Chain Lift Tutorial

There’s been some discussion recently about what AURA calls a “Chain Lift” (other names include “Chain Bar”, “Virtual Four-Bar”), and how it works/how to build one. So we thought we’d whip up a quick tutorial about some of the things to watch out for when trying to build one.

Note that this is just one of many ways to do it, but we’ve actually been through this process and the guy who wrote the tutorial also built Matlab which uses this type of lift.

As usual, feel free to ask us any questions below, or if you’re a bit embarrassed to ask it in public you can e-mail us at

Could you please post the CAD files (preferably in Inventor format, but STEP is good too) used in the tutorial?

Here you go:

I’m new to Inventor so you may find there to be lots of issues. It was originally only intended for screenshots and I think it does that job just fine :stuck_out_tongue:

Any links to VEX specific tutorials would be much appreciated!

Note: I left out most of the delrin bearings because they didn’t seem to be needed for the purpose of explanation (some of the nuts and bolts are missing for the same reason).

I’m using a similar system, but with low strength chain so we can tension it easier. However, I need to make the scoring object chute very light!

Would you mind sending the pictures to me?


Thank you!

Thank you for clearing up the confusion and making this.
I am sure it will help a lot of people.

Thanks so much! :smiley:

It does not open in Inventor 2012.

Has anyone else experienced problems like this?

You’re welcome!

It was put together in Inventor 2010, is there any error that is displayed? Do parts not show up? Could you described said problems please?

The set of images used in this tutorial is available at

Thank you for the images.

I aprreciate you making the CAD on this subject! Really clears things up!

Nice work on the CAD.

Would you mind explaining how you put the chains into the model?



With much patience :stuck_out_tongue:

As far as I’m aware, you have to do it link by link. I followed what LegoMindstormsmaniac said in this thread:, except I joined the links together before applying constraints to the sprocket (I didn’t close the loop just yet though).

To try and get the chain as straight as possible I found it easiest to ground some of the links, namely the first and last ones to contact each sprocket, some of the others around the sprocket and the link that comes close to contacting the tensioners. I also found I was rotating the links that formed the kinks in the chain manually to get it straight (pulling the whole chain wasn’t quite working right)


I was hoping if there was an easy (lazy) way…

Excellent work and patience!

Also, the post (iCLunk posted once already) is very helpful. If anyone doesn’t want to do it link by link, the post directs you to a video with this link:


Very helpful.


When I open up the file (In Inventor 2012), the pieces are scattered and they are all not there.

Has anyone else had a problem like this?

I there a reason that you made the chain so close together with the idlers? I would think it would increase the friction applies to the chain thus putting more strain on the motor?


Have you guys ever had issues with a chain breaking during a match or outside of a match using this setup? Just curious how well it has worked, any failures during critical moments?

“Chain Lift” is completely misleading, that implies a lift powered by chain which this is not. It’s an arm that uses chain as a linkage. Chain linkages can do anything from hold a piece horizontal as an arm goes up (like a four bar) to mechanically creating motion about an arm path without a motor.

Would you mind making a drawing of what you are talking about?

Original post (OP): (nice work)

After several queries about getting Inventor2012 vs Inventor2010 working,
BEB writes:

Looks like all the users of BEB should get together and talk among themselves, or at least reference the first post, which has the drawing.

A few comments may make interpretation of the Original Poster rendering more clear.

  • you can remove the chain idler posts; they don’t do anything critical (except to keep the chain out of the path of something else not shown)
  • the top shoulder sprocket IS NOT mounted to the top pivot axle.
    the top shoulder sprocket IS mounted in-line with the top pivot axle.
    The top shoulder sprocket is bolted to the tower so that it can’t rotate;
    Just like the bottom wrist sprocket is bolted to the C channel hand.

We know, but it’s the closest name that we could think of until someone can tell us what it actually should be called. In reality it’s just a 4-bar isn’t it…