Designing a Power Transmission System

Hello all, i'm an adult learner from Belfast, Ireland studying for a HNC in manufacturing engineering, and I need your help. I have been asked to design a transmission system for a mechanical arm. This arm will carry locking nuts between two machines - a distance of 12 metres. The arm itself weighs approx. 66lbs. It can carry up to 121lbs at a time. 60lbs of this weight will be the nuts, leaving just over 60lbs for the total transmission weight - assuming the transmission is mounted onto the arm. these figures are entirely hypothetical and can be changed to suit if necessary. The problem I have is not locating the necessary belts/motors/sprockets etc., but calculating how to put them together to make this work, i.e. speeds/weights/distances etc. I hope I have provided enough information.