Design problems with Nimbus ISIS hub

[tholub]

I just bought a Nimbus X 20" freestyle unicycle, which is the first unicycle I've owned with the Nimbus ISIS hub. I mentioned back in this thread that the Nimbus design seems to be in violation of the ISIS spec. After looking at the overall hub design, it seems to be only one of several extremely questionable design and/or manufacturing issues with this hub.

YouTube - Nimbus X hub design problems

In this video, I demonstrate that my wheel is not spinning freely, even after I've totally removed the bearing holders. The spacer between the cranks and the bearings is causing friction in the system; the wheel spins more freely when the cranks are removed (which should never be the case). In addition, the Kris Holm-branded bearing shims appear to be of a particularly soft aluminum; they are already deforming and producing aluminum shavings. One of the bearings, I could not get out of its bearing holder, yanking on the frame as hard as I could; I had to chisel it out. Also, on one side, the bearing shim is loose on the bearing itself, creating slop in the system.

unicycle.com needs to come out with a hub which:

• has a real ISIS crank stop
• has bearings press-fit to the axle so as not to require spacers
• uses bearings with steel outer races and/or shims

And while you're at it, do it with 36 holes.

[hungry4uni]

This is really interesting. I've also noticed a bit of difficulty in removing my frame. However, not nearly as much difficulty as yours!


Would it be easier to flip if the wheel spun freely.


Oh, and I may be wrong, but maybe you clamped the wheel in to tight with the bearing holders.

I screwed up my bearings by doing this.

[tholub]

Originally Posted by hungry4uni

Oh, and I may be wrong, but maybe you clamped the wheel in to tight with the bearing holders.

I screwed up my bearings by doing this.

I personally didn't clamp the wheel in tight; in fact, when I got the thing and saw that it wasn't rotating freely, I loosened the bearing holders, thinking they must have been too tight at unicycle.com, but they weren't particularly tight. As I demonstrate in the video, the bearings themselves are working just fine, once you stop rubbing things against them.

[SqueakyOnion]

Your thread got me interested because I have the Nimbus ISIS hub, on the Nimbus 29" (stock) I bought a little over a year ago. I, too, have to use the spacers as the bearings are not press-fit and were sliding off when the uni first arrived to me. Spacers were sent, and I haven't had issue since, and the wheel spins freely. My spacers contact the inner metal race of the bearings, thus creating the correct motion of crank-spacer-inner race moving together. I shot a quick video to demonstrate the rotation with cranks and spacers removed,

embedded here

It appears that the inner race of my bearing is wider than yours; the spacer does NOT contact the black area at all during rotation. Upon close inspection, I see no wear on the spacers, or any other evidence of friction.

Secondly, my bearings never get stuck in the frame. They sit snugly, but come out with minimal force.

This leads me to conclude that the problem may lie in your bearings, which are not the same as mine. Mine are not branded Kris Holm.

[Tyler_N]

Originally Posted by SqueakyOnion

Mine are not branded Kris Holm.

my KH has qu-ax bearings? i don't think KH brands his bearings. at least not on my older model.

[Jeremy R]

I beleive you are using the new ISIS 40 mm bearings, not the usual 42mm.

The smaller bearing changes the size by a milimeter (radius) so the spacer should hit 1 mm of the outer seal.

Get a new 42mm bearings and frame.

edit: if this is the case



As you can see, the spaces makes no contact with the seals. Try getting new spacers if measurements for the bearings are right.


Call UDC, ask for a new hub if all else fails.

[Shug]

Very interesting video ...... way to get to the root.
Always get in a hack when something comes and it isn't quite right. Hope they do you right at UDC.

[rogeratunicycledotcom]

This is all certainly interesting. I am not sure that it is a "design problem with Nimbus ISIS hub" is really a correct thread description. Your problems seam to be associated with the KH 40mm double bearings.

Now, let’s have a look at this.

Bearing shields and spacers...
The spacers for the bearings are supplied to match the bearings (by KH, not UDC or Nimbus). They should not touch the moisture shield at all. I have attached an illustration of how bearing shields work, they are always recessed. This is so that the clamping surface can be larger than the minute edge of the bearing. The design is not at fault here... I have a couple of suggestions for the touching though. The writing on the bearing shield is proportionally higher than on larger bearings and it is this that is touching. The other thing is that the spacer could have been deformed on contact with the thin bearing edge when it is clamped. Both are solvable, a bit of wet and dry on the shield (the problem will be inside and out I guess) and a flattening off of the leading edge of the bearing shield.

Deformation of the bearing outers. The original design was for a steel outer and I am not sure where it got changed to an aluminium one or what specification it is. If the damage to the shield has just been caused by normal use then this is not good, it is odd that it has primarily happened on one side not the other.

It is worth realizing that these bearings are tiny, they are very delicate. Their design advantages are to give a more rigid frame and allow their fitting in to 40mm frames. They will of course not spin as freely as single row bearings, especially when new.


