6-Bar Linkage Help

Hey I am having trouble with my robot. We are using the 6 bar linkage lift design any ideas.

What kind of problems are you having? If you have a pic of your robot and a description of the problem that would help everyone figure out a solution.

Make sure the horizontal bars are parallel to each other, and the vertical bars are parallel to each other (Check the spacing). Also make sure the bolts aren’t that tight where the bars need to rotate.


There are some pictures for you :slight_smile: Be more specific and we can help you out better.

I would probably use a 1:7 ratio. My arm is 1:5 and sometimes we struggle to get off the ground.

This isn’t my video, but you may find it helpful! :slight_smile:


Specify what your problems are, pictures would be helpful! :slight_smile:

Make sure that the C-Channels are parallel to each other and almost touching each other when the lift reaches maximum height, check the spacing and make sure its not too tight… best to use washers! :cool:

I feel bad every time I do this, but I do think it needs to be said. This has pretty much been copy-pasted from a previous comment.

The guy in the video spends the first minute and a half talking about how to make a 6-bar symmetrical and why that matters. symmetry is not relevant. Nearly everything he says up to 1:40 is either wrong or misleading. After that, the video is correct and has some helpful information.

He says that symmetry will make a 6-bar lift higher, which is not true. He says that symmetry will make a 6-bar “lift really well” and “work a whole lot better”. While you might notice a loss of performance if your six-bar is very asymmetrical, for practical purposes this is also not true. There is no reason why a slightly asymmetrical 6-bar would work any worse than a perfectly symmetrical one.

What you do want to make sure of is that your six-bar is parallel, which means the links on opposite sides of each quadrilateral should be of equal length.

Not necessarily. For a better height you can use non-parallell six bar, but of course that is harder to design. And yes, a six bar’ s height depends on the longest bar, the other bars are just assistants and their length don’t matter that much.

I agree that most of the bars are only assists. However a factor in how high a lift can go up is, how high an angle it can lift until the horizontal bars touch (commonly the limit on lift height).
See the left side of the image below:

Since it’s asymmetrical (the top vertical bar is closer to the middle horizontal bar, than the bottom horizontal bar is), won’t it be slightly lower than if it was symmetrical?
I.e in a symmetrical linkage lets say the top horiz bar is 3" from the middle bar and the bottom bar is 3" from the middle bar. (Total spacing 6")
In a asymmetrical linkage lets say the top horiz bar is 1" from the middle bar and the bottom bar is 5" from the middle bar (total spacing 6").
In the asymmetrical linkage the limiting factor is the 1" spacing.
So I think asymmetry can be an ineffective waste of spacing that could’ve been used for more height. I don’t think horizontal asymmetry affects height though.

I’ll do tests in Inventor later to see for sure

Not for better height, usually. The height is still limited by the length of the longest bar for most types of intakes.

But yes, I took the part about non-parallel 6-bars out of my previous post because explaining things well involves explaining the rule before you explain the exceptions.

Ok, this would be true in a situation where one of your binding constraints was the length of the middle vertical bar (like if you only had one 6" piece of metal and all your other pieces were much too long or much too short). In reality that is almost never the case. There is usually a constraint on the vertical distance between the bottom and middle bars and a separate constraint on the vertical distance between the middle and top bars.

For maximum height you need to maximise the gap whose upper bound is smaller, but from a height perspective it doesn’t matter what you do with the other gap. Making it larger might distribute forces better, whereas making the two gaps equal saves a small amount of structural metal. Either way, making one larger doesn’t mean you have to make the other one smaller so symmetry isn’t the right way to think about it. You could have a symmetrical arrangement with too little spacing or an asymmetrical one with more than enough spacing.