Front Hub Motor on a Carbon Road Fork, with what mods ?

[Chalo]

The twist on a hub motor axle is always equal and opposite to the twist the motor puts on the wheel, if that helps you figure it out.

Carbon forks started out with steel steer tubes and aluminum crowns and tip inserts. These days, a carbon fork is likely to be completely made of CFRP-- steer tube, crown, even tips. I imagine that most disc braked carbon forks have a metal insert for attaching the caliper, but I'm not sure of that.

We don't have any busted carbon parts at the shop, but it would be a good idea to keep some around to help demystify the material for people who are curious.

 

[ScooterMan101]

Mikebergy,

The Q100 328 rpm graft on the ebikesca website , under Motor Simulator-Tools is just a Q100 not a Q100H or a Q100H with different laminations.

Supposedly the Q100 H that you and I an others are interested in getting , the one with different laminations are guessed to be 50% more torque, and that might be more than the standard Q100 H,

If I am reading correctly the Q100 has about 25 nm torque at 20 mph, / and about 43 nm at 5 mph / and 54 nm at 0 mph so if adding 50% then it would be 80 nm at 0 mph, etc.

Wonder what the Disc Carbon Road Forks are tested at ?

For anyone who still thinks about just using a steel fork, well this thread has turned into a question as to what a carbon fork can do, and that is still information I would like to know,
even if I were to have to buy a steel fork . Someone out there is going to try it with a carbon road fork.
Endless-Sphere is a great group for finding out technical information, even if one were to go a different route in regards to what component one ends up using.

>

This it a very strange conversation. The OP asked about putting a Q100H into a carbon fork. The Q100H is not a torque monster. I couldn't find any official spec, but the q100 330rpm at 48V on the simulator say 55N-m max torque at zero RPM. That's the equivalent of pulling the fork forward with the force of about 34lb. That's at a full stop, and only decreases from there as the bike increases speed. If you wanted to check if your carbon fork could sustain this, you could just pull on your fork with 35lb of force at the axle. Without doing a bunch of free body diagrams, I'd bet most forks would take that no problem. I bet heavier riders put this much force into the fork just riding the bike.

 

[ScooterMan101]

Meaning Counter Clock Wise then ? , since the wheel rotates forward clockwise to get us down the road,
or
when you say wheel, do you mean the hub ? which would then be different ?

Yea a cut out on different forks would be helpfull, just like gas engine mgf's will do that to help people see how an Internal Combustion Engine works.
A dremel used on forks, to cut out a slot big enough to see how much metal is at the drop out and how far up the fork it goes,
When I get some time next week, I will try to find some busted forks at some of the bike shops.

The twist on a hub motor axle is always equal and opposite to the twist the motor puts on the wheel, if that helps you figure it out.

Carbon forks started out with steel steer tubes and aluminum crowns and tip inserts. These days, a carbon fork is likely to be completely made of CFRP-- steer tube, crown, even tips. I imagine that most disc braked carbon forks have a metal insert for attaching the caliper, but I'm not sure of that.

We don't have any busted carbon parts at the shop, but it would be a good idea to keep some around to help demystify the material for people who are curious.

 

[ScooterMan101]

I just called a local bike shop, asked for a carbon road fork that someone had crashed and broken, that was about to be thrown away.
Bike shop employee stated that they rarely have that,
he said that most people who crash their carbon road bikes, have the bike shop take it apart and ship out the fork or fork and frame
to a place in San Jose, that , now get this, ... repair's it !

With steel forks it is more of a mix of fix or replace.

He said, with all the aluminium forks they wind up replacing, of course we can guess that easily .

Interesting thing here is that even if the carbon fork was snapped in two , it still almost always goes to the Carbon/Fiberglass Repair shop.
comes back , and is ridden .

Edit : to Chalo's experience at his bike shop, ( below post ) Yea , It really surprised me when he said they ( owners of crashed bike ) sent the carbon forks out to get repaired .
I would just replace it since you can get a generic carbon fork for just over $ 130 , or for a brand name one up to $ 500 if your are wealthy and want to spend that much. The repair however seems to be much cheaper.
I have seen carbon frames that have been patched up/repaired, I once saw a carbon fiber wing of a rigid wing hang glider being patched up once, and then flown . I am not ready to write off carbon fiber
for use on a fork that is designed for use with hub motors. Steel is available now, but then again, we do have the future, and the future always brings to us , improvements

 

[Chalo]

Interesting thing here is that even if the carbon fork was snapped in two , it still almost always goes to the Carbon/Fiberglass Repair shop.
comes back , and is ridden .

