Building a triple stator axial flux motor

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Lebowski   1 GW

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Building a triple stator axial flux motor

Post by Lebowski » Dec 22 2012 8:18am

This winter I'll try to build a triple stator axial flux motor for my 'wheelchair' (what my GF calls the recumbent :D )
It's basically v2 of the motor shown here:
http://endless-sphere.com/forums/viewto ... 96#p434496
This motor is on my daily commuter, has done 2000 km and, through the ice, snow
and rain, has not let me down. Power is about 1 kW, delivered straight to the rear wheel.

The plan for the wheelchair is to use the motor to drive the cranks and to have full
benefit of the bikes gears. Power will be around 1.5 to 2 kW. The motor will cool
itself when it spins, this works really well in v1 and will be improved a little bit for v2.
Hopefully it'll be able to deliver 1.5kW continuously...

It's not really difficult to build a motor like this and you don't need any special tools
or anything like that. What you need is access to the basic materials and to be able
to drill and saw accurately (like what they tought you in kindergarten).

Main tools I use for this build (just to show that you too can do this :D) :
DSC01084.jpg
basic drill press
DSC01084.jpg (73.12 KiB) Viewed 15810 times
DSC01086.jpg
jigsaw
DSC01086.jpg (62.46 KiB) Viewed 15810 times
The raw materials:
DSC01078.jpg
sheet aluminium (5mm thick), sheets of galvanised (magnetic) iron (1mm thick). About 20x20 cm
DSC01078.jpg (83.83 KiB) Viewed 15810 times
DSC01077.jpg
magnet wire, 0.8 mm thick
DSC01077.jpg (57.26 KiB) Viewed 15810 times
DSC01083.jpg
good quality, strong, slow-curing epoxy glue for stator
DSC01083.jpg (100.07 KiB) Viewed 15810 times
DSC01082.jpg
5mm acrylic glass plates for stator
DSC01082.jpg (69.8 KiB) Viewed 15810 times

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Lebowski   1 GW

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Re: Building a triple stator axial flux motor

Post by Lebowski » Dec 22 2012 8:37am

The motor will have 9 stator windings and 10 magnetic poles. This is dictated by the outter dimensions
of the motor. The wheelchair will fit a 192x192mm motor, keeping this in mind 9 coils of 4 cm diameter
fit perfectly.

Magnets are 25 mm diameter, 7 mm thick: http://www.supermagnete.ch/eng/S-25-07-N

Professionally done design CAD drawing:
DSC01076.jpg
DSC01076.jpg (95.22 KiB) Viewed 15802 times
I started with the nastiest bit, the pieces that connect the rotor to the axle. First I centered
all the plates for the rotor with a 2.5 mm drill. To scratch circles in the aluminium I use:
DSC01080.jpg
DSC01080.jpg (59.69 KiB) Viewed 15802 times
A good rule to work by is to keep the 2.5mm center hole until the very end, and to cut the
outside of whatever you're making first. Then you'll always be able to use the center until
the very end. In v1 i didn't do this so, the rotor is not exactly in the middle but luckely it'll do 1000rpm
quite smoothly.
The axle with half-finished connector pieces:
DSC01079.jpg
the axle is a deore bicycle axle. Using the rear wheel axle gives you a freewheel and easy attachement of sprockets
DSC01079.jpg (71.54 KiB) Viewed 15802 times
Note how the 16 3mm holes in the connector pieces are offset over 11.25 degrees. This so the 4
6mm holes line up when the pieces are attached to the axle (small screws through the spoke holes).
The center holes were sawed with the jigsaw. Use a sharp metal blade and it'll go through 6mm
aluminium like butter.
DSC01088.jpg
one of the finished connector pieces
DSC01088.jpg (71.74 KiB) Viewed 15802 times

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Re: Building a triple stator axial flux motor

Post by salty9 » Dec 22 2012 9:00am

Lebowski wrote: It's not really difficult to build a motor like this and you don't need any special tools
or anything like that. What you need is access to the basic materials and to be able
to drill and saw accurately (like what they tought you in kindergarten).
Looking good. I often wish for better tools but find that ingenuity is the best tool of all

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Re: Building a triple stator axial flux motor

Post by Arlo1 » Dec 22 2012 10:04am

COOL.
Does your project need a high performance motor drive, battery charger or other power electronics developed? Let's talk!
www.powerdesigns.ca
Leaf motor controller build. http://endless-sphere.com/forums/viewto ... 27#p963227
YSR build http://www.youtube.com/watch?v=BRo8r5g4NBg
Never above 4.2v never below 2.7v EVER!!!
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Re: Building a triple stator axial flux motor

Post by MattyCiii » Dec 22 2012 11:29am

Awesome!
I'll be watching this closely. I hope to build me one like that too. I even went so far as to buy some parts... a bunch of magnets (when it looked like rare earth magnets were poised to skyrocket in price). For stator, I bought some light weight (honeycomb core) fiberglass panel, about 3mm thick if I remember correctly. I got carbon fiber panel for the rotor.

