Scissorlift/sliders/gear racks problem

hello. currently we are using the rack gear box kit for our scissor lift and one of our problems seems to be that there is so much torque in the two motors that it causes friction to build up in the sliders and since teh scissorlift is still trying to move it will pry the plastic slide out of the railing. does anyone have a clue how to fix this and tip to improve on this design photos of the robot so far attached
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This is how we made our scissor lift, using the rack and pinion… We will be adding another motor right next to the one pictured. The way you made your lift, vertically like that has pretty much maximized your friction. I would suggest, moving the slide rail horizontally, which would also help with the size limit going upward. Also move that second motor to the side, and add another gear, so there is more surface area lifting up, rather than just more power. Also don’t use those tiny green plastic slide pieces, use the bigger ones, like in the picture, and flip your slide rail over. Those attach better, and cause less friction. Also you are allowed to add a very small amount of grease or lubricant, but don’t take my word for that, look it up in the manual.

I can see a bag of elastics next to the robot in the last picture, so I’m wondering if you’ve tried elastics? The initial vertical motion of the lift is usually the one that requires the most torque, so elastics would definitely help.

So if i’m understanding this properly, your sliders are popping out.

I’ve never used the new linear slide kits, but I think you should be able to fit the linear slides within your rack bracket. if you can do that, then that means you should be able to mount your plastic slide within the mounting bracket as well so the plastic bracket pushes against the metal slide.

So, if you flip your metal slide 180 degrees so the open side faces down(elevate it off the drive with standoffs or spacers), place the plastic insert inside the bracket, then install the plastic insert into the metal slide, the plastic insert should push against the metal so it’ll never pop off.

the reason why this is happening is because:
this method of powering a scissor lift has this problem

There are many different ways to power a scissor lift and all have their problems.
A horizantal rack and pinion scissor has problem with lifting when the scissor is fully compressed. A vertical rack and pinion in the center like you have has no initial force transfer problems, but its just like the horizantal rack and pinion reversed, when reaching the top of the lift it has a hard time lifting up, in reality its actually impossible because the forces are all pushing against the slide rather than lifting up.

By keeping the rack and pinion in the middle you can not fix this problem. You simply have to limit the amount your lift goes up and add more stages to make up for lost height.
Ways to help are to add rubber bands pulling the green sliders at the bottom of your lift together, but thats about it.
Heres my vertical rack and pinion scissor from to toss up. Sure, it hanged, but in my opinion it was a poor quality lift but the experience taught me a lot about vertical rack and pinion scissors with the slides in the middle.

Elastics or Latex Tubing will help you tremendously, and make sure to split them over each stage, with extra on the area with the sliders.

Search on the vex forum, as there are tons of threads about scissor lifts with lots of good info in them.

Flipping your lower sliders over as Draco said will permanently solve your problem as rather than trying to pull the green insert out, it will actually be pushing it into the slider.

That being said, before doing any changes, I would highly suggest greasing everything and adding lots of rubber bands, both vertically (Pulling your motor pods upwards towards the top of your sliders) and Horizontally (Like you’ll see on most scissor lifts).

I think you’ll find that the horizontal rubber bands will greatly reduce the issue you’re having. I have my own scissor set up so that once it reaches the upper range of its lift, the horizontal rubber bands are doing most of the work and it actually takes significant force to pull the lift down from its highest position.

Before making any extreme changes, I would definitely try it out with strong elastics, they make a huge difference.:smiley:

So if we were to flip the slides 180 degrees…how would we mount the scissor lift onto the slides if it was upside down???

Okay thank you…we will try that and see how it works for us

Currently, you’re scissor lift isn’t mounted onto the slide. It’s mounted onto the bracket which is attached to the slide.

So, do the same as before. Mount the scissor lift onto the bracket, then mount the bracket to the slide.

Only difference is that the slide is upsidedown.

If that’s unclear, look at how your system is set up. starting from the ground up, you have a channel. On top of the channel is the linear slide. on top of the linear slide is the plastic insert. On top of the plastic insert is the bracket. On top of the bracket is the scissor lift

With the method i’m suggesting, you start with the channel on the ground. On top of that is the bracket (but the bracket is not mounted to the channel). On top/within of the bracket is the plastic insert. On top of the plastic insert is the linear slide. Even though the linear slide is on top of the bracket and insert, you can still connect standoffs or screws from the channel to the linear slide. Finally, on top of the linear slide is the scissor lift.