Geared hub as jackshaft

[John in CR]

I know the general idea of using a geared hub as a jackshaft has been brought up before. My interest is in doing so to reduce the torque load on that tranny. It would mean though higher rpms pushed through the hub. Can it handle 1500-2000rpms?

 

[REdiculous]

I've got a geared wheel hub I made that does it..

 

[John in CR]

I've got one of those 3speed self-propelled lawnmower gearboxes too, however I think the Nexus3 geared hubs I also have are more likely to be up to the task.

John

 

[amberwolf]

I'd guess the nexus is almost certainly far better than the mower gearbox, from what few of those I have seen inside of. Assuming you're talking about the non-riding kind.

Part of my plan for ARTOO is looking like using the 3speed hubs as intermediate jackshafts rather than in the wheels themselves.

 

[John in CR]

I'd guess the nexus is almost certainly far better than the mower gearbox, from what few of those I have seen inside of.

Of course, but can I reasonably expect it to handle the rpms of 60mph with it geared down by 2:1 or so compared to if it was inside a wheel, which would be the plan to reduce the torque loads on those gears? There's not much use reducing the torque if the higher rpms will make it fail.

John

 

[amberwolf]

That I don't know. If it has a proper oil bath in it, rather than grease, it might help, and also help conduct heat buildup in it to the outside?

I've little direct experience with gearboxes at anything but slowish speeds so far.

 

[GGoodrum]

I think it will be fine as well, because I haven't really had any problems with a Nexus-3 or the SRAM version, on a 20" folding bike, and that is running a fair bit of power through them (4kW?). Kim (AJ) and Matt (1000w) have trashed these, though, on their cruiser-type bikes, which are significantly heavier. I don't know if it is something related to the fact the toilets flush in the other direction down there, or if it is just the bit extra load/weight that is turning these to mush, but I'm guessing that using them as a jackshaft would be fine. If you had something like a 2:1 reduction, it should keep the torque that the hub sees down to what it can handle.

Anyway, I think this is definitely worth pursuing. Once you prove it out, I'll jump on the bandwagon, and claim full credit.

-- Gary

 

[John in CR]

I have 2 Nexus 3's, and since I already have one readied including a disc brake adapter, I should give it a try in-wheel first. That way I can find out if running them trouble free with Eteks is just urban legend or real. Plus my combining jackshaft/suspension pivot using a hub with 14mm axle is only waiting for sprockets and their spacing. I'm torn in many directions right now, because the Lyen 136v controllers I have now, should allow me to gear low enough for pretty significant hills but still have acceptable top speed. I just won't have that granny gear for billy goat mountain climbing that multi-speed would would give me.

Time to just make some decisions and get to work instead of letting them paralyze me using the rains as an excuse.

John

 

[amberwolf]

I think as long as you keep the possibility of gear lash down, they'll survive ok. I have a feeling based on other people's observations that the main reason they break is the teeth being slammed against each other at startups especially under a heavy load. If you have a softer start to ensure they don't do that I'm sure they'll last a lot longer.

In normal bicycle use they might see some pretty high KW loads under leg power at startup and uphill, but they probably don't see a high shock at that time.

 

[AussieJester]

Kim (AJ) and Matt (1000w) have trashed these, though, on their cruiser-type bikes, which are significantly heavier.

True, mine was skipping from the first time i rode the bike, i don't think
its the weight my bike is 99lb (45kilo) i think its more to do with
the extended wheelbase allowing us to put the traction down unlike
with the boys on their MTBs they aren't able to power from standstill
anywhere near as hard or they end on their ass haha... John
has longer bikes also so he too will be able to put some power
down from idle i think? If you have a few though John i would
suggest trying it, you have legs to push the bike home if it
breaks haha...

KiM

 

[John in CR]

I think as long as you keep the possibility of gear lash down, they'll survive ok. I have a feeling based on other people's observations that the main reason they break is the teeth being slammed against each other at startups especially under a heavy load. If you have a softer start to ensure they don't do that I'm sure they'll last a lot longer.

