Some updates to the blog

I finally found the motivation to do some regular maintenance to the blog. I went through all of the posts and added labels. Hopefully this will make it a bit easier to reference and navigate. The "cloud" of labels is on the left side of the blog. Give it a try and let me know what you think (i.e. do you just want a list?).

Also, I noticed that I never linked to the bearing article I posted a few months ago. By now, that information is up at BMX-U, so have a look.

Chain Tensioners

... Or wheel positioners. It really depends on your purpose for putting them on. You may want them to maintain a consistent chain tension, like my tail-whip fiending friend, so the pedals will stay in position when your feet leave them. Or perhaps your wheel moves on you when you don't have it slammed in the dropouts, but slammed, the chain is too loose. A positioner will allow you to give extra support to prevent the wheel from moving. This post will analyze the various types of possitioners available and weigh their pros and cons against one another.


Pull-Type
The original tensioner design consists of a washer around the axle, with either a stud and nut, or bolt. The bolt/nut tightens against a plate on the end of the dropout
Some pull-type tensioners have issues with shorter dropouts. But as of late, slimmed down designs (such as the Poverty Short Stop shown above) have almost done away with that problem.

A variation on the design is the Premium SS Tesnioner, which uses the bolt to push directly against the dropout. With the proper bolt size, this tensioner can work with any size dropout. Unfortunately with only a bolt in contact with the curved end of the dropout, it can move around pretty easily.


Push-type
These tensioners have appeared in recent years in two variations:

1. Integrated tensioners into the dropout use a set screw or bolt through the dropout to push the wheel back and into possition. The pressure on the axle threads may compact them slightly. This may cause some issues on hubs with threaded collars, and may allow the wheel to slip forward slightly as the threads compact. (ex: Sunday wave dropouts)



2. Bolt-on tensioners use a bolt-on tab similar to gyro tabs and cable guides. They push on the hub collar rather than the axle itself. In some cases there can be interference with the chain and/or driver. (ex: Fly Tierra)



Spacer type
In the past, riders have jammed various items between their axle and dropout to allow their wheel to be "slammed". I used aluminum cable ends crushed down and carefully inserted, but they would continue to compact, and were difficult to work with. Simple BMX has come out with specially cut spacers in 0.1mm variations. With the availability of half-links (albeit current designs are rather flawed in that they stretch easily), a wheel only needs up to 13mm of adjustment as the chain is 12.7mm pin-to-pin. Unfortunately there are reports of these compacting down (or more likely compacting into the threads of the axle)





Drive vs. Non-drive
With the chain on the drive side, tensioners only need to work in one direction (the chain works in the other). As such, tensioners have been designed to work only moving the wheel out of the dropouts. The problem arises when working with the non-drive side, especially with pegs. When a load is taken pushing the drive side axle out of the dropouts (such as an ice pick or tail tap), the tensioner does not support the wheel, and thus it can move out of position. To fix this problem, we may want to start looking into a hybrid push-pull tensioner. I have done some work integrating this into a hub collar and/or guard. I'll post up more info when I get some prototypes done...

Book Recommendations

I've been doing some reading as of late. Here are two of the books I found most useful:


Industrial Design by Jim Lesko

I picked this book up at the local library expecting the usual design crap: Furnature, cars, and hubless wheels. To my surprise, I found a well organized overview of manufacturing methods for a variety of materials. The book doesn't go too in depth into any particular subject, but it provides a nice introduction and reference for the aspiring product designer. More than just an easy read, Lesko includes many informative diagrams. These pictures are worth a thousand words; I highly recommend this to anyone getting into the field/hobby/whatever.




The Ice Cream Maker by Subir Chowdhury

I know what you are thinking, "what the hell does this have to do with BMX?" This short (115 pg.) book is the tale of an ice cream factory manager who develops his company into a more efficient, competitive, and quality-focused organization. The book focuses on how supporting your customers and community (that includes everyone from the employees, to the people who live around you), in order to create a healthier, more self-sufficient organization. For any of you in management, or looking to get into business for yourself, this is a required read :)

Director Patent and Construction

I was pleasantly surprised to find this in my Google Reader list this morning. If you don't know about Reader, it is a web based application for aggregating RSS feeds, updated search results, and other periodicals. The recommendation and searching functions are pretty good, but some of the BMX RSS feeds are surrounded by noise (i.e. one good feed with a bunch of dead ones).


