First custom carbon fork special made for hub motors

avandalen

100 W
Joined
Oct 2, 2010
Messages
175
Location
Maastricht, The Netherlands
Carbon forks are not suitable for direct mounting of hub motors. That's why I want to have strong carbon forks made especially for hub motors. Because expensive molds have to be made for production, I will sell this fork also to other people, otherwise it will be too expensive for me.
If you are interested in this carbon fork too, I would like to know your advice, ideas and wishes.

See more in my article: https://www.avdweb.nl/solar-bike/mechanical-issues/carbon-front-fork-for-hub-motors

Carbon-front-fork-for-hub-motor-fill-327x446.jpg
 
For a prototype or low volume production ... why carbon ?
On a product like this any weight savings would be minor to negligible.

I recently viewed this metallurgy video which you might find interesting ...

https://www.youtube.com/watch?v=ah7Ubbq5EAA&t=590s
 
If you are going through all of the trouble to have a custom piece made you should see about having the post mounts for brakes put on both sides. It would make a nice mounting point for a torque arm that you could also design.
 
DanGT86 said:
If you are going through all of the trouble to have a custom piece made you should see about having the post mounts for brakes put on both sides. It would make a nice mounting point for a torque arm that you could also design.
Is a perfect idea! Thank you.
Still I use a custom fork because the dropout distance is 110mm
 
No lawyer lips? No such thing as a " safety dropout? " Do you wish to meet " compliance testing"?

What of the requirement for a fork to be produced, on a bicycle, and be certified for sale, that a set or lawyer lips need be deep enough that the retaining bolt / or nut can be loosened 360 degrees and the wheel is still retained?

I suppose you do not expect anyone to use this fork for a bicycle wheel... It would only enjoy the hub motor market, and not be good for a bicycle wheel with no hub motor.

Positive retention of the wheel is required by most import laws (CPSC/ISO etc). So either should have 'lawyer's lips' or have a small pocket.

Here is a free, older reference to the standardized test. Compliance testing. You would have to pay for access to the new, up to date, model of this requirement standard.



https://www.cpsc.gov/s3fs-public/Bicycle%20Compliance%20Test%20Manual.pdf?fbclid=IwAR186nl-FoUx9TMu1gCwCoVJx8xXyoRD_IA_rCkwydscpG9MObg44_pAzLU
 

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PaPaSteve said:
For a prototype or low volume production ... why carbon ?
On a product like this any weight savings would be minor to negligible.

I certainly agree. Farm the job out to exotic printing 3D machines..... they are the newest and best thing. I do not think carbon is very suitable to the rigors of hub motor abuse. Nor would the market smile upon the idea.

Sintered trellis lattice 3D printed metal might be a equitable option. Such loads can be designed into the form. Easier than traditional materials .

What is the expected purchase price of this item? Hundreds of dollars or more?
 
Carbon fiber forks with machined steel droupouts is going to cost much, MUCH less, and weight less than a 3d printed one. Much more aero, too.
But yea, integrated torque arm mounting points seem like a very good idea, and given extra wheel security by a non-optional set of dual torque arms, I don't think you neeed lawer lips.

I currently use a hub motor as a generator with laser cut steel torque arms bolted into droputs 3d printed in *plastic* and it works just fine so far...
 
DogDipstick said:
No lawyer lips? No such thing as a " safety dropout? " Do you wish to meet " compliance testing"?

Yes, my front fork will be tested in China according to ISO 4210-6.

In the tests, the front fork is maximally exposed to the forces shown in the figure below. The front fork is also tested for fatigue during approximately 100,000 test cycles.
Front-fork-Safety-Standards-fill-292x372.jpg

It is important to know that in the test standards, the dropout is very heavily loaded with 5000N, see for example the following description in the Taiwanese TBIS 15194 EPAC standard:
Test method: Mount the fork steerer securely in a suitable rigid mount, keeping any clamping forces away from the fork-crown, and apply a tensile force of 5000 N distributed equally to both drop-outs for 1 min in a direction parallel to the axis of the fork steerer
 
DogDipstick said:
Positive retention of the wheel is required by most import laws (CPSC/ISO etc). So either should have 'lawyer's lips' or have a small pocket.

Hi, thank you for your good advice! I will take care of this in the design of the dropout.
 
DogDipstick said:
I certainly agree. Farm the job out to exotic printing 3D machines..... they are the newest and best thing. I do not think carbon is very suitable to the rigors of hub motor abuse.