I'm not sure if these composite parts are any good, I have no experience with this sort of stuff...
1st build: Dahon Jetstream folding bike. Quick, reliable, capable of 32mph. Light enough to lift, folds for easy transport by car/bus/train.
2nd build: RC powered 2009 Norco A-Line. Top speed 39mph. Built like a tank, it's resistant to Boston potholes, can stop on a dime, easily goes up/down curbs when necessary.
3rd build (just started): Scratch build ultimate utility bike. Based on a common power module using a NuVinci left side freewheel.

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Ratking   1 kW

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Re: Building a triple stator axial flux motor

Post by Ratking » Dec 22 2012 11:31am

Lovely name for the bike :D
Really like the idea of building a motor with such simple equipment.
Good luck and take many pictures for our enjoyment :D

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Re: Building a triple stator axial flux motor

Post by ohzee » Dec 22 2012 2:32pm

Man this is pretty awesome.. Looked back thru your other post also , but I cant find a picture of your motor attached to your bike.
You have one of those handy ? What a sweet project. Look forward to watching it evolve.

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Lebowski   1 GW

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Re: Building a triple stator axial flux motor

Post by Lebowski » Dec 24 2012 2:42pm

ohzee wrote:Man this is pretty awesome.. Looked back thru your other post also , but I cant find a picture of your motor attached to your bike.
You have one of those handy ? What a sweet project. Look forward to watching it evolve.
http://endless-sphere.com/forums/viewto ... 26#p574726

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Re: Building a triple stator axial flux motor

Post by ohzee » Dec 24 2012 3:37pm

man that's awesome.. sorry my searching skills were mia that day.

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Re: Building a triple stator axial flux motor

Post by salty9 » Dec 26 2012 9:13pm

Lebowski,

I have been considering in emulating your motor design and was wondering if you had considered casting your stator coils in acrylic resin?

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Re: Building a triple stator axial flux motor

Post by AussieJester » Dec 26 2012 11:42pm

I admired the lovely cnc jobs that pop up but, when I see
The products produced by members with only hand tools
I'm REALLY impressed, best of luck with the motor build
Buddy, soooooooo subscribed!!!!

KiM

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Lebowski   1 GW

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Re: Building a triple stator axial flux motor

Post by Lebowski » Dec 28 2012 9:33am

salty9 wrote:Lebowski,

I have been considering in emulating your motor design and was wondering if you had considered casting your stator coils in acrylic resin?
I didn't really simulate the motor design. Back when I started with v1 the main purpose was to have something
to develop a controller with. I did some calculations at the time which showed me it would be a good bicycle
motor (based on power and efficiency). Calculations and practise was quite a good fit so, I'm very happy with
the way v1 turned out. I've used the same equations on v2...

The very first coil plate I made, I used a special acrylic glue. This did not work at all.... Acrylic glue is solvent
based, it dissolves a bit of the acrylic and this is kind of how it works. When glueing the coils however, everything
is clamped tight to make sure the coils are in the plane of the acrylic glass. This however prevents the acrylic
glue from curing as the solvent cannot 'vent'... it needs a glue that cures based on a chemical reaction, not on
a solvent evaporating. This is how I ended up with using epoxy.

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Lebowski   1 GW

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Re: Building a triple stator axial flux motor

Post by Lebowski » Dec 30 2012 1:44pm

DSC01089.jpg
marking out magnet locations
DSC01089.jpg (51.48 KiB) Viewed 15351 times
DSC01090.jpg
25mm hole saw, lubed with alcohol.
or, making tinsels for the xmas tree..
DSC01090.jpg (112.17 KiB) Viewed 15351 times
DSC01091.jpg
phew, finally all 6 done !
DSC01091.jpg (81.52 KiB) Viewed 15351 times

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Re: Building a triple stator axial flux motor

Post by Harold in CR » Dec 30 2012 3:12pm

Lebowski, I'm going to subscribe to this thread as well. I have all the tools needed to do a motor like this. Thanks for taking the time to record the process as you make the motor.

