RD4B Question

Are the ends of a Reverse Double 4 Bar or the tip of the 2nd 4 bar supposed to move up and down in a straight line? My team’s robot currently has a reverse double 4 bar that has the end of the 2nd 4 bar move slightly backward when it is raised. We were wondering if this is normal or is a problem…

Most DR4Bs have a very slight arc, but any arc at all can cause a problem. However, it probably isn’t a big deal, especially since the cones can self correct so much. If you’re interested, here’s how I would correct the arc.

  1. Make sure the top and bottom 4 bars are the same length. If the top 4 bar is shorter, there will definitely be an arc.
  2. Make sure there are rubber bands on both the top and bottom stages. If the bottom stage is loaded up with rubber bands that are holding the weight of both stages, the top stage may droop slightly and cause an arc.
  3. Make sure the towers and vertical stage of the DR4B (in between the 2 4 bars) are completely vertical. If either stage is leaning backwards, an arc will occur because the 4 bars are offset.
  4. Make sure the 4 bars are synced with each other. Position the bottom 4 bar completely parallel to the ground and check to see if the top 4 bar is also parallel to the ground. If not, there will be a slight arc when the lift is raised.

If you follow these steps, you should be able to eliminate the arc you’re having and get a totally vertical motion. If not, feel free to post a video of the lift and I can give more specific feedback. Good luck!