Ultimate lightweight wheel-motor concept
- Thread starter speedmd
- Start date
speedmd
10 MW
My main concern with one bearing is the weight offset from center of the stator. It is like a car wheel with lots of offset causing additional flex when bumped and require double row bearing setups to keep in check. Additionally the torque arms force will want to twist the stator when trying to resolve the torque. Should work either way.
speedmd
10 MW
Thinking a thin sheet of aluminum for starters. Easy to dimple for offset and the like. .7mm -1mm thick should do it. Easy to punch holes in for venting and glue screen onto for coarse debris filters.
if aluminum we could spin form instead of stamp to save on tooling
http://www.youtube.com/watch?v=CsGVPUGMPXM
A vacuum formed piece of plastic would also work on the cheap (wooo clear cool man)
For the proto we dont even need a cover, but we need to have it designed to leave features for mounting/sealing
It doesn't have to be IP68 or anything too crazy
Also have to consider a very thin piece of aluminum will act like a sounding board and couple sound from the stator coils making it sing. We can add damping pads or ribs or use a material that is inherently well damped
http://www.youtube.com/watch?v=CsGVPUGMPXM
A vacuum formed piece of plastic would also work on the cheap (wooo clear cool man)
For the proto we dont even need a cover, but we need to have it designed to leave features for mounting/sealing
It doesn't have to be IP68 or anything too crazy
Also have to consider a very thin piece of aluminum will act like a sounding board and couple sound from the stator coils making it sing. We can add damping pads or ribs or use a material that is inherently well damped
liveforphysics
100 TW
I went on an awesome Heavenly Tahoe skiing trip this weekend, and come back to see so much fantastic collaborative design occurred! Awesome!
Miles- Your CADoodin' has become amazingly good! Amazing that you've got so much real world craftsmanship skills, as well as serious CAD skills. That's a very uncommon and valuable combination! Not to mention your magnetic design on the first page is incredible and don't believe I've ever seen anything on par with it in the bicycle domain.
DIY will always lead industry, not visa-versa. ES is the living bleeding edge of ebike technology.
Miles- Your CADoodin' has become amazingly good! Amazing that you've got so much real world craftsmanship skills, as well as serious CAD skills. That's a very uncommon and valuable combination! Not to mention your magnetic design on the first page is incredible and don't believe I've ever seen anything on par with it in the bicycle domain.
DIY will always lead industry, not visa-versa. ES is the living bleeding edge of ebike technology.
Miles you do a very great job! I did CAD drawing a few years ago in school, but now i have no license for this software (catia) i have worked with. Have to see if i can make it run, but i think i have not the skills to make such nice drawings (with hub, rim, spokes) as you did 
to the bearings:
if we place both on one side, we will not be able to seal up the motor.
i think at least the motor should be protected against jets of water and if it is open on one side, it will fill up half with water.
The bearings located on both sides would cause more distance between them which is also better (less wobble in rotor), and it would make no difference in total width "wasted" on the hub.
We can still place the motor more to the middle of the wheel if we machine turn some AL adapter disc between inner bearing and case disc, but i think on many bicycle frames there will be enough space between swingarm and motor. or i am wrong?
Miles, can you tell us more about the power this motor will have. for example:
- torque per given amps
- electrical rpm at 1000rpm
- max continuos power / peak power
i think we need very thin lams / good iron to keep eddy current losses low at high rpm
to the bearings:
if we place both on one side, we will not be able to seal up the motor.
i think at least the motor should be protected against jets of water and if it is open on one side, it will fill up half with water.
The bearings located on both sides would cause more distance between them which is also better (less wobble in rotor), and it would make no difference in total width "wasted" on the hub.
We can still place the motor more to the middle of the wheel if we machine turn some AL adapter disc between inner bearing and case disc, but i think on many bicycle frames there will be enough space between swingarm and motor. or i am wrong?
Miles, can you tell us more about the power this motor will have. for example:
- torque per given amps
- electrical rpm at 1000rpm
- max continuos power / peak power
i think we need very thin lams / good iron to keep eddy current losses low at high rpm
At least there is access to free software now. There wasn't when I was learning.....
http://www.designspark.com/eng/page/mechanical
https://www.plm.automation.siemens.com/en_us/academic/resources/solid-edge/student-download.cfm?
It would make no sense to place a bearing on the inner side unless you also make the case on that side a structural element. I think we can make a rigid enough structure with one sided support and achieve sufficient weather protection with a simple cover. Doing it this way simplifies construction.
It's a design choice, not the result of a naive misconception. It can still turn out to be the wrong choice, though.
What does everybody else think?
http://www.designspark.com/eng/page/mechanical
https://www.plm.automation.siemens.com/en_us/academic/resources/solid-edge/student-download.cfm?
All of this was taken into account...madin88 said:
It would make no sense to place a bearing on the inner side unless you also make the case on that side a structural element. I think we can make a rigid enough structure with one sided support and achieve sufficient weather protection with a simple cover. Doing it this way simplifies construction.
It's a design choice, not the result of a naive misconception. It can still turn out to be the wrong choice, though.
What does everybody else think?
speedmd
10 MW
Great work Miles. This is becoming a incredible concept.
