Vex Chainbar Question. Help!!!

I haven’t tested this yet, but I was wondering, instead of both the sprocket on the driving shaft and the sprocket on the intake being the same size, if the sprocket that is on the driving shaft is smaller than the sprocket on the intake, would the chain bar function normally or would the angle change as it moved up and down.

If there is a size difference between the two sprockets then the intake will change the angle it is at, rather than staying at the same orientation as when it started. This rotation is going to be proportional to the ratio of the two sprockets as well.

The angle would change less relative to the arm. If you went back far enough, it would end up perpendicular to the ground

We were thinking about playing with this for our secondary lift, which only moved 90deg from straight forward to vertical. We figured out if we put a 24t on the robot and a 6t on the end of the chain bar, the intake would do a full 360deg flip, and the cone would be perfectly aligned to stack. Obviously we did not implement this 2 weeks before states, but I am considering it still.

Yes that makes sense with the sprocket ratios

Good thing you held off.

No, it doesn’t.

You’re looking at the math wrong. Start with two 24t sprockets with the normal chain bar. From what you’re saying, if you rotate the normal chain bar 90 degrees the cone should go from vertical to horizontal due to the 1:1 ratio. We know it doesn’t, so we know that math is wrong. Thing about it differently. The chain bar rotates 90 degrees. Relative to the chain bar the lower, locked sprocket rotates -90 degrees, which it maintains for the upper sprocket as well. So the upper sprocket rotates -90 degrees relative to the bar that has rotated 90 degrees, meaning it doesn’t rotate at all relative to the world. Your math is missing the rotation v. counter-rotation bit when you’re just looking at 24:6 or 4:1.

So think of rotating the lower, fixed sprocket -90 degrees. Convert that via your ratio. Then add 90 degrees. More generally, let’s say your ratio is n, so n=4 here. If you rotate the chain bar a rotation of r degrees, then the upper sprocket will rotate (1-n)r degrees. When I try this with 18:6, so n=3, and rotate 90 degrees, so r=90, I can see that the little sprocket’s end that had been up now points down, perfectly matching (1-3)90=-180.

I’m confused. I agreed with him, and he did it, he saw it. If the chainbar at the end of a dr4b is moving ~90 degrees and the fixed sprocket is 24t and the effected sprocket is 6t, then the effected sprocket will rotate 360 degrees, since 24/6=4 and 4*1/4(since 90 degrees is 1/4 360 degrees)=1 full rotation of the intake, 360 degrees

I think you both might be right. From what I can tell, @callen was talking about the sprocket at the end’s rotation in relation to the “ground” or 0° plane, while @SkinnyPanda Robotics was talking about it in relation to the arm.
Edit: example, say its a 1:1 ratio with the arm rotating 90°, using the equation @callen has, the sprocket on the end would not move (in relation to the ground). While how @SkinnyPanda Robotics did it would result in a rotation of 90° (in relation to the arm).

Perhaps, but the comment was about picking up a cone and having the intake do a full 360-degree flip so it would be aligned to be stacked.

You’re saying one of these two did it and saw it?

Or maybe you’re talking about me, who actually said he did it:

Yes, I actually did this to confirm the equation I wrote. I knew I had it right, but it never hurts to watch it actually happening.

No, not quite. First, you’ll want to get your directions right. The two rotations are in opposite directions. So one angular displacement should be positive while the other is negative. You rotate the bar +90 degrees. Relative to the bar, the little sprocket rotates 4(-90 degrees)=-360 degrees. Meanwhile the bar has rotated the little sprocket +90 degrees. The total rotation is -360+90 degrees = -270 degrees. This is why I was very specific about my statement about a cone going from vertical to horizontal with such an arrangement.

Yes, you could choose to work in a rotating coordinate system (in which case you have to claim that the entire body of the robot and the rest of the room have now rotated -90 degrees), but that means you’re going to have to know how to deal with rotating coordinate systems in 3-D. Are you making your statements in relation to the bar, considering the room to have rotated -90 degrees? (Another way to say this is that you will only see that full rotation of the intake if you rotate your head 90 degrees while watching the intake.) If you are, the correction is smaller, just changing 4*(90 degrees) to 4*(-90 degrees).