Low-back-clearance robot speed reducer

The invention discloses a low-back-clearance robot speed reducer. The low-back-clearance robot speed reducer comprises a wheel base, a needle tooth shell, a first cycloidal gear, a rolling needle, a second cycloidal wheel, a gland, an elastic piece, cross slide blocks and a crankshaft; two cycloidal wheels are provided, and form a phase relation of 180 degrees; the cycloidal wheels belong to multi-point engagement transmission relation with the needle tooth shell and the rolling needle; two cross slide blocks are provided, and form a double-cross-slide-block structure; groove types of the slide blocks are trapezoidal groove structures; a clearance is automatically compensated through the elastic piece; and the rotating center of the crankshaft is coaxial with the wheel base and the gland. The low-back-clearance robot speed reducer adopts single-crankshaft cycloidal needle wheel to drive, adopts the cross slide block structures to output, belongs to first-grade speed reduction transmission, and has the characteristics of high efficiency and low back clearance.