does it need to be a stationary arm that can reach 5m or can it be a wheeled robot that can pick up a weight and move with it.

100g is not much at all. you can look at my description of Ray1 on my site, or go to my links page to find other peoples description of how to build a small wheeled robot.

there was an article in a past issue of Servo magazine about building a servo driven gripper. it was meant for soda cans, but the basics are there.

RC control is easy. you can either do a standard RC car chassis with a single speed control and a steer servo, or you can mix rudder and elevator to run 2 speed controls to make a tank style differential drive.

contact me through here or my site and we can talk about more details.

A robot is a system of individual mechanical and electrical components controlled by a computer program. You could program your robot and have it run automatically, or in your case it sounds like you would like to remote control it. For the wireless mechanism, you need a simple remote control unit you can buy at many electronic stores, it will need a control for each joint of the robot. The robot itself will be made out of metal or wood arms, metal will be much more resilient. The joints should be motors that are controlled by your remote. Make it like and arm, ie it should have a shoulder joint, a rotation at the base, an elbow joint, a wrist joint, and a gripper at the end which are all controlled by your remote. The building of the machine and aligning all the joints will be the most difficult part of your robot. It should easily handle 100gm, the distance of 5m will test your mechanical design ability to keep the arms from swinging or bending over the large distance. Good luck!