The Halbach Disc Motor Ebike Project

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A Long History With Armature Current Limiting

(Phase Current Limiting)

There are threads on ES that come even before this one, but I've been building and testing these concepts for years now.

Check these out for a blast from the (ancient) past of late 2007:

http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=930

http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=2789

http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=3008&hilit=armature+current+limiting

...so while I'm glad that the Infineon chip is here it's not like there's anything really new going on. Basically we are now seeing products arrive that we've been waiting around for since 2007.

 

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Some Other Controller "Fads"...

Just thought it might be fun to bring up a couple of the humorous controller fads / modifications of the past:

~2006-2007 : Soldering the shunts that control current to override the controller limit. A great idea if you want to overheat your motor.

~2006-2009 : Crystalyte hub motors were the rage and people would overvolt up to 100 volts or more and in order to do that you needed to do some radical changes to the controllers. The hubs weighed 25 lbs.

~2008-2009 : RC motors began being used and they run with an ESC that is "sensorless". "Behold, we have entered the sensorless era!" was the hype of the day. These days "sensorless" is considered a negative and most people are manually reintroducing sensors to their motors.

...I'm sure I could find some more to poke fun at, but that's a pretty good list.

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As for this project... at the time everyone was all excited about ESC's and I thought that direction was junk, so I was searching for other avenues to operate a brushless motor. The idea of Single Phase was appealing because there is a chip that is easy to work with and cheap and it could be scaled to 5000 watts if I wanted.

With the Infineon chip there is plenty of custom controls to fiddle with, but the MAIN change from several months ago is the newly forming 1K Racing (1000W) class. Now I can settle down and ignore the other stuff and just focus on the class that it's best suited to run it. I just don't need the 5000W potential at the moment.

...I try to go with the flow when it comes to parts available.

Keeping the stock settings for the controller is probably where I would start for this Halbach Disc motor. I actually do not need the phase limiting feature because the motor should be able to withstand a lot of heat because of it's open design. But I'd like to fiddle with it... seems like a good chip to base things on.

 

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Okay, well I've done some redesigning of the Halbach Disc motor stator and now it's 60 turn coils in series with 9 coils using 16 AWG (thick) wire. This produces a coverage of 50% of the disc when using Three Phases as needed for the Infineon controller.

Still looks like it's going to work.

By 20 mph the efficiency is already up to 80%. (799 watts delivered)

At 35 mph the efficiency would be around 90%. (898 watts delivered)

The efficiency peaks at 50 mph at 92% (923 watts delivered) but aerodynamic limitations would cap the top speed at 40 mph.

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Question:

I was reading through some of the Infineon "chat" on ES and there never seemed to be a conclusion about what the 120% settings were doing. Seems that it doesn't really give an extra 20%, but is really sort of rescaling 100% down to 90% then giving it back to make for normal when you go to 120%.

Anyway... if anyone knows if there ever was a concrete "knowledgable" conclusion I'd be curious what it was. Seems like no one really knows. (seems like another of those "fad" items that people seem to get overly excited about)

As for this project you can see that top speed would be easily attained even with 90% throttle, so I don't see a need for the feature personally. (or the need for phase limiting either as heat is very much under control) I'd still like to go with one of the Infineon controllers just to be part of the "herd mentality" for them. And for the racetrack it would lesson complaints if I used the same stuff. For 1K Racing (1000W) power is not as big of an issue in total amount as it is in regulation and fairness. I want to appear "fair" in any way I can.

 

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Why Not 24 Volts?

Let's review current trends...

People buy ebikes that are sold in a legal condition such that when their standard voltage is used the top speed of the ebike is 20 mph or less. This HAS to be the case or the seller is not given legal protection and is subject to potential lawsuits. (stupid move if you are a business) So as a result people have bought the ebike and then in order to go above the legal speed and power they overvolt. This has led to a mistaken belief that overvolting is the primary path to higher power levels and more speed because you can also do this by the design of the motor and the selection of alternative rewinding turn counts. Basically if you double the kv by the rewinding technique you can half the voltage and achieve the same result.

I'm of the belief that there is no logical reason for ebikes that are going to satisfy the 1000 watt rule to use any higher than 24 volts as it's just as easy to design for that as it is for 48 volts.

So this is how the Halbach Disc motor could operate using a 24 volt controller (like a Kelly controller) and with a 40 amp battery current limit:

...in fact it could be possible to sell the ebike with the coils wired in a more series fashion in order to make for a 20 mph legal ebike at the point of sale and then with a quick change in the coil sequencing (go from all series to series / parallel) be able to operate at a higher speed. Much like the delta / wye option you can also do the same thing with the series / parallel connections.

So there is a strong "urge" on my part to go with 24 volts just to prove (or maybe I should "disprove a myth") that a 24 volt machine is capable of achieving optimal performance if you design for it. The laws of physics simply specify a kv value for a motor... that's it... as long as the kv and the voltage and the top speed are properly tuned then you have a winning combination.

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The more I read about the goofy stuff that goes on with the Infineon controller the less I want to get into it. Ideally all I want is a 24 volt / 40 amp controller without any bells and whistles so that I can achieve 1000 watts. K.I.S.S. is the rule for 1000 watt racing.

