Pitfalls of 2014(Pun Intended)

As we all know, this year asks teams to scale to heights that(I think), have rarely been seen before. That means one thing, way more tipping. In particular, I’m searching for advice from people who’ve built an elevator lift this year. Does the weight of several cubes in what ever intake you have offset the results of the lift structure placed near the aft of the robot?

We started off this year building a 5 stage elevator lift to reach the high goals. It worked fine with no load(cubes). As soon as you added a cube or 2, the lift leaned forward from the weight of the cube, and the linear slides bound up, going up and down. We resolved the lean by pitching it backwards to compensate for the load. We tried to resolve the binding issue by removing 1 stage of the lift, but it remained. It wasn’t till we removed 2 of the stages that it worked reliably. Unfortunately it wasn’t tall enough at this point, so we went completely in another direction.

Tipping was never an issue at any point, even at 5 stages. We attended a tournament this weekend several elevators were competing and never saw any of them tip.

Tipping in the past has occurred so frequently because most designs used non-linear lifts: 4-bars, 6-bars, etc. These type of lifts would move the center of gravity forward and then backward as the robot raises its arms. Because the process of building a skyrise encourages the use of linear lifts, there won’t be very many tall non-linear lifts. Also, there are no field elements for robots to drive under and run the top of their robot into while lifted up. Robot interaction will also be limited in comparison to other years. I predict that the main reasons for tipping this year will by poorly built lifts and accelerating to quickly while fully extended. It seems as though Vex is trying to make the game safer for robots while still providing a difficult challenge.

The one instance that I encountered a situation where our elevator lift tipped over was during a Sack Attack match against one of the top tier teams in Indiana. Our trough had just been filled and I lowered our intake onto the trough to try and protect it, however the other alliance wanted to de-score. As he pushed against the top half of my scoring mechanism, I made the foolish mistake of trying to drive forward and stay on top of the trough. In the end, his robot was stronger and was able to push our robot over onto its back. The reason it fell over was due to his pushing on the top part of the scoring mechanism and my driving into his robot. This was the only time our robot ever tipped at all, aside from that it never came close to tipping. With this years game being very “No Touchy”, I don’t think that tipping will be a big problem for elevator lifts this year, however it is very helpful to mount the base of the lift in the center of the chassis in order to try and get the weight centered in the center of the robot. I also recommend trying to get the base of the chassis as close to the ground as possible. This will put your center of gravity closer to the ground, plus, you don’t have to worry about a bump or running over any scoring objects this year.

Our three stage 56 inch scissor lift seems to handle tipping fine. We only tipped once at the end of match, due to our driver’s mistake. Without the interaction of another robot, we rarely tipped when scoring on goals and our driver is improving a lot more. I guess that taller scissors are a lot more unstable.

The last time we built an elevator was sack attack, and the tipping we experienced was because our intake forced us to mount near the rear. We might have to face that this year as well, depending on the shear size of the intake. Thank you for your input. About lifts not reaching their optimal height, could you expand as to why?

What do you mean by not reaching optimal height, there has to be some overlap of the linear slides so that the lift doesn’t take itself apart while trying to expand. It is also that there will be some give in the linear slide pairs if you mount them back to back. If they are mounted on the sides of each stage, there will be minimal flex forward, making it easier to reach optimal height. Is that what you were asking about?

No, I meant complications to not being to reach the 63’’+ height required to place cubes at the top of a fully built skyrise. There may be things such as friction in the slides, too much lean, or simply not going up at all with 4 plus levels.

I know that the more stages you add, the harder it can be to keep stable and lift The weight of all of you stages. However It is possible to reach the top of the skyrise (or at least get very close). If you can prevent the lean, you shouldn’t have any trouble using a lift that has 5 or 6 stages. It’s just a matter of building it, and then immensely tweaking it.