I was thinking, the other day, about this blog and how badly
it needs a facelift, and I had a realization. The original purpose of the site has essentially
been realized. No, I did not succeed in
getting a cadre of engineers to anoint and consecrate a set of standardized
dimensions under the alter of “open source.” Nonetheless these last few posts represent
what is pretty much the closing of a chapter, design-wise. After a rather exhaustive assessment of a
variety of issues, it can be said, in most instances, that there is a clear,
best way to accomplish a system with the kind of capabilities I have been
advocating. I had originally hoped to
create some standards for PRT, so that the business would not require a single
company to be the expert in vehicle making, station building, track building, route
planning , system maintenance, traffic management software, etc., etc. What we have, actually, is a pretty good start
in that direction, at least for this one type of PRT. In my last post I outlined a bunch of “pearls
of wisdom” that, if followed, outline how the capabilities of a suspended PRT
system may be greatly extended.
These principles guide track design and therefore bogie
design. Since there is nobody else
really trying to push the performance envelope for suspended systems, I guess I’m
sort of creating the basis for such standards as I go. What I am advocating is an open standards
approach to what I call a “SMART” network. (Suspended Multi-axis Automated Rail
Transport) My vision is to create the cheapest, fastest, least intrusive, most versatile,
method for “air-lifting” a load from any point A to any point B without
actually flying.
At some time in the near future, this site will no longer be
about getting recruits to design a better PRT system, but rather about refining
and promoting those design decisions that resulted from the work already posted.
It took a very long time to do, and
there are still plenty of details to nail down, but longtime readers of this
site have seen the other parts of this system and know that the current work on
the bogie is akin to shaping a keystone – the final piece that must fit in an
arrangement of pieces that have been fashioned just for it. Once the essential geometry is set, and the
capabilities and limitations are known, it’s detail time… time to design a
prototype in earnest. Once again, my
apologies to anyone who has just found this site. I’m sure this bogie (which doesn’t even show
hardware for hanging a vehicle) must be mystifying. I will soon put the pieces together into a unified
system. I promise!
Not that there isn’t a LOT more work to be done here, on
this model. Each piece needs to be
examined for redundancies, interferences, extra weight and manufacturability. This will take days or weeks, not hours. Still, I think the general design demonstrates
that, with the right geometry, extraordinary capabilities can be achieved with
a modicum of inexpensive parts. I have
had to sacrifice almost nothing in terms of speed, turning radius or climbing,
which are over 100 mph, under six feet, and any angle up to 90 degrees, (straight
up) respectively.
One thing that is lacking in many PRT and dual mode proposals
is a practical way forward. Often
concepts are presented that are so early in the research and development stage
that only a physicist can tell if they are even feasible, let alone lucrative. Although parts of any complex machine become
more specialized over time, presenting it with too many of these one-of-a-kind
components too early tends to condemn an otherwise good concept to a life on
the drawing board. Since business
realities demand that commercial incentive surpasses developmental risk, a budget
oriented “proof of concept” design is an invaluable first step.
With this in mind, this bogie design (which is a more
evolved embodiment of the ideas expressed in the last post) uses
“off-the-shelf” components where possible. The motors for this model are dimensioned from
the 7000 watt hub motors from Kelly Controls.
Using four adds up to a bit over 39 hp. The
upper steering guide wheels are hub motor driven scooter wheels and tires. (13”hubs,
from the same source, with Pirelli Diablo tires) The steering guide wheel is designed for
continuous contact and the hub motor can be sized up to 6kw, for an additional
8hp. Although this would compare
favorably with other systems out there, it would still be a bit underpowered
for commuting. Luckily, the main drive
wheels are standard low profile automobile hubs and tires (215/35-18) and so the
motors can be readily swapped with higher power ones, even up to the monster
(80hp per wheel) Protean motors, which would enable performance that would put
most sports cars to shame. For climbing
standard sprockets are used, drilled for lug nut extensions. The design features truck style emergency air
brakes that clamp the track. There are
dual (self-diagnostic enabled) steering guide servos that work together but can
work singly as long as there is power from either the track or the onboard
battery.
In this design the steering guide wheels are not on rocker
arms, like in the earlier design. Although
the rocker design does seem to offer smoother engagement, this supposed
advantage assumes a continuous rail to engage upon. If the steering guide wheels are positioned
first, with the contact rails being tapered to make contact after that, this is
smoother still.
About the upper steering guide wheels: First, the matter of
wear. After all, they are soft rubber,
relatively small, constantly engaged, and contacting at an angle. I would first note that tires for scooters and
other two wheeled vehicles have heavy sidewalls so that riders can lean into
turns, which is an extreme torture test compared to pushing into the smooth
steel of the “diamond” guides. With the
new (counter-rotating) lower guide wheel geometry and wider drive wheels the
forces exerted on the upper wheels is minimal.
Also, engagement between the wheel and guides need not be continuous, or
at least not under significant pressure. I envision the contact being primarily on the
crown of the tire most of time but, unlike scooter use, there is no driver,
second rider, or vehicle weight on them. A good finished design will enable the whole
wheel to be swapped so that the tires can be changed on a bench instead of on
the vehicle. Lastly, the tires are relatively cheap and specialized wheels will
eventually evolve. These should be good
for well over ten thousand miles as they are.
All tires should probably have ribbed
or foam reinforcement inserts, giving them the ability to run properly even if
deflated. After all, tires are hollow
primarily as a cushion against uneven road surfaces, which, of course, does not
apply here.
About the emergency brakes – This aspect has had the least
amount of thought at this point, but I wanted to explore where the hardware
would fit, so I put a crude system in place. The idea is that the lower brake shoes engage
first, pulling the bogie into the track and compressing the tires a bit before
the upper shoes make contact. We don’t
want to have the brakes make the tires lose traction. The brakes are spring
activated, and disengaged by compressed air. Another concern is clamping only on one or the
other side of the track on switches. As
it stands, such a one-sided drag might tend to pull the bogie off course. I am still mulling that one over. The geometry enables some kind of bumper activated
system and/or a passenger activated one well.
I know it is very difficult to understand a system from a
few pictures, but there is only so much that is worthwhile to show at this
point. An exploded view would be
helpful, but most of the parts will still be evolving for a while yet. Another issue to consider is that the ordinary
way such parts are made on an industrial scale is by punching and stamping. These processes are used to cut out a shape from
metal sheet and form it into a 3D shape, which stiffens it in the prescribed
manner. This requires huge machines and
matching heavy steel male and female surfaces to squeeze the plate between,
often at high temperatures. Such a
process is impractical for small scale production, so we are left with making
everything out of plate and profiled stock, such as tubing or angle steel. This compromises proportions and weight
tremendously, and is one reason why I think that such manufacturing should be
separate from the PRT business per se. In
any case, any designs herein will be constrained by processes that can be done
on a small scale, often by hand, but hopefully with shapes also suitable for
mass production. I can say from
experience that, at a certain point, it is better to simply start making the
thing, because the prints inevitably prove themselves short-sighted, and every
change creates a ripple effect.
Well, that’s it for now, but for this closing thought. On Thanksgiving morning, on I-10, (the principle
southern road across the US) there was a massive pile-up due to fog. Over a hundred cars and trucks were involved,
scores were injured and two died. The
highway was closed for nine hours. This
is a system that seems unworthy of the times, if you ask me. We live in a world awash in cheap sensors and
amazing computing power. Yet all of that heavy machinery was being controlled
by people blinded by fog and in too much of a hurry to slow down. This is a systemic problem that needs a
systemic solution. We need an app for that!
