Dish + Concrete Bucket Calculations

[DBordello]

I currently have one of the famous bucket + concrete + pole "mounts" for my single lnb setup.

I am upgrading to a slimline and thought I would figure out if the current bucket assembly was adequate. I am on winter break and reasonably bored so I created a worksheet to calculate if a given setup is OK for a given wind speed.

Attached is what I came up with. Most of those values are correct, just the dimensions need to be changed. I figure that most people are going to be unable to open the mathcad and matlab files, so I added a pdf of a quick calculation I performed.

As you can see it is more of a sheet to "check" a design, rather than to determine what is required. Therefore it will require some guess and check. I may update it to be more design orientated later, but mathcad does not lend itself to doing so as I would like.

Enjoy.

[DBordello]

I was under the impression that I would be able to publish the mathcad sheet to a webpage that all could use. Unfortunately that is not easily done. I guess that means that almost nobody is going to be able to edit it.

Oh well, it kept me busy for a while. If anybody has any comments please let me know.

[houskamp]

problably will need to replace the bucket with a 55gal drum for the added size of the slimline :lol:

[MarkN]

I currently have one of the famous bucket + concrete + pole "mounts" for my single lnb setup.

I am upgrading to a slimline and thought I would figure out if the current bucket assembly was adequate. I am on winter break and reasonably bored so I created a worksheet to calculate if a given setup is OK for a given wind speed.

Attached is what I came up with. Most of those values are correct, just the dimensions need to be changed. I figure that most people are going to be unable to open the mathcad and matlab files, so I added a pdf of a quick calculation I performed.

As you can see it is more of a sheet to "check" a design, rather than to determine what is required. Therefore it will require some guess and check. I may update it to be more design orientated later, but mathcad does not lend itself to doing so as I would like.

Enjoy.

I have a hard enough time trying to figure out was azmuth means, now I'm really confused!!

[JLucPicard]

I won't pretend to understand anything about the math anymore (too many years ago for me), but I'm assuming you will be "making a new bucket" as the pole diameter is different for the Slimline than for a stadard dish.

[hdtvfan0001]

problably will need to replace the bucket with a 55gal drum for the added size of the slimline :lol:
I was going to ask what happens if you ever kicked the bucket, but figured that question might be misinterpreted.. :D :lol:

It's amazing what science goes into these calculations.

[DBordello]

Based on my current setup of a standard 5gallon bucket and pole, the 18" dish should be able to withstand a 21mph wind.

Since a new pole is needed for the slimine I am going to reconstruct the whole setup. I estimage that a 18" diameter bucket and 6" of concrete (approximately 120lbs) should be adequate for a 24mph wind. This should be sufficient based on my experience with the 18" dish.

If I simply mount the slimline on the existing setup it should be OK to 14mph winds.

Note that the design wind speed for the midwest is 90mph. These things are going sailing if that happens.

-Dan

[DBordello]

I was going to ask what happens if you ever kicked the bucket, but figured that question might be misinterpreted.. :D :lol:

It's amazing what science goes into these calculations.

I lot of hockus-pokus also.

I'll try to explain it better.

When there is no wind the bucket is "pushed up on" by the floor equally over its entire area. This reaction upward force is exactly equal to the weight of the bucket and prevents it from plummeting down.

As the wind increases, the bucket wants to tip over. The reaction upward force at the back of the bucket increases. Since the total upward reaction has to equal the weight of the bucket (for equilibrium) the reaction near the front of the bucket decreases.

When the wind is great enough, the reaction at the front of the bucket is zero and anymore wind would require it to pull down on the bucket. Since the bucket is simply sitting on the floor, there is no way for the floor to pull it down. At this point the bucket will begin to rotate (about the back edge) as wind increases. This is the point where I calculate the maximum wind load. Although it may not tip over completely, it will move enough to lose signal.

I hope this clears it up.

[tvl76]

With all due respect, If you know how to engineer a bucket of concrete to support your dish at 17 mph wind speeds, then you should know enough that you will see wind speeds greater than that and you should just put the thing in the ground like the rest of us dummies.

[DBordello]

With all due respect, If you know how to engineer a bucket of concrete to support your dish at 17 mph wind speeds, then you should know enough that you will see wind speeds greater than that and you should just put the thing in the ground like the rest of us dummies.

Probably true. Right now I live in an apartment building though. It is easier just to plop the thing out on the balcony and be done with it. I have had this same bucket for 3 years, and it is amazing how convenient it is when moving. Simply pick it up, drop it back down.

This last move I simply eye-balled it and have signals in the 90s. That obviously is more luck than anything, but I still like to brag.

[houskamp]

Just remember that the larger dish has more torque on the mount... as well as is much more sensitive to movement..

[DBordello]

Just remember that the larger dish has more torque on the mount... as well as is much more sensitive to movement..

I am pretty much assuming that the centroid of each dish is the same.

Neglecting the deflection of the pole (due to it's short length) this calculations assumes no movement. The worksheet reports failure once it starts to move.

