In keeping with my friend's plan to
make a delta using much the same design, I'm making my Python clone
with the same intentions. In fact, the bent and delta rear ends
can be switched in and out of the same front end with the only change
being disconnecting the cabling for the rear brake(s). The Python
Delta sort of looks like an adult sized Big
Wheel.
The front end is the
same one as the Python clone. Same angles, pivot, seat mount,
etc. The change starts behind the front seat mount. The
long backbone is made out of the same 1¼" mild steel box
tube and is parallel to the ground. Again, it's a hardtail and
we'll see if the frame and seat mesh flex enough to soften the ride
a little. The rear cross member is made out of 1" x .064
(or .049") steel box tube. The "L" shaped sections
going forward at the rear are the support arms for rim brakes and are
3/4" x .064" box tube.
This is a close-up view
of how the rear wheels are attached. This trike is modelled with
305mm wheels and mounts for rim brakes. A version with disc brakes
is a little further down the page. The axle goes through
the same kind of axle tube as I use on the trikes, a 1¼"
long piece of 3/4"OD x 1/2"ID steel tube. A piece of
3/4" x .064" box tube connects the axle tube to a piece of
3/16" steel plate. An identical piece of 3/16" steel
plate is welded to the end of the cross memebr, at right angles to the
ground. The two plates are bolted together with four 1/4",
grade 5 bolts and you can set both toe in and camber by using thin washers
as shims between the steel plates. In the picture, a 1/32"
shim between the rear of the plates sets a 1/16" toe in for each
wheel, for a total of 1/8". Camber could also be set by shimming
the bottom bolts in the same way, at the same time if desired. Later,
if I want to change to 20" (or larger) wheels, all I need to do
is unbolt the axle mounts and bolt other adapter plates on in place.
The only provison is if the wheels are so large that they start
interfering with the rider's arms and shoulders.
The nice thing about
a delta like this, is it can be made fairly narrow just so long as there
is enough width for the tires to clear the outside of the rider's arms,
or the rear wheels are far enough back to accomplish the same thing.
Additionally, spray off the rear wheels should miss the rider
with a fender/guard being needed primarily only for the front wheel.
With three wheels for stability, the 48/38/28 chainring should
more than suffice for the hills in my area where very low speeds on
the steeper hills would be problematic for balance on a 2 wheeled bent.
While the rear end might
look a little spindly, I've been building the tadpole front ends like
that and have had zero problems in over 3,000 km. I think it'll
be fine too.
Below, is a version of
the trike mocked up with 16" Al rims and mecahnical disk brakes.
Looks a little more "pro" than rim brakes but the U-brakes
I've been using, up until now, have tons of stopping power. Discs
might add a level of complexity and fine tuning that isn't worth the
stopping power increase(if any). I have a pair of discs and rotors,
so I'll be using them on something - just haven't decided on what yet.
:) It looks very much like Greg's trike aside from the lack of
the rear tilt mechanism.
Here is a closer view
of the rear disc set-up. The toe-in/camber adjustment is identical
to the rim brake version. A short section of 3/4" box tube
at a 30 degree angle is welded onto the side of the axle supports. A
piece of 1/4" mild steel is welded to that which acts as the actual
caliper mount. The disc parts are modelled exactly to scale and
the hubs will be used on other projects that use the Alex 305mm rims
pictured here.
The specs should be close to the following:
| |
Concept |
Delta Ice Racer |
| Pivot Angle: |
- |
59º |
| Trail: |
- |
11¾"(30 cm) |
|
Seat height:
|
7½" |
10"(25cm) |
|
BB height:
|
16½" |
16"(40.5cm) |
|
BB-Seat diff.
|
- |
6"(15.5cm) |
| Ground clearance: |
3½" |
2" (5cm) |
| Wheelbase: |
44" |
45¼" |
| Weight: |
- |
53lbs |
| BB-FWA: |
- |
14½"(37cm) |
| Turning Circle: |
- |
9' (2.75m) |
| Length: |
71" |
73" in ice racer config (~3" longer than
normal due to larger rear wheels) |
| Height: |
25" - to top of front wheel, ~22" to
top of seat |
25"(10cm) |
| Width: |
28" to 31" |
30" |
| Track: |
26½" |
27" |
| Weight Bias: |
- |
55/45 front/rear |
| Front wheel: |
26" AL, VRB-182 26 x 1.25 tire, 7 or 8 spd |
26" x 1 3/8", 95 psi, 9 spd 11 - 34 cassette,
~300 #6 x 3/8" screws |
| Rear wheel: |
16" AL Alex X-101 rims, Kenda Kwest 16"
x 1.5" tires |
two 20" x 1.5" with ~250 screws each |
| Gear inches: |
21.41 to 113.45 |
21.41 to 113.45 (don't anticipate needing any lower
than 29) |
|
19 Jan 06
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 though, I'm making
a tilting delta rear end for it using the same design
as one that Paul
Sims', from Greenspeed
trikes, built. With that in mind, I assembled and cut a
few of the parts I'd need. The wheels are 20" stroller/jogger
wheels with built in precision bearings and a stub quick release
axle already installed. I'm using the same style 1/2"
kingpin with bushings that I use on my trikes, plus an old Huffy
20" fork and head tube. The original idea was to make
a straight delta trike, but I thought I'd incorporate the tilting
feature at the same time.
