Linear Slide insert
Carriage and bearing block that runs inside an extrusion. The reusable building block for cascade lifts, arms, and extensions — design it once and it shows up on every robot.
Before you start
Decide which extrusion family you're committing to. Standard FTC choices are U-channel, box-tube, or MGN railU-channel is cheap and forgiving but flexes. Box-tube is stiffer but heavier. MGN rails are precise and frictionless but expensive and need a flat mounting surface.; pick one and stick with it across the robot.
1Set the inner-extrusion dimensions in a sketch
Open a part studio and draw the inner profile of your extrusion. The carriage has to slide inside this profile with consistent clearance — usually 0.3–0.5 mm per side.
If you use goBILDA 1106-series U-channel, the inner ID is 24mm. Build that as a variable so future-you can swap channel sizes by changing one number.
2Model the carriage plate
Extrude a plate that fits the inner profile with your clearance gap. Cut mounting holes on a 5mm × 16mm gridAlmost every COTS FTC part bolts to a 5mm × 16mm hole pattern. Cut it on every plate by default so you can re-mount mechanisms without redesigning the carriage. across the face that faces outward.
Leave the inside face flat for mounting bearing blocks.
3Add the rolling bearing surfaces
Mount four small bearings (or roller wheels) to the carriage, one near each corner. They roll against the inner walls of the extrusion and keep the carriage centered.
Preload the bearingsIf the bearings are dead-flush you'll have slop. Mount two of them on a slotted hole so you can shim or push them outward until they preload against the extrusion walls. against the inner walls so the carriage doesn't rattle.
4Add a string anchor point
Drill a single 3mm hole near the top of the carriage. That's your string-pull anchorWhatever drives the slide — a winch, a cascade pulley system, or a rack — eventually pulls on the carriage. One clean anchor point is better than designing for one particular driver now. for whatever lift system you build later.
5Run a stress check in the assembly
Drop the carriage into the extrusion. It should slide the full length without binding. Tilt the extrusion in the assembly's Play view — gravity should drop the carriage smoothly with no catch points.
If it catches, the issue is almost always asymmetric bearing positions. Recheck that the four bearings sit on a true rectangle.
This carriage is now the foundation for every linear extension you build. Cascade lift, arm extension, hang mechanism — they all bolt onto a variant of this part.