How to apply loadings through clump with an constant velocity

Hello, everyone,
Thank you for your help all the time. Now, I want to simulation the single particle breakage, and I want to apply the loading with clump instead of wall for the custom contact faces.

For wall, it is easy to set a constant velocity with “O.bodies.state.vel”, however, for clump, O. bodies.state.vel just can provide an initial velocity instead of a constan velocity. Although I can use PyRunner to set velocity every step, it is difficult to keep a constant velocity and sometimes the movement of loading plate is very slow, even stopped due to the uncontrollable speed.

I want to know how to apply a constant velocity to a clump as a loading plate.

Thanks a lot!