find out which Hall corresponds to which phase wire by inspection, as it's too much like hard work!

The technique I use is to power the motor with a sensorless controllers at a reasonable rpm, then I connect one scope channel to one of the motor phase wires and the other to Hall wires in turn (with them connected to pull-up resistors). It's then usually easy to see which Hall has edges that align with the phase switching point. By going through each phase in turn I can quickly determine which Hall corresponds with each phase. If I also note which direction the motor is turning, I can correctly label them so that I can then hook the motor up to rotate in either direction. My hack sensorless controller already has the three phase wires labelled, which makes life easier.

Jeremy

[olaf-lampe]

OK ,
I just ordered a 2 channel scope. Always wanted one, but never had a real reason. I hope it'll arrive soon, time is running out...
-Olaf

[Burtie]

...The Hall angular position datum is relative to the stator, as the Halls trigger commutation. The timing is relative to the magnet position. This means that the Hall sensors need to provide either 120 electrical degree or 60 electrical degree (relative to the stator) outputs. Because all slots are the same, in effect, the three Halls can be placed (at the correct angular spacing) relative to any of the 12 slots.

Timing variation is relative to the magnet pole passing position, so is angularly related to 360/7 per cycle, rather than 360/12 per cycle.

Jeremy

Thanks for the explanation Jeremy and gtadmin.
I just had a feeling that the stator slots were not all exactly the same for a 14 mag DLRK motor, since half of them are between different phases and half are in the center of a phase.

For Aa we would have in-phase, but opposing stator poles either side of the slot.
For ab we would have stator poles which were 120 deg out of phase either side of the slot.

If this were the case, the rotational symmetry for the stator would be every two slots i.e. 360/6 =(60 mech deg).
So it might make a difference which slot you choose as your timing datum.
I wonder if this could explain why your most recent motor conversion did not run very well when you randomly chose the slots.

If this were the problem, it may have shown when you looked at the Phase / Hall signal correlation during the setting up
with the sensorless controller.

I probably need to go and read some books on electrical machines...

[Burtie]

I did a bit of surfing and found this link:

http://groups.yahoo.com/group/lrk-torqu ... sage/12567

Here is a snip from the page, about half way down:

"
..From what I remember, on my distributed LRK motor, I put the sensors between the
two teeth that were wound with the same phase when in Delta and between teeth
from 2 different phases when in Wye...
..hope that helps

-ryan
"

This would seem to support the theory that there is a net 30 e degree phase shift between using 'same-phase' and 'different-phase' slots for hall placement.

ryan = (ES) Biff ??


Burtie

[Biff]

yep, thats me.

What you posted is correct, you put the hall sensor between teeth of the same phase if in delta. and make sure you put it between same direction wound pairs between teeth as well. So if you put it between the Aa pair, make sure you put the other two between Bb and Cc pairs rather than bB and cC pairs, otherwise you will get 60deree. That is just using my mental picture so I could be a little off on that, you also have to get the sensor in between the right pair of teeth for the direction you put in the sensor, otherwise it will be 180degrees out, if that is the case, leave it in the same place, but just flip the sensor over to the other side to get it to 0degrees. If you want to hook up in WYE, you put the sensor between teeth of different phases, that advances the timing by 30degrees, you will still have to figure out which hall sensor goes into which input, either by trial and error, or scope it out.

Now comes the complicated bit. If you angle the sensors a bit you can advance or retard the triggering, advancing is good, retarding is bad, you need to advance the timing as frequency increases to counteract the increased impedance due to inducance of the coil. In many peoples experiance, actually advancing the hall sensor 30 degrees by putting it in the position for WYE connected motors, but actually connecting the motor in delta, produces better power at high speed than if the hall sensor were in its 0degree advanced position.

That problem should be fixed by using a smart controller, or something like burtie's timing adjuster, which is designed to compensate for inductance (hence more advance as speed increases). Read about that here if there isn't a link already in this thread viewtopic.php?f=2&t=19054

I have always had an oscilloscope to help me place my hall sensors so I don't have any tips on proper positioning without using a scope.

To figure out what the phase angle between teeth is you use the magnet / tooth ratio, for LRK that is typically 7 magnets for each 6 teeth, so since there is an odd number of magnets, you get 180degrees electrical difference equally divided by 6 teeth, so therefore each adjacent tooth is 30degrees different.

-ryan

[Jeremy Harris]

Thanks for that, Ryan, looks like I just got lucky with all the other motors I'd modded this way and unlucky with the 6374 I did at the weekend.

Jeremy

[olaf-lampe]

Thanks Biff for the summary,
I can imagine how difficult it must be to find out the Aa or aA winding in an already wound HK motor.
Once you've found out where the first hall has to come, it automatically fulfills the 'Aa,Bb,Cc'-rule when the other halls were placed in a 120degree/4slots distance.
I'm glad, I mark my handwound stators with the winding-pattern. Makes it easier to follow the 'rules off hall placement'.

-Olaf

[Burtie]

+1
Yes thanks Biff for all the very useful information. You have cleared up some thoughts that have been nagging me for a while.

..I can imagine how difficult it must be to find out the Aa or aA winding in an already wound HK motor.

-Olaf

I agree Olaf, this could be a bit of a problem.

One method I have used, is to energise a pair of phase wires with 2 or 3 DC amps, and then examine the field produced by each stator pole using a magnetic compass.

This is not the easiest thing to make sense of if the windings are terminated in delta, or wye, but it does give some useful clues.

