[EricH]

First piece of advice when it comes to scissors lifts: Don't. It's almost certainly more complexity than you need, and the math is... well, I've heard that even veteran engineers get scared at it.

But, let's see if I can translate the issue. The OP has "slack in the forklifts" on a scissors lift. To me, this says that when the lift moves up or down, there's a bit of slop or backlash, causing delays in motion, and quite possibly damage to motion parts in the long term. The problem is, they don't want to make modifications to the drive.

Now, I've been on quite a few scissors lifts lately. Every single one had noticeable backlash when stopping going down. Meant that in some cases, I had to stop higher to avoid hitting an obstacle--something like a 1-2" drop and return depending on how high it was coming from and the weight aboard the platform. These lifts are built by professionals. I think some of the backlash was intentionally left in, as a hard stop can damage the lift equipment. But in other scissors setups I've seen, including some in FRC, I've seen some of the same thing. I would guess that it's inherent in the design somehow.

What I mean is: You're not going to be able to remove all of the play from the system. If you just can't have backlash and play in the lift, you should probably switch lift types to an elevator lift (see FRC 254 in 2007 for an example).