Three-Stage Fold Out Tray (complex)

Before anyone says, yes I have looked around at practically every other topic on this forum about this, and no, I have not found a working solution.
When our robot’s third stage for its tray flips out, instead of flipping out, it moves in the opposite direction and embeds itself inside of the second stage, preventing it from unfolding.
See this video

Edit: our tray is designed to unfold after intaking a cube.

In your video, the rubber bands are held the same distance away on both sides. banding

This means that the force is pretty much equal on both sides so they cancel out and the tray won’t flip out. Instead, you need to offset your banding so that the top part has less distance to the turning point and your bottom part has more:
correct banding

This way the bottom part has a greater pulling force than the top causing it to flip out better.

Your bands are also way too close to the turning point. If they are held farther away then the bands would have to exert less torque to flip out the tray (Although there is a point at which they are so far apart that they just break, you would have to figure this out experimentally).


What I did was I made the tray fold in the shape of an N or an upside-down-U, and the rollers released the tray by reversing.

@AryanG 20200217_133457
Just tried this, was able to use less rubber bands for the same force (obviously) but still can’t unfold.

@Riptide I don’t want to decrease our tray capacity, I’m trying to fit at least nine cubes, and if I were to do that I’d have to make the middle and top sections smaller, holding maybe seven or eight

I can hold 9 in the upside down u shape but if you want more cube capacity you can add another flip out or add a slider tray

Try adding more bands.

I don’t want to use an excessive amount of rubber bands, just to make sure, I tried 16 (I have pretty strong rubber bands), and still having the same issue. At one of our competitions, I was resetting our tray and it gave way, clocking me right in the forehead and caused a huge gash. If possible I’d like to avoid this. (We used 12 rubber bands at the time)

Any good sources for slider trays? I saw the trays that some guy posted with blow-up CAD gifs and videos, but I wasn’t able to recreate them because I couldn’t see everything going on. I couldn’t get a good understanding of what was going on.

Also note that we are already pushing the 18x18x18 limit, I might have to move our intakes back one hole. With our tray right now, if I were to fold it in a U shape, it extends wayyy outside the limit, and to fix this I’d have to decrease our cube capacity.

Try to include a stopper so that the stages can’t fold into each other. We had to do that for a previous iteration of our design and it worked well.

It still won’t unfold until it reaches a certain point. I can fold it down to near parallel and it still won’t unfold.

As long as the stopper ensures that the stages don’t fold parallel, the force from intaking cubes should be enough to push the tray more, allowing the rubber bands to take over in unfolding.

Adding stoppers still made our tray extend further out of bounds and didn’t work when sucking in cubes. I think I’m going to try a telescoping tray on the third stage just can’t find a solution for it

Is the metal of the third tray catching on the metal of the second?

Yes. With the stoppers, it doesn’t but it still won’t unfold

I do notice that when it’s folded down the third tray isn’t parallel with the second tray, maybe you can make something to prop that up more near the hinge so that flipout is easier?

Connect the rubber bands to the c channel brace on the very bottom of your third tray. This is what I did for a while and It worked well.

Try to use the momentum of the 2nd stage to fold out the 3rd stage. I have 4 stage fold and it works pretty well


I’ve pretty much determined this is what I need to do but how to do it with my current set up is the issue

I can think of 2 ways

  1. loosen the 3rd stage’s grip on the 2nd stage, by expanding it a bit, bending metal, etc.
  2. place weights on the end of the 3rd stage; the momentum of the 2nd stage opening should be enough to pull out the 3rd stage

The way we made our 3rd tray flip out was to make it so that the rubber bands go above the joint the attaches the 2 & 3rd tray. We did this by adding c-channels that could stop the tray as well as make the rubber bands go above the joint.
Hope this helps!

1 Like