Sunday, February 24, 2008

Another Day of Surgery

Today was a big day for PhattKatt as more upgrades were fitted to the little kitty's body. Today's surgery involved the PhattKatt's very reflexes... messing with the drive line.

The first upgrade started over a week ago by obtaining true Teflon tuning. Experience has shown that Teflon is the perfect material for guiding bicycle chains as long as the taught side of the chain always runs in an arrow-straight line. So the first challenge was to straighten out the tubes delivered from a spool and rolled up in a box. Turns out that placing the curled 1/2ID; 1/16" wall tubing in a large PVC tube while blowing a hair dryer on full heat through the tubes would relax the material enough to straighten itself out. Once cooled, the tubes maintained a pretty straight profile.

Today, the tubes were flared with a tapered grinding bit in the drill press and a coned grind stone in the drill. Only the entry sides of the tube requires a prominent flare but all 4 ends were rounded to some extent. The slack side receiving end got the best flare as you can see in the pix below. Each tube length can be best optimized when you know where the trike or bike boom will be set. In this case, the boom is set to the shortest position it can go. This is a picture of the tubes ready to install:

Here is a view of how the insides of the Teflon tubes look:

Even after years of use, these tubes will look nice and shiny and they will wipe clean by running a cloth through the tube. People have complained of noise with these tubes. I can't detect any.

I haven't told you yet why we are doing this... seems a lot of bother, no? Just wait, the bother has only just begun, but let it suffice to say that these are the modern edition of chain guards. These are installed to keep the ever popular chain tattoos away from your legs and your cloths. Having had excellent success with these on the *other* trike, PhattKatt is certainly deserving of having the same treatment.

From afar, it seems a simple thing to add; put tubes over the chain your done... right? NOT! The art is in making sure the chain tube will stay on place. This is easy for the slack-side chain; we use a tube clamp... and we also put a tube clamp on the power side with a few caviats. Trick here is to make sure that the tube is directly in line with the chain while in all three chain rings. The key is to make sure that you capture the tube near the idler since that is where the deflection is least. In the following series of pictures, you will see a lot happening on the idler axle. From the outside inward, you have: a) tube clamp for the slack side tube b) the chain keeper that keeps the chain from falling off the idler c) the idler d) a flat plate [bracket]; which holds the tube clamp; which holds the power side chain tube. I've provided lots of images in hopes that these references will help you determine the best way to implement these in your application:

You can imagine how this area could foul pretty easily. Indeed, it is an area that gets the regular once-over and general maintenance. When something goes wrong in this area, you know it pretty quick. I don't see how it can mess up to such an extent that it will be completely disabled, though.

The results are spectacular. After all this careful work, these tubes are carefree as they simply allow the chain to glide along and a major portion of the messy part of cycling has been held at bay. The entire power side chain tube floats from the one tube clamp at the idler, which was carefully adjusted to make sure that the chain goes into the tube unhindered from the idler. If you look carefully at the next image, in the lower left corner, the slack side chain tube has been captured with a pair of zip-ties around the trike's cross member [from the left side] to help manage this tube, and the chain, in left hand turns. This particular tidbit is also from experience. Have a good look at how it all ended up:

Surgery one accomplished... but wait; we're not done. We still have a chain ring to replace. We learned that PhattKatt has a pretty high strung gear train. So we're going to calm down the climbing gears. This is a 2 part operation where the first is to replace the 30 tooth [30T] with a 24T chain ring. Here is the gear chart that we are aiming for:

We will be adding two more teeth to the rear cassette to get to the 13.2GI [gear inches] but let it suffice to say that the swap of the 30T gear for a 24T gear is providing a significant change. In preserving the larger chain rings, we have not sacrificed any of the top end gearing as was the consideration with the chart. Take another look at the image above for how small that little 24T chain ring looks in the chain ring set! Here is a shot after changing out the ring on the crank set off the trike:

One consideration often talked about on forums, with my vocal input as well, has been dispelled as myth today. Specifically, when you exceed the chain wrap capacity of the rear derailleur, the derailleur should cause the chain to crash into itself potentially causing problems. This means that when you exceed the chain wrap capacity of the rear derailleur, you need to avoid certain gear combinations. The SRAM X-7 rear derailleur is a 45 tooth chain wrap capable derailleur. I have now exceeded that capacity by 4 teeth. But look! the X-7 doesn't have enough return spring to lift the long length of the recumbent chain high enough; it just goes slack! This certainly is not true for all rear derailleurs but in this case it is an interesting phenomena. I'll let the two pix talk for themselves as the chain is on the 11T cassette cog and on the 24T chain ring:

So we still have the 11-34 SRAM PG970 cassette to put on PhattKatt. This will involve splicing in a longer bit of chain. Everything is on the bench; just gotta do it. We'll let you know how that goes as well. But for now, time for the mechanic to rest.

Over and Out.

P.S. when viewing larger images by clicking on the pictures, if you change the *...s800...* in the web address to *...s1600...* you get the larger images just in case you want to see more detail. One of those hidden little blog secrets.


rshaver said...

Where did you get the teflon tubing? Waht diameter did you use? Did you use the clamps that came with the trike? Bob

Simple Nature Spirit said...

Man I hate when I miss a comment; So my appologies.

The tubes were ordered from Actionbent. These can also be ordered from Hostel Shoppe although I cannot guarantee that they are the same material.

The clamps came from McMaster-Carr: p/n 3177T13. I reemed out the hole to fit the 8mm idler axle shaft.