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Let's also remember that 50 DC volts is recognized as the "threshold limit" at which the potential of death by electrocution occurs. Below 50 VDC and people are most likely to live and above and there is a good chance you will die. 24 VDC is well below the death threshold and since the goal in a consumer product is "safety" it seems only logical to want to make every effort to get things to work in a "safe" manner.

 

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After several hours of running simulations to get the data I've been able to figure out the predicted force for the Three Phase configuration.

The power is delivered sooooo much smoother than with Single Phase and the results are very similiar as far as magnetic strength due to core positioning. The cogging is less and the peaks are less, but overall things come out the same.

Still getting roughly 1 Tesla of peak magnetic flux... which is good.

 

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Let me describe what you are seeing here.

This is a cross section going from one side of the Halbach Disc motor through the core and out the other and is a cross section of what is going on in a coil when energized. Those two spikes are caused by the edges of the core (the core is shaped like an I-beam) and so that's the peak magnetic flux.

What's interesting is that if I were to not use a core the magnetic flux would drop from about a value of 1 Telsa (average and "true force") down to maybe half a Tesla in the middle. Note that on the two sides the magnets themselves only produce half a Tesla! At peak the cores are producing an astounding 2 Tesla's despite magnets that only produce half a Tesla. (peak is 4x the magnet strength)

So the thing about cores (even in something like this that is normally designed as being coreless) is that they SIGNIFICANTLY increase the strength in that little area in between the arrays of magnets.

"Enhancing" the Halbach arrays with cores does introduce cogging (as seen above) but it seems to be manageable. The cost benefit of cores seems to merit their use. (2x power output)

Note: Without the use of cores for "enhancement" you would have to spend more money on bigger and stronger magnets, so it's worth the money to think about doing this.

 

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Correction

When I was doing the calculations for Single Phase I had set up my spreadsheet to account for each coil as being able to "push pull" on every pole. This is the big advantage of Single Phase because you can in a sense "overlap" coils and they self reinforce each others magnetic fields.

As a result I was calculating the Three Phase wire turn count based on the optimistic Single Phase situation and that's wrong.

So the "bottom line" is that each turn of wire in a Three Phase configuration only achieves half of what it does in Single Phase. (for the same copper fill percentage)

...it kind of sucks.

It might still be workable as Three Phase, but it also makes me realize that for optimal power I might actually want to go to Single Phase after all.

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The positive side is that now I know that from the magnetic disc side nothing changes, (magnetic flux is always 1 Tesla) so I can go ahead and build the disk without any more math and then when it comes time to do the stator coils I can decide between Single Phase or Three Phase.

There is a clear advantage in power and efficiency with Single Phase for this type of design. Since there are 72 poles in the disc the Single Phase does not suffer from the same level of power surges because the electrical rpm rises very fast. If this were a 4 pole motor or even a 12 pole motor the oscillations might be unpleasant and torque ripple a real problem.

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If you skip back to page 10 I talked about "Push Pull" and how it aided in the design.

This is how a Single Phase is able to double it's effectiveness:

...notice how in a Single Phase the coils of one pole spill over into the next and you've probably seen how some motors get rid of the idea of coils altogether and switch to a snake like zig zag pattern built into plates.

Compare that to Three Phase... the coils are cut in half:

...backemf is determined by the maximum magnetic flux, but motive force is determined by the coils, so while Single Phase will be less smooth it's peak is better.

It's sort of a design "trap" to use cores... because they "digitalize" the motor and make it behave more like a Step Motor. Three Phase ends up overlapping the very thing you are trying to maximize, so it's sort of working against the central idea.

If I drop the cores then I lose half the power... so either way it's going backwards.

 

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Recalculated

So this is a configuration that adapts to the differences that Three Phase involve and the results aren't bad. Peak efficiency drops from around 92% to 90% and the losses happen at lower speeds as well. It still would make for a nice motor, but it's losing a little of it's "idealized" potential.

Hmmmmm... Three Phase is easier.... but maybe I lose a little peak performance with it...

Maybe the first version gets done as Three Phase just to have something to run, then I can always make a newer version (of the stator coils) later.

At this point ToddMoto's RC motor with a direct drive should have about the same performance profile, that's fair. I love that enormous clear rear disk... would be interesting to know where it came from?

...tough luck about the rain. I kind of figured those RC ESC's are a lot of trouble.

 

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If you joined Endless Sphere you would see that Todd Moto is Thud and he is very skilled machinist he made this clear sprocket from lexan on CNC machine. The RC ESC weren't problem he blowed up 3 of the infineon controllers he was not using rc esc on this yellow bike. There is much information on the Ohio race thread on endless sphere forum about this bike safe. I don't see how that this yellow bike is same performance as your 1000watt design motor, the motor in the yellow bike is a rc motor 6500watt.

 

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My understanding is that he was planning to just reconfigure the controller to run in the 1K Racing class (1000 watt restriction) and if he did that it would be the same.

I don't really care about the "moped class" (above 1000 watts) as I don't see any future for that sort of thing.

The only class I see as important is the 1000 watt class.