My RD4B has a 6 bar on top instead of the standard 4 bar. Before I added this attachment the robot would be able to go up straight and down without the issue of tilting to one side. When I added the 6 bar attachment it started to go up straight but on the way down it leans to the right. I will be able to give pictures of the problem later today but was wondering what possible solutions I could try before I get to it. The lift is powered by 2 high speed motors with rubber bands on the top 6 bar and the bottom 4 bar. There are 2 84 tooth gears with axels going through them and not screws( couldn’t find ones long enough ). I have crossbars going across but they were put on with little care because the arms are now angled in and are not perfectly spaced. I suspect this is the reason but my old Rd4B had the same bending inward.
Here are photos of my robot. The lift leans to the right as it goes down. Almost as if the right side is faster, but I’ve switched out motors on both sides and also have checked my code. If you would like the part of my code referencing driver functions I could post it.
So we’ve actually had similar problems as well. In our case, the slight twisting of the bottom set of arms is exacerbated over the height of the lift and causes it to sway. I’m not sure specifically what your issue is, but you can test whether it is a physical issue by pushing the top of the lift to the side, and see what parts move. One of the best ways to support something like this is with c-channels across the bottom set of bars. This helps to prevent some of the difference between the angles of your bottom set of bars.
Although my robot don’t have a top 6 bar it could be the same problem I would check that the rubber banding is consistent on both sides as even one rubber band will mess it up if thats not it check all your joints if the right sides are looser it will fall quicker because of less friction on the joint another thing i did for my robot was adding a brace on the bottom then taking to more bars to make a triangle on the bottom or it could just be that your battery’s are the cause make sure that they’re both fully charge so they drain energy evenly. good luck
I would also check the hole that your drive axle goes through. If the screws attaching the motor comes loose then it will bore the metal into an oval and the motor will turn when it is run. Easy way to check this is to wiggle the motor. If it has a lot of wiggle room then the screws are either super loose or the one hole is now an oval. This could cause the one side of your lift to lean to the right, as the drive gear can move forward on the gear it is driving or backwards. I would also use actual spacers on your lift instead of just collars. It will keep the meshing of the gears better. Good Luck! I hope you fix it!
My students have also had luck just making sure that any pivoting points are tightened. They seem to work loose over the course of usage and will sag to one side or the other. Just checking that often has helped with the consistency of their robot.