Roger

[Big H]

Originally Posted by tholub

I just bought a Nimbus X 20" freestyle unicycle, which is the first unicycle I've owned with the Nimbus ISIS hub. I mentioned back in this thread that the Nimbus design seems to be in violation of the ISIS spec. After looking at the overall hub design, it seems to be only one of several extremely questionable design and/or manufacturing issues with this hub.


In this video, I demonstrate that my wheel is not spinning freely, even after I've totally removed the bearing holders. The spacer between the cranks and the bearings is causing friction in the system; the wheel spins more freely when the cranks are removed (which should never be the case). In addition, the Kris Holm-branded bearing shims appear to be of a particularly soft aluminum; they are already deforming and producing aluminum shavings. One of the bearings, I could not get out of its bearing holder, yanking on the frame as hard as I could; I had to chisel it out. Also, on one side, the bearing shim is loose on the bearing itself, creating slop in the system.

unicycle.com needs to come out with a hub which:

• has a real ISIS crank stop
• has bearings press-fit to the axle so as not to require spacers
• uses bearings with steel outer races and/or shims

And while you're at it, do it with 36 holes.

I am pretty sure that UDC US has decided to get rid of theyre old (40mm) frames by using the new KH bearings to allow them to use the ISIS hub. I would be fairy annoyed with this too if I was not aware of this when I bought it. It appears to me that all of your problems are associated with the bearings, not the hub, as Roger Mentioned. I have 1 nimbus hub and 2 KH hubs (that are basically the same) and they all have the 22x42x12 "ISIS" bearings, without any shims.

I have some issues with some of your other statements though.

As I stated in this thread there is no reason not to use the spacers as crank stops, and they are a very real crank stop. You could machine the axle with solid crank stops, but this would require larger bearings and hence another frame type, just when they are fairly standard.

I agree that the bearing shims should be made of steel, better is to not use a shim at all (ie supply the frame that is designed to work with the hub)

The nimbus ISIS hub is avaliable in 36 Hole, but the Nimbus X (and most freestyle uni's) come standard with 48 hole wheels. That is quite clear on their website specs, so I think you have to wear that one if you are unhappy.

[rogeratunicycledotcom]

I think you may be missing the point a little with these bearings.... they are considered an upgrade! They are lighter (a lot!) and are twin row of bearings so create a more rigid system. I use them on my 36".

As for the bearing fit on the ISIS hubs, they are all non standard and are outside the normal criteria for bearings. To get the ISIS to work on unicycles at all a lot of work has been done to specify and manufacture bearings that will do... (the nearest standard bearing is the 6005-2rs which is 25x47x12) there has of course had to be compromises here. Basically the outershells on our bearings have to be thinner.

Normal bearings can be fitted on the shaft using a H7/s6 press fit, with our bearings this would not work as they would distort due to the thinner shells. We have to work with a slacker tollerance, the theoretical tollerance (from memory) is H7/n6 which is transition fit. These are tight tollerances and once we have paint/finishes on this does vary. This is something we of course keep an eye on.

On a sideline.... the ISIS complience of the current hub and KH cranks is correct as far as we can determine. There are some ISIS cranks that do not meet 100% of the criteria due to clearances, but work. That is overall... looking in detail at tollerances, the ISIS standard is actually rather slack and the unicycle manufacturers have agreed a tighter standard to work to amoung themselves to help with compatibility. We have also received different advice about the requirement for the locking surface for the cranks, we use our spacer to produce this. There are definately 2 camps, one says don't need, one says do need. So we now supply them with them (unless you have old stock and it slipped us by) so you can take them off if you want.

Roger

[Emile.m]

I have non of these problemes with my Nimbus X I bought last october.

[DSchmitt]

Originally Posted by Emile.m

I have non of these problemes with my Nimbus X I bought last october.

yeah..on a different note i have 3 nimbus trials and have not had these problems.

the problems I do have on 2 of 3 of the nimbus are just with the frames..they were manufactured incorrectly or something. one side of the frame is longer than the other, so i have to cut some aluminum strips from cans and shim it...but I don't mind this too much...they're only 45$ and didn't snap after 3 months like my kh frame did.

[tholub]

Originally Posted by rogeratunicycledotcom

This is all certainly interesting. I am not sure that it is a "design problem with Nimbus ISIS hub" is really a correct thread description. Your problems seam to be associated with the KH 40mm double bearings.

Now, let’s have a look at this.

Bearing shields and spacers...
The spacers for the bearings are supplied to match the bearings (by KH, not UDC or Nimbus). They should not touch the moisture shield at all. I have attached an illustration of how bearing shields work, they are always recessed. This is so that the clamping surface can be larger than the minute edge of the bearing. The design is not at fault here... I have a couple of suggestions for the touching though. The writing on the bearing shield is proportionally higher than on larger bearings and it is this that is touching. The other thing is that the spacer could have been deformed on contact with the thin bearing edge when it is clamped. Both are solvable, a bit of wet and dry on the shield (the problem will be inside and out I guess) and a flattening off of the leading edge of the bearing shield.

