Front suspension forks question

General Discussion about electric bicycles.
AngryBob   10 W

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Re: Front suspension forks question

Post by AngryBob » Aug 15 2019 5:35am

Motor torque alternating with regen braking can act to loosen your nuts.

The resulting crash can rip them clean off. Your own personal nuts, that is.

Just yesterday, I snapped off my derailler mount on my aluminum frame. No crack, no bending, no warning whatsoever, it just snapped off, without any huge load.

Steel would have most likely bent a bit, or shown a crack, there would likely have been some warning first, and the greater strength would probably not have broken.

Where I was with the traffic conditions, if that had been my front fork, I would probably not be making any more posts, here or anywhere else.

Steel fork. No suspension. No regen. Low power.

Alternative would be to get a really nice insurance policy for your surviving next of kin.

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neptronix   100 GW

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Re: Front suspension forks question

Post by neptronix » Aug 15 2019 9:22am

AngryBob wrote:
Aug 15 2019 5:35am
Motor torque alternating with regen braking can act to loosen your nuts.
Can, yes. However, with a very solid torque arm setup, this is no problem, as you prevent 99.9% of the motion of the axle.. so at worst, the axle nuts can only rotate or counter rotate a millimeter or so. Meaning that they loosen and tighten themselves and sort of maintain a stasis, at the worst.

I had a super stiff torque arm setup and 1kW of regen, 4kW of motion power... nothing

Meanwhile i've thrown 900w peak into a solid front fork and looked down and observed the fork twisting diagonally with the application of power. The axle nuts are not my concern. Work hardening/stress on the fork legs is what kept me up at night on that one.

Now if we're talking about a 20" BMX front fork, which is designed to have >100% of your body weight on it ( cuz you like doing tricks, right? ), then i have no worries about the fork legs distorting under power. Then, you just have funky steering effects and traction issues to contend with, instead of those issues plus the small possibility of the weakest interface on the bike failing on you.
AngryBob wrote:
Aug 15 2019 5:35am
Just yesterday, I snapped off my derailler mount on my aluminum frame. No crack, no bending, no warning whatsoever, it just snapped off, without any huge load.
That's rather abnormal. Any hints as to the cause? ( are you running a mid drive? )
AngryBob wrote:
Aug 15 2019 5:35am
Where I was with the traffic conditions, if that had been my front fork, I would probably not be making any more posts, here or anywhere else.
I flew over the bars on a bike because of an unseen road hazard at 20mph, and it was about as painful as you think it is. The injury still hurts today.
Efficiency is everything :bolt:

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The new all-arounder: Leafmotor 1500w @ 4kW on a Turner O2 full suspension.
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Whipper-snapper: ? on a lightweight BikeE Semi Recumbent

AngryBob   10 W

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Re: Front suspension forks question

Post by AngryBob » Aug 15 2019 9:56am

Yeah, I found it rather abnormal, as well.

This was on my unmotored road bike, climbing a small hill. My second downshift was not entirely clean and I was just about to downshift again, not pedaling very heavily at all, when it just snapped off. Pedal and chain were still powering the wheel up to that point, but sounded like was not cleanly on the cog.

A guess would be the chain got wedged somehow, but again the pedal strokes were not that heavy.
Not sure of the terminology, but the main mount snapped off the frame, also the mount for the two tensioner cogs also snapped, looks twisted a bit.

The timing was also a near-perfect crap storm. Would have made the money I need for replacement bike if I had completed the trip, what was going to be extra money is now needed for essentials, which essentials I need to get paid, which I have not been. Ah, crap.

Fairly frequent high-speed truck traffic right next to me.

The point of this story was to emphasize no aluminum fork with hi-powered motor.

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Re: Front suspension forks question

Post by sleepy_tired » Aug 15 2019 10:22am

If you look closely at the snap you might be able to see some striations... sort of like half-rings on a tree or variations in the texture. Or some discoloration on one side or the other. Some part of the metal that is darker and then a nice brightly colored bit.

That would indicate that it was damaged and cracked sometime in the past and gradually worked it's way free. A crack can work it's way through like a saw would and then when it got most of the way through the rest just snapped off in one big go. If that is the case then it probably has been slowly breaking loose for a while and you just didn't notice the cracks. Sometimes you can't see that sort of thing under paint and grease and such.

If it broke off in one go then the metal would be pretty uniform in texture and color. Maybe with one part in a half-circle line and shinier part where it held on a little bit longer then the rest.

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Re: Front suspension forks question

Post by AngryBob » Aug 15 2019 1:14pm

Interesting.

Looking at the break, it is uniform in color and appears to be somewhat an inverted V shape, lower on both sides and higher in the middle.

Much more grayish than silvery, vaguely resembles finely porous concrete than most metals I am familiar with. Which is not that many and not that much.

