rapik Posted June 25, 2011 Posted June 25, 2011 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): Quote
Parax Posted June 25, 2011 Posted June 25, 2011 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. Did you solve the problem, of rotation transferring to the other actuators, mechanically, or by programming it out at the nxt? Parax. Quote
DLuders Posted June 25, 2011 Posted June 25, 2011 For ideas, TechnicBRICKS had an article about a "Lego PF 3D Light Show" using Power Functions (PF) motors for 3-dimensional movement. If you don't mind the BASE ITSELF moving, perhaps it could be replicated using your NXT motors: Quote
rapik Posted June 25, 2011 Author Posted June 25, 2011 Did you solve the problem, of rotation transferring to the other actuators, mechanically, or by programming it out at the nxt? 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. Quote
rapik Posted June 25, 2011 Author Posted June 25, 2011 (edited) Have you seen Sariel's "PF Arm" for ideas? 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. Edited June 25, 2011 by rapik Quote
grindinggears Posted June 26, 2011 Posted June 26, 2011 I wanted to create a robotic arm with three motors, where all motors are fixed to the base. What are the possible solutions? Congrulations to your MOC. I hope you will win that contest! Having three functions of which one is rotation of the turret means that you have to transfer two functions through one turntable. I can't see your solution exactly but it looks like you transmit the second function coaxial to the first which is the most common way of doing that. You can reduce the slack in the transmission by using one differential inside the turntable. Greetings from Greifswald! Quote
Silcantar Posted June 27, 2011 Posted June 27, 2011 Possibly the simplest solution would be to put all the motors and the NXT in the rotating top part of the tower. That would eliminate the need to transmit any rotation through the turntable. Many of the best Lego robotic arms I have seen used this solution. Quote
rapik Posted July 3, 2011 Author Posted July 3, 2011 Congrulations to your MOC. I hope you will win that contest! Having three functions of which one is rotation of the turret means that you have to transfer two functions through one turntable. I can't see your solution exactly but it looks like you transmit the second function coaxial to the first which is the most common way of doing that. You can reduce the slack in the transmission by using one differential inside the turntable. Greetings from Greifswald! 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? Possibly the simplest solution would be to put all the motors and the NXT in the rotating top part of the tower. That would eliminate the need to transmit any rotation through the turntable. Many of the best Lego robotic arms I have seen used this solution. Yeah, it seems to be the easiest solution. But I wanted intentionally all motors and NXT to stay at the bottom part. Did you see this video? No. Thanks! This topic actually is what I needed :) Quote
jovel Posted July 3, 2011 Posted July 3, 2011 It''s possible but pretty tricky. You need to use differentials. One for each function that goes through the turntable. Notice the 14z : 12z ( old to new style bevel ) combination. Idea by Alexander Burgers. Quote
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