Director Forks have interested me since they were first unveiled. Integrating the dropouts with the fork legs is a logical step that was taken by road and some mountain quite a while ago. Eliminating the weld at the dropout avoids cracks there as well. And using a simple insert gives good compression support, while maintaining a hollow dropout for weight. Overall a nice design. Unfortunately, since this is included in the patent, any other company who wishes to go the integrated dropout route will have to find a manufacturing method that does not violate George's patent.

The crown junction is another unique feature of the directors (unless you look at sunday's chainstay wishbone that G had a hand in as well). The claim is that it reduces localized stress and extra material found in conventional open ended steerers.

I'll dig into this deeper after some discussion, but I really have to head off to class, so this simple post is all that is going up for now :)



Some random feeds I subscribe to (post yours up!):

- Bicycle Design is not updated all that often, but can be interesting.

- Sweeter Skins for those of you with Android phones, this is really the future in UI.

- Roues Artisanales mostly posts in French about the road bike weight weenie scene.

- Cool Tools updates often with some neat little productivity tools.

- Scheier on Security is one of my favorite blogs. Written by a security expert who is often contacted to comment on security issues by media, government, and private agencies. He takes a very logical approach to dissecting issues. His post "Fear and Over-reaction" really struck a chord in me.

- Google Patent "Bicycle" Search feed updates every so often with new results (usually patent applications or updates). You can use Google patents to get customized results.

- Endless Innovation has some good posts, but can be a bit repetitive at times.

- Physics World has some neat, informative updates about research findings in classical, relativistic, and quantum physics.

- The Big Picture has great photography, and is updated very regularly. Each post contains a link to 40 high-def photos about a certain topic.

- F-Secure has regular, detailed computer security reports.

- Cycling Tech hasn't been updated in 2 months, but it has some cool stuff when they do.

- Industrial Design has a lot of design *cough* Crap *cough*, but you can find some real gems in there. Be weary of hub-less bicycles, there is a reason they haven't gone to production.

- Ted Talks are a great way to look at a situation from a particular (speaker's) perspective. They are all free videos on a very wide range of topics.

Sprocket/Crank Interface

In recent years we have seen a shift in sprocket/crank interface paradigm... Ok, that may be a bit exaggerated... At least there has been a change in design.

Traditional, Perpendicular Bolt

My first introduction to crank torque transfer was with the integrated stud on one piece cranks. Although effective, tolorances were often poor, and low-end sprockets were usually thin steel, further compounding any issues.

As BMX progressed, we moved to a bolt to secure the sprocket to the crankset (usually 3/8" or 10mm). Today, virtually all cranks use the bolt-on design. This helped solve some of the tolerance issues and has served as the standard for bmx. From a structural perspective, this design requires either a larger spindle boss or a separate hole cut in the crank arm for a sprocket boss.

A slight hybrid of one and three piece mounting systems, that has resurfaced recently is the use of a headless bolt. Mechanik makes a bolt called the Pin Head. The purpose of this design is not to hold the sprocket to the crank, but only to transfer torque. Using this design allows small spacers to be inserted between the arm and the sprocket to dial in the chainline.

Nano-drive

As Sprockets reduced in size (with flatland at the forefront), a need for less offset in the mounting position. Enter the nano-drive. Most nano-drive bosses use smaller bolts than the standard bosses.

Spline Drive

When faced with the challenge of small sprockets, Tree Bicycle Co. decided to redesign the mounting design. What they came up with was transfering torque through the spindle, rather than the crank arm. With most cranks now using 19mm, 48 spline, Tree's spline drive has a large potential market. Recently Profile decided to release their own version of spline drive (releasing a spline drive sprocket was logical for Profile as they are known for their 48 spline cranks). Unfortunately, Profile decided it was best to use 8 large splines on the adapter, rather than the 9 available on the Tree. I don't know why this happened, but it may be just to avoid any patent issues.

There is one big problem with spline drive: it is limited to 19mm, 48 spline cranks.

