rapik

Thanks! You are right. To transmit the second function I use two "empty" differentials connected with this ring. I didn't get your idea about using the differential to reduce the slack... Can you explain it, please? Yeah, it seems to be the easiest solution. But I wanted intentionally all motors and NXT to stay at the bottom part. No. Thanks! This topic actually is what I needed :)

Thank you for the link. It's cool construction! However I was not able to find there any reusable ideas :) This arm has motors on the rotating part. And it cannot rotate to one side infinitely because of connections (both pneumatic and electric) going from the base to the top.

It is not solved yet. When the bottom part is rotating then both other actuators are slightly rotating too. I was thinking that nxt should be programmed to compensate these rotations. In this model this parasitic rotation can be critical for the linear actuator, which I have used on the end of the arm, since it has limits.

I wanted to create a robotic arm with three motors, where all motors are fixed to the base. What are the possible solutions? The problem I faced: if the arm should rotate over 360 degrees, then it's not obvious how to utilize two other motors. Rotations from one motor is transferred via the axis. Rotations from the second - using same axis but with help of special parts, that can freely spin over the axis. I came out with the following construction: Side view on the central axis: Placing of motors: A video showing this arm (I used my construction to take a part in a German non-Lego contest):