3D Printable Cascading Linear Slide

This Instructable will describe how to design an inexpensive linear slide prototype. This is intended for FIRST Tech Challenge Robotics teams, however is also widely applicable to hobbyists and other robotic systems. The lightweight slide can extend many times its own length, and is quite fast.

A quick word on terminology for those unfamiliar: a stage refers to one slide section, which is repeated to create the full slide The terminology can be ambiguous, however for this purpose a "two stage slide" refers to using three stages: a fixed stage, and two that move along it. Furthermore, the stage that does not move is the "base stage" or "zero stage", and each following stage is one, two, etc. In this tutorial I'll be using a two stage slide, meaning three pieces that can extend almost twice the original height.

To start, download the following thingiverse file, this provides all the pieces you need to begin. Each stage uses the exact same pieces, so the file can be printed 2,3, or 4 times for each stage you'll need. I'll be creating a two stage slide so will need three sets. If you have a specific extension length in mind, the following equation can be used to determine stages:

(total displacement) / (shaft length - 60) + 1

Thingiverse Files: https://www.thingiverse.com/thing:4958057

You will also need the following:

• 2 linear shafts per stage
  • Amazon
  • Servocity
  • Note: Amazon and Servocity shafts are not the same. The Amazon link is hollow aluminum, which is very lightweight however slightly out of tolerance and softer, making the slide less smooth. Servocity is precision steel, which is much heavier but also much smoother.
• 2 linear bearings per stage
  • Amazon
  • Servocity
• Belt
  • Servocity: 10 feet
  • Servocity: 25 feet
  • 10 feet can suit up to four stages, however extra is often good in case you cut it to the wrong length.
• Screws: 2 M4x25mm, 4 M3x20 and 6 M3x12mm per stage
  
  • Amazon: M3 + M4 set
  • Servocity: M4x25mm
  • Amazon: M3 set
• Optional: Bearings, 4 per stage
  • Servocity
• Filament (any will do, I used PLA): approximately 70g per stage

If you chose to print the pulleys with the bearing bore, press a bearing into each side. If possible avoid hammering, as it can damage the pulley and/or the bearing. Clamp, vice, arbor press, or gripper can all work. For pulleys with screw bore, drill out the hole to ensure it slides easily on the screw. A 4mm drill bit works, or 5/32 for non-metric bits.

Gather the top and bottom pulley attachments. These are the two largest pieces. The top pulley attachment is smaller with just two holes for shafts, and the bottom pulley attachment is larger with the two holes for shafts and two for bearings.

Screw the pulley onto both the top and bottom attachments of all the stages you're constructing. Note that one side of each pulley mount has a larger hole than the other, so the screw should slide through one side and be tapped into the other. Don't tighten the screw all the way, doing so may cause the pulley to rub on the mount. The screw only acts as a shaft for the pulley to ride on, not to fasten pieces together.

On just the bottom mounts, place bearings into each of the mounts, and screw them together with an M3 bolt, around 12mm works best. Note that 3D printed plastic can not withstand large amounts of force, so don't over tighten the screw. If using a drill to screw it in, don't rely on the drill's torque breaking point, as even the weakest setting on most drills still strips the screws.

Additionally, install the belt mounting plate onto the ends of both the top and bottom pulley attachment. Use longer screw, around 25mm, and leave a gap of 5-10mm between the plate and the mount.

Finally, attach the shafts to just the bottom mount, once again using ~12mm M3 screws.

With the stage without linear bearings as the base stage, slide each additional layer onto the previous. Then, place the top pulley attachments onto the top of each stage, with the side with the protrusion facing towards the next stage. Downloading the 3D model linked on Thingiverse can help visualize the direction.

Slide the belt along the first stage, going over both pulleys and into the slots provided. Measure and cut a length of belt, with about 50mm of overlap. Slide the two ends of the belt into the belt clamping mount, tighten the belt, and then screw it tight. If everything worked correctly, you should now be able to pull the belt and raise the first stage lift.

Attach each belt on the following stages the same as the first stage: looping around the top and bottom pulley, and screw into the next stage. The last stage does not need belt attached to it. When finished, pulling each belt should be able to lift the next stage.

Finally, screw the top of the of the pulley into the stage previous to it. This does not need to be done for the base stage. For example, the top pulley mount of the base stage should attach to the belt of the first stage, the top of the first stage should attach to the belt of the second stage, etc.

To better visualize how to do this, and gain intuition to what is happening, see the video I created above.

If everything was done correctly, pulling the bottom stage will extend all the stages. This can also be demonstrated by pulling the base and final stages apart, and each intermediate stage extending equally.

If using this to attach to a project, modify the file to create a motor mount. The easiest way to do this mounting the motor directly underneath the base stage. However you can also use pulleys to extend the belt to more convenient locations. Additionally to mount the slides modify the file with preferred hole placement and slide orientation.