Strong Arm - Fully articulated - Robotic Arm built with Mindstorms by Ricardo Oliveira aka blu3-fir3
About this creation
Video: http://www.youtube.com/watch?v=zHT1J8Aun_4
Specifications and dimensions:
Element: 971 (arm) + 185 (control) = 1156 pieces
Axis: 5
RCX: 1x
Motor: 6x
Gear: 64
Sensor: Touch sensor 3x
Weight: +/- 1.6 kg (with RCX and some extra batteries to keep the balance)
Maximum length of arms: 43 cm
- with its back (horizontal): 52 cm
Vertical travel : 0 – 51 cm
Horizontal travel : 9 – 43 cm
Shoulder angle : 90 degrees
Elbow angle : 180 degrees
Wrist angle : 180 degrees
Wrist turning (ignore cabling) : 360 degrees
Turntable angle (ignore cabling) : 360 degrees
My lego arm has different and independent parts. It has 3 axles which movement is similar to each other: they have the same torque and the same velocity. I hope you understand these terms: the mechanism makes the axles turn once when the axle of the motors makes 240 turns! This means that we have a very slow movement but very strong; with a lot of torque.
(In case of not being used to build robots:
You can see these relationships through calculating the relation between the number of teeth of each gear. Look at the picture 0074: the first gear with 12 teeth is connected to a 40t gear; so, we have a ratio 12/40; then there is a worm gear in which, one turn makes the second connected gear turn 1 tooth. Thus, you need to turn it 24 times to make the 24t gear turn once. Finally, there is a 8t connected to a 24t gear = 8/24 = 1/3.)
I’ve built these mechanisms to the 3 axles that are responsible for the vertical travel. This allows you to turn two axles in opposite directions, making a balance with the object taken.
The shoulder seems not to have the same mechanism, but it has. The point is that I have duplicated the mechanism: 2 motors – built in opposite positions, like symmetric mechanisms.
Besides these 3 mechanisms, there are a control of the rotation of the shoulder and a control of the wrist, to split liquid, for instance.
In the pictures you see a 6AA battery box in the base. I used it to get more weight to the balance.
Manual control:
To make easier the control of the arm, I have made a joystick. This also happened because I didn’t have 2 RCX’s at that time. The joystick uses 2 pieces which control the direction of the motors (http://www.peeron.com/inv/parts/6551). As you can see in the picture 0127, it controls the wrist and the shoulder. When the joystick is in the standard position, the “switches” do not let the motor rotate. This is made without any lego controller; I have connected those two pieces to an AC/DC adaptor (pic. 0126). I hope you know what I mean.
You can use a second RCX to do this work and also to control the lamp placed on the hand. Instead of using those two switch pieces, you can use either rotation or touch sensors.
Feel free to ask anything you need.
