Extrusion slides are made up of a stack of extrusions that extend by sliding along each other. There are two ways to make this happen: bushings or V-wheels. Bushing slides connect the two slides with two self-lubricating plastic pieces that slide smoothly along the slots in the extrusion. V-wheel slides have V-shaped groove bearings on both sides of the extrusion that bite intro grooves on the extrusion, allowing the stages to slide smoothly.
REV, Actobotics, and goBILDA all sell extrusion slide kits that integrate nicely with existing FTC kit parts. Beyond this, MakerBeam sells components for a V-wheel extrusion slide, and Misumi offers a few different sizes of bushing-based extrusion slides. REV furthermore sells a 8020 v-groove bearing slide kit for FRC®, that is not recommended for FTC use cases.
We recommend that newer teams stick to slide kits designed for FTC instead of DIY alternatives.
REV Robotics 15mm Linear Motion Kit¶
The REV 15mm Linear Motion Kit is based off of the 15mm extrusion system. This extrusion kit does not perform spectacularly without modification. This has been partially remedied by REV as they have developed a second iteration of their slide kit, which has much better tolerances on the Delrin sliders.
Still, you’ll see a lot of competitive teams use this kit with multiple modifications, such as adding lots of lubricant and mounting the sliders differently. Teams have also 3D printed their own sliders, though this is not a great idea for teams without much 3D printing experience. One of the biggest issues with the stock REV kit is the tendency of the slides to bind. Additionally, since the only thing attaching one extrusion to another is the plastic slider, the REV slides are not particularly sturdy, and require crossbeams to keep alignment.
Overall, this kit is lightweight, simple, and cheap. It can be a good start for teams using REV and needing a linear extension, and is generally usable out of the box. However, it is not very smooth and only achieves its maximum potential when modified and tweaked.
REV has complete guide on how to rig the linear slides
Easily interfaces with REV building system
Lightweight, should be used for light/medium loads only
If tweaked, can be a very efficient linear slide
Does not perform perfectly out of the box
Can flex under load, needs additional support
May need some modifications such as custom sliders
Actobotics X-rail Slide Kit¶
The X-rail Slide Kit works well out of the box. However, the main caveat is that the kit has a very low maximum load (2lb. at maximum extension).
Teams will have to keep their designs on this kit particularly lightweight. This slide uses elastic retraction through the use of surgical tubing, which means that instead of having both an extend and return string, there is a retraction force applied at all times. This helps simplify tensioning and spooling, however, limits how fast the slide can be run. Additionally, the plastic end caps have a reputation of breaking regularly because they endure shock load every time the slide extends to maximum. 3D printed alternatives may be more sturdy than the stock end caps.
It is highly recommended that teams add an additional set of v-groove bearings at the end of each piece of extrusion to give each stage an additional point of support. This will increase load capacity and possibly smoothness.
Easily interfaces with Actobotics building system
Elastic retraction is a simple way to retract
Should be used for light/medium loads only
Will flex under load, needs additional support
Elastic retraction slows down extension speed and retraction will be slower than string retraction