Ultimate lightweight wheel-motor concept

[speedmd]

Thinking, any of the grain oriented types would most likely be grain oriented in the wrong direction for slinky construction regardless. Anyone have a feel of what is going on here in the strip forming stage of these types of metals.

The more I think on the grain orientation, the more I am ruling out possible benefits that grain oriented steel would have in the stator. Certainly as the backer to the PM's it looks a bit more direct a flow, but the stator tooth carries the magnetic flux from tooth to tooth through more than 270 degrees or rotation. Am I missing something here?

 

[liveforphysics]

On the simulation miles you were getting torque estimates of around 25nm. Not sure if this will be enough for slow moving heavier load situations/hills without burning up relatively quickly. Folks with hub motor experience should have a better feel for this and can judge this better. If not we may want to keep it on the larger diameter side for general purpose, but also would like to see a smaller lighter version explored as weight is a critical factor here.

I was simulating for 25Nm of torque....... I was getting about 85 Watts of heat at 25Nm. Would 30Nm continuous be enough?

30Nm continously is likely beyond the capabilities of many hubs that are many times more weight.

I love that with open free idea exchange and development that we can create a simple and silent direct drive no-compromises(except cost) motor system in a matter of a week or two.

 

[liveforphysics]

Can't seem to figure out how to move kick-starer post to new thread so it's not in the way here

Before anyone takes a cent from anyone who is expecting to get a working product delivered, we MUST make the initial proof of concept motors and test them throughly.

The crew of folks willing to roll the dice with there resources (myself included of course) will handle this.

Then once we can confirm we have a solid product, we can consider taking some 3rd party's money expecting something that works in return.

Just my $0.02 as a guy who has backed a number of kickstarter projects that weren't even tested yet (dispite what the nice video may lead you to believe), and getting to see the fall-out associated with it.

Throughly test anything before you setup for volume production or take anyones money. You won't regret it. Lol

 

[speedmd]

Agree Luke

This is still in the stages for the more serious risk takers. We should not be promising anything deliverable. No place for rose colored glasses. Having been developing my own small niche products for a few decades now, I am clear that many times it just becomes a learning exercise/ large time suck and financial drain just to prove out /refine a simple design. Normal design build manufacturing stuff. Have had my share of over extended payback scenarios and having to pull the plug on stuff you end up obsoleting too quickly with significant design improvements or product / market swings. Education takes time and costs money, no matter how you get it.

 

[flathill]

30N-m continuous sounds like a great all around motor. For the average ebiker who actual pedals this should even be fine in a 700c rim (similar to bmc/mac thanks)

When you say continuous do you mean it will never overheat at the level?

What kind of peak torque can we expect before seeing second order saturation effect?

Have you settled on 20mm long for the small motor?

 

[Miles]

Here are the first simulation results for the small motor. Not optimised for torque ripple etc. yet.
Simulated at 400rpm (226.7Hz) 15mm stack. Circa 2kg active motor weight. 0.55 slot fill factor.

[pre]Current Torque Eta Power out Heat out
14A 12.0Nm 94.6% 487W 28W
20A 17.0Nm 94.3% 701W 42W
30A 25.6Nm 93.0% 1058W 79W
40A 33.4Nm 91.4% 1382W 140W[/pre]

 

[Miles]

When you say continuous do you mean it will never overheat at the level?
What kind of peak torque can we expect before seeing second order saturation effect?

That's what I mean by continuous.
Heat will be a problem before the effects of saturation becomes significant, I think. Bear in mind that if you don't have the thermal mass that other direct drive hub motors do, you won't have the same scope for pushing things beyond the true continuous rating.....

 

[madin88]

miles, was this a simulation of the 300mm motor?
The motor will have a big cooling area if we turn some fins to the stator case and use AL sideplates. the case will heat up quick due to low mass, but it will cool down very fast.
we could do some calculations how much continuos heat out the motor can handle at a given case surface area and given airflow.

im still for a sealed motor with two structual sideplates

 

[speedmd]

This is a relatively large diameter thin motor. Lots of area connected directly to the stator/windings via the housing, and moving in somewhat open air as you ride. IMO it has a Major advantage this way over a standard outrunner hub motor. Iron losses are relatively low also if we can assume roughly the same ratios as before. Unless your throttling it non stop at a near stand still, I do not see it cooking at these power levels. Just a gut feel. Going by the ebikeca simulator it does appear in the same torque range as the hubs mentioned above.