Edit:
Update- Here is a practical demo using two sets of halls in adjacent sets of slots on an 80-100
viewtopic.php?f=30&t=15686&p=526585#p526585

Burtie

[Biff]

Thanks for that, Ryan, looks like I just got lucky with all the other motors I'd modded this way and unlucky with the 6374 I did at the weekend.

Jeremy

Yep, just unlucky. Since you can actually advance the electrical signal quite a bit and the motor will still work at low speed and work better at high speed, you really can put the hall sensors almost anywhere (as long as they are all 120deg electrically apart) and find a combination that gets the motor working.

[bobc]

I am looking to modify a large "scorpion" outrunner for hall effect sensor operation. Couple of issues with this: 1) the motor has 18 stator poles and (I think) 20 magnets; and 2) being an "upmarket" type of motor, it seems to have a much better magnetic circuit in the bell. The upshot of this is that very little flux leakage occurs - ferrous items simply don't stick to the outside. Compared to the big turnigy that catches any nut or screw I drop...
The problem is that I've managed to convince myself that external hall sensors are the way to go; better than internal in that
1)easy timing adjustment
2)no grinding of stator
3)no routeing issues with sensor wires
4) less work (I need a lot for my project)
and sensorless operation seems to be unreliable below 10% speed
I'll make up a jig with 3 sensors at 60degrees mechanical on the outside & see what the signals look like; but I do fear the signals will be noisy. (60degrees signals is a single signal inversion away feom being 120degrees signals, but far more attractive mechanically! Or I could just fit the middle sensor upside down??) Originally I thought the halls could be right next to each other - getting the 120degree phasing from a single magnet... but this thread has shown the error of that assumption!
By the way - the project will have quite a lot of motors in fairly close proximity, which will also screw about with external fields... (90mm centres, 65mm rotor diameters)

[Biff]

I'll make up a jig with 3 sensors at 60degrees mechanical on the outside & see what the signals look like; but I do fear the signals will be noisy. (60degrees signals is a single signal inversion away feom being 120degrees signals, but far more attractive mechanically! Or I could just fit the middle sensor upside down??) Originally I thought the halls could be right next to each other - getting the 120degree phasing from a single magnet... but this thread has shown the error of that assumption!

You can glue the same number of magnets to the outside of the can as there are inside and use those for position sensor, you can use any sort of little magnet as long as each side only has one pole. I am pretty sure someone already mentioned that in this thread, I am just to lazy to try and find it. I think the flexible magnets (like you would put on a fridge) have south and north poles on the same side, so they won't work. Use a compass to make sure you alternate positions. To figure out the mechanical spacing between sensors, use the following logic/math.

each pole pair is 360electrical degrees
If you have 20 magnet poles in the rotor, that gives you 360degrees electrical is 18degrees mechanical. or 1degree electrical is 0.05degrees mechanical.

That means that 120degrees electrical is 6degrees mechanical. So as long as you put your sensors multiple of 6degrees apart from each other, you will get some form of 120 degree commutation, There is a little bit more to it to make sure that they are all in the proper phase, but if you keep them all equally spaced, it should work. The 60deree separation that you proposed should work fine, but something that comes out of the above calculation is the precision that you have to have on your sensor placement. If you are out by 2 mechanical degrees, you have just moved your timing out by 40electrical degrees, so when you built your sensor mount, you need to ensure that the sensors are accurately placed relative to each other.

-ryan

[JEB]

There was some time ago a plastic film with magnetic particals in it, in a window on a paper card, placed on a magnet you could see the shapes of the magnet flux.

[Biff]

There was some time ago a plastic film with magnetic particals in it, in a window on a paper card, placed on a magnet you could see the shapes of the magnet flux.

Yep, something like this

http://www.teachersource.com/Electricit ... rCard.aspx

Or it looks like you can make your own.

http://www.instructables.com/id/3D-Magn ... ld-Viewer/

[Ludo91]

Hi, exactly what hall sensor have you used? may you tell me its specific code so I can look it up on DigyKey?
thankyou so much

[Jeremy Harris]

Hi, exactly what hall sensor have you used? may you tell me its specific code so I can look it up on DigyKey?
thankyou so much

I've used Honeywell SS411A sensors and found them to work very well.

Jeremy

[Ludo91]

extremely fast reply! thnakyou so much dude

edit: have you tried those sensor both glued between stator poles and outside the motor`s can?

[Jeremy Harris]

extremely fast reply! thnakyou so much dude

edit: have you tried those sensor both glued between stator poles and outside the motor`s can?

Yes, they work fine either internally or externally, no problem.

Jeremy

[olaf-lampe]

Yesterday I got my two channel scope and checked the hallsignals of my first sensored colossus.
At first I was dissapointed, because the scope didn't show anything on the halls output, but then I remembered Jeremy mentioned pullup resistors
FYI; I glued the sensors upside down in the slot between two twin tooth. ( should be OK for Delta ) I thought it was easier this way, because the 45°edges of the sensorfront snugs neatly in the slot.
But I couldn't find a matching phase. Either the halls were advanced, retarded or 180° shifted. Maybe that's another reason why the motor is so noisy ?

On my second motor, I glued the halls face up between two phases and wired it in wye. What a difference! Not only the hallsignals matched the phases. The motor only has a 0.1A no load current at 46V, spinning with 800rpm. And it's quite powerful. If it wasn't built for an airco-compressor drive, I would use it with a single reduction on my recumbent!

t80-85_100t_w_halls.jpg (127.22 KiB) Viewed 773 times

-Olaf