Elevator Design - Rack and Pinion Cascaded - 772

[akoscielski3]

My First Elevator System

- Currently 28 lbs
- Fully extended in ~1 Second (possible to raise in 0.22 seconds but i geared it down)
- Run off of two 550 Series Motors into a VersaPlanetary 2 stage gearbox (1:20)
- Rack and pinion style for bottom
- Carriage is attached to a fixed Belt or chain that will move the Carriage up to the top when the middle moves up. (hard to explain, but no motors required)
- Rail design Inspired by 228's 2011 Elevator Design.

Design later found to be almost the same as 973's off season Robot in 2011 "Emperor Swerve"

Feel free to criticize, and suggest things to change.

[akoscielski3]

Posted Pictures rather than having to Download PDF's. Sorry for double post.

[BJC]

Hey there,

Here's some basic questions to start you off:

-Is this the lightest way you can build an elevator?
-Is this the least resource intensive way for your team to build an elevator?
-Why is a rack and pinion setup better then a string and drum?
-Will the channel of the middle stage deform being pushed on from the inside and outside by the inner stage and the rack and pinion?
-Is putting the motors up high on the elevator really the right place?
-Will your roller brackets deform over time or when the inner/middle stage takes an impact?
-Is using the motor as the front top middle stage container really a very good idea? If so could the motor be moved higher to improve your lever arm in the front containing the middle stage?
-How is this going to be attached to the actual robot?
-Is the single round crosspiece on the middle stage enough to keep it torsionally stiff?
-Do you have a plan to closely control the motor and pinion relative to the rack? (spacing wise?)

Looks pretty good overall.
Regards, Bryan

[akoscielski3]

-Is this the lightest way you can build an elevator?
I have some thoughts about making everything lighter, first off would be getting smaller bearings. But the rack and pinion style cascaded does seem lighter than the others because I don't have chain or require a bunch of pulleys.

-Is this the least resource intensive way for your team to build an elevator?
I did keep resources in mind while designing, for example most of it has angle iron rather than water-jet plates. But all of these parts are possible to make with our resources. I want remove some parts that are only there for support or spacing, but we'll see.

-Why is a rack and pinion setup better then a string and drum?
The first reason I dis it this way was because of a meeting I had with my designing team (Mechanical Section). On of my members suggested a rack and pinion rather than using the strings or chain. It was really a "shot in the dark" but I like how it is.
The second reason would be simplicity. Though some people will argue how simple this is, i believe it ia a simplier set up than a string and drum. This way the only moving parts is the gear on the rack, and the carraige (moved with belts), rather then having string or chain all through it.

-Will the channel of the middle stage deform being pushed on from the inside and outside by the inner stage and the rack and pinion?
Something I never really thought about. I will be doing stress analysis soon on it to find out.

-Is putting the motors up high on the elevator really the right place?
There is no other logical place to put them. If i had them at the bottom the gear would run off the pinion almost emediatly, and if i were to put it on the inside rail it would make me have to put more wires and there would then be more moving wires, which can get annoying.

-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.

-Is using the motor as the front top middle stage container really a very good idea? If so could the motor be moved higher to improve your lever arm in the front containing the middle stage?
I think it's fine, but i am thinking of putting some bearings on there also. Im not sure what you mean for the second part.

-How is this going to be attached to the actual robot?
I'm going to add brackets to the back to help stabalize it and mounts to the bottom to mount onto a chassis.

-Is the single round crosspiece on the middle stage enough to keep it torsionally stiff?
Wasn't thinking of torssion. That brace was for the pulley, but now i realize i needto add strength there.

-Do you have a plan to closely control the motor and pinion relative to the rack? (spacing wise?)
I have it slotted at this moment, but should I consider doing something more??

Thanks for the questions, it really got me thinking about it

[BJC]

Ok, I have a little more time now to type out my thoughts in a little more detail.

-Is this the lightest way you can build an elevator?
I have some thoughts about making everything lighter, first off would be getting smaller bearings. But the rack and pinion style cascaded does seem lighter than the others because I don't have chain or require a bunch of pulleys.
-A rack and Pinion setup is not lighter then a well thought out solution using spectra cable (high strength kite string) and pulleys. Even if it wasn't the rack and pinion forces you to put all of your motors/reduction at the very top of the robot (bad) and requires much higher precision (meshing gears) then a string design does (generally aligning pullies.)

-Is this the least resource intensive way for your team to build an elevator?
I did keep resources in mind while designing, for example most of it has angle iron rather than water-jet plates. But all of these parts are possible to make with our resources. I want remove some parts that are only there for support or spacing, but we'll see.
-Allowing the Grounded stage's width to be adjustable is a very good idea. It's very unlikely that you're stages will match up as perfectly as in CAD so leaving room for adjustment there can make a big difference between good and bad.

