Requesting help to conceptualize a project (keeping an object level)

[I Question]

Hello!

I would like to design and ultimately create a medium sized, self-levelling shipping container. I imagine the container would consist of two spheres of different sizes. The smaller of the two spheres would be contained within the larger of the two, and be the part of the container which is self levelling. The larger (exterior) sphere would likely be permanently attached to a base which would allow it to rest on the floor without movement.

The design of the larger sphere and base are straightforward. Could you please suggest how I might go about making the smaller sphere self-levelling? I thought about using ball bearings between the larger and smaller spheres but would welcome any other (and perhaps better) ideas you'd care to share.

Thank you for your input!

 

[jedishrfu]

How about placing the smaller sphere in a bath of water.

You might be able to search on patent ideas for self leveling things. I found this one for chairs:

https://patents.google.com/patent/US3632076

and here's a self leveling table:

 

[berkeman]

Could you please suggest how I might go about making the smaller sphere self-levelling?

Welcome to the PF.

Could you post more about the project requirements? That would be a big help.

• What volume is involved?
• What weights are involved?
• What tilt angles must be tolerated? +/- 5 degrees? +/- 45 degrees?
  
• What frequency response is needed for this "self leveling" feature? Is it because the container ship is rolling slowly, or because the shipping 18-wheeler truck is taking mountain roads too fast?
• What accuracy do you need for "level"?
• What power sources do you have available for an active leveling system (versus passive gravity-based leveling)?
• What are the consequences of the system failing? Loss of revenue for the cargo (how much revenue?)? Loss of life for the animals in the cargo?

 

[I Question]

jedi and berkeman, thank you both for your replies.

jedi: I never thought to use liquid as a medium, and am embarassed for not having done so. The simplicity of water is elegant--thank you for that. Unfortunately, other contraints (the container's use on an aircraft, in a cargo hold) prevent me from doing so for this project. I welcome any other ideas you might have.

berkeman: Thank you for your questions, as they helped me figure out certain things I had not yet considered. My answers (at present) are below:

What volume is involved? I am not certain of this figure yet but have realized in answering your other questions that the container will likely be somewhat larger than I first conceived. Design also plays into this uncertainty: if the container is approximately Dalek shaped (as I first imagined it,) its dimensions would be different than if the self-levelling sphere were placed inside a 3’x3’x3’ box of some kind.

What weights are involved? The weight of the container and base, which are variable (I am thinking of using carbon fiber for this), the weight of the liquid and dry contents of the container, and one 15 pound cat. Here I might guess that the total weight could approach 50 pounds, maximum.

What tilt angles must be tolerated? +/- 5 degrees? +/- 45 degrees? The container will be used on a commercial airliner, though I don’t know which kind of plane I will ultimately be scheduled to fly on. Consequently I would guess that the maximum tilt angle the container would have to adjust for is 25 degrees upon takeoff (using Boeing MD11 figures), and perhaps as much as 11 degrees (maximum) throughout the flight (again, based on the B-MD11). The container would also have to adjust for rotational changes (when the plane banks left/right to change course), which I believe is constant at 30 degrees maximum.

This is why I thought of using ball bearings between two spheres—the container must account for changes in pitch and roll, and at four points in the flight must do so simultaneously. (I have not committed to this idea, however, and welcome more elegant solutions!)

What frequency response is needed for this "self leveling" feature? Is it because the container ship is rolling slowly, or because the shipping 18-wheeler truck is taking mountain roads too fast? The frequency response (as I understand it—please excuse my ignorance if my apprehension is incorrect) should be constant, in that it should keep the container level throughout the climb phase of the flight, throughout all course changes (banking), and then correct to adjust for the pitch of the nose of the plane while in flight, for the entire flight.

What accuracy do you need for "level"? At least 97%. The goal of this project is to get my cat from where I am to where I am going as comfortably and cleanly as possible.

What power sources do you have available for an active leveling system (versus passive gravity-based leveling)? As this container will be stored underneath the plane, I can safely guess that levelling the container must be gravity based.

What are the consequences of the system failing? Loss of revenue for the cargo (how much revenue?)? Loss of life for the animals in the cargo? Relative to the container and its contents, system failure would include an uncomfortable, ill-tempered, and physically quite dirty cat upon arrival, as all of the liquid and dry contents of the container (cat food, water, both fresh and soiled litter) would not be where they were supposed to be inside of the container. Relative to the aircraft, I would expect that some of the liquid/dry contents of the container would end up soiling the cargo hold, which would be an embarrassing, thoughtless thing if it happened.

 

[I Question]

A note to jedi, berkeman, and any other future contributors:

I should have been clearer in my first post, but I'm seeking guidance in how to consider this project as a concept, not in how to actually build the container (yet). berkeman's questions helped me realize that I needed to account for two different changes in position (pitch and roll) which I hadn't considered before. That sort of insight is invaluable, and what I humbly request from all. Thank you again!

 

[Tom.G]

It sounds like you are basically trying to counter/mask the direction of the local Gravity vector. A non-constrained pendulum does this nicely. Although you may need some damping.

Cheers,
Tom

 

[berkeman]

It sounds like you are basically trying to counter/mask the direction of the local Gravity vector. A non-constrained pendulum does this nicely. Although you may need some damping

Exactly what I started picturing as I read the OP's responses. Making it pendulum based may take up more volume than the concentric spheres with bearings, though. Interesting design challenge.

 

[berkeman]

BTW, you may also want to think about incorporating some vertical damping in the design, to help with air turbulence. Even if the cat is held pretty level, it probably will not appreciate a couple minutes of clear air turbulence (which is ironically abbreviated CAT).

 

[russ_watters]

one 15 pound cat...

What tilt angles must be tolerated? +/- 5 degrees? +/- 45 degrees? The container will be used on a commercial airliner, though I don’t know which kind of plane I will ultimately be scheduled to fly on. Consequently I would guess that the maximum tilt angle the container would have to adjust for is 25 degrees upon takeoff (using Boeing MD11 figures), and perhaps as much as 11 degrees (maximum) throughout the flight (again, based on the B-MD11). The container would also have to adjust for rotational changes (when the plane banks left/right to change course), which I believe is constant at 30 degrees maximum.

It sounds like you are basically trying to counter/mask the direction of the local Gravity vector. A non-constrained pendulum does this nicely. Although you may need some damping.

Erm, the local gravity vector of a plane is *always* through the vertical axis of the plane to the best of the pilot/autopilot's ability to control! That's why flying in a plane is a much more comfortable ride than riding in a car or bus; you never feel it turn!

So I don't think your requirements for this device actually exist...

...Your biggest issues with keeping a cat level are loading and unloading and the drive to the airport.

* Exceptions: When changing speeds (primarily takeoff and landing - at all other times it's too low to notice) and in variable winds. I've only very rarely felt the gravity vector shift horizontally (yaw) and it is quite disconcerting when it happens.

**Need to find a place to insert a joke about cats being self-leveling while in flight. And maybe one about them being prone to flattening under the influence of gravity.

 

[anorlunda]

Just ask a mariner. Ancient mariners invented the double gimballed oil lamp. I used two of those for 60K nm of sailing, so I can tell you they work almost perfectly.

 

[CWatters]

Something like the double gimballed lamp would tip when the aircraft accelerates or brakes. Is that ok? I guess it depends what you mean by "level".