Mysterious Screw

[MrForbes]

Ball screws have been used in automotive steering gears for the past 50 years or so....

[spazdemon548]

Ball Screws have less friction and maintain a lot higher linear tolerance than lead screws.

[MrForbes]

They can also handle a heavy load with marginal lubrication.

[bduddy]

Originally Posted by synth3tk

Actually, the primary operators of this device should be those who cannot land the lead position for "Time Waster", whose sole purpose is to use the Igus track throughout the entire season.

Hmm, your team is organized different then mine... I always thought the head time-waster got the screw, and the assistant was stuck with the track... especially considering we actually used the track this year!

[Smaug]

you will find lead screws and ball screws in machines such as lathes and mills.
they are both do there job very well as for which is better it depends on what you are doing i have been told that for mills and lathes if set up right ball screw tend to be more accurate but u can get real accurate lead screws as well.

[Dick Linn]

Lead screws can be made exceptionally accurate. Moore Tool developed jig boring machines that are very accurate and they used lead screws. Richard Moore has been recognized as the man who "gave the world’s industry an additional decimal place of accuracy!"

His son Wayne wrote the book "Foundations of Mechanical Accuracy".

I don't know what they use these days, but they have jig grinders that will position within 90 millionths of an inch in 18 inches of travel.

[Taylor]

Originally Posted by bduddy

Hmm, your team is organized different then mine... I always thought the head time-waster got the screw, and the assistant was stuck with the track... especially considering we actually used the track this year!

From what I hear, on team 829 the Head Time-Waster becomes the Lead Button-Maker.

[Teched3]

Ball screws provide less friction in the mechanism, and you could find them at the end of older vehicles and truck steering columns before rack and pinion became the norm.

[joshsmithers]

As a warning: MULTIPLE leadscrews are a MUST for any build team if you have too many freshmen. Just tonight, in fact, we had a minor argument over who's turn it was to hold the "cool screw thing."

We've never used it, but it is notorious for being either the the most useful or useless thing in the KOP. Come to think of it, didn't 330 use it in 2007 inside their arm to activate their claw?

EDIT: Nevermind, that was pneumatically actuated.

[Akash Rastogi]

Hehe, I found one application that I think I need it for.

Need help with this. So for robotics, I'm creating a simple manufacturing workcell that autonomously places sheets of aluminum into a dye and then pneumatics come down to just bend the sheets. What I wanted to use the lead screw and a motor for is to have a custom made vice run on a bed (much like a vice would on a mill) to come forward and make sure the sheet is positioned correctly but I don't know how to set up the lead screw to do this. Also which motor should I use to have the sheet of metal positioned quickly using the vice and screw? Thanks, any help would be appreciated.

[EricH]

Originally Posted by joshsmithers

We've never used it, but it is notorious for being either the the most useful or useless thing in the KOP. Come to think of it, didn't 330 use it in 2007 inside their arm to activate their claw?

EDIT: Nevermind, that was pneumatically actuated.

330 hasn't used one on a competition robot since 2002. Then they used two small ones...and come to think of it I'm not even quite sure they were leadscrews. I do know they came out of a gearbox that we haven't gotten since then.

The leadscrew's only function other than wasting time is to turn rotational motion into linear motion. While it is theoretically possible to go the other way, reality wins and it's pretty hard to do so.

[MrForbes]

But you can have fun with the concepts of friction and angles by figuring out just how steep the thread angle has to be to keep it from backdriving.

The fancy coating, low friction plastic nut, and multiple threads make it so that the KOP lead screw can indeed be back driven, but normal nuts and bolts can't.

[DonRotolo]

Originally Posted by Akash Rastogi

I'm creating a simple manufacturing workcell that autonomously places sheets of aluminum into a dye and then pneumatics come down to just bend the sheets. What I wanted to use the lead screw and a motor for is to have a custom made vice run on a bed (much like a vice would on a mill) to come forward and make sure the sheet is positioned correctly but I don't know how to set up the lead screw to do this. Also which motor should I use to have the sheet of metal positioned quickly using the vice and screw?

First, Pneumatics are not a good choice for bending metal, you cannot get the power required. Hydraulics are the better choice. But, that's not your question.

To use the leadscrew as a positioning element, you first need to create the system that drives the leadscrew - for example a window lifter motor. Then, you need a system to know the exact* position of the nut on the screw. Using a PID loop, you drive the motor until it is in the desired location.

*Exact is relative. 0.001" is hard to do with a quadrifilar leadscrew, 1/8" should be possible.

For repeatable. low-load positioning, you should consider pneumatics. Use an adjustable end stop on your mechanism to set the exact spot to push the material to. That also actuates a switch, which makes the hydraulic press come down onto the die and do whatever you want. Then another thingus comes up and pulls the workpiece off while a new one is being put on.

[ks_mumupsi]

take a look at the 2016 robot when you get a chance... we will post more details when we get to competition.
you can also take a look at 2753's arm as we have a joint effort here.

That lead screw is an integral part of our design and it works amazingly well.

[Al Skierkiewicz]

Large versions of this little screw are used to adjust position on satellite dishes all over the world. I work with one dish that has a lead screw for elevation and it is connected to a 3/4 HP motor with an electric brake. The screw is about 4' long and at least 2" in diameter. Another dish that is much larger has two, one for azimuth and one for elevation. Both can be operated by a hand crank or electric drill attachment. The dish is 6 meters in diameter.