-Why is a rack and pinion setup better than a string and drum?
The first reason I dis it this way was because of a meeting I had with my designing team (Mechanical Section). One of my members suggested a rack and pinion rather than using the strings or chain. It was really a "shot in the dark" but I like how it is.
The second reason would be simplicity. Though some people will argue how simple this is, i believe it ia a simplier set up than a string and drum. This way the only moving parts is the gear on the rack, and the carraige (moved with belts), rather then having string or chain all through it.
-You kind of make it sound like you didn't really think through your elevator options and just picked one. Do you have any reasoning aside from personal preference? I'm not trying to be mean or anything, just trying to better understand your reasoning.

-Will the channel of the middle stage deform being pushed on from the inside and outside by the inner stage and the rack and pinion?
Something I never really thought about. I will be doing stress analysis soon on it to find out.
-I would guess that this will occur a little over the course of the season. Maybe just keep an eye on it throughout the season if you actually build this for 2013.

-Is putting the motors up high on the elevator really the right place?
There is no other logical place to put them. If i had them at the bottom the gear would run off the pinion almost emediatly, and if i were to put it on the inside rail it would make me have to put more wires and there would then be more moving wires, which can get annoying.
-I was kind of leading you on with this question. No, there's not anywhere else to put the motors except for at the top. I'm a CoG and weight management freak which really stems from my understanding of how it affects drivetrain performance. I pretty much dislike any design in which the motors, gearboxes, and other heavy stuff isn't all the way at the very bottom. It's a primary reason I would never build an elevator this way. Of course, your robot, your preference.

-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.

-Is using the motor as the front top middle stage container really a very good idea? If so could the motor be moved higher to improve your lever arm in the front containing the middle stage?
I think it's fine, but i am thinking of putting some bearings on there also. Im not sure what you mean for the second part.
You have to think about lever arms. When the middle stage is all the way up and you pull on the top it needs to be supported at two points in order to not come out of the Grounded stage. The further apart these two points are the better your lever becomes such that the pulling at the top exerts a lesser force on the bottom then it otherwise would. To maximize this you would want to put the contact points from the Grounded stage to the Middle stage as high as possible and vice versa for the middle stage.

-How is this going to be attached to the actual robot?
I'm going to add brackets to the back to help stabalize it and mounts to the bottom to mount onto a chassis.
-If the elevator wobbles at all very bad things will happen. Whatever you do make sure the bottom is very well secured.

-Is the single round crosspiece on the middle stage enough to keep it torsionally stiff?
Wasn't thinking of torssion. That brace was for the pulley, but now i realize i needto add strength there.
-The Middle stage needs much more support. If the middle stage can twist, besides introducing slop into your rack and pinion you end up with a big wobbly thing up in the air and potential binding. Maybe try to get a 2x1 1/8" thick box tube across the top and bottom of the middle stage.

-Do you have a plan to closely control the motor and pinion relative to the rack? (spacing wise?)
I have it slotted at this moment, but should I consider doing something more??
-I would guess that if your hand making the brackets supporting the motor this could be a problem. Slotting the holes seems like a good solution to me.

Thanks for the questions, it really got me thinking about it

-That's what design reviews are for! I just went through the 3rd review of a sheet metal and thinwall Aluminum tubing elevator. At the first revision it had a bunch of complicated folds and extra material. By the third it weights 14lbs and has been optimized for ease of manufacturing and assembly for my team. Every time you go through the process you make your product a little better until you end up with something that's awesome.

Keep up the good work!
Regards, Bryan

[billbo911]

Originally Posted by BJC

...

-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]

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]

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]

Originally Posted by akoscielski3

@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.

[akoscielski3]

Originally Posted by Ether

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]

Originally Posted by akoscielski3

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.

[BJC]

Originally Posted by akoscielski3

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

[Cory]

Originally Posted by BJC

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.

[Ether]

Originally Posted by akoscielski3

Currently 28 lbs... Fully extended in ~1 Second (possible to raise in 0.22 seconds but i geared it down)

Can you say approximately where is the center of mass in the the fully retracted and fully extended positions?

[akoscielski3]

Originally Posted by Ether

Can you say approximately where is the center of mass in the the fully retracted and fully extended positions?

I can edit this to tell you the exact in about in hour. But if i remember correctly its 12" when down, 22" when fully extended.

EDIT: I was way off when it was down its 31" from bottom, and when it's fully extended it's 57" from bottom of the Elevator.

When it has a 40lb chassis mounted to the bottom (just mated, not having mounting brackets or anything) the center of gravity is 11" from bottom of elevator (elevator down) , and 22" when Extended.