# How would rotary motion be converted to linear in robot?

1. Aug 7, 2017

### Tabaristiio

How would the rotary motion of a robot / exoskeleton arm be converted into linear motion so that the arm can move objects and lift weights in a conventional manner, such as when people are weight lifting in a gym?

2. Aug 7, 2017

### Staff: Mentor

There are an infinite number of ways to do that. You'll have to be more specific.

Think of how rotary motion of your shoulder and elbow produce linear motion.

3. Aug 7, 2017

### Tabaristiio

So how would the rotary motion of an electric motor allow a robot / exoskeleton arm to lift weight linearly? What is the best method in this particular situation?

4. Aug 7, 2017

### Staff: Mentor

It is up to you to define best. Cost, weight, strength, range, speed, durability, power consumption, other possible motions?

Below is one of thousands of methods. It is best in some cases, not best in others.

I don't think you should use an internet forum to do your design project for you. Propose your own solutions. Post them and tell us why you think those are best.

5. Aug 7, 2017

### Tabaristiio

When I wrote 'best', I was referring to purely the robot / exoskeleton itself. This ignores any other factors such as cost because this question was purely a theoretical question that ignores practical factors such as cost. So what I meant by 'best' was what was the best way to convert rotary to linear motion in the exoskeleton / robotic arm so that it gives as many benefits as possible in relation to moving / lifting objects, such as comfort, strength, speed and etc.

Also, I asked the question purely out of curiosity whilst researching. I didn't intent on pursuing any projects related to my question. I simply wanted to learn how specific aspects of an electric motor and a robot / exoskeleton works. I couldn't find much elsewhere.

6. Aug 7, 2017

### Staff: Mentor

In that case, I recommend searching exoskeleton on YouTube. There are many designs there. Many use hydraulics rather than electric motors. But study of the pictures show how they convert rotary to linear.

7. Aug 7, 2017

### jim hardy

You're asking us to imagine what you have imagined. I have no idea what that is.

or

8. Aug 7, 2017

9. Aug 7, 2017

### tygerdawg

Some well-defined methods come to mind:
• rack & pinion of course as previously mentioned
• ball screw assemblies
• motor driven hydraulic pump driving a hydraulic actuator cylinders
• ditto for pneumatics cylinders (also could include inflatable bladder mechanisms)
• gearmotor-driven spool and cable
• rotary cam and linkage mechanisms
• crank-slider mechanisms

10. Aug 10, 2017

### Tabaristiio

Thanks for an actual HELPFUL response / answer. I'll research and look into those things in more depth.

11. Aug 10, 2017

### Tabaristiio

Would you be able to provide an explanation and an example of how rack and pinion can be used in a robotic / exoskeleton arm to convert rotary motion of an electric motor into linear motion when lifting / moving objects linearly with the arm / hand? How / where would the rack and pinion be assembled relative to the arm and how would the rotary motion of the motor be transmitted?

12. Aug 11, 2017

### tygerdawg

It's not wise to attempt to do mechanism design via email or forum. You original question was rotary-to-linear, wasn't it? An idea for rack & pinion: the rack is attached to cables, around a pulley, which is attached to pivot links for angular motion of the pivoted link. But it seems more complicated than other suggestions.

13. Aug 11, 2017

### jim hardy

How about if you draw a picture of the robot arm and hand you are trying to control ?
This isn't some "I've Got A Secret" parlor game.

Here's the common man's tried and true rotary to linear motion converter.
Note it's a variant of rack and pinion, just the rack is wrapped around a spool..

Or you might think the other way - rack and pinion is just spur gears with one of them straightened out.