 

[Miles]

miles, was this a simulation of the 300mm motor?

Yes.

 

[flathill]

Hey Miles,

What do you think about a segmented stator? You would gain copper fill but there would also be more losses in the lams. Probably not worth it for such a short motor and so many poles (you would want to wind with the segments spaced and laid flat in a jig and then form into ring or you would have a million connections, see page 3), but let's see how much Luke can get a lasercut 500mm diameter ring of hiperco50. Maybe he has a hookup but I suspect we are looking at 2k just for the lams on a 500mm motor (laser cut and welded or bonded hiperco50)

http://www.trafomotor.com/wp-content/uploads/2012/08/Sipro-motor-winding-system-PART.1.ppsx

 

[Miles]

What do you think about a segmented stator?

With a 2.8mm stator yoke?

 

[JennyB]

Forgive me if this is a stupid question (I'm not at home so can't check the chainline on my bike), but is there enough space to mount three sprockets on the remaining cassette splines and use a derailleur? Then only the human drivetrain is through the gearing.

Either way, is three-speed on the rear enough for the serious cycling enthusiast who might want an expensive, featherweight motor such as this?

Yes, I think there will be room left for 3 sprocket. You will need a freewheeling crankset, though. You could have 3 sprockets for the pedals plus the 3 gears of the Dualdrive for the motor and the pedals...........

If a singlespeed without a motor is enough for some.... Surely, 3 speeds and a reasonably powerful motor should be enough for most?

At the power levels you are suggesting, I would be very happy to ride singlespeed. There's something very satisfying about just riding without having to worry what gear you are in. 8)

As I see it, the market for this will be with the MAMILs* and the attraction will be simple - same bike, same effort, up to 50% further or faster. The competent cyclist can ride like a local hero; the local hero can ride like a pro.

It would be great, too, for the cycle couriers and wannabes currently riding overgeared fixies! :lol:

Cassette versus Disc Mounting

There seems enough space on either side. In each case you would need a torque reaction bracket mounted on the seat stay, probably outside the stator ring. I'd see this as the place where the motor wiring exits. To mend a puncture, undo the qr and rotate the wheel around this mounting to get clearance to replace a tube or tyre. If the wheel or motor is shot, unplug and replace. No dangling wires.

Cassette

• Fixed gear: Need to disable cassette freewheel. Add single sprocket and spacers
  Single speed with regen: As above, but freewheel (14 tooth min) or freewheeling crankset
  Singlespeed without regen: As fixed, but without disabling cassette
  Other: Cassette-compatible with up to three sprockets. If using a derailleur, needs freewheeling crankset.

Disc

• Any disc-compatible hub. No modifications to transmission needed. The motor always drives directly. If there is an existing disc, remove it and the caliper. Its function is replaced by regen braking.

* Middle-Aged Men in Lycra

 

[speedmd]

im still for a sealed motor with two structual sideplates

I hear you and do also like a fully supported and sealed structure but have some other considerations some may wish to ponder a bit further. Minuses I see are the structural inside cover would possibly be a bit more difficult to make and fit less universally. Pluses of a relatively thin open inside cover and using a split freehub or second freewheel, are that we could add to this design a active regenerative braking clutch. Certainly not a light weight addition, but. 8)

 

[Miles]

At the power levels you are suggesting, I would be very happy to ride singlespeed. There's something very satisfying about just riding without having to worry what gear you are in. 8)

I agree.

Cassette versus Disc Mounting

Each side has things in its favour.

What swung it for me was the possibility of:

Dualdrive hub with single or double speed freewheel.

Sturmey S3X hub with single sprocket and freewheeling crank.

I'd see this as the place where the motor wiring exits.

Yes, that's the plan :wink:

 

[Miles]

im still for a sealed motor with two structual sideplates

I hear you and do also like a fully supported and sealed structure but have some other considerations some may wish to ponder a bit further...........

For me, a significant advantage of doing it as a cantilevered structure, at least for the prototype, is that it makes it possible to run the motor with the case open.......

