Pulley and Belt System Adapters

[snyder.wths]

For our shooting system, we are trying to operate it with a pulley and belt system. With our prospective motors, we would need to adapt from a 1/8" shaft diameter to possibly 1/4" -1/2" (the final diameter from the pulleys is subject to change). So, I am asking if anybody has an effective way of adapting from a 1/8" shaft diameter to any greater diameter. Any products or tips will be helpful.

Here are two links to two of our prospective motors:
-http://banebots.com/p/M7-RS775-18
-http://banebots.com/p/M5-RS550-12