I have 1 question. Do you think this will also make a low power generator ? I need something for my Micro Hydro system, that can be in a hostile environment, splashing water, even though I will try me best to keep water out. I can only get 100W max from the system, at low flow rates, when we are out of the rainy season, otherwise, I can get up to the 1KW with ease.

I need to do some figuring for charging 12V battery systems, so, if I can push the AC from this motor, up to the house, this will be perfect, and, I can build a spare, in case one goes out for some reason.

This is going to be a GREAT thread. Thanks again.
Thanks to Justin, the forum is open source and NON-commercialized.

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Lebowski   1 GW

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Re: Building a triple stator axial flux motor

Post by Lebowski » Jan 03 2013 4:44am

I mean, any motor can be used as a generator so yes, that's possible. What's nice about this
motor (or, v1) is that unloaded it runs as smooth and easy as a bicycle wheel. I managed
to make v1 rotate with only 0.03 W, so it should be good as a generator even if very
low power is available. There's virtually no 'binding'

About a hostile environment, I think that just depends on how good you waterproof it. v1 has
no waterproofing whatsoever (except this black shrink stuff in the wiring) and does fine
even though some of the untreared iron starts rusting now (with all of the salt on the roads
etc... remember salt on the roads from back in the day when you were not living in a sunny
tropical paradise ? :D ). I think if you spray the magnet plates with paint this should be no
problem though...

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Re: Building a triple stator axial flux motor

Post by Harold in CR » Jan 03 2013 5:54am

You have confirmed exactly what I was thinking.

Proceed with the build. 8) 8)

Thanks Lebowski 8)
Thanks to Justin, the forum is open source and NON-commercialized.

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Lebowski   1 GW

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Re: Building a triple stator axial flux motor

Post by Lebowski » Jan 07 2013 7:40am

DSC01094.jpg
drilling out the spoke holes to 3 mm
DSC01094.jpg (79.07 KiB) Viewed 15358 times
DSC01093.jpg
this is the drawing for the rotor (kinda :-) )
DSC01093.jpg (112.29 KiB) Viewed 15358 times
DSC01096.jpg
the axel has to fit through the rotor plates for assembly
DSC01096.jpg (78.58 KiB) Viewed 15358 times
DSC01095.jpg
a tripple stator motor has two center magnet plates and two end magnet plates. The center plates are made using 2 aluminium plates sandwiching a thin (magnetic) steel plate
DSC01095.jpg (60.13 KiB) Viewed 15358 times
DSC01097.jpg
some extra holes cut to facilitate sawing out the centre
DSC01097.jpg (95.7 KiB) Viewed 15358 times
DSC01098.jpg
slowly getting there
DSC01098.jpg (71.95 KiB) Viewed 15358 times
DSC01099.jpg
the centre steel plate is cut a little bit smaller so that it won't cut your fingers when the motor is spinning
DSC01099.jpg (72.41 KiB) Viewed 15358 times
DSC01100.jpg
tapping 4mm threads in one aluminium plate
DSC01100.jpg (97.44 KiB) Viewed 15358 times
DSC01101.jpg
countersink the screws in the other aluminium plate.
note that I use stainless steel screws which are non-magnetic, so they won't influence the magnetic field
DSC01101.jpg (79.77 KiB) Viewed 15358 times
DSC01102.jpg
one center magnet plate put together :-)
Notice the 4 mm holes in the centre, close to the 6 mm holes. The 6 mm holes are for fixing the rotor plate to the axle. the 4 mm holes are to later aid in the dissassembly of the motor. When put together the maget plates attract each other with about 100 kg of force. To pull them apart the 4mm holes will be used to attach a puller construction.
DSC01102.jpg (106.25 KiB) Viewed 15358 times
DSC01103.jpg
and the other side
DSC01103.jpg (106.56 KiB) Viewed 15358 times
now I have to make one more of these....
Last edited by Lebowski on Jan 25 2013 8:13am, edited 1 time in total.

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Re: Building a triple stator axial flux motor

Post by Lebowski » Jan 08 2013 8:05am

found an interesting site for calculating the magnetic fields and such in a motor like this. With the magnetic field
the back-emf of the motor can be calculated. If you then calculate the wiring resistance a good picture of the motors
efficiency at different rpm's and power outputs can be made.

http://www.kjmagnetics.com/gap.calculator.asp

I use 25mm magnets, 7mm thick with probably a 7 mm gap. The configuration to use ín the calculator is
the 'two disk magnets with yoke.

