The current team that I am mentoring is using the Tetrix rack and pinion kit for linear motion applications. And there are problems with it like the small plastic guides. If you have them to tight the system will not slide easily and if they are loose they won’t stay in place. So they want to give drawer slides or similar slides as an option. After looking at some examples I’m not seeing how they are being lifted. We understand the rigging of a cascading elevator but are not sure how to set it up with a drawer slide. Do you use pulleys to hold the wires? Or what?
Yes, I’ve seen teams use pulleys sticking out sideways from the structural members that are connected by the drawer slides. They can range from something simple like a bronze bushing sticking out to something fancier like pulleys with ball bearings.
Are there easier ways to do it? If not how do they attach the pulleys to the drawer slides?
My teams use drawer slides on their robots. They stick sheets of metal between each drawer slide, and attach the pulleys to the u channel brackets that are on the sheets of metal. They make the pulleys out of bronze bushings and 3D printed parts.
How heavy is this? We would like it to be light as possible. Have you done it without using the sheet metal in between?
What’s the rationale behind wanting it light? I’d imagine the extra weight and the sheet metal make the system more stable than a typical drawer slide setup (which in my experience are incredibly unstable).
We are using aluminum drawer slides (http://www.homedecorhardware.com/ss-ar3-400.html ) It works great - they are much more precise and lightweight than the steel ones from HomeDepot, but also much more expensive. We put a length of square aluminum tubing (3/4") between the slides and attach small ball bearing pulley wheels to it.
If you are interested, check some photos of our robot in our album:
We actually have four 16inch slides in there. It is a little heavy, but we run this lift with 2 tetrix motors, no problem.
We have found that constructing them this way is the lightest weight that we can make them, along with not taking a whole lot of space…
In the picture, the last pulley that is up in the air to the left, is actually strung wrong. When it is strung right, all four slides move at the same time. With 1 inch of lift on the main slide, means 4 inches in all. Makes for a very quick lift.
*If you do decided to go with drawer slides, I have this:
Granted with these slides, we have noticed a small sag in them after a few months of use, but was an easy fix, and we have only had to do it once. There is a small tab at the bottom of the slides that stops all the metal from falling off the back. This piece of metal is thin and not meant to hold all the weight of the slides and extra metal. Drawer slides were not meant to be used vertically on robots like teams have been doing, but they are perfect.
You just need to take care of the slides, and they will work great. Just like any other lift that you would make…
Just keeping it light as possibe should mean we don’t have to gear it down to get the right more power to lift it up. That means we go slower and we want to lift it as fast as we can. But yes of course you’re right we want it stable to.
We currently have our lift geared down 1:2, with a 1in diameter barrel. It lifts to its max height in 4.5 seconds. We don’t need to go to our max height though, so that makes the lift time even sorter. We are also looking to do a larger barrel, which would decrease the lift time.
Placing the cables in the right way can increase your speed. Don’t do one long cable. Use multiple, to lift each section at the same time.
We have done that before and it didn’t work out so well. So we’ll be doing different sections now.