 

[flathill]

What do you think about a segmented stator?

With a 2.8mm stator yoke?

I'm thinking splitting the 360 ring into 60 or 120 degree segments to reduce scrap, not every tooth

If you draw a box around the one piece stator and calculate the scrap you will see it is probably around 94%

You can reduce that to ~50% with a few cuts

Yeah you use the scrap to make smaller motors but it doesn't always happen

 

[Miles]

I was thinking splitting the 360 ring into 60 or 120 degree segments to reduce scrap, not every tooth

Ok. You still haven't got much material to do the joint...... It's probably the only way to afford Hiperco 50 lams, though...

 

[flathill]

If you draw a box around the one piece stator and calculate the scrap you will see it is probably around 94%

You can reduce that to ~50% with a few cuts

Yeah you use the scrap to make smaller motors but it doesn't always happen

Maybe the joint won't be perfect and there will be a few hot spots but the stator will be fit into the Al ring frame and bonded in place. If you make the ring frame separate from the side panels/spokes the motor can be wound easy

 

[Miles]

Luke posted the relative material costs. I'd like to know the proportion of the costs that are for the material and the proportion for the machining?

 

[flathill]

These guys stock Hiperco50

http://www.polarislaserlaminations.com/laser-cut-laminations.html

When you finalize on the design send out a quote for a single piece stator and a 3 piece stator (120 deg)

Enough to make say a dozen motors? They are going to laugh if you try and get a quote on one motor

Even a dozen 20mm motors only makes one regular size 240mm long motor...

They will do single motor custom lams....for huge industrial motors where they can make a nice profit

The good thing about lasers though is there is no tool costs, so setup is minimal, and if you are nice...

If the company doesn't already stock Hiperco you are going to have no chance. They are not going to order a large batch for your small order

Who did Farfle use to cut his custom lams? I think it ended up costing him around 5-600. As an independent most USA mfg won't give you the time of day, but once you have a large company email address you get a reply right away.

Maybe Luke has connections through a Zero supplier

 

[Miles]

I've corresponded with Polaris before. They'll make any quantity you want, of anything.

Farfle got his laminations from Laser Laminations Inc. They only have M15 or M19 steel.

It's probably not worth the hassle of segments for the prototype.

 

[Miles]

NB The simulations above used Sura 30 for the lamination material.....

 

[speedmd]

im still for a sealed motor with two structual sideplates

I hear you and do also like a fully supported and sealed structure but have some other considerations some may wish to ponder a bit further...........

For me, a significant advantage of doing it as a cantilevered structure, at least for the prototype, is that it makes it possible to run the motor with the case open.......

Should be a major advantage in the cooling department having it open. Do not want to think about what could happen if a spoke breaks when it is like that and the motor eats bits of it: :x

 

[liveforphysics]

I have vendors who will make any qty, even a single sample lamination, in any obtainable material.

The laser cutting and coating and heat treating is surprisingly cheap. With Hyperco50, I think you can safely assume materials will be at least 75% of the quote's cost if that helps you ball-parking pricing, even with it's exotic handling needs.

I'm thinking you make a nested cut-layout that has all the part for the large diameter motor with the small diameter motors parts nested into it, and I will send it on to be quoted ASAP, and I will request quotes in both Hyperco50 and something cheaper (suggestions?) so we can see the price differential to make the most educated choices in the design. The sheet will always be a rectangular, so if you want to fill the otherwise wasted corner area with segmented stator chunks, the cutting isn't very pricey to give it a shot. I think if you designed it around having a 50% overlap alternating every other layer and used a proper adhesive that it might have a shot at providing the rigidity needed if it's getting bonded to something adequately rigid to not rely on the lamination for support. Seems like a huge PITA of assembly effort just to save a little on materials cost though, but if we can fit the pieces into the scrap margin we can get it quoted with and without to see the cost difference.

Have you been sizing/scaling it around a given available in N45SH magnet type my friend? I'm in China right now, and ironically just a few blocks away is a MASSIVE rare-earth magnet factory. I'm gonna try to get a tour if I can find time, and if nothing else hopefully get purchasing contacts and a list of what they offer off-the-shelf.