projects – Personal blog of Peter "Sci" Turpin

Shimano Roller Brake: No User Servicable Parts

If you have to cut through a product with a hacksaw, it’s probably never going back together again.

I was fortunate enough a couple of weeks ago to win an Ebay auction for a Shimano Nexus 7-speed hub gear unit. It was a bit grubby and didn’t come with the shifter, but I did manage to get it with the roller brake unit thrown in.

Ordinarily you can get the Nexus hub without the brake unit and a little bushing-cum-cover for the blank side of the hub, but I have a different idea. I think I can use the brake mount to fit a hub generator to.

I’ll probably go over this in more detail once I acquire the needed dynohub to gut and show some of the reasonably minor mods I’ll be making to the Nexus hub itself (all reversible I expect, so don’t panic). But for now I just need the plate that meshes with the gear hub.

The whole brake — The middle bit with teeth is what I'm after

The other side of the brake was brown from overheating, and the drum’s aluminium heat-sink was pretty warped too, so there wasn’t much guilt in tearing it open. Plus the frame I have is made for rim-brakes (even if it wasn’t, I’d rather not put that extra force on the spokes of using hub-braking).

I clamped it carefully in a vice, after finding there wasn’t enough clearance to simply pry up the three retaining lugs and release the brake drum, and used a hacksaw to cut across the fold of the lug. I cut through enough that it folded back and the drum got a lot freer.

Tab cutting — A lucky fluke, the tab stayed attatched but folded aside

That didn’t quite get it loose enough though, so I had to do the same to another tab until it finally popped free.

These things are not meant to be taken apart. They’re sealed units that are only available for replacement whole.

From here it just took a few taps with a leather mallet to knock the steel drum out of the heat-sink. It was just a press-in fitting with some mating teeth.

The 4 holes, btw, are for the dust-seal which I’d already removed before cutting began.

Hopefully I’ll attach this to a custom aluminium enclosure I’ll be housing the guts of a Sturmy Archer Dynohub in. It’ll be a lot easier than designing and making my own generator from scratch, and I’m pretty sure it’ll fit once all the heavy steel shell is removed. But anyway..

The mechanism of the roller brake is interesting. It’s similar to a drum brake, but the brake pad is spring-retained. The “nut” in the middle turns when braking is applied, pushing the rollers in a carrier outward as they’re usually against the flats of the nut, but get pushed to the higher corners. This makes the rollers push the brake pad outward in all directions against the brake drum. I thought there might be some braking force applied against the rollers directly, but the brake pad doesn’t move relative to the rollers.

Like the hub gear, these brakes need an anti-rotation/non-turn washer on the axle as that’s what it uses to anchor itself, not to the frame directly.

Unless I’m missing something, calling this a roller brake seems mostly a way of avoiding calling it something as old-fashioned as a drum-brake. But that’s essentially what it is, though with a clever mechanism for increasing brake-pad contact area.

It’s probably about the same contact area as rim-brake pads, only without the benefit of as much mechanical advantage on the wheel.

Scavenging log

Friday 4th, Friday Hill recycling center

Rolled leather hammer and cross-peen hammer. 20p.

Sighted a lawnmower sans-engine with exposed drive pulleys. Slightly too burried under a sofa-bed frame to reach or extract. Shame.

Located small bag of bolts. Insigifigant to them, so got for free. Turns out has some welding bits in. Copper rollers, massive earthing braid, some rolled steel pins.. Also two bits of phenolic board held together with wing-nuts. May be a flower-press.

Saturday 5th, Friday Hill recycling center

Arrived 20min from closing. Rushed around and found a silver steel wood auger (7/8″), an octagonal bread plate (matches one I have already), a brass door pull with a fun latch mechanism (should be easy to fix/reproduce), a pair of soft-close drawer runners, a kitchen pot hanging rail, and 4 alloy bike pedals.

On the way home I also found someone chucking out some old bike wheels, one with a Sturmy Archer hub gear. Cleaned up turns out it’s a 1948 Model “AM” gear set. According to Sheldon Brown, that’s a rare type from old British “club bikes”. So will try to sell instead now. May be of use to someone doing an accurate restoration or such.

Alloy pedals aren’t of immediate use. One pair is a high-spec Crank Brothers 5050X set, but very chewed up and missing one of it’s plates (that you don’t seem able to buy separately). The other alloy set is of no current use, one missing it’s spindle. The 5050 seems to use a very short spindle tho, so stripped of the plates and studs (basically grub screws. Handy) I should be able to cut the pedals down to be narrower and use the threaded holes to attatch the “horse legs” to the unicycle cranks on the proposed art-trike.

Sunday 6th, London Hackspace

During the (excellent) party, was informed it was ok for anyone to rummage through the “rubbish” boxes. These are boxes where odds and ends people find and donate are put. If no one takes them in 3 weeks, they go in the skip (and often back out and back into the boxes as someone freshly “discovers” them there).

After a couple of beers, felt comfortable rummaging as others were and found a tiny blacksmiths vice, a robot insect, a usb card reader with no cable (soldered one on while there. Tested at home. Detected, but very broken.), a colour security camera with IR lamp removed, and a tiny 5mm square camera module (probably from a phone. Probably useless, but so cute.).

Will have to fix up the trailer or something. If it’s okay, I have a lot of things that are too good to throw away but that I’ll never use that I could donate to the Hackspace. And probably a number of other things I could happily give on extended loan (like the homebrew equipment).

Picking up more pieces

I am officially looking for a treadmill to rip apart. I almost had one tonight but went to make a sandwich and got bid-sniped before I got back.

I know, with all I’ve said about just going straight in with your max-bid.. :P

Maybe I just want something new to mess around with.

Thinking of combining several of my existing half-done projects to conserve resources. Like taking the steering rack off the electric kids car, the motor and axle from the golf-caddy and the wheels from the big robot to make an electric go-cart. I can allways re-use it for the robot project later anyway.

Likewise thinking to combine the never-quite-functional robot dog thing with the robot camera-arm to make a sort of Scutter robot.

The treadmill I’m after with a view to fixing up the milling machine more with new head. Would be relatively easy to mount a slender DC motor on the mill’s front compared with a chunky AC motor of similar power. Plus I’d get a nice flat torque curve and less pully-gearing requirements (I anticipate at least 3 “gears” to give additional range. 8000rpm motors will probably only go down to 150rpm before stalling. Proper mills can get to low double-digits).

I suppose they’ll always be these things around, and I should concentrate on more pressing matters. But likewise I want to feel like I’m progressing. And the easiest way is to try and buy progress.

I’m acting no better than those militant Doomers who pile up their homes with survival gear they’ve never used and have no idea how to, just for the safety blanket of feeling more protected.