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Difficulty with belt mates

wesley_churchwesley_church Member Posts: 10 EDU

Created this model of the chassis and drive train of an FRC robot; the drive motors and transmission on the subject side of the model, as well as a frame member have been hidden so the belts and pulley can be seen.


I attached each of the belts to the outermost wheel pulleys in the drive train with a cylindrical mates, and "pinned" them to the edges of the pulleys on the front and rear wheels so they wouldn't overlap with planar mates.  I cannot find any mate that works for now mating them to the double pulley on the center drive wheel; everything I try creates an overdefined situation. Pretty much an OnShape newbie migrating over from > decade of Solidworks.  Anyone have any suggestions?



  • DrewB_PTCDrewB_PTC Member Posts: 1 PRO

    The belt center-to-center distance is 10.752", while the axle center-to-center is 10.742". I'm not sure which of the two you'd prefer to change, but once the two center-to-center distances match, you should be able to create a cylindrical mate on the center double pulley.

    Hope this helps!
    - Drew
  • wesley_churchwesley_church Member Posts: 10 EDU

    Great having a fresh pair of eyes look at it!  Thank you!!!!
  • alnis_smidchensalnis_smidchens Member Posts: 291 EDU
    For higher performance, I recommend this for belts:
    1. Make sure your frame is fixed and will not move
    2. Hide everything except the components relevant to the powertrain (this helps with in-context performance)
    3. Create a new display state called "belt in-context view" or something similar (this will let you return to the minimal/high-performance visibility of parts later)
    4. Create new part studio in context
    5. Create skeleton geometry with surfaces for the pitch diameters of the pulleys using in-context references
    6. Use the belt custom feature to make each of the belts
    7. Insert all of the parts from the part studio into the assembly, clicking the green check mark directly instead of clicking in the viewport first to ensure they are at their original part studio locations (and thus positioned correctly)
    8. Create a new group and add all of the belts + frame to it
    This will help with assembly performance by reducing the number and complexity of mates to solve. Plus, if your model changes, just go to your display state and right click any of the belts you inserted and update their context. Everything will automatically move and update to the right positions.
    Get in touch: [email protected] | My personal site: https://alnis.dev | My YouTube channel (I make tutorial videos for Onshape & Inventor): https://www.youtube.com/c/AlnisSmidchens
  • wesley_churchwesley_church Member Posts: 10 EDU
    First, back to Drew: turns out fixing the distances didn't solve the issue; I could always MAKE the mate, OS just always said that adding that mate overdefined the assembly.

    Second, for Alnis, it'll be a while before I'm up to speed enough on OS to go this route.  I had come across some featurescript add-ins for belts digging through the forums, but currently have no idea how to use them.  I'm also a ways away from being comfortable with in context editing; still making the mental adjustment from SW's assembly features (I'm a retired biochemist who got involved in helping mentor a HS robotics team 13 years ago, and wound up becoming the CAD mentor simply by having some interest in CAD and started playing with the stuff available through FIRST.  Definitely NOT a comp sci person who "gets" coding well; last "coding" I did was using PL1 over 45 years ago!)
  • wesley_churchwesley_church Member Posts: 10 EDU
    Alnis, son of a gun, but I screwed up my courage and jumped into your suggested approach and it WORKED!  I was able (through a fair bit of trial and error) to figure out how to use the belt featurescript function and got the exact belts I wanted inserted exactly as I wanted them.  Thank you so much for the step by step guidance.  Took this newbie a bit of time to figure out the lingo ("skeleton geometry"), but I muddled through. 

    Thanks again!
  • alnis_smidchensalnis_smidchens Member Posts: 291 EDU
    @wesley_church glad to hear it worked out! I'll try to be more clear with my wording in the future. Thanks for the update and feedback :)
    Get in touch: [email protected] | My personal site: https://alnis.dev | My YouTube channel (I make tutorial videos for Onshape & Inventor): https://www.youtube.com/c/AlnisSmidchens
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