Metal Ball Omni-Directional Caster Wheel

A differential-drive robot needs a third contact point that does not fight the two driven wheels for direction, and that is the entire job of a ball caster: a free-rolling steel ball in a zinc-plated housing that supports the chassis's weight while adding effectively zero resistance to turning. Unlike a fixed caster wheel, the ball rolls equally in every direction, so it never binds or drags during a sharp turn the way a wheel-based caster can.

Rated for 10kg, well past what a typical hobby chassis weighs, and the 38mm mounting hole pitch matches the standard pattern most acrylic and plastic robot chassis kits already drill for - a straightforward bolt-on rather than a custom mounting bracket.

Standard third or fourth support point on 2WD and 4WD differential-drive robots, line followers, and any small wheeled robot build that needs a stable, low-friction trailing point.