I was looking at some peoples designs and I’ve been thinking that the double reverse 4-bar is the way to go. The only problem I have here is when the arm raises it needs to be fast but with the bottom section and the top section moving at the same time it gets too fast and you can lose valuable time by overcorrecting, so what if i could control the top section and the bottom section individually. My teammate will be driving the robot and I will be controlling the arm so i could use the left stick to do the bottom and the right stick for the top and use the bumpers for the claw. I was just wondering if this has any flaws or downsides, I couldn’t think of any but since it’s summer and I’m out of school I can’t test it so I would like some more opinions. Thanks!
The point of the DR4B is that the top and bottom are in sync, so that the top of the lift always goes straight up and down. Think of it this way - when you have a 4-bar, there is some horizontal displacement as well as vertical. When you have two four-bars, facing opposite directions, their horizontal displacement offsets each others.
I don’t think you need to worry too much about excessive speed (if you have problems, just slow it down). Personally, I’m going to let the robot drive itself by setting PID height targets based on the height of the stack I’m building on.
Do not do what I think you want to do. That’s a horrible idea. If you want to have it be incredibly accurate, do this:
Acquire rubber bands and put them on 3 points (you can look at other rd4b designs to see what people have done)
keep adjusting the positioning and amount of rubber bands until the lift is equally “buoyant” (I don’t have a better term for this, sue me)
By equally buoyant, I mean that the lift stays in place when you leave it at a certain position. It doesn’t go down that much, nor does it go up that much. The amount that it goes down when no motors are on should be negligible, but by no means should you use enough rubber bands that the lift slowly raises.
Consider things like these:
You could have two pairs of buttons to raise/lower the dr4b. One pair could run it quickly and one slowly. Switch to slowly for fine tuning, like you do with a microscope.
If you’re using axes, do something like squaring the values and dividing by 127. Be careful of the sign as you do so, and of 0 when you divide by the absolute value to get the sign. Squaring the values still allows you to hit ±127, but now more of the axes are used for low-power motion, for careful control. If that’s not enough, go to cubing, which avoids the sign issue but needs proper ordering of /127’s to make sure you don’t exceed the limits of int.