Looks like part of the dropout is missing, and also that a metal insert into the frame also failed.

The hanger or bracket for the two tensioner cogs is not twisted so much as pried apart.

Does not appear to be fixable, got the bike cheap as a backup, and other than the tall gearing I did not really like it that much. Too light and whippety, if that is a word. Also a bit small, actually the recommended size for me but for some reason I prefer the larger frame.

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Re: Front suspension forks question

Post by john61ct » Aug 15 2019 3:41pm

I thought aluminium was a categorical no-go?

Cross-reference

viewtopic.php?t=101831

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neptronix   100 GW

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Re: Front suspension forks question

Post by neptronix » Aug 15 2019 4:27pm

Aluminum frames are fine if the motor is in the rear because the rear is around 3x stronger than the front on basically every bike.
As always, you need torque arms, especially at the level of power you'll need.

Aluminum front forks are a bad idea at anything other than 1/10th of the power you'll need. Solid aluminum front forks have a tendency to transmit motor vibration and noise to the frame.
Efficiency is everything :bolt:

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The new all-arounder: Leafmotor 1500w @ 4kW on a Turner O2 full suspension.
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Whipper-snapper: ? on a lightweight BikeE Semi Recumbent

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Re: Front suspension forks question

Post by e-beach » Aug 15 2019 8:49pm

Well, proly time for me to say a bit as I had been riding around on a front hub motor on suspension forks for something approaching 18,000 miles. (a few hundred miles short when my motor lost a hall sensor which has now been repaired.) I suppose I have some experience about it.

Most of what others have said is true. Your forks will need to be a robust alloy. You will need two really good torque arms. The motor pulls the forks forward so when you hit a bump under power the forks don't dampen the shock much. However with steel (rigid) forks it feels like a bomb has gone off underneath you. The answer is to get off the throttle if you see the bump/pothole/whatever coming. I have gone through One steel and one aluminum frame. I am on my second aluminum frame. I am also on my third fork. I got rid of my rigid steel frame due to a really harsh ride. My first aluminum frame cracked at the steerer tube weld after 15000 miles or so. My first suspension fork broke at the fork brace due to stresses from only running 1 torque arm. That took about 6000 miles I think? And the second one I am still on despite the cracked dropout that I have been running on for almost 2 years. My torque arms keep the axle in place. :wink:

When my front hub workhorse bike lost a hall sensor, I moved some components to my full suspension rear drive bike and have been using that this summer. It offers a much more plush ride for sure.

So here is what I think. Go with a rear motor or mid drive motor, it is easier to install, allows the forks to dampen the first impact on a bump, put the batteries in the triangle and enjoy the ride.

Front hubs have there propose, and they might be a little more efficient then a rear hub motor on a full suspension bike, but to get them going, but a rear hub motor with batteries in the triangle will be easier to install, easier to maintain and give you an easier ride.

My 2¢.

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Previous Build:1992 Trek Antelope 800 - Bone Crusher (no suspension) - Yescomusa 800 watt 36 volt front wheel kit. Don't do it! Get suspension!!!

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MadRhino   100 GW

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Re: Front suspension forks question

Post by MadRhino » Aug 15 2019 9:09pm

john61ct wrote:
Aug 15 2019 3:41pm
I thought aluminium was a categorical no-go?

Cross-reference

viewtopic.php?t=101831
Alu frames are best nowadays, except that... If you are gonna spend 200$ on a bike, cheap steel is better than cheap alu.

A DH racing frame can be built a better, safer ride than most motorcycles.
Make it fool-proof, and I will make a better fool.
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Re: Front suspension forks question

Post by markz » Aug 16 2019 3:43pm

If your buying new, dont go front hub motor just buy a rear hub motor.
Front hub motors are narrower, less heat can be shed, and there is less power, you cant hide a front motor that easily like you can with a rear hub motor.

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dogman dan   100 GW

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Re: Front suspension forks question

Post by dogman dan » Aug 18 2019 8:35am

You might want to hunt down an ancient thread of mine where I build a 50 mph bike for a race, using a front hub. look for the keyword death race in the thread title.

Summing it up, I started with a very good quality cromoly fork from a high price MTB. It was old, back to when MTB's did not have shocks. But basicly, look for a good fork, not something off a huffy.


The key to pulling 4000w on that front hub was the torqe arms. I welded steel plates to the fork for the common torque arm to bolt to, with two allen wrench bolts. No way that motor budged.


The real trick to it though, was never give it full throttle in a corner. Wheee!

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Re: Front suspension forks question

Post by john61ct » Aug 18 2019 2:35pm

dogman dan wrote:You might want to hunt down an ancient thread of mine where I build a 50 mph bike for a race, using a front hub. look for the keyword death race in the thread title.

Summing it up, I started with a very good quality cromoly fork from a high price MTB. It was old, back to when MTB's did not have shocks. But basicly, look for a good fork, not something off a huffy.


The key to pulling 4000w on that front hub was the torqe arms. I welded steel plates to the fork for the common torque arm to bolt to, with two allen wrench bolts. No way that motor budged.


The real trick to it though, was never give it full throttle in a corner. Wheee!
You Da Man dogman dan!

Could you be a bit more specific about suitable fork-donor bikes?

I am willing to scour CL etc to find such a fork, but have literally no idea about brands or years, never heard of Huffy for example.

Also, are there size issues, fitting to an old Columbia tandem frame for example?

Will look for your thread.

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Re: Front suspension forks question

Post by john61ct » Aug 18 2019 2:41pm

Hmm

started with
https://www.google.com/search?q=site%3A ... +front+hub

more detailed: https://bit.ly/2YWqda1

Fertile research rabbit hole, but looks like the one right thread is a bit buried?

Lots of ads for new forks jump out at me too, is that an option?

Is Chromoly always better than just super-heavy gauge SAE steel?

Weight is not an issue, trying to get more forward, will likely put a battery or other cargo in a basket.

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ddk   1 MW

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Re: Front suspension forks question

Post by ddk » Aug 18 2019 3:59pm

neptronix wrote:
Aug 15 2019 1:02am
Of you want strong braking, then a rear DD with regen is the ticket. it can slow you down better than any mechanical brake. I'd absolutely not run high power regen on the front though as you're liable to be thrown off forwards.
O RLY?
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O RLY.jpg
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O RLY.jpg (66.16 KiB) Viewed 188 times
note: both trikes have front and rear motors whereas the front motor regen provides much stronger braking than the rear braking. :pancake:
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Re: Front suspension forks question

Post by neptronix » Aug 18 2019 4:07pm

Oh, you can get away with that on something like a big ol' heavy or just long trike..

What i wouldn't do strong front regen on is a run of the mill 2 wheeler bike frame!

Also, that extended length springer fork bent at that insane angle gives me the heebie jeebies.
Efficiency is everything :bolt:

My first major build: 1.6kW 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w @ 4kW on a Turner O2 full suspension.
The monster scooter: 20" eZee on a Cannondale Semi Recumbent.
Whipper-snapper: ? on a lightweight BikeE Semi Recumbent

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Re: Front suspension forks question

Post by ddk » Aug 18 2019 4:28pm

neptronix wrote:
Aug 18 2019 4:07pm
Oh, you can get away with that on something like a big ol' heavy or just long trike..

What i wouldn't do strong front regen on is a run of the mill 2 wheeler bike frame!

Also, that extended length springer fork bent at that insane angle gives me the heebie jeebies.
I'm just having fun with your (incomplete) statement :lol:

... as for the springer fork, I've been using that design for 8 years and have worked out any kinks a long time ago.
I even tested it at 60 some miles an hour (over-heated brake failure down a mountainous 7%-11% grade - why it now sports regen in the front wheel)

...and you might notice I'm still somewhat alive.
"How can we play Hot Wheels without lighter fluid? " -Serge

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Re: Front suspension forks question

Post by john61ct » Aug 18 2019 7:00pm


ddk wrote:both trikes have front and rear motors whereas the front motor regen provides much stronger braking than the rear braking
Exactly why I'm starting off focused on the front hub first, and multiple motors is likely where my design is headed.

I'm very willing to do whatever it takes wrt the forks and frame to accomplish these goals, including dogman style custom welding.


Last edited by john61ct on Aug 18 2019 7:00pm, edited 1 time in total.

john61ct   100 kW

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Re: Front suspension forks question

Post by john61ct » Aug 18 2019 7:02pm


ddk wrote:O RLY?
(I always wanted to use that meme)
O RLY.jpg
My noobish eyes are really not sure what I'm even looking at there.

If they come from build threads with actual value, would appreciate links.

If just funny/silly then never mind 8-)



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ddk   1 MW

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Re: Front suspension forks question

Post by ddk » Aug 18 2019 7:23pm

john61ct wrote:
Aug 18 2019 7:02pm
...My noobish eyes are really not sure what I'm even looking at there.

If they come from build threads with actual value, would appreciate links.

If just funny/silly then never mind 8-)
they are both trikes with dual motors, so I doubt their builds would satisfy your requirements, as trikes are much easier to work in a multi-motored system.
And they were built before certain developments have changed the para-dimes, or para-quarters of e-motored stuff. i.e it's a lot easier these days.

That said the post in question was meant to be a silly j/k
...and anything is possible with the right sort of bicycle/tricycle
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