DR4B vs Six Bar

I was wondering why so many people are planning on building a double reverse four bar for their bots, instead of a six bar. I don’t believe that the extra height is needed, so why are a majority of people building a double reverse four bar?

I don’t understand why you would need that height, either. Having a perfectly linear lift is nice, and it could be familiar after Skyrise. That could play a part.

Frankly, I agree with both @Aponthis and @novaabhi . If you also take a look at how the hanging pole is attached, it will be really awkward trying to align and hang if your lift is completely linear; it will be useful for it to extend somewhere in front of the base while lifting.

I think they are also talking about just getting the stars and cubes over the fence, which is a mere 2 ft tall while a DR4B can get 3 times that height if built to.

That’s a good point as well. Perhaps you could have manipulators at both the halfway and top of the lift? Use halfway for scoring and top for lifting maybe? Might be an interesting combination.

but even then the fence is 21.255" and 25.255" and the lifting bar is 30". you get 18" to begin with, so you only need ~12"+ (however much higher you need to be). That doesn’t require anything as high lifting as a dr4b. I think there is such thing as overkill when it comes to lifting.

How do you feel about a glorious 1 bar? (I don’t know how to classify it, but think clawbot-style)

Just doing the math in my head, you should have ample height to go over the fence with just a simple c channel screwed onto a gear.

We call it a 2 bar. It’s definitely enough this year, but some might want to keep the intake at the same angle throughout the lift, so a 4 bar linkage is the next step. I feel that even a 6 bar is overkill this year.

I don’t know if a scissor lift would be considered overkill this season?

It may be a good candidate as It can be made to the exact height needed.

Familiarly horrible that is shudder

If we remember Skyrise, then we should remember that rd4bs, scissor lifts, and elevator lifts are bad. If we remember Toss Up and Sack Attack and Gateway, then we should remember that n-bar linkages are good.

I don’t understand why people need “lifts” this year. A claw bot style arm is good enough.

To knock the stars off the fence onto the other side

The double reverse 4 bar can give you a more centered center of mass. You don’t need to use full length bars for wicked high height. Six or 8 bars can make the center of mass too far up and forward depending upon what you put for the manipulator and launcher.

If you want a catapult or dumper on the end of the linkage, getting your robot not to tip over when shooting with some force is very beneficial. Manipulating the center of mass placement goes a long way to not tipping over. Catapulting in the down position is safer, but takes more time.

But then again, how many times will you be going up to the fence but to retrieve the elements if you have an effective ground catapult?

perhaps the DR4B could be used in end-game for the hang. In addition to ‘top’ stability when compared to a 6 bar, it easily start under 18", and also has the potential of going above 18" perpendicular to the ground.

I’m not sure what you mean. The positioning of the post makes it extremely difficult for linear lifts to line up with the post. As for top stability, the DR4B has way more mass going up and down than a standard 6-bar and therefore moves the CG higher and makes it more unstable (although CG is more centered). A 6-bar obviously has the potential to go above 18" as well.

DR\$B’s are unnecessarily complex, and heavy. They would not be able to lift itself without even more weight and power.
For people who have not competed in Skyrise from a couple years ago, it might be hard to appreciate how complex these lifts are compared to others. I don’t think there is any good place for a DR\$B this season. You could make a small DR4B lift work, but it is not going to be any better than one of the simpler lifts.

But it looks cool!!! OK maybe that’s just me. I’m was actually thinking of a sort of squished short flat dr4b i saw a picture of once

Can you explain the reasoning behind using a DR4B?

it does not have to be full length like that. The original DR4B 8059B from Singapore used a more central lift location. That is a slightly more centralized center of gravity than skyrise robots.

They were awesome.

https://vexforum.com/t/8059b-robot-reveal-warning/21175/1

My idea is to use it in a similar way to a scissor lift. Or at least in that sort of configuration.