Geared hub failure mode

I have disassembled the geared hub (I just couldn’t wait) and found the failure mode. One of the 440 stainless steel planet shafts (part number 3 on my drawing number 2) was completely galled and spun in the axle/planet cage (part number 1 on my drawing number 2). The bore of that planet gear (part number 2 on my drawing number 3) was destroyed. At one time during the day I could get the hub to turn relatively freely, but mostly it was bound up.

I intend to machine the planet cage off of the axle and locate the shaft holes (correctly this time) on a new piece that I can press onto the axle and spot weld. The 440 stainless steel shafts will be replaced with hardened steel dowel pins that are undersized (1/4" instead of 8mm). I will bore out the planet gears and press bronze bushings into them to fit the dowels. In other words…I’ll do that part correctly this time.

Interestingly, even at that INCREDIBLY ABRUPT change in velocity no damage was done to the gear teeth. This is a good thing…it shows how rugged the gears are. Knowing of this mishap, I wonder how much interest will remain in beta testing after I modify the hubs.

I’m sorry I have posted no photo yet. My camera and the hub parts are in two different places. I will certainly get a good close up of the galled shaft but the gear bore may be impossible to see.

Re: Geared hub failure mode

I’m shocked- I expected the gears to become shrapnel… wow! I know you turned the hub in a mechanism before spoking it up- do you think a longer run on the machine would have exposed the weekness?

If the menace makes it’s way to me, I’ll be wairing my Kevlar Magic full face helmet, and this:

Christopher

Chris-

It hurts me deeply knowing that you named that image “harperproof.jpg”. I take it you’re ready to beta-test as is then? I, of course, was riding naked as I had promised but my wife refused to take any photos.

Harper -

The catastrophic failure of you hub is a bad deal! I know that stainless steel is notorious for galling in stainless-on-stainless applications but I wouldn’t have expected any problems like that since the gears aren’t stainless and they were running in grease.

Sounds like you have a proper fix in mind though … I wouldn’t have a second thought about giving old “one fifty” a spin after the modifications.

Good luck!

Steve Howard

Thanks for the vote of confidence, Steve. I will have second, third and many other thoughts during the testing phase after the mods, though. I will still remember seeing that pavement suddenly sliding underneath me 3 inches from my nose.

Re: Geared hub failure mode

Hi!

Yesterday I rode my geared unicycle without any problems. But when I
first did some riding on the street i promised to ride only with full
protection at higher speed. It is really dangerous because you don´t
feel how fast you are and running after an unwanted dismount is nearly
impossible.

I hope you will be back on your uni soon!

On Mon, 25 Feb 2002 20:48:43 -0600, harper
<harper.nvqb@timelimit.unicyclist.com> wrote:

>
>I have disassembled the geared hub (I just couldn’t wait) and found the
>failure mode. One of the 440 stainless steel planet shafts (part number
>3 on my drawing number 2) was completely galled and spun in the
>axle/planet cage (part number 1 on my drawing number 2). The bore of
>that planet gear (part number 2 on my drawing number 3) was destroyed.
>At one time during the day I could get the hub to turn relatively
>freely, but mostly it was bound up.

I think the problem is that the shafts are only fixed at one side. In
my hub (which uses parts from a 7speed bicycle hub) the shafts are
supported on both ends. And all of the bicycle hubs that i have
checked have such a planet cage which encases (?) the planet gears.
They know why…

See my hub on

My hub also needed a little improvement today: i felt that the tube
(yellow part on the CAD drawings, it carries the gear ring) between
the spoke flanges (green) twists on the spoke flanges when full torque
is applied. That was very interesting: to stop you could just block
the pedals and you had about 70% of your maximal braking power. But
not only at the horizontal positions of the pedals but steady. Very
interesting feeling. But because this was not really controllable i
inserted 3 bolts to lock the spoke flange to the middle tube.

Today I will take my uni to a gym (there´s a heavy storm in germany
today, no fun riding outside) and have some inddor riding. Perhaps i
will try to set a new world record in juggling 5 balls on a geared up
unicycle…

Get well soon, Greg!

UniFrank

Re: Re: Geared hub failure mode

I ran out a UPD yesterday about 4 miles before I faceplanted. You are right in that after awhile you don’t pay attention to how fast you are going…and on these geared unicycles you are always going fast. But it was different from a Coker in that when my foot came off of the pedal, the pavement was right there. It wasn’t a long drop to the ground like from the Big Boy. Also, I had a 15 pound unicycle with a 24" wheel chasing me as I held onto the seat rather than a 27 pound unicycle with a 36" wheel chasing me. It was much easier to stop without dropping the unicycle.

I can picture attaching a ring to the planet cage offset by spacers and bolts. It could have holes bored for the six shafts to capture the ends and hold them fixed radially. Does your system work in some similar way?

Re: Geared hub failure mode

harper.oxp0@timelimit.unicyclist.com writes:
>Unifrank wrote:
>>
>> It is really dangerous because you don¥t feel how fast you are and
>> running after an unwanted dismount is nearly impossible.
>>
>
>I ran out a UPD yesterday about 4 miles before I faceplanted. You are
>right in that after awhile you don’t pay attention to how fast you are
>going…and on these geared unicycles you are always going fast. But it
>was different from a Coker in that when my foot came off of the pedal,
>the pavement was right there. It wasn’t a long drop to the ground like
>from the Big Boy. Also, I had a 15 pound unicycle with a 24" wheel
>chasing me as I held onto the seat rather than a 27 pound unicycle with
>a 36" wheel chasing me. It was much easier to stop without dropping the
>unicycle.