Well, that has me thinking, if we added a voice coil to it , you could play some radio, or make it sound like a harley/ moto-gp/or your favorite dirt bike :lol: Better yet, add a diesel locomotive horn to it. Best yet, you could add a feed back noise cancellation program to it and run near completely silent. 8)
Well, that has me thinking, if we added a voice coil to it
, you could play some radio, or make it sound like a harley/ moto-gp/or your favorite dirt bike :lol: Better yet, add a diesel locomotive horn to it. Best yet, you could add a feed back noise cancellation program to it and run near completely silent. 8)madin88 said:
Give me a chance to do some simulation, first
The fundamental frequency will be low enough that stock 0.35mm laminations will be fine. This will save a lot on what is probably going to be the highest cost item.
In the long term, this is a perfect candidate for 'slinky' core construction......
speedmd
10 MW
Yaa man, we can hopefully get a free sample also!
Do we set a cont. torque target or a weight target?
My inclination is to do a prototype that will, at least, fit all sizes of wheel and to set an all up weight target of 2 kg.
You can only push the diameter so far, for a given weight, before the reduction in width causes endturn losses to dominate.
My inclination is to do a prototype that will, at least, fit all sizes of wheel and to set an all up weight target of 2 kg.
You can only push the diameter so far, for a given weight, before the reduction in width causes endturn losses to dominate.
Miles said:
It's rare to hear such a good piece of news in a project
Intuitevely, the single-sided bearing should work fine - just look at the stub-axle arrangement on most road-going vehicles. Nowadays a double-row ball race, formerly a taper-roller. If the rotor isn't subject to axial loads then a straight roller ought to do the job (the efficiency of roller bearings falls drops as the angle increases). I suspect it will always be a heavier design than double ended as the bearings will see greater load if the distance between them is less, so they'd need to be bigger and the axle would need to be stiffer.
However, the absolute difference probably isn't that great, and may even be offset by the savings of only one structural cover. Plus the design simplification...
I know plastic is tacky, but vac-formed polycarbonate could be a good option. Very cheap and tough. The equivalent weight of cast Al would be rediculously fragile and even spun sheet would be prone to dents (and artisan to produce).
The cassette-drive idea is sounding better. Initially it seemed to greatly limit the potential motor width compared to a hubbie, but I like the idea of it being plug and play with any cassette wheel you care to pick up. No more custom lacing jobs or big headaches if you bend a rim.
Would anyone be kind enough to clarify the issue of gearing? Will the SRAM gear hub reliably take the motor power? Will the efficiency be an issue?
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...........Punx0r said:
If a singlespeed without a motor is enough for some.... Surely, 3 speeds and a reasonably powerful motor should be enough for most?
Miles said:
thx for the links to the free software. i think i will give them a try if i have some time.
I understand what you mean. fabricate only one structual disc with press fit for bearings, press fit for stator iron, cooling fins is a good and simple idea, but how will you seal up the motor if there is no bearing or shaft seal on the inner side?
that is the question
Miles said:
that sounds like a problem. if the motor turns, the pedals will also turn. not good.
to make it perfect we would need about 3 freewheels:
- one in the cassette to keep the pedals from turning with the motor
- one in the motor to keep the rotor from turning when pedaling
- one in the hub (already there)
Miles said:A bearing isn't sealed unless it has a seal
Does it really need to be sealed?
i would prefer a sealed motor
with two sidecovers of AL there also will be better heat dissipation (twice the suface area). the covers can be thinner so about the same weight..
sealed bearings are normally no problem to find.
Good point on the heat dissipation!
That is great news
A free-wheeling crankset does sound good as it keeps the solution off-the-shelf? Simplifies the design of the motor side of things.
Still a little concerned about the longevity/reliability of putting the motor power through a geared hub? Or am I just being ignorant of their robustness?
Miles said:
That is great news
A free-wheeling crankset does sound good as it keeps the solution off-the-shelf? Simplifies the design of the motor side of things.
Still a little concerned about the longevity/reliability of putting the motor power through a geared hub? Or am I just being ignorant of their robustness?
That is the beauty of this design
The sram dual is just an option
But to answer your question: http://endless-sphere.com/forums/viewtopic.php?f=28&t=15216
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Miles, are you zeroing in on a final size and offset or do you need more frame and wheel models to make the final decision? Can you show a couple different perspectives with only the rotor, and only the stator, etc (mounted on the bike). It is hard to get a feel for the bearing arrangement from one picture
We also need a chain guard
The sram dual is just an option
But to answer your question: http://endless-sphere.com/forums/viewtopic.php?f=28&t=15216
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Miles, are you zeroing in on a final size and offset or do you need more frame and wheel models to make the final decision? Can you show a couple different perspectives with only the rotor, and only the stator, etc (mounted on the bike). It is hard to get a feel for the bearing arrangement from one picture
We also need a chain guard
I think I have enough info, thanks. The offset is governed by the airgap diameter chosen, in relation to the largest wheel size the motor has to fit on. The diameter is governed by what will fit on the smallest wheel size (406). It's a bit of a compromise but an airgap diameter of 292mm and outside diameter of around 325mm is what I've arrived at.flathill said:
