Reverse Double 4-Bar Thread

Why doesn’t it use the power the motors supply efficiently?

its hard the explain without a drawing. most of the weight is up front and providing negative leverage on the motors like most lifts. The part that is different is that a reverse double 4 bar has 2 of these pointes. the second point does not have any power except for the motors on the back.

these remind me of half a skizzer lift

:slight_smile: yes it is popular good prediction

I love the double 4-bar in this game. It should get sufficient height and I think it’s more reliable than either a scissor or elevator lift.

I would definitely not be surprised to see over 50% of the bots at World’s having reverse double-4 bars. However, I don’t think they’ll be quite as mainstream as 6-bars were this year.

Here is a post with some back of the envelope torque calculations and a few pictures for a 60 in lift.
Simple in concept but challenging to build.

Hi all,

I’ve recently had a bit of a look into RD4B lifts with my robot which I’ve already competed in a scrimmage in and done quite well. I don’t exactly want to share pictures at the moment on the forums but if anyone wants to message me about building one or designs I’d be more than happy to help out.


My own lift (which was only a prototype and is being rebuilt over the next couple weeks) could reach 60" without any trouble at all.

My personal opinion on RD4B lifts after my experience with mine is that these lifts are fantastic if well built and I’m really enjoying the lift on my robot. Theres been a few issues I’ve come across when building V1 of my lift but V2 will hopefully overcome all these issues.


I did talk to a one-girl-team who used a double-reverse 4-bar at one of the Auckland Skyrise scrimmages, and it worked incredibly well and seemed well-balanced. I didn’t get the chance to ask her about the more technical side of things, though.

In terms of balance, it was certainly better than a six-bar, because most of the six-bars at the scrimmage looked as if they would tip.

Our team is planning to build a double-reserve 4-bar for Skyrise, too. It just looks a lot easier to drive and I’m just really fond of how stable and balanced it seems. :slight_smile:

@the Singaporean team who built the double-reserve 4-bar: I just wanted to know what were the main difficulties in building the robot that a team who wanted to try out building one should watch out for?

The double reverse 4 bar will generally get you height faster but not at a constant center of gravity front/back like a scissor will.

I am not sure which one is heavier though. We will have to weigh a few as they get built this year. Scissor plus the lifter is not light. Enough drive train in the double reverse 4 bar and it adds up in weight too.

Scissor has more joints and pinch points to stop motion while a double reverse 4 bar once it “clicks” out of sync is a pain to reset.

They both seem like effective lifts for this year.

The proble our team ran into is we only couldn’t only adjust 1 bar, so we are still
Working on that. So I was wondering what you guys think we should do, to make it so we could adjust only one bar.

Why would you want to only adjust one bar? That would cause you to lose the vertical motion and provide no benefit over just having each 4-bar move half as far…

Forward reach is still a useful factor in scoring. If their is no cost to controlling the bars separately and you get the option to reach farther why not control them separately?

This, and the fact that gearing or linking the two 4-bars together adds weight and friction, whereas controlling them separately makes for a cleaner and lighter system.

The only drawback I can think of would be that the bottom lift would be under more strain than the top, and whether this extra strain is worth the reduction in friction remains to be seen.