Requirements
The suspension requirements for this project have to potential to be fairly complicated. Fundamentally it will do what any other suspension does; stabilize and support the vehicle while maintaining an adequate level of comfort for its occupants. However, with the bogie and cabin hanging below its support, we will need to design a way to convert the tensile loading into a compressive load for the suspension components. This isn't 100% necessary, but in my experience suspensions are generally designed to operate in compression and rebound in tension. Therefore, if we were to use "off-the-shelf" parts in our prototype, it makes more sense to design a suspension that is capable of using readily available parts rather than something unproven or with little known characteristics.
There are a number of areas that we need to focus on and address in terms of what motions are desired from this suspension:
Basic Travel Around The Track
-Vertical Stability: keep the cabin from oscillating up and down over uneven parts of track and through transitions.
-Horizontal Stability: keep the cabin level to the ground when negotiating turns to avoid a "pendulum effect".
Arrivals and Departures
If some of the stations are to built at street level (which seems practical) then the cabin/bogie will need to ascend/descend to pick up passengers. With the track sloping to and from street level, we will need to design a way to "self-level" the cabin/bogie with respect to round so that the passengers do not experience a huge change in angle(pitch) as the bogie leaves each station.
In addition to the leveling of the cabin, our team discussed that full cabin will obviously weigh more than an empty one. When the cabin arrives at the station, it should maintain a certain height in relation to the platform passengers load and unload from, especially for safety reasons. To accomplish this, we will need to design a way to adjust the "height" of the cabin under various loading conditions, while still maintaining functionality in the other situations.
Where to Start?
This will no doubt be a challenge to incorporate all of these features into a cohesive suspension system that works in unison with a variety of sensors to monitor and control the position of the cabin.
I think a good way to start designing would be to generate the specific motion and mechanics required. Once we are confident and satisfied with the basic functionality, we can then figure out how to integrate controls in the system.
I read a bit from my teammate Scott's blog post on a suspension idea utilizing a cantilever system. I too had thought about such a route when I was brainstorming. There may be some potential for this type of a configuration. The way a cantilever suspension works is through the use of a push-rod, and a pivot arm (cantilever) where the push-rod and spring/shock are attached. This can be designed as a very compact system, where the spring and shock actually operate perpendicular to the motion of the vehicles oscillation. This is no doubt a unorthodox method, but it can be extremely versatile and has the advantage of being compact due to the fact that there is a ratio involved with the amount of travel by the vehicle, and the suspension components. A traditional suspension is setup in parallel to the motion of the oscillation, so if the cabin where to move 6", the springs would move 6" (if there is no spring/shock angle). With a cantilever system, a mechanical ratio is induced due to the pivot arm and push-rod dimensions, meaning, depending on the design, a 2:1 or 3:1 ratio of cabin to shock movement could be implemented; lending to a very compact suspension system.
This explanation is probably a bit hazy if you have never seen a cantilever suspension before, so here is a picture to give you a better idea of what it might look like:
I read a bit from my teammate Scott's blog post on a suspension idea utilizing a cantilever system. I too had thought about such a route when I was brainstorming. There may be some potential for this type of a configuration. The way a cantilever suspension works is through the use of a push-rod, and a pivot arm (cantilever) where the push-rod and spring/shock are attached. This can be designed as a very compact system, where the spring and shock actually operate perpendicular to the motion of the vehicles oscillation. This is no doubt a unorthodox method, but it can be extremely versatile and has the advantage of being compact due to the fact that there is a ratio involved with the amount of travel by the vehicle, and the suspension components. A traditional suspension is setup in parallel to the motion of the oscillation, so if the cabin where to move 6", the springs would move 6" (if there is no spring/shock angle). With a cantilever system, a mechanical ratio is induced due to the pivot arm and push-rod dimensions, meaning, depending on the design, a 2:1 or 3:1 ratio of cabin to shock movement could be implemented; lending to a very compact suspension system.
This explanation is probably a bit hazy if you have never seen a cantilever suspension before, so here is a picture to give you a better idea of what it might look like:
This is meant to be used on an offroad vehicle, but the concept is the same. The lower horizontal tube represents the axle that travels vertically up and down. The shocks are then actuated via a pushrod (lower vertical shorts arms mounted between axle and cantilever arm) and the cantilever arm that rotates about a fixed point. There are many ways to modify this design, this is just an example of the concept.
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