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-   -   Elevator Design - Rack and Pinion Cascaded - 772 (http://www.chiefdelphi.com/forums/showthread.php?t=110094)

billbo911 18-12-2012 23:08
Re: Elevator Design - Rack and Pinion Cascaded - 772
 
Quote:
Originally Posted by BJC (Post 1203031)
...

-Will your roller brackets deform over time or when the inner/middle stage takes an impact?
Another thing I never thought of. Again I will do stress analysis on it soon. However I don't believe it will be an issue. Because there is so much contact space between the bearing set up and the bracket it will be tought to deform. Unless you're talking about where it mounts on the rail, and in that case it may be able to deform, but i dint think by a lot.
-These are actually very concerning to me in this design. Cantilevering those rollers through only a 1/8" piece of metal is simply not enough. I bet if you put the elevator all the way up and pulled on the top you could bend those brackets right out. These defiantly need to be strengthened or I guarantee that they'll fail at some point in the season.

....
Keep up the good work!
Regards, Bryan
Here's a picture of the lower bearing mount 254 did on their lift in 2011. If you recall, it was a fantastic design.



These did not get bent throughout the entire season that I am aware of.

BJC 19-12-2012 07:42
Re: Elevator Design - Rack and Pinion Cascaded - 772
 
Hey there,

I agree that that is a fantastic design. The cantilevered roller in 254's design is going through a ~1" thick milled block of aluminum. I would stand by that cantilevering the roller off only a 1/8" thick piece of angle is not enough.

edit: and that was 2011.

akoscielski3 19-12-2012 08:42
Re: Elevator Design - Rack and Pinion Cascaded - 772
 
My team does have acess to CNC mills, however we have never used this resource before because it is new, Nd to be honest right now I'm unsure about how to persue this resource and what they will offer. It's our local College who has a mew machine shop, and they are going to let us use the machines.
So really I want to know what is an easy alternative to doing it exactly like that without a CNC.

Bryan, I have read all of your messages before and it kept me thinking about how to improve the design, so I'm not gonna go through to answer them again. But thanks :)

@Ether I still don't quiet understand what you mean with the 28lbs moving, I don't know if its just me miss understanding, or what? :/

@Adam
We can make a water jetted gear out of Aluminum if we wanted, unsure what is more logical for us though.

Ether 19-12-2012 09:03
Re: Elevator Design - Rack and Pinion Cascaded - 772
 
Quote:
Originally Posted by akoscielski3 (Post 1203067)
@Ether I still don't quiet understand what you mean with the 28lbs moving, I don't know if its just me miss understanding, or what?
In this post you said the assembly weighs 28 pounds.

In this post you said that the center of mass of this 28 pound assembly changes from 31" to 57".

That's a change of 26".

To change the center of mass of a 28 pound assembly from 31" to 57" requires 28*(26/12) foot-pounds of work. This is true regardless of whether you are lifting the entire 28 pound assembly 26", or lifting half the 28 pound assembly 52", or anything in-between.

BJC 19-12-2012 09:39
Re: Elevator Design - Rack and Pinion Cascaded - 772
 
Quote:
Originally Posted by akoscielski3 (Post 1203067)
Bryan, I have read all of your messages before and it kept me thinking about how to improve the design, so I'm not gonna go through to answer them again. But thanks :)
I'm glad I could help. In another revision or two you should be comfortable actually building this for the pending game that will probably require something to be lifted/placed high up in the air.

Best of luck.
Regards, Bryan

akoscielski3 19-12-2012 12:17
Re: Elevator Design - Rack and Pinion Cascaded - 772
 
Quote:
Originally Posted by Ether (Post 1203072)
In this post you said the assembly weighs 28 pounds.

In this post you said that the center of mass of this 28 pound assembly changes from 31" to 57".

That's a change of 26".

To change the center of mass of a 28 pound assembly from 31" to 57" requires 28*(26/12) foot-pounds of work. This is true regardless of whether you are lifting the entire 28 pound assembly 26", or lifting half the 28 pound assembly 52", or anything in-between.
I'm going to believe you in this because you are an engineer and I am just a student, but I have a hard time wrapping my head around the fact that I should include the weight of the Assembly that doesn't move.

Ether 19-12-2012 12:43
Re: Elevator Design - Rack and Pinion Cascaded - 772
 
1 Attachment(s)
Quote:
Originally Posted by akoscielski3 (Post 1203106)
I'm going to believe you in this because you are an engineer and I am just a student, but I have a hard time wrapping my head around the fact that I should include the weight of the Assembly that doesn't move.
If you want to use the weight of only the moving piece, then you can do that... but the distance you would use is the distance the moving piece moves, not the distance the center of mass of the assembly (including the non-moving portions) moves.

edit:

See attached sketch. On the left is a "system" consisting of a 10 lb red block and a 10 lb blue block. The center of mass of this system is located at the gray circle between them in the middle.

I now lift the blue block 2 feet. The center of mass of the system is now 1 foot higher than it was. I can calculate the work either way:

1) work = weight of system * distance I changed the center of mass of the system = 20 lbs * 1 ft = 20 ft-lbs.

2) work = weight of the piece I lifted * distance I lifted that piece = 10 lbs * 2 ft = 20 ft-lbs.

akoscielski3 19-12-2012 12:59
Re: Elevator Design - Rack and Pinion Cascaded - 772
 
Quote:
Originally Posted by Ether (Post 1203108)
If you want to use the weight of only the moving piece, then you can do that... but the distance you would use is the distance the moving piece moves, not the distance the center of mass of the assembly (including the non-moving portions) moves.
So the way you were telling me is a different technique used to find the Energy needed to move my parts? I am not there in in Physics/Engineering yet so I had/have a hard time understanding it. I would prefer to do it how far each part moves, because that's what I understand at this moment, with my education so far.

Ether 19-12-2012 13:03
Re: Elevator Design - Rack and Pinion Cascaded - 772
 
Quote:
Originally Posted by akoscielski3 (Post 1203111)
So the way you were telling me is a different technique used to find the Energy needed to move my parts? I am not there in in Physics/Engineering yet so I had/have a hard time understanding it. I would prefer to do it how far each part moves, because that's what I understand at this moment, with my education so far.
See the sketch I just attached to my previous post.

Perhaps that will make it clearer.

akoscielski3 19-12-2012 14:48
Re: Elevator Design - Rack and Pinion Cascaded - 772
 
Okay makes sense now. Just never thought of it that way.

Cory 20-12-2012 17:55
Re: Elevator Design - Rack and Pinion Cascaded - 772
 
Quote:
Originally Posted by BJC (Post 1203062)
Hey there,

I agree that that is a fantastic design. The cantilevered roller in 254's design is going through a ~1" thick milled block of aluminum. I would stand by that cantilevering the roller off only a 1/8" thick piece of angle is not enough.

edit: and that was 2011.
1/8" isn't good enough but we used 1/4" L brackets in 2007 and it worked fine.


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