# Expandable Arms (like Transformers)

1. Apr 2, 2005

### PrudensOptimus

Hello,

Anyone who is kind and knowledgeful please provide me some links and/or detailed explainations on how to produce Expandable Arms... The reason is that I am interested in how to create Arms which can be expanded using Motors, and/or other types of technicles. Arms with such capability can reduce space. (ie. it can prostrate downward in a "bent" position)

2. Apr 2, 2005

### Integral

Staff Emeritus
I am not sure I understand what you want. Here is a link to robots with "expandable" arms. That means they can reach out several feet to pick up and move very delicate objects. These guys can be taught to return to the same spot time after time with an accuracy of a few microns.

3. Apr 2, 2005

### PrudensOptimus

In Engeinnering, how do you produce an arm that can be expanded? Say when a motor is turned on, the arm raises.

4. Apr 2, 2005

### brewnog

A nice simple example would be a scissor jack which you might find in the boot of your car.

5. Apr 4, 2005

### Cliff_J

Break this down to the simple machines level and think about it.

A robot arm will have joints for motion, either rotation or sliding motion.

An electric motor rotates and with gears can rotate an axle attached to the arm.

Connect the motor with small gear to a row of gears in a straight line (rack) and now you have a rack and pinnon for linear motion.

Connect the motor with a sprocket and chain or pulley and rope and you can accomplish the same rotation-linear motion conversion.

Connect the rack and pinnion, chain, or rope to a arm that rotates and you can convert the linear motion back into rotational.

To pivot an joint the easiest choice in a robot arm would be a worm gear. It offers good mechanical advantage and has the advantage of only allowing movement by the electric motor.

6. Apr 4, 2005

### PrudensOptimus

Thanks for the prompt responses guys,

Cliffj, could you provide an illustrated example of what you are referring to? I understand it, but I understand it better with step by step and visual. Hopefully it will not cause you too much trouble.

-great thanks to all

7. Apr 4, 2005

### Integral

Staff Emeritus
In many industrial robots (like the Genmark which I linked to above) the z axis motion uses a lead screw/ball nut type drive. To see this take a screw and nut, thread the nut onto the screw, now place one end of the screw on a table so it cannot move, hold the nut so it cannot turn and simultaneously turn the screw. You will see the nut move up and down. So in your robot you would mount the screw vertically with a motor on one end. Fasten the platform you wish to raise to the nut. Now use your control systems to turn the motor on and off. Some safety features would be top an bottom limit switches at the end of mechanical motion. The switches can either directly control power to the motor or provide a input to the computer which shuts the motor down when the mechanism is about to do damage to itself.