[python] Re: Question for the experts
- From: "25hz" <25hz@xxxxxxxxxx>
- To: <python@xxxxxxxxxxxxx>
- Date: Mon, 17 Jul 2006 23:10:17 -0400
Very cool concept, but ifit does work, it will be quite . . . huge and
probably not suitable for what you want to use it for. But hey, it's worth
a shot right? :) A couple replies in line . . .
> The way I am envisioning this is as follows.
>
> 1) Rear wheel drive.
> 2) Standard Tadpole boom setup
With a tadpole boom, and the pedals out on the end of it, you might find
that python style steering will cause the front wheels to hit your legs,
pedals or both and put big limits on how tight you can turn. The only fix,
it to make the thing about 36" wide or wider, and even then, you still might
have wheel - leg issues.
> 3) The front Cross bar of the tadpole will be completely horizontal with
> the standard python steering frame joints on the outer ends of the cross
> bar.
> 4) Standard Python front sections using a front wheel instead of a rear
> wheel.
> 5) Where the bottom brackets on a python normally is, having a linkage
> join the two python booms together.
This might prove problematic. Remember, your legs will be out there
spinning around on pedals, and from personal experience building tadpoles,
the average person needs a clear space of about 16" or more for their heels
to clear the crossbar. If the linking rod is high, it needs to be really
high to get knee clearance. If it is low, it runs the risk of being torn
off by being too close to the ground. If you make a linkage at the rear,
near the python pivots, you will need to make the tie-rod bullet proof
because the long lever of the front wheels in front of the pivots coupled
with the weight of the tadpole/rider trying to force the wheels straight
will put a tremendous load on the linkages.
> 6) some type of handle bars to allow the rider to induce the lean for
> the steering.
I don't think you are going to be able to lean the trike. When turning, it
will swing up to the outside of the turn, and swing back down to center, but
it can't lean - at least the way it looks to be explained so far . . .
> The purpose of this is to design is as follows:
>
> 1) A self centering trike that can be the base platform for a
velomobile.
It will self center all right, but think about how far out to the sides the
wheels and/or wheel fairings will stick when turning, especially if they
have small wheel fairings. If you plan to enclose the front wheels in the
body of the velo, again, the front end of the fairing will need to be crazy
wide.
> 2) It will allow the use of standard bicycle parts without relying on
> special hubs for the front wheels.
You can already use standard bike parts for the front wheels without any
special hubs. BMX front wheels come with 14mm axles which are more than
strong enough to be used on a tadpole. Myself and many others have used
them quite successfully with simple rim brakes. You can also get disc front
hubs with a 12mm axle and sealed bearings made by Formula - no machining
required.
> 3) Allow higher gearing using as 26" rear wheel and using 16" or 20"
> front wheels with disk brakes.
You can get higher gearing with just about any size rear wheel now by using
a Shimano Capreo rear hub that has a small cog of 9 teeth without having to
go for crazy 60T chainrings on 20" wheels.
> 4) If building a velomobile the python frame joints could be built
> into the faring design for the front wheel mounts and to total encase
> the front wheels for aerodynamics.
It's a cool idea, but honestly, for a tadpole, just build a tadpole -
they're not difficult or expensive to built. If you want to utilize the
python design, then built a python delta like some others have. It makes a
great delta, which you can still turn into a velo if you want, much simpler
steering, chainline and frame design. A whole lot lighter too. Good luck
whatever your choice though :)
> If someone is good with a sketchup I can try to provide further details
> if need be to help developing the plans.
>
>
> Doug Morency
> Osgoode, ON Canada
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