In normal bicycle use they might see some pretty high KW loads under leg power at startup and uphill, but they probably don't see a high shock at that time.

I just wish someone would come up with a 4 or 5lb version with disc brake attachment designed for smallish emoto's. Good hardened gears, built in torque arm, dual sets of holes in the flanges for bike or motorcycle spokes, .5, direct and 1.5:1 gearing should do the trick (though a smaller difference between top gear and direct may be better for a small gearing diff for efficiency in headwinds and minor uphill grades). There must be some solid units with expired patents that can be upsized for our needs. We just need a factory to realize the need.

 

[GGoodrum]

It's not an urban myth. The guys name is Dave, and he runs a bike shop in Pacific Beach, CA called Rusty Spokes. He's used all sorts of Nexus hubs on several different cruiser bikes, not unlike Kim's, using Etek and Mars motors. Like Kim, he's also using belt drives to the rear, but the difference is that he lets the belt slip a bit on takeoff. That's probably the reason right there that he hasn't had the same sort of problems. I too agree with Kim that the wheelbase probably has a lot to do with it as well. No way I could even do much past 1/2-throttle, or I'd end up on my ass.

-- Gary

 

[John in CR]

Gary,

Thanks for pointing out the belt slip thing. Nexus3's are out of the picture pending a low power build or slapping a clutch on the HXT I just picked up from swbluto, or maybe something for the kids. Power and speed are the name of the game with my current builds, and I have little interest in walking a bike home. I have no problem experimenting with something new, but in this case there's clear evidence of probable failure. I prefer to learn from others' mistakes as well as my own. I may try the jackshaft approach to reduce the load at some point down the line.

I think maybe it's better for the community if I explore high power using bike chain and large sprockets to reduce the load on the chain, while permitting multi-speed. I've been wanting to do that anyway, it's easy, cheap and carrying an extra chain and tool for a road repair is no problem.

John

 

[Papa]

FWIW,

Some of the hub manufactures' specify allowable input torque. I have the numbers handy for Rohloff, but I believe the data is also available for iM9 and some of Shimano's hubs.

http://www.rohloff.de/en/technical/speedhub/efficiency_measurement/index.html

I also agree that spinning the hub at higher RPMs would necessitate oil filled lubrication for survival.

 

[John in CR]

...I also agree that spinning the hub at higher RPMs would necessitate oil filled lubrication for survival.

That's 2 votes, and good enough for me. I'll have to open one up and get the grease out and add oil. My machine shop buddy brags about being able to copy anything, so while I have it open I'll tell him I want the same thing but stronger.

John

 

[amberwolf]

Just remember that the hub might not be sealed for liquid like oil, as it might just use a grease barrier at seal points to keep water/etc out. You might wind up adding o-rings or similar to keep oil in.

Some, like the Sturmey Archers, are meant to be oiled rather than greased, but the oil cap is just a flip lid, so a lot of oil in there will probably just leak out. Might require simply adding oil often, and potentially putting an anti-splatter fender around it.

I haven't experimented with the oil-fill yet, but will once I get the right tools made to take these hubs apart correctly and still get them back together.

Also, I have some service manuals for various hubs I've been downloading as I find them on the web. I'll see if I have one for the Nexus3, and if I do I can try to post it here.

 

[Papa]

Just remember that the hub might not be sealed for liquid like oil, as it might just use a grease barrier at seal points to keep water/etc out. You might wind up adding o-rings or similar to keep oil in.

yup... A few IGH owners have tried switching to liquid in pursuit of efficiency.... with messy results. Seems the 8-speed, Alfine SGS501 and the Nexus SG-8R36 (premium) have improved seals for such a conversion, although not a recognized practice by Shimano and will no doubt void any warranties. I've not heard of anyone 'liquefying' a Nexus 3-speed.

John, if you don't already know, there's a IGH Yahoo group at:

http://groups.yahoo.com/group/Geared_hub_bikes/messages?o=1