What is the expected purchase price of this item? Hundreds of dollars or more?
about $150
I have added things to the article, maybe that will clear things up
 
avandalen said:
To estimate the size of the market, who has any idea how many bare hub motors are sold worldwide?

Bare motors? As in DIY kits? Keep in mind that based on the posts I see around here and on other similar forums, most of those are sold to people with very low budgets, generally converting a bike that is not even suitable for their usage--so at a guess, "most" consumers of bare hubmotors are not even potentially in your market.

For an actual number, I couldn't even hazard a guess--you'd probably have to check with manufacturers of the motors to see how many they sell as bare motors to places that sell them for DIYers, etc., rather than to companies that build bikes.

If you want a bigger market, you'd probably have to sell to those companies instead (but they will probably not buy it, but instead take one to the place that builds their frames and say "hey, can you copy this real cheap for us?").


What kind of torque limit are you placing on the motors to be used in the dropouts? Looks like it might be fairly low, as even at 10mm thickness, they still look like standard dropouts, which can't really take anything significant (since they're not intended to).
https://www.avdweb.nl/Mavik%20thumbnails/Article_files/Solarbike/Images-mechanical-issues/Carbon-fork/Slotted-U-shaped-dropout-for-hub-motor-fill-442x210.jpg
Slotted-U-shaped-dropout-for-hub-motor-fill-442x210[1].jpg

If you really intend this fork to be used for hubmotors, you could design the dropouts around that purpose, not just making them thick, but with a pinchbolt at the opening, to prevent rotation of the axle, so that the system doesnt' require the end-user to incorrectly mount a random poorly designed torque arm that either came with their motor or that they randomly found on the intarwebz for cheap, and then destroy the dropouts on their very expensive fork.

There are plenty of design examples of clamping or pinching dropouts in the Torque Arm Picture Thread, among other places here on ES, if you need inspiration.

I would also not shape them the way you have there, like "typical" dropouts--I would make them more or less rectangular so the material is still there between the arm inside the fork and the maximum-width portion of the dropout area, which will aid in resisting spread of the dropouts. It adds a little more mass, but it should be stronger this way. You'd have to do stress modelling to see if it is worth doing for your application.
 
amberwolf said:
>>>most of those are sold to people with very low budgets
thank you, I hadn't realized this.

>>> at 10mm thickness, they still look like standard dropouts, which can't really take anything significant
I think, that all hub motors for front forks have axle diameters of 12mm with a flat side of 10mm (also 1000W motors) else they will not fit to any fork.

Carbon-forkSlotted-U-shaped-dropout-for-hub-motor-fill-452x228.jpg


>>>If you really intend this fork to be used for hubmotors, you could design the dropouts around that purpose, not just making them thick
I think that a dropout like the image, of 6mm thick forged chromium-vanadium alloy steel is strong enough, what do you think?
 
Flat mount disc brakes are a boondoggle— they solve no problem with IS mount brakes, but they impose difficulties in getting the brakes adjusted, they introduce a bunch of new adapters, and they cost more like for like.

I consider the presence of flat brake mounts to be evidence that the designer wasn't thinking. It makes me wonder what else they weren't thinking about.

If you want your fork to be specifically hub motor compatible, you'll omit the lawyer lips from the fork tips, use a tough strong material (like 4130 chromoly or cold rolled, laser cut stainless), use generous material thickness (6mm or thicker), and provide a longer than normal axle slot to provide purchase for tabbed axle washers. The resulting fork tip won't look like a normal pedal-only bike fork tip, because it isn't that.

I would take pains to laser cut the fork tip from a flat 1/4" plate, because production will be much cheaper that way than a design that requires bending, milling, or both. Get 4mm thick laser cut C-washers at the same time, and they'll provide the offset you need between the fork tip and an IS caliper tab.
 
DogDipstick said:
No lawyer lips? No such thing as a " safety dropout? " Do you wish to meet " compliance testing"?

What of the requirement for a fork to be produced, on a bicycle, and be certified for sale, that a set or lawyer lips need be deep enough that the retaining bolt / or nut can be loosened 360 degrees and the wheel is still retained?

That's a CPSC requirement for bikes, not forks. Lawyer lips aren't the only way to fulfill that requirement; they're just the most annoying way that's hardest to get rid of.

