To answer your first question: The robot you referenced, 202Z, did use only 2 motors on their dr4b along with with many other extremely good robots during In The Zone (929U, 8825S, 5225A, 8675A, etc…) so I would imagine that you would have no problem with a 2 motor dr4b. Even more so, that a Turning Point dr4b would be smaller than an In the Zone one.
For your second question: What I would recommend using are single rotating joints. The video from BNS shows them but in case you want some more detail you would firmly attach a screw to one of the bars with a fully tightened Keps nut. This will remove a lot of the slop and keep the screw perpendicular to the bar. Then you would run it through a bearing on the other bar so it can rotate, and then hold it all together with a Nylon Lock nut, just tight enough to keep it from coming apart. This joint only rotates in one place and you don’t have to compromise between a tight lock nut to remove slop and a loose lock nut to prevent friction.
Other than this I would recommend:
- Reducing friction to a point where if there are no engaged motors it is buttery smooth(no metal to metal contact, once your lift is to a point where it feels “frictionless” … it will never be frictionless but you get the point… add some white lithium grease on any rotation points or gears just to make it even smoother)
- Use rubber bands in a triangle shape to better the linearity of the force applied
- Only use aluminum. A light robot is a happy robot… just don’t use 1 by L channel on the bottom bars or on anything directly attached to a gear because in my experience it will snap
- Don’t use excess amounts of gears, you should only need a total of 6-12 gears depending on how you are powering your lift
- Have the top and bottom 4 bars directly connected to the gears transferring power from the bottom to the top.
- Bracing is your best friend. Use X braces on your actual lift bars (straight across bracing does basically nothing and bars in between a 4 bar do nothing)
- This is what I would say was most beneficial for me building a multiple dr4b’s all throughout Starstruck and In The Zone… STUDY! There are so many great dr4b’s that have already been displayed in the vex community so look at those.
I would look at these for help:
I would also STRONGLY suggest studying 8675A’s dr4b from ITZ because I was lucky enough to be able to feel their lift at Worlds and have never felt anything so close to frictionless
Other recently incredible dr4b’s that pop out in my head would be:
Skyrise: 118, AURA, 2915A
Starstruck: 134D, BNS
ITZ: 5225A, 8675A, 202Z, 2131, 1961U/X, 929U
Good luck! Let me know if you have any more questions!