Deformation of the bearing outers. The original design was for a steel outer and I am not sure where it got changed to an aluminium one or what specification it is. If the damage to the shield has just been caused by normal use then this is not good, it is odd that it has primarily happened on one side not the other.

It is worth realizing that these bearings are tiny, they are very delicate. Their design advantages are to give a more rigid frame and allow their fitting in to 40mm frames. They will of course not spin as freely as single row bearings, especially when new.


Roger

Bearings: The damage to the bearing shields appears to have happened really before "normal use" even started. I've barely ridden the thing. There is damage on both sides. The bearings actually spin perfectly well; it's only friction in the overall system which keeps them from spinning properly.

Thanks for the response.

[tholub]

Originally Posted by rogeratunicycledotcom

I think you may be missing the point a little with these bearings.... they are considered an upgrade! They are lighter (a lot!) and are twin row of bearings so create a more rigid system. I use them on my 36".

As for the bearing fit on the ISIS hubs, they are all non standard and are outside the normal criteria for bearings. To get the ISIS to work on unicycles at all a lot of work has been done to specify and manufacture bearings that will do... (the nearest standard bearing is the 6005-2rs which is 25x47x12) there has of course had to be compromises here. Basically the outershells on our bearings have to be thinner.

What's wrong with the bearings used on the KH hub?

Normal bearings can be fitted on the shaft using a H7/s6 press fit, with our bearings this would not work as they would distort due to the thinner shells. We have to work with a slacker tollerance, the theoretical tollerance (from memory) is H7/n6 which is transition fit. These are tight tollerances and once we have paint/finishes on this does vary. This is something we of course keep an eye on.

On a sideline.... the ISIS complience of the current hub and KH cranks is correct as far as we can determine. There are some ISIS cranks that do not meet 100% of the criteria due to clearances, but work. That is overall... looking in detail at tollerances, the ISIS standard is actually rather slack and the unicycle manufacturers have agreed a tighter standard to work to amoung themselves to help with compatibility. We have also received different advice about the requirement for the locking surface for the cranks, we use our spacer to produce this. There are definately 2 camps, one says don't need, one says do need. So we now supply them with them (unless you have old stock and it slipped us by) so you can take them off if you want.

Roger

This sounds like you're saying two different things; are the spacers required or not? It would certainly be possible to install the cranks without them, but you say the bearings aren't press fit, so it sounds like the spacer is needed to keep the bearings from moving on the axle. I would be glad to ditch the spacer if I could.

The ISIS spec clearly requires a crank stop, though it will probably basically work without one. The spec isn't explicit about whether the stop can be a loose spacer or not; my reading is that a loose spacer is not sufficient to meet the standard. In any case, the use of a loose spacer, which also appears to be required to hold the bearings in place on the axle, makes the whole system seem pretty hokey and subject to a number of potential problems which are not problematic in other designs. You've added dependencies to the system; the proper functioning of the bearings is dependent on the tolerances and installation of the cranks, which is not the case in other designs.

[rob.northcott]

Originally Posted by tholub

What's wrong with the bearings used on the KH hub?

Nothing (they're the same as usually supplied on the Nimbus hub AFAIK), except they're 42mm outside diameter and wouldn't fit that frame.

The ISIS spec clearly requires a crank stop, though it will probably basically work without one. The spec isn't explicit about whether the stop can be a loose spacer or not; my reading is that a loose spacer is not sufficient to meet the standard. In any case, the use of a loose spacer, which also appears to be required to hold the bearings in place on the axle, makes the whole system seem pretty hokey and subject to a number of potential problems which are not problematic in other designs. You've added dependencies to the system; the proper functioning of the bearings is dependent on the tolerances and installation of the cranks, which is not the case in other designs.

As far as I see it, the bearing inner race and the spacer together ARE the crank stop. As long as the spacers supplied are the correct width to put the stop in the right place relative to the splines then what's the difference between that and having a stop machined into the axle? And it has the bonus of holding the bearings still on the axle so avoiding having to have a really tight interference fit and making changing bearings easier. Fitting the cranks without the stop/spacer would just rely on them bottoming out on the splines, which would be far less secure and lead to crank creep like people seem to be finding on Schlumpf hubs.

If the spacers supplied are interfering with the KH 40mm ISIS bearings though then that is a problem (they're fine with the normal 42mm bearings), so is a wobbly bearing after so little use (could be just unlucky with the particular bearing) and the soft shims getting stuck in the frame. Out of interest, how tight did you do up the bearing holders? When I got my new Nimbus muni frame with machined bearing holders I sort of expected the two halves of the holder to touch at the ends like on a KH frame, but they don't, so you still have to be careful with tightening up the screws the same as with the cheap pressed bearing holders, otherwise it squeezes the bearing (which would be even more of a problem if the shims are a bit soft).

For the record, my two Nimbus ISIS hubs have performed perfectly. They're both running on 42mm bearings, with spacers, 36 spokes. One of them is in a Nimbus frame with machined bearing clamps like yours (but obviously a 42mm version) and the other is crammed into an old QuAx Coker-copy frame with 40mm pressed clamps.

Rob