Welcome to the Onshape forum! Ask questions and join in the discussions about everything Onshape.

First time visiting? Here are some places to start:
  1. Looking for a certain topic? Check out the categories filter or use Search (upper right).
  2. Need support? Ask a question to our Community Support category.
  3. Please submit support tickets for bugs but you can request improvements in the Product Feedback category.
  4. Be respectful, on topic and if you see a problem, Flag it.

If you would like to contact our Community Manager personally, feel free to send a private message or an email.

What is the proper practice to make these two bearings rotate together?

cmot17cmot17 Member Posts: 6 EDU


As you can see, there are two bearings supporting this hex shaft, and they should rotate together. As I see it, there are 3 ways to accomplish this:

  1. Fasten one of the bearings to the other with an offset. This seems suboptimal because if I were to change the thickness of the tube or other parts the bearings would not react properly.
  2. Mate both of the bearings as revolute and use a parallel mate between the internal faces on them (the inner race is hex shaped). This works well, except that according to the help page and the Onshape courses only 1 mate should be used whenever possible.
  3. Use a gear relation at 1:1 to make the two rotate together. This feels like I'm misusing the tool, but maybe this is correct? This is minor, but when I do this I often have to reverse the direction of the gear relation to get them to move correctly.

Is there a more elegant solution here that I am missing?

Answers

  • PrachiPrachi Member, OS Professional Posts: 262 ✭✭✭

    Here's a sample of using geometric center of face as revolve axis. Animate the revolve and all will perform as you need.

    When making a mate connection, you can move over a face until the centroid of the face is high lighted. In this instance it will be at the center of your square cut out.

    https://cad.onshape.com/documents/8525fa6135959f486e8693b0/w/bdb49177466ff2ac5c1cf1d7/e/c0a41fd534d741f6c6f97d79

  • cmot17cmot17 Member Posts: 6 EDU
    edited October 2020

    So that document seems to be using the 1st solution I described, with offsets. It works the way I want it to, but it still has the issue of not responding to changes in the thickness of the tubing. In the screenshot the bearings are mounted in the bearing blocks on either side of the tube and the thickness of that tube is driven by a sketch. Essentially I would like it so that my mates do not break when I change that thickness. The 2nd and 3rd solutions I posted accomplish this but I am not sure if they are considered best practice.

  • PrachiPrachi Member, OS Professional Posts: 262 ✭✭✭

    Try this iteration. Change the shaft or shaft_length variable in the part studio and the assembly will update and continue to animate correctly. The parallel mate you are using is a problem. No off sets used.

    https://cad.onshape.com/documents/8525fa6135959f486e8693b0/w/bdb49177466ff2ac5c1cf1d7/e/c0a41fd534d741f6c6f97d79

  • matthew_stacymatthew_stacy Member Posts: 475 PRO

    @cmot17 , could you make your document public and share a link to it? I'm not understanding why you wouldn't apply mates as consistent with "real world conditions" as possible.

    Aren't the inner races of both bearing fastened to the same object, presumably the shaft? And both outer races fastened to another object/s? I'm making the assumption that you bearing is modeled as a subassembly to allow rotation between the inner and outer races.

  • cmot17cmot17 Member Posts: 6 EDU
    edited October 2020

    @matthew_stacy

    https://cad.onshape.com/documents/697207e2fe24e7edbb988915/w/28df6a7204e9e92ee847164d/e/c5053d8479e3307c9d6f70a8

    "Drivetrain Assembly" is the important part.

    The bearings are one part, as the CAD from the manufacturer is like that. The outer races of the bearings are mated as revolute to the blocks that are holding them.

  • cmot17cmot17 Member Posts: 6 EDU

    @glen_dewsbury that works great, but it seems like a much bigger pain that using parallel mates - is that really the best way that exists to accomplish this?

  • PrachiPrachi Member, OS Professional Posts: 262 ✭✭✭

    Think about how you want the parts in the assembly to behave then apply mates as required. Using parallels in this case doesn't seam to get where I'd want to be. Using variables in the example just makes a quicker change but is not a requirement.

  • matthew_stacymatthew_stacy Member Posts: 475 PRO

    @cmot17 if you make the document PUBLIC, I can make a copy and try a few things. Currently it is view only and I can't do anything meaningful with it.

    Based on what I can see, I recommend that you FASTEN both bearing to the Thunderhex shaft, with appropriate Z-offsets to position them along the length. The outer race will be spinning in the Versa-block when you animate the shaft (I really haven't looked at how you mated the shaft yet), but that will still look better than having the hex shaft spinning freely with respect to the inner race.

    I love the omni wheels! Not quite sure what your doing with them though. FIRST Robitics platform?

  • cmot17cmot17 Member Posts: 6 EDU

    @matthew_stacy Sorry, just made it public.

    The fastened method works fine but that comes back to the issue i mentioned in my original post of it not reacting to changes in the size of the tubing.

    And yes, this is a drivetrain for a FIRST robot - hopefully to be used in the 2021 season if that ever happens.

  • matthew_stacymatthew_stacy Member Posts: 475 PRO

    @cmot17 ,

    You're asking great questions. There is often a compromise between modeling speed (FASTEN the bearings together with an offset) and expressing design intent. There are no universally right answers, just ever-present compromise. I am generally biased toward design intent. Be thoughtful and do what works best in your specific circumstance.

    I recommend that you mate the first VersaBlock to another feature in the assembly (such as the rectangular tube.

    Then mate the two VersaBlocks together with a SLIDER mate to provide the axial alignment that you need (planar mate to the other side of the tube will provide the width float that you are concerned about). Mate each bearing to it's VersaBlock with a revolute mate. Consider rearranging the bearings with respect to the VersaBlocks. I believe that those blocks are designed for the bearing flange to be pressed into the counter-bore. Also note that if you download bearings from vendors like McMaster Carr in .SLDPRT format they will import into Onshape as multiple parts in a Part Studio. This is extremely convenient because you can easily make a subassembly comprised of inner race, outer race, and a circular pattern of balls. This would make your model even more realistic ... but reveals that ever-present compromise between modeling time and expressing design intent. You'll never escape that.

    FASTEN the shaft to one bearing and mate it to the other bearing with a SLIDER.

    Here's my copy of your model. The 'Assembly 1' follows my recommended approach: https://cad.onshape.com/documents/2371fb083346cfad0670c874/w/d121775895466196e707e07a/e/c01cdf93db44bf2580524b5a. I also compiled a short video to summarize the key points:

    Good luck with the FIRST competition. Always exciting!

Sign In or Register to comment.