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peretz87
Apr 10, 2012, 11:31 PM
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Hello, maybe you can help me with my project about cams.
I need to design cam and determine the width, length, material... I start with the lobes, after i find the forces, how can i calculate the stresses on the lobes?
I need the stresses for finding the dimension no?
Please help me... Thanks.
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Colinhoglund
Apr 10, 2012, 11:55 PM
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peretz87 wrote: Hello, maybe you can help me with my project about cams. I need to design cam and determine the width, length, material... I start with the lobes, after i find the forces, how can i calculate the stresses on the lobes? I need the stresses for finding the dimension no? Please help me... Thanks.
Start with a constant camming angle of choice, 13-18*. Figure out the forces and go from there. Also, it might help to copy an existing unit.
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vinnie83
Apr 11, 2012, 3:14 AM
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peretz87 wrote: how can i calculate the stresses on the lobes? I need the stresses for finding the dimension no?
Can you give us a little background on the scope of the project or what type of class this is for? From the nature of the post it appears that you aren't an engineering student and I'm not sure you really understand what stresses are.
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peretz87
Apr 11, 2012, 8:43 AM
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I do an engineering student (Mechanical engineering actually). it's my first project and i'm not sure of what i'm doing...
The camming angle is 14 (deg) and i found the forces.
now i need to continue with my design and i'm not sure what to do.
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vinnie83
Apr 11, 2012, 8:16 PM
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Since stress is generally defined as Force/Area the logical next step is to choose a material which will help you determine a maximum stress. With both a known force and a maximum allowable stress you can solve for the dimensions of the different components.
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peretz87
Apr 11, 2012, 8:35 PM
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Thank! but what about bending/shear/torsion stresses?
there is just compresion stress in the lobes?
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kennoyce
Apr 11, 2012, 9:37 PM
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peretz87 wrote: Thank! but what about bending/shear/torsion stresses? there is just compresion stress in the lobes?
Cam lobes are a bit more complicated then what the normal equations can handle. The only way to really determine the stresses is with FEA. Again, the more info you can give on your project the better. FWIW I am a mechanical engineer and have designed and built prototypes of several differenc cams for fun (allthough I don't work for any climbing related company).
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peretz87
Apr 11, 2012, 9:45 PM
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This project is open. there are no requirments for the design.
I chose aluminium 7075 T6 for material and 14(deg) angle.
Applyed force is 14kN. Now i need to choose dimentions and for that i need to calculate the stresses. I can't use programs, just hand calculation.
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shimanilami
Apr 11, 2012, 9:47 PM
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You're basically asking people on the internet to do your homework for you. Frankly, I'm disgusted.
Why don't you try applying some of your Mechanical Engineering education to solve this problem? Seriously, this is ME-101.
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peretz87
Apr 11, 2012, 9:52 PM
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No. It's not what i'm asking...
i'm not sure of the stresses in the lobe. don't know if there is bending stress, maybe torsion stress, maybe shear. If you feel that i want someone from here to do my project than you have a big mistake...
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johnwesely
Apr 11, 2012, 10:23 PM
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peretz87 wrote: No. It's not what i'm asking... i'm not sure of the stresses in the lobe. don't know if there is bending stress, maybe torsion stress, maybe shear. If you feel that i want someone from here to do my project than you have a big mistake...
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vinnie83
Apr 12, 2012, 1:58 AM
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kennoyce wrote: The only way to really determine the stresses is with FEA.
+1 although I think you could get a good enough estimate, or at least good enough for an entry level ME course, using a lot of the normal equations.
As far as the different stresses have you tried drawing a free body diagram? This is probably something that one of your professors could go over better in person as opposed to someone trying to type out an answer in an online forum. You are paying for school after all, might try getting your money's worth.
Kennoyce- Your cam design looks nice! How much time did you put into making that?
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peretz87
Apr 12, 2012, 11:12 AM
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Yes i did. I draw this diagram. But you all didn't understand my question, I didn't ask for you to do my h.w, just to help me determine what stresses are on the lobe so i can go on with my calculations. But never mind, i quit.
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shockabuku
Apr 12, 2012, 1:45 PM
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peretz87 wrote: Yes i did. I draw this diagram. But you all didn't understand my question, I didn't ask for you to do my h.w, just to help me determine what stresses are on the lobe so i can go on with my calculations. But never mind, i quit.
It is clear that determining what stresses exist in the lobe is not part of project.
These people are just giving you a hard time because they're jealous that you get a chance to get an education.
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peretz87
Apr 12, 2012, 3:20 PM
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It is part of the project. I need to know what stresses are.
I think bending and compression but i'm not sure...
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shockabuku
Apr 12, 2012, 4:36 PM
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peretz87 wrote: It is part of the project. I need to know what stresses are. I think bending and compression but i'm not sure...
Oh. So I guess you did ask them to do part of your homework for you.
What's confusing you about the type of stresses?
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peretz87
Apr 12, 2012, 4:47 PM
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I don't know if there is shear stress and torsion stress on the lobe. When i will know what stresses there is on the lobe i will calculate them...
I think the force from the axle and from the wall apply compression and bensing stresses but maybe more stresses the i can miss.
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Rudmin
Apr 13, 2012, 2:01 PM
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I think the only thing that you would be expected to analyze for an undergrad project would be static axle loading. which is basically just a bunch of point loads at different angles. It should be basically a variation of what you see in any mechanics of materials text book.
Identify the peak stress and location and compare it to the material properties. Maybe quantify the axle flex distance under peak loads and make some comment about not placing tipped out cams.
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patto
Aug 17, 2012, 8:07 AM
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peretz87 wrote: No. It's not what i'm asking... i'm not sure of the stresses in the lobe. don't know if there is bending stress, maybe torsion stress, maybe shear.
peretz87 wrote: I don't know if there is shear stress and torsion stress on the lobe. When i will know what stresses there is on the lobe i will calculate them... I think the force from the axle and from the wall apply compression and bensing stresses but maybe more stresses the i can miss.
It is quite clearly that you have little understanding of how cams operate and how to resolve forces adequately.
This is all engineering 101. If you can't figure this out then are you really doing the right course?
The basic analysis of an SLCD is relatively easy and you can have a look at a comprehensive variety of stresses, shear, compression, tension. Buckling can also come into it too. But all this your should be able work out yourself.
(This post was edited by patto on Aug 17, 2012, 8:15 AM)
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jowybyo
Aug 17, 2012, 3:22 PM
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I think everyone is being rough on this kid. For all we know this is for an Intro to Engineering class and none of the students have taken Statics or a mechanics of material course yet.
Being that this is likely in intro class, I would stick with calculating the largest forces. The lobes are mostly in compression (and account for the shear force from the axle acting on the cam lobe itself). Bending and torsional forces will likely be low comparatively. On the axle you will have large bending and shear forces.
-Joe B.
(This post was edited by jowybyo on Aug 17, 2012, 3:39 PM)
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marc801
Aug 20, 2012, 5:58 AM
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Hmmm.... the OP was in April - now it's August. I'd guess the class has ended and grades given.
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billcoe_
Oct 31, 2012, 9:15 PM
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marc801 wrote: Hmmm.... the OP was in April - now it's August. I'd guess the class has ended and grades given.
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