# A passenger car with an non-shaking room

A-A
I have been thinking whether it is possible to make a car with non-shaking compartment.
Meaning that when the car moves, its internal compartment will not shake at all such that a passenger may just place a cup of coffee on the table while the car is moving on a rough surface.

## Answers and Replies

Science Advisor
My gut feeling is yes, under certain conditions. Correct me if I'm wrong, which I probably am, but it seems that one could represent bumps and potholes as modified step and ramp functions, then use Laplace Transformations to find accelerations and things like that. A computer would more than likely just do it numerically, but with that I would think you would be able to adjust the suspension to account for it.

However, there would be certain things that would either go out of the throw of the suspension, and the suspension would have to return from being displaced.

i.e. You hit a bump, the wheels go up instead of the compartment, however, once the wheels are up, they must come back down so they can absorb another hit. If they come down too slow, then another bump can come by and set you past the max throw. If they come down too fast, then there may be a noticeable acceleration and force in the z-direction.

Just some thoughts, I'm sure someone else will have some even more in-depth explations why/why not

A-A
To be more precise, I am thinking of using magnets (opposing forces of magnets to be used for compartment suspension). This should be irrespective of the wheels and physical structure of the passenger car.

Homework Helper
When mag-lev trains were in development, they thought that there wouldn't be a need for a lot of suspension, but it turned out that the reaction was about the same as having actual wheels, and they had to resort to supension systems similar to trains with wheels.

MechanicalMan
Bose has developed an active electromagnetic suspension that accomplishes exactly what you are looking for. Here's a link to a video comparing the Bose suspension to your standard, everyday hydraulic suspension.

http://youtube.com/watch?v=eSi6J-QK1lw

Fundamentally, if you wished to design something like this, you would need a very strong background in mechanical vibrations.

This video is in French, but it shows how the suspension works: http://youtube.com/watch?v=Lyf4rfT7bHU&mode=related&search=

Let it load and fast forward to about 1:52.

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A-A
Bose has developed an active electromagnetic suspension that accomplishes exactly what you are looking for. Here's a link to a video comparing the Bose suspension to your standard, everyday hydraulic suspension.

http://youtube.com/watch?v=eSi6J-QK1lw

I watched the clip (I appreciate it). but It is not good enough. I want the passenger to be resting in the car as if he is at home (sitting on a carpet). further more bose is using bumps. but I want purely magnetic suspension. I may however need to regulate magentic forces.

verafloyd
Electromagnets are highly non-linear in nature. You have to have a closed-loop control scheme incorporated with an actuator system having linear characteristic (like hydraulics maybe).

Colin1
when the car moves, its internal compartment will not shake at all such that a passenger may just place a cup of coffee on the table while the car is moving on a rough surface.
How would you counter inertia in, say, an emergency-braking scenario?

Science Advisor
Similar things have been done with mechanical means. However, they were with rather complex mass-spring dampers. They are quite large and heavy. Their use would be negated by the decrease in fuel efficiency.

Gold Member
How would you counter inertia in, say, an emergency-braking scenario?
Clearly they're talking apples you're talking oranges. There would be a threshold under which you'd damp movement, but anything over a few inches would overwhelm the damping mechanism and the compartment would behave as if undamped.

Colin1
Clearly they're talking apples you're talking oranges.
Possibly
but if we're talking about placing a cup of coffee on a table in a car while the car is moving, it becomes pretty difficult to bifurcate the apples from the oranges. Changes in inertia are inextricably linked to rough surfaces as part of the same (typical) driving experience for the occupants, along with other independent influences such as swerving to avoid an animal. Surely you would need to solve for all conditions?

Gold Member
Surely you would need to solve for all conditions?
In general, that is an unreasonable expectation of a suspension system. In specific, the OP is asking about shaking on rough surfaces.

Colin1
In general, that is an unreasonable expectation of a suspension system. In specific, the OP is asking about shaking on rough surfaces.
Maybe I need to step back from the plight of the coffee.
The OP is simply looking for a smoother ride, he's not expecting his coffee to come safely to a halt or avoid errant wildlife as a result of his smoother ride.

A-A
you talked about inertia. "Yes, the coffee must be there". however, when the whole compartment is not moving at all do you think inertia would be a problem. inertia is true if you are attached to compartment by any means. imagine a car is moving and and at the same time an appel is floating on the air some where inside the car. suddenly the car brakes. does it affect apple?

Staff Emeritus
Science Advisor
Gold Member
you talked about inertia. "Yes, the coffee must be there". however, when the whole compartment is not moving at all do you think inertia would be a problem. inertia is true if you are attached to compartment by any means. imagine a car is moving and and at the same time an appel is floating on the air some where inside the car. suddenly the car brakes. does it affect apple?

Not sure what you mean by "does it affect the apple". If the apple is moving at the same speed as the car, and it must be to stay inside, it will continue moving, unaffected by the motion of the car, until a force is applied perhaps by the windshield or the head of the driver.

The thing is, we are assuming that even though the compartment is not bouncing around due to the road it is still moving at some non zero velocity, any change in compartment velocity will be felt by the passengers. This unavoidable.

A-A
think of fastening the cup (or other relevant objects in the campartment) with magnetic (invisible) force. The force must be activated only when the sensors predict a near braking incident. At usual times external regulated force should suffice.

A-A
This will produce a sense of detachment.