Socket Drive/ Nonogram

Flatware's (Odyssey) response to shrinking sprockets was to standardize. Well, sort of. They are the only company making a crank that works with the 9-sided mating surface, but do provide the specs and drawings(PDF) on their site. If this design is adopted, adapters can be made to adapt socket drive to a 48-spline crank, in effect making it another spline drive. The big advantage to this over standard spline drive is it does not limit the spindle design.

BMX-U Sprocket Page

KHE Clone Hubs: Calculating Slack

I recently posted this on BMX-U

Ok, this should apply to all KHE Clone coasters, as well as Odyssey and other "butterfly spring" coasters (though they may have different room in the hubshell. However, if you have an externally adjustable hub, you will just have to measure by backpedalling 1 revolution to 0* (or 90, whatever works for you), then pedaling forward and guestimating. Note: You cannot get 90* slack on these hubs, even with a relatively low 2.5 gearing and min spacers!

Driver/clutch thread pitch: 15mm per rotation (23mm/1.53 total)

KHE Spacer thickness: 1mm

Tophat Spacer: 5/7.5mm depending on orientation.

X= Total spacer stack (i.e. tophat set regular 7.5mm + 1mm spacer = 8.5)

G= Gear Ratio or Chainwheel (sprocket) size / Driver size (i.e. 25/9= 2.78)

( 12.7 - X ) / 15 * 360 / G = Degrees slack at pedals*

*assuming good chain tension, etc.

Bearing Specifications

Another great link. This one about the different designations given to bearings. It has helped me with bearing selection in some components.

EDIT: Wow, a long time later, I finally realize that I never posted the link. Sorry about that. The info its up at BMX-U now

Interesting Chain site

It's not BMX, or even bicycle specific, but a great link I picked up:

http://chain-guide.com/toc.html

BMX Wiki!

It's been a while since I posted, I have been working on getting a bmx wiki up. Thanks to a few cats over at http://www.bikeguide.org/forums it is getting filled up. Take a look, and please contribute what you can. Even the smallest stuff helps. http://www.bmx-u.com

Freecoaster Clutch Styles

Essentially, there are two styles of clutches: Axial Clutches and Radial Clutches. The differing characteristic being The direction the clutch moves, along the axle, or radially out.

Axial (KHE Geisha):

Radial (KHE Rollex):

Axial Clutches

The majority of clutches are axial because of the system offers. For the purposes of this analysis, axial clutches can further be broken down into sub catagories:

• Push type clutches push the clutch from driver to hubshell (only stock ones I know of are the Sym Hub and the Stolen/Chosen.

• Pull type clutches pull the clutch toward the hubshell and driver (Geisha, reloader, etc)

An inherent characteristic of the axial mechanism is side load on the bearings. Push systems side load both the driver bearing(s) and one of the hubshell bearings. Which bearing is loaded is dependent on whether the push mechanism is located between the hubshell bearings, or outside the bearings.

Axial-outside-push system (sym-hub)

Welding two clutches together work to convert to a LHD-axial-inside-push system (modified taska)

In Contrast, pull type systems only load the drive-side-hubshell bearing. In all unsealed and some sealed hubs (such as the KHE Reverse ACB), the balls contact the races at an angle, which supports side loads much better.

Axial-inside-pull system (KHE Geisha)

In hubs where the drive-side-hubshell bearing rests on the driver, not the axel, the driver bearings must withstand sideloads from axial wheel loads (i.e. when whipping and the wheel lands at a funny angle). Repeated impacts can cause damage to the drive bearings. Interestingly, unsealed hubs are much less likely to have damage to the bearings. This is due to the angular contact that the cup and cone system provides.

Radial Clutches

Radial clutches are much less comon. The only two I can think of are the KHE Rollex, and the yet to be produced, G-sport Coaster*. The former uses roller bearings and ramps, while the G-coaster uses a cam mechanism and, what can be compared to brake shoes.

The major advantage of radial clutches are they do not interfere with the hubsell bearings, and no sideload is on the driver bearing (unless you are pedaling really hard while landing a tailwhip at a funny angle). These systems avoid the major durrability issues that are all too common in coasters.

We must, of course, note a potential issue of radial clutches: contamination of the freecoaster mechanism. Any hubs that come out with a radial system will have to make sure a good sealing system is in place.

KHE Rollex Explosion

* George from G-sport confirmed that he is still working on the coaster. Seeing how the rollex never quite succeeded, it's probably a good thing he is taking his time.