Interesting off the shelf transmission
 

My wife recently purchased an 80s vintage cruiser bicycle at the local Goodwill -- a Murray Monterey. She said it was a three speed, but I said no way since there were only two sprockets. Closer inspection revealed a neato planetary gear box in the wheel hub. The exploded view here made me think they were super pricey:

http://en.wikipedia.org/wiki/Sturmey_Archer

but they start at $60:

http://www.permaco.com/en-us/dept_8.html

The higher end ones even have an integral brake. They are certainly robust enough and already have a #35 sprocket and straight forward mounting. The gear ratios are not stellar (1:0.75, 1:1, and 1:1.33), so perhaps this is more a discussion of a cool arcane technology then a possible FIRST part, but I am glad to have them in the back of my head should the need arise.

Travis

Re: Interesting off the shelf transmission
 

Sturmey Archers are pretty cool. I have one on one of my bikes and it's a nifty little contraption. The shifting mechanism is very picky though it doesn't like to be too sloppy but if it's too tight sometimes it won't shift right. It'd be cool to see one on an FRC robot or a transmission made with a similar design.

Here's a link to the site:
http://www.sturmey-archer.com/index.php

Re: Interesting off the shelf transmission
 

Sturmey Archers freewheel ...

Re: Interesting off the shelf transmission
 

We worked with Shimano a bit on trying to adapt similar gearboxes for robotics use. One of the first problems that you'll need to overcome is the transmission's one-way operation. It's possible to use two transmissions in tandem to eliminate the problem, but such complexity starts to diminish the benefits these transmissions might provide.

Re: Interesting off the shelf transmission
 

Maybe I'm revealing my age but,... This type of 3 speed hub has been around a long time. I remember specifically this type of hub being on my older brothers bike when we were kids.

As it has already been mentioned, this hubs application in FRC may be a bit limited. That being said, it is definitely useful for the purpose of learning. :)
My bet is, if I say it has no use in FRC, some team will use it to perfection!
I couldn't ask for anything more.

Re: Interesting off the shelf transmission
 

Besides the single direction problem stated by Madison, would something like this hold up to the punishment of a robot drive train?

Re: Interesting off the shelf transmission
 

One of my buddies I work with is currently developing an 8-speed planetary gearbox for the same application.

Re: Interesting off the shelf transmission
 

I'll really show my age. I had one of these on my bicycle. :eek:

Re: Interesting off the shelf transmission
 

I'll really show my age. I have one on my current bicycle!

Re: Interesting off the shelf transmission
 

One nice thing to come out of the fixie fad is a new three speed fixed hub (no coasting whatsoever). Not sure when it will be available for purchase, but it's looking pretty cool. (link)

Sheldon Brown also has an article that discusses converting a 3 speed Sturmey Archer hub into a fixed two speed hub, here.

Re: Interesting off the shelf transmission
 

The whole one way business got the old noodle working...

Say you have two things that don't need to run at the same time, and each only needs to run in one direction. I'm thinking a ball gathering brush and a ball shooting brush. By linking two sturmeys to one motor, forward runs the first brush and backward runs the second, all with one precious motor.

Of course there are easier ways to skin that particular cat, though they might not be OTS with a #35 sprocket.

I am having trouble seeing the benefit of shift-on-the-fly in this case, but ease of adjustment is killer. Every year we find that we are pulling 21 amps somewhere -- click it down 25% and no more breaker pops, without rebuilding a complicated drive train.

Travis

Re: Interesting off the shelf transmission
 

Keep in mind that bicycle chain is not #35 chain. It will also be necessary to modify the output somehow to accept a different sprocket or to otherwise drive something.

It might be interesting to use these in a one-way bearing application, as most one-way bearings of FIRST-robot size -- at least those that I've seen -- are not rated for the high-torque applications present in our mechanisms.

Re: Interesting off the shelf transmission
 

I'd be interested if it could be modified to be a brake by locking one stage and removing another. So, just works as a one way bearing with a brake, one that would have to switch under load.

Other than that, I really can't see a use in FIRST worth the effort (and even at that, I'm thinking there are easier options).