pic: Linear bearing rails: the Cheesy RAWC way



Just a late night CAD project. enjoy!
inspired by a demo in the pits! RAWC and the Cheesy Poofs really made a top notch machine.

Pretty, but… What keeps it from pulling apart vertically?

take a look at 254’s lifter for that answer, i cant explain it that well. or ask Cory :wink:

They had two of these mounted exactly as shown, but mirrored so that the inside rails could be connected via cross members. Then the outside rails were firmly mounted to the drive train frame and cross-braced at the top. It required exact spacing at the top and bottom to be smooth, and I will conjecture that the force that pushed/pulled it up had to be almost dead center as well. If you got to see their model up close, it was smooth as butter and very lightweight.

Maybe I’m missing something. Where can I "look at 254’s lifter " . Are there any close up pictures posted?

From the CAD, I can see how it is restrained in two dimensions, but not the third.

Any time anyone uploads a photo to CD Media it auto-tags the photo with ‘frc###’ (or ‘ftc###’) where ### is the Team Number in the profile of the uploader.

Try searching ‘frc254’ and ‘frc968’.

Thing is, there aren’t any pictures of it on CD media… ill try uploading a few I have…

Exactly my point. In fact, when you search CD for pis using “FRC254” or “FRC968” you will find pics of your slide, but not theirs.
Please upload what you have. We are always trying to improve our lifts. I would love to see some that worked better than ours.

my pictures are taken with a nice SLR they are over 2.0 mb!! aaa! ill try and crop / downsize them

This was the little demo we had set up in our pit in Atlanta, that allowed people to play with it. It’s not representative of the actual setup.

The outside is a plain 1x2 that makes a U frame, with the bottom being solidly attached to the robot base, and the top the open portion. The top is held at the correct width by a spanner that goes across the two beams. You can see this in pictures of our robot–it’s the piece the pulley/flag holder/spring mounts to. The bearings then mount as you see here, top and bottom.

The inside is a rectangle made of channel on the left and right sides, and 1"x2" on the tops and bottoms. it rides inside the bearings, as shown.

I think this is a “Picture paints a thousand words” situation.

http://thumb7.webshots.net/t/66/666/5/82/65/2702582650055556207hJeknB_th.jpg](http://entertainment.webshots.com/photo/2702582650055556207hJeknB)

This is the 2007 robot, by the way. The only difference is aesthetically the bearing mounts on the 2008 are prettier, and the 07 doesn’t have the bearings at the top like the 08. To help with racking side to side in 07 we used teflon pads on the inside of the 1x2 uprights. For 2008 we added the bearings and removed the teflon.

33 actually used some benchmarking off of 254 for our elevator this year. It was a really cool experiment in the importance of certain dimensional tolerances. While many dimension in this system can be reasonable, many have to be extremely precise. Too tight and the system will die a binding death. Too loose and it will beat itself to death.

Overall it was a very cool project, but tough on a mill without a digital readout. Definitely gave me additional respect for the POOFS craftsmanship.

If you have never built an elevator it is definitely a good off season project to learn what is important.

As usual, while doing my cardiovascular workout today I had a brain flash. Suddenly I realized what everyone had been saying and it all made sense. A cross member at the top of the slide is what prevents the rails from pulling apart. I was viewing the CAD drawing and not realizing it was rotated 90°.

Cory, thanks for the pictures. They’re a little fuzzy but they confirm what I finally realized.
I’m glad that you mentioned you were using Teflon as a glide surface. In some situations it makes perfect sense, this being one of them. It is also much easier to manufacture a Teflon glide that fits properly then it is to manufacture a bearing mount without access to a decent mill.

Actually our glides (254) for 2007 where simply adhesive backed Teflon from McMaster, they where really easy to manufacture, we just cut them out with scissors. :slight_smile:

yep, this model is of the demo sliders they had in their pit. They even have “slide me” sharpied on! i am working on figuring out the entire lifter mechanism, coming soon.

Excellent! I have seen multiple posts from people looking for lift design ideas. This will definitely be a great addition.

Tolerances…

The Poof frame is welded, heat-treated, and then powder coated. And yet when it all goes together the bearings rest perfectly on either side of tubing. Amazing? I think so…

They probably took into acount how much the frame would expand and contract after each process to get it that perfect. Having welded an elevator myself this season, I fully appreciate that kind of craftsmanship.

I am working on packing the entire 2008 robot cad, when I have the elevator done I’ll post a .stp file for everyone.

Cory,

What kind of bearings did you use for the lift, and where did you get them?