Hi im having really hard time trying to fathom how to attach my scissor lift to the rack and pinions that are located in the back of my robot any suggestions in general. If you need pictures ill be glad to post them once i get my hands on a working camera. ps. it is a vertically powered scissor lift.
Edit: I got the pictures now here is the link: http://imgur.com/a/a1IOx try to ignore the lack of reinforcements and messy wire will be fixing that when i get the time.
The scissor lift experts here will almost certainly need to see some photos in order to help you.
when you say rack and pinion at the back of the robot
do you mean like this robot?
yes i do 
but i dont know if it is better than this attachment cant seem to decide [https://www.youtube.com/watch?v=QQBs6ypH8VM
unless its attached on identically?](https://www.youtube.com/watch?v=QQBs6ypH8VM)
I’ve mocked up a scissor lift like this before. It worked well through testing and did great once stabilized but I never could manage to pick up 2 cubes without breaking teeth off the vertical linear slide racks. Anyways, to help you out I included a picture of the way I found most efficient in mountin the scissor lift to the racks/gearboxes. Hopefully you can use these to come up with something that works for you. Good luck!
I would highly recommend you don’t use this lift design, scissor lifts are great but only when you have them geared, my team has a 25:1 gear ratio on it, I would recommend you don’t use the system you have pictured
Having a high gear ratio on a design that is powered from a gear on the middle (the chinese style) is desirable. However, the method shown here can also be very effective and you don’t need a high gear ratio, because having a small gear (12 tooth) moving on a rack and pinion is very powerful.
To the OP, have you tried mounting the vertical slides in the center. This seams to be a more common method, however you will need both end of the lift to slide, whereas if the current method works you only need one end to slide.
This thread lived quite shortly but due to stanley’s link we have figured out how to attach the scissor thank you guys for all your suggestions and tips. 
Im bumping this thread again because I want to make some things clear about this scissor design.
I have experience with horizantal rack and pinion, vertical rack and pinion attached to the center of the scissor, and lastly my most recent build, vertical rack and pinion attached at the back of the scissor, which I built in 2 weeks with minimal testing. The idea with attaching the rack at the back is to elliminate the problem with non linear force output with horizantal rack and pinion, reducing the likelyhood of tilting, and also the problem with the vertical rack and pinion attached to the center; where the force output is non linear at the upper range of motion.
I set it up as 3 motors on a rack and pinion slide(there are two so 6 motors on the lift in total) geared 1:1 with internal high speed motors. I did not put that many rubber bands and also the tensioning wasnt really that great but I still got it to lift 2 cubes just fine. The rack teeth never got near to the point of breaking. I attached a hinge to each bracket and attached that to a bar accross the scissor. Note that you have to put the pivot(hinge) closes to the back as possible or else the position of the scissor will shift as you lift up, meaning that you can no longer rig down one side of the scissor and have instead both sides sliding. It’s actually slower than a 1:7 rotational scissor, to my dismay, because I wanted something just as fast with minimal gearing, and the anti-tilt advantage.
My verdict is that of all rack and pinion scissor lifts this is the best way to power it, but in the end rotational scissors are still the best.