Belt-driven vs. screw-driven linear actuators

A belt actuator (LYNX SBA) moves a carriage with a toothed belt over pulleys; a screw actuator (LYNX LSA or BSA) moves it with a rotating screw and nut. Belts are for speed and distance: 850–2,500 mm/s, travels to 1,275 mm, loads to 50 kg with a gearbox. Screws are for force and holding: 20–500 mm/s, travels to 500 mm, self-locking on vertical axes. Almost every multi-axis system uses both — belts on X and Y, a screw on Z.

How each one moves the load

Belt. The motor turns a drive pulley; a steel-reinforced polyurethane belt carries the carriage. One motor revolution moves the carriage one pulley circumference — about 65 mm on an SBA45 — so speed is high and the motor spins slowly, but the belt stretches slightly under load and there is no mechanical holding when power is off. Travel is limited only by rail length. Screw. The motor turns a screw; a nut on the carriage advances one lead per revolution — 1 to 25.4 mm. Force is multiplied by the small lead, position is held by friction (lead screw) or by the motor and a brake (ball screw), and the screw's critical speed limits long travels, which is why screw actuators top out around 500 mm.

The decision in three questions

Does the axis move more than 500 mm? Belt. No catalog screw actuator goes further. Does it need to hold a load vertically, or push against something? Screw — a lead screw if the load must stay put with power off, a ball screw if the axis cycles continuously and can carry a brake. Does it need to move faster than about 300 mm/s? Belt. A 25.4 mm-lead screw reaches 500 mm/s but only at 1 kg; a belt does 850 mm/s at rated load. If none of the three applies — a short, horizontal, moderate-speed axis — the screw is usually cheaper and more precise under load, and the belt is usually simpler.

Why gantries use both

A pick-and-place gantry travels far and fast in X and Y and short and forceful in Z. The LYNXSYS kits and every system the engine builds therefore put belt actuators on the horizontal axes — SBA45 for payloads to 7 kg with a gearbox, SBA60 to 10 kg, SBA90 to 50 kg — and a lead screw on Z, where the LSA45 or LSA60's self-locking nut holds the tool over the work when the e-stop drops power. The engine sizes the belt axes on their torque curves and the screw axis on its lead and load rating in the same pass, and it caps the whole system's payload at the Z rating.

Belt stretch, gearboxes, and what the engine checks

The belt's elasticity shows up as a small positioning spring under acceleration, which is why belt axes carry a repeatability spec but not an accuracy spec at speed, and why heavy payloads on a belt get a 3:1 or 5:1 planetary gearbox: the gearbox multiplies torque, reduces reflected inertia by the ratio squared, and brings the inertia mismatch under the 10:1 limit that keeps a stepper from losing steps. The engine computes that mismatch for every belt axis and adds the gearbox only when the numbers require it.