33's parallel bar mechanism

Technical Technical Discussion
1

How does 33’s parallel bar function?

2

the elevator from last year?

3

Despite this vague question, I’m betting you’re referring to a double reverse 4 bar?

4

if you’re thinking about making that mech, just bear in mind the center of gravity. 33 fell over at least once, and last year the neutral zone rules prevented contact that would lead to tipping. The same bot would probably fair far worse in this years game.

1 Like
5

yes :grinning:

6

They used a double reverse 4 bar. This thread could probably answer most of your questions. Also take a look at the side of This picture.

7

Most of the information from the double reverse 4 bar can be found in the picture linked above, but if you have more specific questions feel free to PM me.
As for the fact that we tipped a few times last year, that may have a little bit to do with the dr4b, but is probably more due to the ~20 lb collector we had on it and also the smaller wheel base (swerve). At iri, with a lighter collector, we had almost no CG problems.
Here are a few general tips for doing a dr4b if you plan to take that course of action:

  1. If the math is done properly, it can go insanely fast with just 1 motor. Ours was originally able to extend in under a second with 1 cim but was geared down due to the lack of control with the heavy collector. If you’re limited on motors this could be a good route to go.
  2. Make sure you don’t put a heavy device on it. Not only does it affect your CG, but it also gets super bouncy. We could have eliminated the bounce in the code (by effectively make it accelerate slower and decelerate sooner), but decided not to care since height didn’t matter too much last year. Towards the end of the season it got worse due to our jointing getting opened up through use during the season. This was way more apparent on our practice robot though.
  3. Don’t move sideways with a dr4b. It’s not as strong laterally. You might tip too.
  4. In terms of construction, it’s paramount to keep the center distances the same, but other than that it’s fairly simple to fabricate, as it’s a bunch of tubes with 2 holes.
    In general it wasn’t a bad experience using one last season, but I personally think it would have been a way better experience if we didn’t also do a swerve. Also if we had kept a better eye on the weight of our collector, it would have been amazing. If your team believes that the pros outweigh the cons for this years game, then go for it. Good luck to you guys!
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8

thanks for the tips

9

I would highly suggest not going for a DR4B, coming from vex, almost every game that requires things to be lifted they use some version of it, this is mostly due to the fact that elevator clearances in vex are too loose so it creates slop. Elevators are easier to keep consistent and it has the added benefit of having a lower CG. Dr4b also need more programming dedicated to it verses a elevator that you can keep a string potentiometer so its faster to create set heights as this year everything will be at 1 of three heights. I don’t mean to make you hate the mechanism its just needs more time to prototype then an elevator that most teams don’t have the time for in a build season and it gives around the same results or less.

10

What does this mean exactly? What is the “center distance”?