Main Capsule – Design Candidates

This entry is part 2 of 3 in the series Main Capsule

We have several candidates right now for a permanent solution to our capsule problem:

  • Metal plate: Instead of using the four corner screws, we will instead place a metal sheet over the top of the capsule and screw it into four standoffs. This will put even pressure over the entire capsule, instead of just on the four corners, which will reduce the likelihood of the plastic cracking over time. Additionally, these screws will be on the top of the robot, instead of the bottom. This will greatly reduce the time needed to screw in the capsule. 
  • Metal capsule: We noted that the main point of failure was the weak plastic at the corners. Casting a metal capsule would be much more structurally sound and reduce the possibility of cracking. Moreover, as Polycase has discontinued the capsule we need, it would be nice if we could make our capsules when needed. 
  • 3D-printed metal covers: As epoxy didn’t appear to reinforce the corners well, a more sturdy option would be to 3D print small covers out of titanium that sit above each corner and endure the bulk of the stress. We would also be able to print many of these and have extras if they happen to break. 

We ended up choosing the metal plate solution for several reasons. First, it was easiest: ordering a metal plate is relatively cheap, and we have experience making similar designs in-house. Moreover, this can be easily prototyped out of cheaper materials like cardboard or wood to check sizing before we cut the metal. Additionally, after some discussion with the mechanical engineering faculty, we concluded that casting a capsule would be time-consuming and likely still not produce a precise enough result. Likewise, after some investigation into the metal 3D printer we had on campus, we realized the print quality left a lot to be desired. While surely stronger than plastic prints, the resultant prints were still brittle. 

Secondly, this solution would greatly reduce our installation time. The two other solutions: metal capsule and 3D-printed metal covers, would still require a perfect fit and four bolts screwed in on the underside of the robot.

The titanium 3D printer we have on campus – 3D Systems ProX DMP320
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