It's like putting a cast on your broken leg, only your leg never heals and the cast never comes off. But yeah, you can do that.

At my shop, they mostly leave with the owners as keepsakes/curiosities.

 

[Mikebergy]

Interesting thing here is that even if the carbon fork was snapped in two , it still almost always goes to the Carbon/Fiberglass Repair shop.
comes back , and is ridden .

It's like putting a cast on your broken leg, only your leg never heals and the cast never comes off. But yeah, you can do that.

At my shop, they mostly leave with the owners as keepsakes/curiosities.

That's not really a great analogy. When the carbon is repaired, they usually remove the broken material, and then replace it with new material, taking care to orient the fibres in a way that works the same way as the original. There is also a lot of surface prep involved so that the new material bonds adequately with the original material. I believe most shops probably use Calfee for their repairs, but I am sure others are out there. You could probably call them, or Enve, or IRD, if you wanted to see what these forks are capable of from the people who design them. Given the number of large folks riding around on these bikes, I would not be surprised if these forks were able to take the loads similar to any modern steel fork. This doesn't account for your need to secure it with torque arms, but until I'm pointed to a thread where someone broke their carbon fork at the crown due to adding a motor, I'll not be to concerned. I plan on using proper nuts to secure my front motor, and as I will have dual motors, there should be less stress as the load will be distributed for me.

Regarding the torque direction, since the wheel needs to be spun forward for forward motion, the opposing force will be backwards, 'pushing' against the front of the fork arms.

 

[Mikebergy]

Mikebergy,

The Q100 328 rpm graft on the ebikesca website , under Motor Simulator-Tools is just a Q100 not a Q100H or a Q100H with different laminations.

Supposedly the Q100 H that you and I an others are interested in getting , the one with different laminations are guessed to be 50% more torque, and that might be more than the standard Q100 H,

I am not overly concerned for the increase in torque, I'm chasing better efficiency. There will likely be an increase in torque but it probably won't be at the zero RPM, probably just a less steep dropoff as RPM increases. Sorry to be off-topic.

 

[Punx0r]

Disc brakes don't snap carbon forks because of that bend about 3/4 of the way down the fork-Notice how it bends forwards? So, a hub motor would apply torque in the opposite direction. BUT! if you use a geared motor, it will be spinning backwards (With the gears spinning forwards) and will apply torque in the same direction as a disc brake.

Both geared and direct-drive hub motors result in torque reaction to the fork in the same direction. It has to if you want to accelerate forwards!

 

[Jasonv8z]

S works Venge:
7.7Kg
+ 2.7kg (250w hub)
+ 5 Kg (Bats+controller)

Assuming 48v and a Kv of 9.8 we get 5 amps of load, and figuring our Kq at 30/(3.141*9.8) at ~0.9, you get 5 Newton Meters of torque.
F=MA
T=FR
A=T/R/M
0.98km/h per second of acceleration

Shitey. No fun at all, and at 250W you'll take 30 seconds to reach 30, maybe 15 if you pedal. Crap.

Or we go with steel forks (+5 Kg to be hyper pessimistic and prove a point) and for less cost than this stupid carbon torque arm business get a bigger motor (1000w) at 48v with a Kv of 9.8 at 25A (KQ 0.9)

22.5/0.33/20.4= 10 Kmh/s of acceleration! Crazy!

There's a problem with this math. Due to inductance, phase current is much greater than battery current at startup. Run a simulation on ebikes.ca and you'll see even tiny 250W motors with tiny controllers with 40+ N.m of torque at statup.

I do agree that the fastest bike will be the one with the most powerful motor regardless of extra weight, but some of us are building lightweight bikes for reasons like having to carry the bike up the stairs or wanting a bike that still feels like a bike and not a slow motorcycle.

 

[Mikebergy]

Just an FYI, I did a little reading, and ASTM standard testing of forks requires a minimum pull test of 170lb perpendicular to the fork angle, in both directions, push/pull, so unless you have a motor with 180-200/lb-ft of torque, all you have to worry about is stripping the mounting points.

