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How to calculate needed horsepower for radial travel

by Grunig
Tags: horsepower, motor size
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Grunig
#1
Apr10-13, 05:09 PM
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I have a conveyor that travels radially. I need to calculate the HP needed to move it. It works on a concrete slab. The Motor RPM is 1750 and a reducer of 180:1. Any help would be great. Thanks
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Simon Bridge
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Apr10-13, 07:02 PM
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Welcome to PF;
You need to know how much resistance there is to the motion, what speed you want it to move at, and how fast you need it to get to that speed. Much of the power is just to overcome stuff like friction...

I don't know what you mean by "a conveyor that travels radially" - to me, "travels radially" means something that travels to or from a center (i.e. along a radius) - but I don't see how that's different from a regular conveyor.
Danger
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Apr10-13, 07:28 PM
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Quote Quote by Simon Bridge View Post
I don't know what you mean by "a conveyor that travels radially"
While it's not a technically correct description, my first thought was that s/he means a rotating disc, something like a simplified version of an airport baggage carousel.

Gibsons77
#4
Apr10-13, 07:56 PM
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How to calculate needed horsepower for radial travel

Honestly, if you want an accurate answer, you're going to have to give an accurate description. What loads is this thing going to carry? Is it going up hill? A sketch/3d model is needed if you want any sort of accurate sizing. You say you need gearing with 180:1; that's quite the gearing ratio, you're going to be losing a lot of power due to friction alone. What kind of material is the conveyor made out of? What do you mean, it "works on a concrete slab"? You might want to check to see if you're going to have heating issues if your moving big loads. So you already have a motor? That's a bit backwards, you're supposed to size the motor before you purchase one. A "radial" conveyor is no different than a "longitudinal" conveyor with the exception of the addition of a normal and tangential force, both of which will contribute to dynamic friction (so you're going to need a dynamic viscosity term, which is a material property as a function of speed). Also, the speed of your converyor around a semi circle is a function of the radius. The rotational rate and the moment arm are used to find your velocity, which you can then use to find your forces.
Simon Bridge
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Apr10-13, 09:10 PM
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While it's not a technically correct description, my first thought was that s/he means a rotating disc, something like a simplified version of an airport baggage carousel.
That's what I thought too ... the mention of a concrete slab also made me think of the rotating milking sheds we have in NZ. Then I realized that I'd describe these differently so figured that I'd better not guess.
russ_watters
#6
Apr10-13, 09:12 PM
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Quote Quote by Simon Bridge View Post
Much of the power is just to overcome stuff like friction...
Actually, for a conveyor that is level, all of the continuous power is to overcome friction. Placing an object on the conveyor will result in a momentary spike, to accelerate the object, but not enough to matter for sizing calculations: less than the starting power requirement when you first turn it on.

So based on that, the way I've seen conveyor motors sized is by assuming an unreasonably high friction coefficient rather than trying to use a cataloged value The problem with a cataloged value is that it isn't accurate in real-world conditions because it requires continuous, perfectly smooth contact and no debris, wear or fluid, none of which are reasonable possibilities and unless the conveyor is massive, it isn't worth the effort to try to trim the size.

So what I've seen done is to add-up the weight of the objects on the fully-loaded conveyor, add-in the weight of the belt, then use a friction coefficient of 1. Then multiply by conveyor speed and boom: there's your power.

I don't know what you mean by "a conveyor that travels radially" - to me, "travels radially" means something that travels to or from a center (i.e. along a radius) - but I don't see how that's different from a regular conveyor.
I agree with Danger's view on what that describes.
Grunig
#7
Apr11-13, 07:05 AM
P: 2
I attached a pdf of the problem. It is sizing a motor on the powertravel to allow 150' conveyor. Assumptions are on a flat surface with no debris in the travel path. It will be moving 230,000 lbs.
Attached Files
File Type: pdf physics.pdf (25.0 KB, 9 views)
File Type: pdf Drawing4-Model.pdf (55.4 KB, 11 views)
Travis_King
#8
Apr11-13, 11:19 AM
P: 823
These are used a lot in heap leaching.

First off, if you are talking about starting the conveyor, then the starting torque to get the belt moving is your big issue here, as others have said. You've got a lot of weight and you're trying to move it up hill.

Look up info on CEMA design standards.
There are ways to get ballpark estimates, and there are ways to get pretty accurate ones. How you go about this problem depends on how detailed and accurate your answer has to be.

But if you are wondering how to move the whole thing radially, as I suspect, then you have to consider where you are rotating from. Are the wheels powered or does something else rotate it from another location? Generally in leaching applications I've seen the treads powered and controlled by the operators.(treads are used on heap leach pads for lower ground pressure, something you don't need on concrete). If so, it's once again a problem of overcoming friction and accelerating the mass, only in this case it's friction in/between different components.

So, where are the various points of friction?

Edit: similar to Russ_Waters' suggestion, if this is an actual application and you are not part of an engineering firm, this is a time when you should hire one. If you yourself work for an engineering company, then seek the guidance of a mentor or superior for assistance (they'll have the resources you need for this sort of stuff) and be sure they check your work. If this is a theoretical design for your own edification, then by all means go ahead and see what you can come up with.
russ_watters
#9
Apr11-13, 11:25 AM
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I retract my previous recommendation. That is an enormous conveyor/load and you should hire an engineering firm to do a detailed design of it. It is way too big/expensive to risk an ad hoc design on.
Simon Bridge
#10
Apr11-13, 09:59 PM
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I agree with russ_watters: the project is too big for an internet forum.
Hire a professional.


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