After about 6 hours of work
over a few days, the new delta rear end is assembled enough to
try a test fit on the python and see how it looks and fits. I
used a couple clamps to hold the rear end roughly in position
to see how close it is to the seat. It will actually be
a little further to the rear, and mounts to the rear dropouts
using a quick release, and a single bolt connecting to the brake
mount. I want to be able to switch back and forth between
the 2 and 3 wheel version with as little effort as possible. The
rear wheels will have rim brakes but the brake supports aren't
completely fabricated yet and the ends can be seen sticking out
in front of the wheel a little.
The rear end will tilt/rotate
independently of the steering and just allows the rider to lean
into a turn like a normal two wheeler. The wheels rotate
on horizontal kingpins and will tilt left and right. I'll
set a stop at 45 to 60 degrees once I find out how far it can
lean or how far the rider needs to lean. I'll put a tilt
brake on it too but I haven't decided whether the brake is on
or off at it's default setting. For ease of riding, I think
I'll make the tilt lock on by default, and you can squeeze a brake
lever to release the lock so it will tilt. I still have
to install a center post on the steerer tube and the two tie rods
as well as the adapter to connect the steerer tube end to the
drop outs and brake mount. Tomorrow I'll go see if I can
pick up a bunch of 1/4" rod ends for the steering linkages.
|
|
|
6 Feb 06
So, been pretty busy with ice
race preparations, and now that the ice races are done, a little
time for updates.
The delta config is done and
pictured to the right. To me, it handled amd felt just about
identical to when it only had two wheels. The idea was to
be able to lock it out whenever I didn't want it to tilt, or when
a new rider was on it and couldn't balance it. A spring
loaded ¼" pin would automatically slide into place
when the python was vertical, and it would "lock" in
the upright position on it's own. To unlock it, you simply
squeezed an extra brake lever and it would slide the pin out of
its socket and it would tilt/lean like a normal python. As
an aside, it's sort of comical to use the words "normal python"
together, yes? :) Anyway, a small strap would keep the lever
squeezed so the python would remain in "unlocked" mode
for normal riding. It worked fine, but when locked in upright
mode, it tipped very easily, due mainly to the seat height combined
with the narrow track. Steering inputs were difficult because
you had to make sure you leaned before turning or you would tip
just about every time at any speed other than quite slow. I
was concerned about this, but as I had no experience with it,
I thought I'd try it and see. Turning it only with my legs
was a little different but not difficult to do, especially with
SPDs. The tilt-stops are set up for about 45 degrees which
is more than enough tilt for any cornering except for a rare high
speed, sharp turn. I know . . . I tested it :)
As for it's performance as an
ice racer, even with all the screws in the tires, there wasn't
enough weight on the two rear wheels to provide adequate traction
at speeds approaching race requirements. It cornered well
but nowhere near as fast as my ice
trike. Once the rear wheels started to slide, I was
just about guaranteed to 1st) do a 180 degree snap turn, and then
2nd) fall over :). Python deltas don't "turn into the
skid" very well at all unfortunately (even using my inside
hand as an outrigger), and then, because I had the python leaned
into the corner, with the sudden spin-out, all the weight was
to the inside, and I simply fell over. It would work quite
nicely on a longer, slower race or on a bigger track with larger
radius corners, but inside a rink, it's a little lacking.
So, I'll take the delta rear
end off and convert the PC2 back to a "normal" python.
I'll change the delta rear end so that the default mode
is "un-locked" and I'll replace the pin-lock with a
disc rotor and a disc caliper, the same as this
and this.
Then, I'll mount the delta rear end on my BHP and do some
long distance/long term trials on the delta rear end.
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25 Oct 2006 - Update
After removing the delta rear
end and cleaning it all up, I noticed that the cross member was
bent. Not sure how or why, maybe in one of the wipeouts
at the ice rink. Fundamentally I like the design, but I
won't put the tilting rear end back on a Python, instead I'll
use it on a normally steered, twist chain FWD delta. By
"use it", I mean using the design, but with a beefier
cross member, lower to the deck and with a cleaner disc rotor
for the tilt lock. If all goes well, it'll be a chassis
for a fully faired trike which should be good for commuting.
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