# Reverse Double 4 Bar for a Beginner

I’m relatively new to VEX but I want to learn as much as I can this season. I’ve seen a ton of stuff about the reverse double 4 bar and I want to try to make one (probably not to compete with but just so I can learn something). Can someone explain the concept to me a little better? I honestly don’t understand all that much about VEX so you need to dummy it down for me ;-;

“Reverse Double 4 Bar for a Beginner” The RD4B inherently isn’t for beginners. I would suggest learning about various linkages such as the 4 bar, 6 bar, and so on before proceeding to a more complicated combination of the aforementioned linkages like a RD4B.

Since you are new to VEX, I would suggest going through the VEX curriculum linked below. It should acquaint you with the basics of robotics as well as a few different lifts.

http://curriculum.vexrobotics.com/curriculum

I would also recommend reading through team 400x’s forum post on game analysis, linked below.

https://vexforum.com/t/how-to-win-worlds-guaranteed-why-game-analysis-is-the-most-important-step-in-robotics/42066/1

Sure. Are you familiar with the 4-bar in general? Basically, it is a parallelogram where one side is fixed to the robot, so the opposite side will always be perpendicular to the ground as the linkage is raised.

This gains vertical height, but this perpendicular bar also moves horizontally. In order to counter this, a second, congruent four-bar is built on top and geared together. This ensures that the two four-bars stay in phase, and the horizontal displacement of either one remains the same.

The top is (kind of???) a 6-bar, just to get a little bit of extra height compared to if the bottom bar of the full-length bar was the bar directly attached to the gear. The lift can be raised by turning the gears in the middle, or by a gear at the bottom angling the bottom bars upward.

Let me know if you have any questions!

This video explains what most of the basics are I would caution trying to build a R4DB as your first lift as it requires a lot of small technical braces and elastics in order to make them work well. What you could do first is build a solid four bar lift with a manipulator. After that you can then add the extra gearing to add a second 4 bar stage. The main basics is a four bar lift has a gear box with another four bar geared on top of that gear box.

Note - the point of that post is that you should do your own analysis, and Maxx himself has said that his post shouldn’t be taken as gospel since getting 52 cones is a bit unrealistic.

I didn’t link that because of what Max said about RD4Bs. I linked because it’s genuinely good advice for all teams, especially for new ones. Setting aside the analysis he did in that thread, the concept of the thread itself and the overall message it delivers is what I was trying to get across.

I would actually highly encourage competing. Even if you aren’t very experienced in VEX, competing is the best way to learn. It encourages you to improve. When I first started VEX in 6th grade, I didn’t even know what a bearing block was or that friction could cause problems. Despite this, I competed and I learned a lot because of that.

Getting back on topic now, watch this video:

It really explains what a RD4B is and their advantages.

And I didn’t think you linked it because of what he said about the DR4B. I’m just saying that the whole point seems to be going over a lot of people’s heads.

Can someone post a picture of the gearing on the actual lift? I don’t completely understand how to make it so the two four bars don’t hit each other.

@hannahrose @quack. That is a good question, but I’m afraid no one who has a DR4B is willing to reveal theirs this early season. I’ll try my best to explain.

My teammate was prototyping a DR4B and had an “ah-hah” when he asked the same question. The solution is to off set the two sets of four bars so they are not on the same plane. Take a look at the thumbnail of the video that is 2 posts above this one. That is the basic concept, however if you decide to build a DR4B then you should try to come up with a more reinforced solution to off set the 4 bars than the thumbnail above. We just put the lower arm on one side of the gear and upper arm on the other side.

Here’s Anti-Chamber’s reverse double four bar in the early season. Pause at 2:54 and you can see two gears lined up, and the bottom gear has the metal on the right side, and the top gear has the metal on the left side.