If the OP is into selling forks rather than complete bikes, it won't matter whether they have lawyer lips or not. But having them will make lots of people's applications needlessly complicated.
 
Chalo said:
>>> I consider the presence of flat brake mounts to be evidence that the designer wasn't thinking. It makes me wonder what else they weren't thinking about.
I have not delved into this issue, please tell me more about it or where can I find it?
Chalo said:
>>>>I would take pains to laser cut the fork tip from a flat 1/4" plate, because production will be much cheaper that way than a design that requires bending, milling, or both. Get 4mm thick laser cut C-washers at the same time, and they'll provide the offset you need between the fork tip and an IS caliper tab.

Thank you good advice!
 
I would avoid putting in the "idiot washer" hole, because it takes out material that's under high tensile stress when the axle is trying to pry the slot open.

Also I'd orient the slot facing forward, so reaction forces from the disc brake aren't in the same direction as the slot opening.

And if increase the width of the material around the corners of the axle slot. Have a look at open end wrenches for well iterated designs that do the same kind of job.

avandalen said:
Chalo said:
>>>> That's a CPSC requirement for bikes, not forks. Lawyer lips aren't the only way to fulfill that requirement; they're just the most annoying way that's hardest to get rid of.
So it isn't mandarory?

Not for forks. It's also at odds with what you're trying to accomplish in terms of compatibility with a range of hub motors.

If you make both sides with identical IS disc tabs, then the right side can be used to anchor a torque arm (which you can also make and sell). Or silly people can put together dual disc setups.

Even if you don't do that, you should incorporate some mounting point that can be used for a torque arm. Best if it's also able to serve another purpose, for instance a fender mount, rack mount, or disc tab.
 
avandalen said:
I think, that all hub motors for front forks have axle diameters of 12mm with a flat side of 10mm (also 1000W motors) else they will not fit to any fork.
What I posted has nothing to do with their axle diameter. (except that smaller axle diameters are harder on the dropouts than the larger diameter ones, for the same applied torque, since it is applied at a smaller radius and over a smaller surface area, and being smaller diameter it is easier for it to spread the dropouts far enough to be able to spin out in them). (also I don't know that all the front motors have only 12mm "tall" axles...I'd have to research that).

Everything to do with the total torque applied to the dropouts, which acts to try to spread any open-ended dropout apart.

Keep in mind you are posting to a forum where quite a few people use much higher current controllers on their motors than the motors were "intended" to be used with, which typically results in higher torque from the motor. While those people often use rear motors for this, not all of them do, and if a fork were designed specifically for a hubmotor to be installed into it, it's likely that more people would use a front motor for this purpose.

Also, regen braking forces from motors capable of it will rock a motor's axle back and forth in teh dropouts, "trying to" pry them open even harder.



FWIW, I have some thick heavy-steel pedicab dropouts to install on my SB Cruiser's fork, that I will then be putting a motor with at least a couple of kW available to it, as well as regen braking. I expect they will probably work well enough, but still wouldn't trust them to not pry open at least a tiny bit, allowing the axle to start rocking back and forth, and prying them more at each brake/accelerate cycle. So I will be adding a pinch bolt to them, as is shown in various such dropouts in the Torque Arm Picture Thread.

These are the dropout plates, just sitting on an "idea" of the fork, from a few years back
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833&p=1466757#p1466746
https://endless-sphere.com/forums/download/file.php?id=252402
dsc08268[1].jpg
 
amberwolf said:
avandalen said:
I think, that all hub motors for front forks have axle diameters of 12mm with a flat side of 10mm (also 1000W motors) else they will not fit to any fork.
I don't know that all the front motors have only 12mm "tall" axles...I'd have to research that.

I have a Leaf front motor with a 14mm axle. I have a Crystalyte front motor with a 14mm axle.

It's easy enough to provide a fork tip that will work equally well with 12x10, 14x10, and 16x10mm axles.
 
I put 3 thousand miles on a Bike Direct Motobecane drop bar bike with a 9c front hub motor @ 1000w and carbon fork. Just used the Grin small torque arm that fit onto a fender brazeon at the dropout. Had to keep an eye on the nuts because I used regen and the back and forth seemed to want to slightly loosen them once in awhile. Other than that I had no issues, just decomissioned it in favor of another build of the same flavor using the Grin All Axle. I was not easy on the bike either and rode it in terrain from sea level to 9000'.
 
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