Using Extruded Aluminum to telescope.

Hi, My team and I are interested in knowing how one would use extruded aluminum, since it is slotted, as a rail system for telescoping part of am arm. We purchased a kit that comes with 80’ of the 3/4" material along with a bunch of small pieces used to connect them all but no manual whatsoever. The aluminum is from Item. Does Item make any piece that can freely slide along the slots in the aluminum for which a team can motorize and power? I tried searching myself but I turned up only more confusion, any help would be appreciated. Thank you! :slight_smile:

I know 80/20 sells linear bearings for their extrusion so they can freely slide past each other.

I’d be surprised if they didn’t include a catalog with your shipment. (especially that it is Item, those guys are really pushy salesmen) Regardless, you can go on their website and find the linear bearings, rollers, whatever, that you need to make a linear slide.

A couple years ago we used plastic slides, with the aluminium, worked really good, with grease on it.

We have milled slides out of plastic-type material practically every year and it works great.

I want to know where u purchased a rail system for telescoping from.

you can buy Delrin(sp?) sliders that is made specifically for Extrusions. They come in different profile. 115 used it for their 2003 robot to build an elevator.
Google “Bosch Rexroth”
check out their catalog. There are many other suppliers that sell extrusion materials, fasteners, linear motion etc…

Team 401 did a great three segment telescoping mechanism that worked like a dream. I know this isn’t the greatest picture in the world, but I’ll see if I can’t explain it and point you in the right direction.

In the dynamic elements section of the Item catalog are several different setups for roller guides. In order to make a telescoping mechanism you need several things: two or more pieces of extrusion to be used as your telescoping sections, shaft-clamps that fit whatever profile you’re using (I’m assuming you’re going with profile 5) and the shafts that fit in the shaft clamp profile. I know this is probably pretty confusing, but download the Item catalog and look at some of the pictures to match what I’m saying with the actual product.

Now last year was the first year I personally worked with Item and I was extremely impressed with their product line. If I can also throw in several suggestions. First, go with the adjustable roller bearings, part number 0.0.390.16 (assuming you’re going with profile 5 extrusion). Buying the adjustable bearing unit allows you to get the right amount of pressure between the bearing and the rail that it guides on. You get less slop in your telescoping mechanism that way. Second, if you’re short on weight don’t buy the Item’s shafts that clamp in the shaft-clamp profile. Instead, but stainless steel tubing from McMaster (5mm OD i believe, with the thickest wall available). This saved us an amazing 6 pounds last year, so it does add up. We didn’t encounter any issues with binding or bearings seizing and it was probably the most robust part of our robot.

Here are two pictures that I have of the telescoping mechanism. If you’d like to see more, email me at

if you are thinking about this route check out team 340’s bot from last year because they used extrusion with slides and a timing belt system to telescope

there are alot of good photos here

Team 56 used extruded aluminum and sliders from 80/20 to build their elevator for last year. We used a chain drive with the van door motor, and had enough power to lift our robot on the bar. See the attached pictures.

Team 56 El-2.JPG

Team 56 El-2.JPG

Small Parts sells aluminum tubing in graduated sizes that are intended to fit inside one another. You will still have the problem of how to get a lift to work with the small tolerance between sizes.
Be careful when purchasing off the shelf aluminum tubing, it may not be extruded. This tubing although theoretically able to nest inside each other, has some added material on the inside that prevents the tubing from sliding inside a larger piece. (This experience comes from trying to build vertical antennas out of tubes that start at max diamter of 1-1/2"’ and go down from there.)

Hi Al
You mentioned experience building vertical antennas - knew you must be an amateur radio op. I’m Bill Bennett, N7DZ, licensed since '68, originally WB8ALU in Cincinnati.

This is my third year with Team 1011 in Tucson. We’re working on a telescoping arm design using a 2.5 x 1.25 tube inside a 3 x 1.75 tube. Plan to only have rollers at the bottom outside of the inner tube and the top inside of the outer tube. Have never done any kind of telescoping arm before, so we’re out on thin ice here…

Also working on a design to PUSH the telescoping section, and a sliding apparatus inside it, up from the bottom using spring steel push tape, along the same idea as electrician’s fish tape. No cables or chains. Hope we can get it to work…

Any comments or suggestions about this from Al or anybody would be welcomed.


Welcome aboard, Bill, de WB9UVJ (usually /9 or /0)
Your roller idea should work but I have noticed that rollers bind with a little dirt in the path and stop rolling. Sliding delrin or nylon followers work but need some lube to keep them happy. It will be interesting to see how your tape idea works, the tetras are heavier than they look. We have used “spectra” cable (a nylon string stronger than steel, available from McMaster) and a couple of pulleys coupled to a two sided drum. The motor pulls down in one direction and pulls up in the other direction. A silicone super glide spray works for lube. Don’t forget a couple of microswitches back to digital inputs on the RC to prevent over travel. (backed up by mechanical stops. back up the backup)
QTH 25mi. NW of Chicago-- licensed in '76, now an Extra–wthr hr cold abt 6 this am–cul–

We have done many arms using either nested Al tubing or monocoque. We make slide bearings out of HDPE tosit between the inner and outer arm. We also use window tape to run the arm in and out. Just a couple ideas to ponder…

Our team used telescoping extruded aluminium last year to get the hook up to the bar. It seemed to work well.

I posted a picture on CD of our 2004 robot’s sliding nylon piece of our scissor lift. We manufactured it.

Can you elaborate a bit on “window tape”?

Do you use it as a spring to extend the arm, then pull it back some other way? Or do you push with it? Or what? Can you say where you get it, what product?


Three years ago my team Had to manufacture our own sliders out of nylon, it was tedious work, but they held up well. You want to also watch out for how you have your mast arranged, because if you use a lot of cable and oulleys the upkeep on it is horrid :slight_smile: .

Window tape used to come in the KOP (until 2001?). It is a black nylon ribbon about 1/8" thick that has rectangular cutouts in it that keep it tracking on pulleys. I believe it is available through Small Parts. (Don’t remember because we have so much of it we haven’t bought it in a while.)

We have a design that allows us to use the “track” on the tape to both extend and retract the arm with a motor driving it. We drive the arm up the tape more or less. Below are the best 2 picture I could find on our website. We have used this mechanism in 98, 99, 01, and 03. I’ll see about getting some better pictures of it at tonight’s meeting.

Edit: Forgot the URL of our homepage.

Cybersonics has been making telescoping structures out of extrusions for years, mostly 8020 1010, though we used Bosch 2020 last year. Instead of using linear bearings, they just interlock parallel extrusions and apply a little lithium grease.

The engineer in me cringes every time I look at how we do it, but it’s simple, it works and is very light weight. I think the key to this working is the hard anodized coating on the aluminum keeps it from galling. Needless to say, I wouldn’t expect this to work for a real long time, but the only problem we’ve had (besides cringing engineers) is when the strut gets bent, but that would be a problem with linear guide bearings, too.