The interesting thing is that the gap is small enough that adding iron to the motor doesn't bring that much (factor 2 only).
Two magnets with a 7 mm gap: about 8000 gauss
Same but with a 0.5 mm gap: about 12700 gauss

Since you've to integrate over the whole area and the 7mm gap has a more bowl shaped curve, lets say the difference
integrated over the magnet area is about 2.

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Re: Building a triple stator axial flux motor

Post by salty9 » Jan 09 2013 11:38pm

Jon Stewart tells me there is a new book out - "The Dude and the Zen Master". Don't know if it has any insights into motor building but it sounds as if it might be interesting.

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Re: Building a triple stator axial flux motor

Post by Lebowski » Jan 13 2013 8:21am

DSC01104.jpg
and then there were two
DSC01104.jpg (74.02 KiB) Viewed 15151 times
With the two middle magnet plates finished it's time for the two end plates. These plates carry magnets and have a thick iron backplate.
Typically said these backplates are to close the magnetic field, which is a load of BULL, magnetic field lines know how to close
themselves and don't need any help from a bit of iron. No, the iron backplates in effect doubles the internal magnetic field strength in the
motor by routing the returning field lines through a neighbour inductor.
DSC01106.jpg
DSC01106.jpg (96.64 KiB) Viewed 15151 times
the above picture shows the situation without backplates The magnetic field from the center two magnets returns in whatever way it
sees fit. The returning field lines have no usefull contribution.
DSC01107.jpg
DSC01107.jpg (97.5 KiB) Viewed 15151 times
The iron backplates (in green) act as a conductor for the magnetic field. The (effectively) shortest route for the field lines to
return is now via the backplates THROUGH THE NEIGHBOURING COILS. So in effect the returning field lines contribute
to the field in the neighbouring coils. Similarly, the field lines from both neighbour magnet pairs returns through the central coil,
doubling the magnetic field.
IM000124.jpg
IM000124.jpg (70.73 KiB) Viewed 15151 times
In v1 the backplates were made using a 25mm by 5mm iron bar cut into wedge shaped pieces. This is however a lot of work (especially
since I had to cut the bar by hand) so for v2 I decided to go with metal sheets instead.
DSC01105.jpg
DSC01105.jpg (55.42 KiB) Viewed 15151 times
For each endplate I use 4 1.5mm sheets of galvanised steel.

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Re: Building a triple stator axial flux motor

Post by Njay » Jan 13 2013 8:39am

At least some (not sure if it's your case) axial flux motors are closed only by the magnet's force. So, if we could slightly adjust the separation of rotor and stator "on the fly" by some screws or whatever, that would give us a kind of transmission box (continuous or discreet), having a torque-oriented final reduction and increasing separation to achieve higher speeds.

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Re: Building a triple stator axial flux motor

Post by Lebowski » Jan 15 2013 6:18am

Njay wrote:At least some (not sure if it's your case) axial flux motors are closed only by the magnet's force. So, if we could slightly adjust the separation of rotor and stator "on the fly" by some screws or whatever, that would give us a kind of transmission box (continuous or discreet), having a torque-oriented final reduction and increasing separation to achieve higher speeds.
Ehm, this is torque control by decreasing efficiency, not the way I would want to go :?

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Re: Building a triple stator axial flux motor

Post by Lebowski » Jan 19 2013 2:19pm

Now to make the endplates of the rotor. each plate consists of an aluminium holder with holes for the magnets, and
4 1.5mm thick metal rings as the magnetic backplate.
DSC01108.jpg
alu and steel screwed together to make sure all screw holes line up
DSC01108.jpg (62.26 KiB) Viewed 15024 times
DSC01109.jpg
drill the center through the steel plates
DSC01109.jpg (87.95 KiB) Viewed 15024 times
DSC01110.jpg
draw inner and outter circle for the steel rings
DSC01110.jpg (91.99 KiB) Viewed 15024 times
lots of sawing later....
DSC01113.jpg
end plates done !
DSC01113.jpg (101.03 KiB) Viewed 15024 times
DSC01114.jpg
magnets plates together with axle
DSC01114.jpg (94.66 KiB) Viewed 15024 times
now for the stator plates...

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Re: Building a triple stator axial flux motor

Post by liveforphysics » Jan 21 2013 10:21pm

I'm excitedly following this thread Lebowski. :-) I'm excited to see how it turns out, it's a clever design.
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Re: Building a triple stator axial flux motor

Post by Lebowski » Jan 25 2013 12:25pm

Just a cool present I just got :mrgreen:
IMG_2013012545897.jpg
IMG_2013012545897.jpg (61.54 KiB) Viewed 14877 times

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