Monday, April 18, 2011

122> Still Toying with Trikes

Well folks, they say a picture is worth a thousand words, so here are a couple thousand worth. Shown above is how a three-wheeled PRT vehicle could be tipped forward to create a ramp, and how the swing-arm can be detached to allow the vehicle to travel away from the track.  The second picture illustrates how the swing-arm can be used to tilt the vehicle back to give it a more even aerodynamic profile.  In this embodiment I assume that the vehicle will not be roadworthy, and that it would have very limited range and speed on battery power.  The steering would be accomplished by having a pivoting back wheel and independently controlled front wheels. The rear wheel would extend downward for boarding, and retract for high-speed use, as shown. 

In this design windows were minimized to avoid the high air conditioning requirements of a vehicle with lots of glass.  Anything short of completely automated driving, however, requires high visibility for the driver, even if the vehicle only goes 10 mph and is controlled by a joystick, so some configurations might need more glass than what I have shown.  I envision the ground-driving capability to be primarily for parking lot use, for either ferrying people to their cars or from the PRT station to the front door of a store or other destination. In this capacity it would go one way empty, on autopilot.  Allowing passenger control risks taking a vehicle to where it could get stuck or get into traffic, so perhaps the manual-drive option should be limited to privately owned vehicles. Such personal vehicles, in addition to the extra glass and AC requirements, could also have extended range, greater speed, more ground clearance and better suspension.  The bogie would only accept a limited amount of weight, however, so such modifications would be at the expense of payload capacity. After all, if we want to have cheap, extendable track we need to draw the line on weight somewhere. In the example above the extra hardware (two motorized drive wheels with rudimentary suspension, rear pivoting wheel with a screwjack for tilting the vehicle forward and a small battery pack) adds an estimated max weight of (perhaps) 100 lbs.


Juho said...

In two of the presented examples the distance that the dual modes travel is short. One could consider also the following scenarios. The store could have a passenger drop track/terminal from where the vehicle (private or public) would move automatically to a nearby vehicle storage area/track. The car park could have a guideway that circulates everywhere around the parking lot (plus a vehicle storage track nearby).

If dual mode use is limited to some small known area, building some extra guideways could be a cheaper and more practical solution than using the dual mode feature of the vehicles. If dual mode is the only well working approach in some places, that would also make dual mode capability to some extent mandatory to all vehicles that visit that place.

The short distance dual mode capabilities can be very useful e.g. for elderly people to move around, but in order to keep the weight and cost of the vehicles (and guideways) low, one should encourage also single mode use wherever possible (=primary approach?).

Dan said...

Dan the Blogger responds from on the road…
Welcome back, Juno… I have not spelled out in too much detail how such dual mode capabilities would be used precisely because I am not really sold on the approach myself. I see it as sort of a transition phase, probably where pavement already exists. Obviously private vehicles would only come into play after there is plenty of track deployed.
One thing I guess I should add is this; I arrived at these dual mode capabilities mostly as a byproduct of other design issues. The vehicles need some way of setting down anyway. The space between overhead track and the ground cannot easily be made to be perfectly exact, so unless they set directly (vertically) down, there must be some kind of roller or wheel that actually rests on the ground to stabilize the vehicle in the boarding area. Compressible tires and/or suspension can allow the vehicle to be squeezed between the track and ground. It is possible that the swingarm alone can be used to set the vehicle into a boarding position, meaning that no wheels would be necessary. At some point we’re going to have to access all of the potential vehicle types and station types and make sure that there is a track design that is optimal for those short, slow, very local runs – that is if we are really serious about keeping those runs elevated.

Dan said...

Dan The Blogger is up at the cabin... No internet, Just cell phone and battery power. New post in the works though!