 

[Deafcat]

Bike Nashbar sells a carbon fiber 700C Cyclocross fork with both cantilever and DISC brake mounting on it... available in both 1 inch and 1-1/8" diameter steerer tubes. took me a week of digging to find out about it, the best part is they are not expensive (and are on sale right now). Picked one up for 100 USD plus cheap shipping... absolutely solid price if you're planing to experiment.

As for your questions about reinforcing a carbon fork to take a front drive hub: I have no doubt this is possible, you just need to be smart and not cut corners. first choice of reinforcement material would be 6-4 titanium (my fav), in lieu of that I would use formed steel, and under no circumstances would I use aluminum. I would comprise the reinforcing elements out of two-part design, on both forks, with a rigid thermoformed plastic to insulate between the metal housing and the carbon fork. the surface area of contact needs to be spread out, but this doesn't mean it needs to be heavy... it's a matter of creating a strong interface over the carbon fork in such a way that it does not create intense stress zones when lateral forces are applied (such as disc braking, and most of all, motor torque in relation to the ground). the two part/clamshell construction could be held together with a series of small high quality fasteners, with threadlocking compound. it's not a simple process and most of all requires a serious degree of fab talent to do it properly (forming, welding, D+T, or CNC the whole thing if you're nuts), but I've no doubt it can be done... It's too bad I'm a RWD kinda guy or I'd do it myself and help ya out. (I got these forks with only the intention of attaching disc brakes, for which they were designed).

the best idea though, is just use steel forks... they are easy to modify and weld, and failure states for steel forks are very forgiving!

 

[4sken]

Disc brakes don't snap carbon forks because of that bend about 3/4 of the way down the fork-Notice how it bends forwards? So, a hub motor would apply torque in the opposite direction. BUT! if you use a geared motor, it will be spinning backwards (With the gears spinning forwards) and will apply torque in the same direction as a disc brake.

Both geared and direct-drive hub motors result in torque reaction to the fork in the same direction. It has to if you want to accelerate forwards!

AFAIK some hub motors actually run backwards due to the gear reduction-Two stage planetary requires the motor to run backwards to get forwards at the final stage.

 

[Mikebergy]

Disc brakes don't snap carbon forks because of that bend about 3/4 of the way down the fork-Notice how it bends forwards? So, a hub motor would apply torque in the opposite direction. BUT! if you use a geared motor, it will be spinning backwards (With the gears spinning forwards) and will apply torque in the same direction as a disc brake.

Both geared and direct-drive hub motors result in torque reaction to the fork in the same direction. It has to if you want to accelerate forwards!

AFAIK some hub motors actually run backwards due to the gear reduction-Two stage planetary requires the motor to run backwards to get forwards at the final stage.

Yes but the resulting force still pushes on the bike the same way at the mounting points.

 

[Deafcat]

I think they call it Newtons 3rd law, applied to rotation :wink:

the simplest way to think of it: your bike is being thrusted forward in (equal and opposite) reaction to the rotational torque being applied to the ground by your motor-wheel... so your fork in this case, better be up to that thrust load, or you and the rest of the bike will not be able to keep up so well.

 

[Punx0r]

Yes. Motor direction is irrelevant, only the direction of the output shaft matters

 

[ScooterMan101]

That is what I thought,
So we see that even though a disc fork is stronger,
there is still a problem with a hub motor and a typical torque arm, on a fork that was not designed for a hub motor in the first place .

For instance: using a torque arm that would reach around towards the rear of the dropout/lower fork leg, on up to the bottom attachment point
of the disc caliper bolt / leg support , would result in the torque arm wanting to be pulled down and out of the threads .
Not the best point to attach a torque arm.

The typical ( old fashion way of resting the torque arm up against the fork leg , with a hose clamp, is so archaic that it is a last century band aid , mickey mouse , design .

The much better solution is to design a fork ( Chromoly , And , Carbon )
That has the same type of disc brake caliper attachment points on the ... Front of the fork as well .



That way the force of the torque arm/force will be pushing on the leg of the fork. with a stronger system, Much stronger
( this can easily be done with a carbon fork by using more material at the bottom of the fork legs , making it be much thicker all
around on the lower 25-35% of the fork legs. )

So Both Cromoly , and , Carbon Forks need to be redesigned for use with a front hub motor !

Yes but the resulting force still pushes on the bike the same way at the mounting points.