KrankiKobra - rideable?

He got me curious about the "Python" low-racer recumbent that he referenced as the inspiration (seen below). The Python freewheels, it has a rear brake, it has 21 gears, and the rear wheel doesn't articulate. The python looks odd, but it actually is ride-able. I understand this guy had an idea that he thought would be a fun project, but I think the rear articulation would make it almost as difficult to ride as a unicycle.

Acertula_4_2.jpg
 
ran across this electric 2wd 2ws recumbent... weird..
http://rohorn.blogspot.com/2006/11/my-first-venture-into-recumbent-design.html


"The python looks odd, but it actually is ride-able"

i test rode a "center-steered" recumbent back in the 90's
its weird, took about 10 minutes for me to get it going...

it might have been this guy's bike,
edit, tom traylor
http://traylor_fwd.home.mindspring.com/
tt017.jpg
 
Since that early video, I've been tweaking the KrankiKobra. I had originally gone with a pivot angle of 60 degrees on fore and aft. Those angles were intended to provide more stability than steering. I've left the rear angle alone, but have increased the front angle to 65 degrees. I wasn't getting enough steering authority to stay upright. The point of no return, before falling over is very narrow. It took very coarse movements to stay balanced. The minimal angle change has made things much easier.

I haven't spent a lot of time riding and am no where close to riding downtown with it yet. At certain speeds and pedal cadence, a harmonic is set up on the rear pivot. It's not harmful, just disconcerting.

As far as difficulty of riding...about the same learning curve as a unicycle. I find I need absolute focus to stay upright. I tend to go into auto mode like riding a bicycle and then the diversion happens. Even hearing traffic behind me on our quiet street tends to derail my efforts. It has been fun though and once mastered and painted, it will be a keeper.

Here's some more video of straight line riding, first with the back pivot locked, them unlocked. Warning: soundtrack is a little "over the top".
[youtube]DPxDHTL1Kts[/youtube]
 
You know it would work a lot better if it didn't have the single pivoting rear wheel. It would work a lot better if it had say two 16" tilting rear wheels. It would be a lot more stable and would still turn well. His starting gear is also way too hard. The smaller rear wheels would also allow for more seat clearance. He should lose that big chain ring in between the hub and crank and put a three speed cassette on the hub with a small boom for a three speed derailleur. To still keep it hands free, he could use one of those auto shifting derailleurs with the flywheel. Another idea would be to put some kind of positive, negative spring tension force on the rear pivot to make it more stable and keep it from wobbling all over the place and also a smaller wheel with a much wider tire. I don't know I just had some mental images I needed to share.
 
lbz5mc12 said:
You know it would work a lot better if it didn't have the single pivoting rear wheel. It would work a lot better if it had say two 16" tilting rear wheels. It would be a lot more stable and would still turn well. His starting gear is also way too hard. The smaller rear wheels would also allow for more seat clearance. He should lose that big chain ring in between the hub and crank and put a three speed cassette on the hub with a small boom for a three speed derailleur. To still keep it hands free, he could use one of those auto shifting derailleurs with the flywheel. Another idea would be to put some kind of positive, negative spring tension force on the rear pivot to make it more stable and keep it from wobbling all over the place and also a smaller wheel with a much wider tire. I don't know I just had some mental images I needed to share.
Click to expand...

I appreciate the comments and suggestions. I will attempt to respond to your points.

This has been and will continue to be a design exercise. It was never meant to be a stable docile machine. I have a tadpole trike for that:) The second pivot was designed in to facilitate faster turning. I also want to be able to crab sideways down the road for no other reason than to amaze onlookers.

I looks like I have a tall gear in the first video. It's actually okay. The difficulty in starting was because the seat back was bending back and rubbing on the rear wheel for a very effective brake.

I'm not sure how smaller wheels and better seat clearance would make a difference. I was looking for the largest wheel that would fit my inseam measurement. A larger wheel is also more gyroscopically stable.

I had considered a three speed hub, but went with the one speed coaster brake for simplicity and to ensure hands free operation. This thing is pedaled, steered and braked with your #12's.

The big ring (ghost ring) serves a purpose of tensioning the chain in both directions as there is no chain adjustment on the forks. And it looks cool:) Here's a short video of the ghost ring at work.
[youtube]lp-hTW-N0Hc[/youtube]

I may yet add some kind of dampener on the rear pivot. As mentioned in a previous post, there are some harmonics at play with certain speeds and cadence. I had the same kind of issue on a fixed gear aircraft I built. At certain tire pressures and speeds the gear would go into a shimmy. I quickly learned to transition through that speed with either throttle or brakes.

All in all, this has been a fun project. I'm less scared of it now, even though it has bitten me many times.
 
sk8norcal said:
Hi Spinner,

how about handlebars attached to the rear fork?
sort of a reverse swing bike deal...
Click to expand...

There is just so many ways to take a perfectly engineered design and turn it into an unstable unsteerable monster :lol:
I do plan on putting a detachable tiller of some sort on the rear wheel. Just to facilitate a speedier method of getting injured.
 
^ what i am really amazed at is bmx rider that can go backwards...
the pros make it look easy..
http://www.youtube.com/watch?v=m6sSpJO7zkM

lbz5mc12 wrote:You know it would work a lot better if it didn't have the single pivoting rear wheel. It would work a lot better if it had say two 16" tilting rear wheels. It would be a lot more stable and would still turn well.
Click to expand...

found it,
python tilting trikes,
http://www.darinwick.com/python_trike.shtml
http://fleettrikes.com/python%20delta.htm

spinner, check out this one.
http://www.bentrideronline.com/messageboard/showthread.php?t=79570
 
One way to achieve the stability issue through use would be to put a wider rim and tire on the back and maybe lower the pressure a little. Kind of make it like a training wheel until you figure out the balance. Then as you get better you could gradually narrow your rim and wheel size until you get down to something well narrower lol.

The Python trike is similar to what I was thinking but with a closer together and narrower wheel base so it could still have a streamlined look. Also with smaller rear wheels which would be less weight and less drag.
 
Ypedal said:
roller gloves ?
Click to expand...

I always wear heavy gloves, and elbow pads, and helmet, and wrist protectors and 911 pre-dialed on a cell phone.

I've played around with an outrigger setup like this.
IMG_0368.JPG


And a less tortured view.
IMG_0369.JPG


And it had surprising, painful results. When the castors touched the road, that was pretty much the last sound you heard. The bike would violently twist sideways and disembark me somewhat ungraciously in a heap. It was an unintended auto-eject feature. I had to lock the rear pivot to make it even possible to ride. I didn't keep the outrigger on very long. I wouldn't let my children use training wheels, why should I.

This past weekend I've shortened the wheelbase by aprox 1.5" and increased/decreased (I get confused) the rake by one more degree. Either that made a huge difference or this white haired old dude grew some new neural pathways. I rode down the block and back with little issue. I even made a turn onto another street. Hmmm.

BTW, the build name was the articulator and the photo log is on my signature, if interested.
 
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