Interestingly, my brother’s injury (bone bruise from a nasty fall) came on
a 28" Sem, not his Coker. The advantage to the big boy is that you might
have a bit longer to react before your foot has to hit the pavement.

David Stone

Co-founder, Unatics of NY
1st Sunday / 3rd Saturday
@ Central Park Bandshell
1:30 start time after 11/1/01

Re: Geared hub failure mode

In article <rhysling.nxcp@timelimit.unicyclist.com>,
rhysling <rhysling.nxcp@timelimit.unicyclist.com> writes:
>
> I’m shocked- I expected the gears to become shrapnel… wow!
>

But the moment they seized, the rider was chucked off. Even a
fairly innocuous binding that a bicycle could ride through, would
have triggered a catestrophic dismount. Angular momentum of the
wheel would easily translate into angular momentum of the
wheel-and-frame, and the rider would create very little force to
keep the wheel turning through the failure of the gearing. Without
that force, the gearing is not greatly stressed.

Picture the unicycle suddenly turning into a vertical stick. There
is no force that causes the stick to scrape end-wise across the
ground, just a tendency for the whole stick to fall over - and dump
the rider.

============================================================
Gardner Buchanan <gbuchana@rogers.com>
Ottawa, ON FreeBSD: Where you want to go. Today.

There was an impulse during which the rider was rotated flat onto the pavement. During that impulse there was a tremendous change in the angular velocity of the elements of the gear train. This did, in fact, greatly stress the gear train.

Re: Geared hub failure mode

> Picture the unicycle suddenly turning into a vertical stick. There
is no force that causes the stick to scrape end-wise across the
ground, just a tendency for the whole stick to fall over - and dump
the rider.

Don’t try using SPD pedals until you work out its mean time between failures
!

Leo White

Re: Geared hub failure mode

On Tue, 26 Feb 2002 23:31:42 GMT, gbuchana@gromit.dhs.org (Gardner)
wrote:

>Angular momentum of the
>wheel would easily translate into angular momentum of the
>wheel-and-frame.
>Picture the unicycle suddenly turning into a vertical stick. There
>is no force that causes the stick to scrape end-wise across the
>ground, just a tendency for the whole stick to fall over - and dump
>the rider.
Your “angular momentum” statement is only a little part of what
happened. Because it not only has to translate into wheel-and-frame,
but wheel-and-frame-and-rider angular momentum. And with so much mass
in the rider, the rotational speed would be low if it were for angular
momentum conservation only. Your second paragraph tells the rest. It
is forward (translation) momentum that carries the rider forward, and
because of the friction between tyre and road (combined with blocked
gears) the whole system topples over.

Klaas Bil

“To trigger/fool/saturate/overload Echelon, the following has been picked automagically from a database:”
“Taliban, Kalifaatstaat, Gore”

Re: Geared hub failure mode

In article <3c7d62f8.1887140@newszilla.xs4all.nl>,
klaasbil_remove_the_spamkiller_@xs4all.nl (Klaas Bil) writes:
> On Tue, 26 Feb 2002 23:31:42 GMT, gbuchana@gromit.dhs.org (Gardner)
> wrote:
>
>>Angular momentum of the
>>wheel would easily translate into angular momentum of the
>>wheel-and-frame.
>>Picture the unicycle suddenly turning into a vertical stick. There
>>is no force that causes the stick to scrape end-wise across the
>>ground, just a tendency for the whole stick to fall over - and dump
>>the rider.
> Your “angular momentum” statement is only a little part of what
> happened. Because it not only has to translate into wheel-and-frame,
> but wheel-and-frame-and-rider angular momentum. And with so much mass
> in the rider, the rotational speed would be low if it were for angular
> momentum conservation only. Your second paragraph tells the rest. It
> is forward (translation) momentum that carries the rider forward, and
> because of the friction between tyre and road (combined with blocked
> gears) the whole system topples over.
>

The energy that went into gear-bashing is partly the energy that
was transferred from the spinning wheel to the frame - through the
seized gears. There would also be some more input (briefly) by
the rider’s pedaling against the seized gears. Most of the energy
stored in the system - the rider’s forward inertia - is harmlessly
spent in smashing up the rider’s body, and does not travel through
the siezed gears.

Therefore the gears, at least, come through without too much damage
because they didn’t dissipate much energy during the failure.
Small consolation to the rider, but maybe a plus for the guy who
wants to fix the gears. I wonder if Greg sees it that way?

============================================================
Gardner Buchanan <gbuchana@rogers.com>
Ottawa, ON FreeBSD: Where you want to go. Today.

Yes I see it that way. The same gears will go into the modified unit. I turned down the axles tonight and took some photos but I won’t post any until I make the planet cages which are substantially different.

Most of the the energy, which is stored in the moving mass of the rider, is thrown forward and away from the unicycle entirely. There is that component which threw the rider flat on the pavement with no time to get a foot out. Why is that? The seatpost, loaded with the full weight of the rider, rotated forward abruptly. The back of the seat through a frictional force, pushed the rider down. This is the impulse which stressed the gear train. In a perfect world (or on a greasy seat which I consider an imperfect world) the rider would have flown/slid off with much less stress to the gear train and may even have had time to put a foot down.

I’m shocked Sir, shocked I say! Considering the level of intimacey you shair with your saddle, that you do not employ this fine product:

Unicycle.com- Butt’r

It’s the least you can do.

Christopher

Chris-

I did not know that a multipurpose lubricant like this was made for the cycling community. The add was goading me to “click here to see more” but at that point I killed the window in shear terror.