Hey everyone, my team has just recently finished building a DR6B. Yes I know that height may not be needed this year, 13 cones as the “magic number” and all that, but we have discussed it and we have our reasons for building it. However, I am wondering if anyone has any tips to stabilizing a double reverse 6 bar or 4 bar lift. Right now ours is decently stable and we have some other ideas to improve it, but it’d be great to here from you guys if you have any thoughts our tips. Thanks!
off set the 6 bars so that when on two different planes it has some leverage so it doesn’t sway as much
Obligatory mention that my 13 Cones Analysis was just a thought exercise and example of a possible Game Analysis and was definitely not intended as gospel truth or anything like that. If you’ve thought about it and judged In The Zone to require a taller lift than just 13 Cones, then do it and do it with confidence. I’m not even convinced that a Double Reverse Lift is unnecessary, I just thought everyone might have jumped to conclusions without thinking things through and figured someone needed to play devil’s advocate.
I don’t have as much direct experience with DR6Bs, but I have a lot of people I work with very closely who do, and I’ve definitely been around the block when it comes to building tall lifts. If you want very in depth advice, you might consider posting some photos of your robot, but I know a lot of teams aren’t willing to do that for different reasons, and that’s totally fine.
Obviously, you want to figure out where in the lift the instability is coming from and reinforce or tighten up that part of the system. That’s pretty vague advice, but definitely good to keep in mind in your overall thought process. I always try to break things down into their most simple form and work from there, turning a complex problem into a simple one makes it a lot easier to work with. Instead of looking at the whole lift for instability, analyze it one section at a time.
There are a lot of ways to “stabilize” a lift, one way you can remove a lot of the slop is by using Single-Rotation Joints. That’s a video on common joint designs in VEX from Owen of BNS. I’ve linked to the last part of the video. In case anything was unclear, you’ll want to firmly attach a Screw to one of the bars with a tightened Keps nut. This will remove a lot of the slop and keep the screw perpendicular to the bar. Then you would run it through a bearing on the other bar so it can rotate, and then hold it all together with a Nylon Lock nut, just tight enough to keep it from coming apart. This joint only rotates in one place and you don’t have to compromise between a tight lock nut to remove slop and a loose lock nut to prevent friction. I would highly suggest using these wherever you have a joint using screws.
You will definitely want to run some cross supports between the two sides of your lift to prevent it from swaying side-to-side. Make sure the spacing is correct so you aren’t pulling them together or pushing them apart and adding friction. You want the bars to always be parallel between the left side and the right side. This isn’t referring to your actual linkage, there are some instances where the bars within the linkage could be non-parallel. I mean when you look top-down at the robot, not from the side.
Not as many teams do this, but I always like to sync up the two gearboxes when I build a lift. This would mean running a shaft that goes through the left gear train and the right gear train to forcibly keep them in sync. This helps a lot with tilting side-to-side. Its best to have that shaft on as small a gear as possible because x Degrees rotation on the smaller gear will equate to less vertical movement in the lift versus the bigger gear. If I haven’t explained that clearly I can expound on that and break out my best friend, MS Paint ;p.
I would highly suggest studying 118’s Skyrise reveal very intensely. A lot of teams have made great DR4B’s and DR6B’s, but 118 was one of the pioneers of this design. The Double-Reverse lifts had extremely limited use before Skyrise and 118 had an insanely fast and stable lift from the very first competition that year. Other teams may disagree, but as a South Texas competitor, I always see 118’s DR4B as the beginning of the era. They didn’t invent the design, but theirs was miles ahead of any other I’d ever seen before. A very important thing to note was how they used C-Channel Extenders to increase the stability of their joints and reduce torsion on the bars within their lift. Freeze frame here at 1:09 and look right above the 84-tooth gear on the left. They’ve put a C-Channel Extender inside the main C-channel and run the joint all the way through. 2587z was another brutal Double Reverse Lift that year as well as AURA in VEXU.
That’s all the specific tips I have at the moment. Keep in mind the different ways the lift can be unstable, and I’m sure you’ll be able to invent your own solutions as well. It can sway sideways, the lift can tilt sideways (One side is higher than the other), and then these could both happen forward and backwards as well.
Keep your joints tight and your COG centered, and I think your DR6B will be very successful.
@400X Wow. Thanks for the very in depth response, I really appreciate it. Luckily our team has already been using the screw Nylock solution to help stabilize, but all your other tips will be very useful. Thanks again!
Just to add to that response, the best type of cross bracing between the bars in my experience looks like an X. This can keep the lift from flexing more than just a bar across, since it reinforces the lift in the direction that the metal is strong in. (it would need to lengthen or shorten to flex much with X bracing)