-Dan

[tvl76]

I admire your approach. If you get paid to be an engineer at work, then there is nothing that can't be engineered at home.

[hdtvfan0001]

Just remember that the larger dish has more torque on the mount... as well as is much more sensitive to movement..
That's why mine is anchored into the ground on an 8' post (4' in the ground) and 2 1/2 bags of concrete - also a bracket mounted to a concrete/brick wall behind it as a windbreaker --- it ain't going anywhere.... :D

[DBordello]

That's why mine is anchored into the ground on an 8' post (4' in the ground) and 2 1/2 bags of concrete - also a bracket mounted to a concrete/brick wall behind it as a windbreaker --- it ain't going anywhere.... :D

I'd agree that isn't going anywhere. Also the the unbraced length of the pole is short, keeping deflections low. Deflection is related to the length cubed.

[hdtvfan0001]

I'd agree that isn't going anywhere. Also the the unbraced length of the pole is short, keeping deflections low. Deflection is related to the length cubed.
...and since this photo, it is also braced - bring on the winds.... :D

[harsh]

Did you establish that the concave face wind was the worst case scenario? As a sailor (and someone who just had a dish blow down in strong a West wind), I suspect that this isn't necessarily the case.

I would have set the model up to establish concrete depth as a function of wind speed as that is what you need to know. I would also chastise you for not considering the wind loading of the bucket itself.

Obviously, you've determined that your bucket model isn't feasible, but what's the point of math if you have to mess with numbers? MATLAB (and MAPLE before it) seems to be fostering a community of "lets plug some stuff in and see what breaks" spreadsheet weenies.

[JeffBowser]

That's a fine looking mount there, I wish I had such a protected area in my setup.

Oh, and nicely groomed yard - you do more than just watch HD, eh :D

...and since this photo, it is also braced - bring on the winds.... :D

[hdtvfan0001]

That's a fine looking mount there, I wish I had such a protected area in my setup.

Oh, and nicely groomed yard - you do more than just watch HD, eh :D
Thanks. You're right, no wind concerns here.

I'm also the gardener, lawn maintenance, electrician, plumber, dog feeder and groomer, occasional cook, chauffer, fix-it guy, toilet unplugger, floor washer, among other things....

But not to worry, with 3 HD DVRs and the rest of the setup inside, I watch LOTS of HD (ergo my name)....

[JeffBowser]

I sure hope that the floor washing and toilet unclogging were not related to one another :D


toilet unplugger, floor washer, among other things....

[DBordello]

Did you establish that the concave face wind was the worst case scenario? As a sailor (and someone who just had a dish blow down in strong a West wind), I suspect that this isn't necessarily the case.

I would have set the model up to establish concrete depth as a function of wind speed as that is what you need to know. I would also chastise you for not considering the wind loading of the bucket itself.

Obviously, you've determined that your bucket model isn't feasible, but what's the point of math if you have to mess with numbers? MATLAB (and MAPLE before it) seems to be fostering a community of "lets plug some stuff in and see what breaks" spreadsheet weenies.

Unfortunately I left my fluid dynamics book at school. I had a friend lookup the drag coefficient for a parabolic dish and he gave me the value in each direction. I went with the worst case scenario. He stated that it was "in the direction" of the dish, which I interpreted as the concave side. This seems logical to me.

In the spirit of making it easy for others to read, I chose to set it up to check a given design. It would be very easy to set it up as you describe, but you end up inverting a bunch of equations and the readability goes out the window. If I get time today I may do that, as it will be more useful.

I chose to neglect the wind on the bucket for several reasons:

1) There is generally some sort cover near the ground protecting it from the wind
2) The drag on it will be significantly smaller than on the dish
3) The associated moment arm is also small, approximately 6in


Obviously, you've determined that your bucket model isn't feasible, but what's the point of math if you have to mess with numbers? MATLAB (and MAPLE before it) seems to be fostering a community of "lets plug some stuff in and see what breaks" spreadsheet weenies.


Not sure I follow. What is the point of math if you have to mess with the numbers? MATLAB (using it's MAPLE backend) was simply used to perform the symbolic integration, no numbers were harmed in the process.

It sounds like you are criticizing me for creating a worksheet that analyzes rather than designs. I believe both have a use. But before one can design, he has to be able to analyze.

-Dan

[Sirshagg]

That's why mine is anchored into the ground on an 8' post (4' in the ground) and 2 1/2 bags of concrete - also a bracket mounted to a concrete/brick wall behind it as a windbreaker --- it ain't going anywhere.... :D

Looks nice but it must be really easy for the neighborhood kids to "mess" with you/it. :)

[hdtvfan0001]

Looks nice but it must be really easy for the neighborhood kids to "mess" with you/it. :)
The nearest kid in my 500+ home subdivision is about a block away. These are not exactly "starter homes" - averaging 4,200 sq. ft.

The dish is actually located / pointed in a cul du sac, only "in view" to 2 other homes anyway, so I'm not worried...
I sure hope that the floor washing and toilet unclogging were not related to one another :D
That's always been my hope as well.... :lol: :lol: