Sept 21, 2005

     To the right is the new python so far - pretty standard, no big changes.  You're probably noticing how the wheel is NOT mounted on top like we wanted to.  That's because I thought I could be clever and make the bottom mount work without major frame mods to Marcel's front end design, but it didn't work.  I hate cutting up things that work, so I mounted the wheel the way we did the first two pythons, but I did manage to a) use 1 1/2" x 1/2" box tube, so it's smaller and lighter, and b) I used a simpler, lighter pivot housing with the 1/2" rod ends.  You can see some scribbling on the side of the chainstay where my friend and I were working out a little math for how we're going to change the stays.  

     I have some 1/4" steel plate cut to 4" x 1 1/2" to bolt the rod ends into, and will run the backbone up and back at a 25 degree angle (65 degrees) from the pivot.  I'll see how far I need to run it up before bringing it back down to the rear wheel.  I'll make a quick 3D version of it and I want to make it as "Z" shaped as I can so the front and rear ends are at the same angle.  The pivot is further back and should be closer to where my hips pivot - so I'll see how that feels.  Not sure if the pivot will be too close to the ground or not, but if it is, I can move the pivot housing closer to the rear wheel and shorten the pointy rear end a bit.  Any pivot angles changes this makes can easily be accounted for by adjusting the rod ends.  

     Marcel has made one wooden seat, is making the mold for a second, larger (read "adult" sized :)) wooden seat, and he's also going to do some small mods to his chain stay jig to accomodate the front end design changes we've made.  More to follow.

Oct 1, 2005

     First I decided I was going to change the design purpose of this python to figure out a couple things.  First, what pivot angle feels best, and secondly, what wheelbase feels the most comfortable.  The pivot angle is easy to adjust because of the rod ends, and the wheel base will be adjustable by sliding the main backbone and rear wheel back and forth.  By "rough" guestimate, I want to be able to adjust the pivot from about 58 to 73 or 74 degrees, and the wheelbase from 38" up to about 50".  As I was sort of designing on the fly, I hope I can hit these objectives without running into too many design problems and compromises.  As a side note, I was experimenting with the "stiffness" of the pivot, in other words how easy it is to pivot the front back and forth, and it is pretty easy to set up a preload and increase the stiffness simply by how tight I tighten the main pivot bolt.  As this will be harder to quantify, I'll just compare it to the couple pythons we already have.

Oct 2, 2005

     Construction mods start.  Based on what I now want to do with the python's pivot, I doubt the current pivot tube design will work - it'll be WAY too close to the ground.  So, I stuck another tube in front of it to get it closer to the rear wheel and give me some more ground clearance, and lopped the old one off.  It's a little more squared off, but it clears the plate I will bolt the rod ends too, plus it gives a mounting plate for the front brakes, similar to what I did with the first python clone.  Nice thing about rod ends, is you can slap the pivot housing in much faster and with less concern about getting the angle right, as you can easily correct it by adjusting the rod ends.

Oct 3, 2005

     Tonight I wanted to get the main pinch tube/seat frame built including the rear seat support.  Time seemed to go faster than I was working, so I only got the main slider tube done, and got the 4 pieces of EMT cut to length for the seat frame.  I only get about 3 hours, at best, to work on projects during the week, so I need to plan my work better I guess :)

     Anyway, the final adjustments for wheelbase are 42" at the shortest to 48 1/2" at the longest.  This is only basically the same measurements as the BHP when it was modded the first time, to the wheelbase of the current config.  I wanted to be able to go both shorter and longer to get a good range, but it didn't quite work out that way.  The spring is stronger than the rubber stopper I originally used and should be fine for anyone under 200 lbs, but in a pinch, I can always lock the rear end with a metal insert.  The BHP has no active suspension and the ride isn't bad on it, so even if I make this a hard tail, I think it'll be fine.

     Tomorrow I want to get the seat frame on, the rear seat support and get the brake mount on the rear forks.

Oct 4, 2005

     Got some half decent progress, I think.  Took me an hour and a half total to make the seat.  Made it out of 3/4" EMT and used the same style and jigs as on all my recent seats.  I could have used smaller diameter seat tube, but this is designed for adjustability and crash-proofing, so I'm not too worried about weight.  The top picture shows the python at 42" wheelbase, the bottom with it stretched out to 48 1/2".  The seat angle is a little more upright than the BHP as I think that will make it a little easier to learn to ride.  My daughter is very excited to learn to ride the new python too.  She rides around on her unicycle just fine, so I think she'll pick up the python balance pretty fast.  There are 2 quick releases on the seat, and two on the pinch joint to allow tool-less wheelbase adjustment (at least initially).  The python comes apart very quickly and I'm interested to see what the final weight will be.

     Tomorrow, I'll finish up the top rear seat clamp, get the rear brake mount welded into the rear forks, and then all I need to do is lace up the seat cover (which is already made), reinstall the chain and derailleur, and it's ready for the first test ride.  I've got about 16 hours in it so far.

Oct 6, 2005

     Took last night off :)  All work and no play, makes . . . well, you know the rest.  So, tonight, I accomplished all my goals.  I finished the seat, added the brake mount/stiffener for the rear fork, drilled the holes for the seat adjustment, and took the baby out for its first test ride.  To the right is the center section.  The whole thing is made out of 1 1/4"(32mm) x .064"(1.6mm) mild steel.  The two black skewers are the pinch mechanism to hold the rear end's sliding boom.  The two rod ends can be seen at the front, and the holes are for the 6 adjustment spots for the seat.  The 1/2" bolt that goes through the rod ends requires no washers and no shims.  It simply tightens and squeezes the rod end balls against the pivot tube - and that's it.  There is a 4" long section of 1 1/4" x .100" box that the skewers are mounted to.  The thicker wall makes it a tighter fit on 1" square tube, that slides inside, that is used for the rear boom.

     These are two shots with the PC2 beside the BHP.  This is just prior to my test ride.  I set it up to be static in the 4th gear, on the middle ring for now because the testing doesn't require gear changes as yet.  I also don't have any brakes on it yet because I didn't have time and we can't get it going fast enough to get into real trouble with it in the test area . . . yet :)  You can see the 4 black, quick releases.  Two to pinch the rear frame, and two to hold the seat on.  It's a little shorter overall than the BHP due to the 16" wheel vs the 20", but the wheelbase is just about identical.  The pivot angle is set at 65 degrees, but when I sit on it, the angle is steeper than that.  Not sure what the angle was because I didn't measure it, but I'll do all that tomorrow at lunch.  At rest, you can see that the PC2 has the same seat back angle as the BHP, but again, with a rider, it lays back flatter - need to measure that too.  With the seat angle being further back than the BHP, it still feels like I'm sitting up straighter because of the top of the seat being angled forward and raising my shoulders and head.  It feels very nice.  Even though my less-than-narrow butt pretty much maxxes out the suspension, there's still just a wee bit of spring left and it really makes a noticeable difference in the ride with the 95 psi front and 110psi rear tire.

     I took it for a few rides and adjusted the wheelbase.  I definitely prefer the quick and nimble handling feel with the wheelbase shortened right up.  With a 48" wheelbase, it feels "slow" to make steering corrections and feels like it takes a lot longer to accomplish the same kinds of turns and maneuvers.  I like short, that's confirmed.  I was also experimenting with the pivot stiffness, but need to do more experimenting as well as adjusting the pivot angle too.  I really like the way this one rides, even without the experimenting, it feels more stable and forgiving than the BHP.  There are a bunch of new aspects to this python that the BHP and Marcel's don't have, like suspension and being able to greatly vary the pviot stiffness, not to mention the angle, and the feel of the tilted up seat back.  Hopefully I'll be able to quantify all these small differences into something that definitively narrows down the "optimum" configuration.

19 Jan 06

     Ok, so the "tomorrow" was a little further off than anticipated once other projects came up, but we're back at the PC2 finally.  To the right is what the PC2 currently looks like.  Rides very nicely and much more user friendly to learn than the BHP was/is.  Still needs the fender tabs and a front brake, but other than that, it's quite rideable.

     Right now it's being converted to a tilting delta ice racer for some ice races coming up.  Details here.

27 Mar 07

     So, after a very long time of no updates, the Python 2 is done.  Actually, it has been back to a 2 wheel python for a little over a year now, I've just been preoccupied with other projects.  I put it all back together and painted it a nice gloss red, and there she is.  It is very easy to ride due to both the seat height and angle, as well as the current pivot angle of about 63º.  I haven't ridden a python in almost a year, so after taking it down off the wall hook, cleaning it up and pumping up the tires again, I was a little curious as to how I would do.  Going down the driveway I was pretty wobbly as I was frantically going through my head looking for the memories marked "How to Ride a Python".  I was quite pleased to find that I quickly regained pretty good control, and after about 3 or 4 minutes of riding, I was back to roaring around on the road at about 35kph, and really enjoying the python's ability to do fast, sharp 180º turns.  I'm not where I was when I was commuting every day on the BHP, but I had no worries about riding on the road in and around traffic.

    The ½" rod ends were smooth and tight and still provide a simp[le and robust method of pivot adjustment for later experiments.  I took the spring out of the suspension and tried a 120lb rated rubber vibration dampener, but alas, my butt is a little too heavy at the moment and I fully compress it.  So, I took it out and put in a ½" square tube piece to act as a compression tube and turn it into a hard-tail for the time being.  It rides great, and I just have to slow down a little for big bumps because of the high pressure tires.  The only thing I need to do is switch out the rear derailleur because the tension pulley has a bit of a flat spot from one of my wipeouts and while it works fine, it sometimes makes a little extra noise.  Aside from that, it's done.