Telescoping Arm

[ArmoredFairy698]

With all the robotic arm designs out there...has anyone created a telescopic arm that looks like a telescope?

(As in 2 or more cylindrical pieces that extend out of one another...think toy lightsabers, how they fit inside one another and extend to a larger length).

If you have created one, would you be willing to share how you automated it? Did you use some sort of gear box? Pneumatics? A pulley system?

I'm looking into making one, but I don't know how to keep it entirely self contained and automated. It needs to be some sort of interior mechanism that has the ability to move the "arm" up and down.

Is there any way a servo motor could be brought into this and be used to power the up and down motion of the arm?

Any ideas/suggestions are welcome and appreciated!!

[Collin Fultz]

Originally Posted by ArmoredFairy698

I'm looking into making one, but I don't know how to keep it entirely self contained and automated. It needs to be some sort of interior mechanism that has the ability to move the "arm" up and down.

A nu-matic could get the job done, and be fairly self contained. The only problem is the speed. Depending on the length of the extension, it could get pretty slow (and fairly large in a diametrical sense).

Good Luck!

[sanddrag]

A servo (at least the ones in the kit) is far to small for any task like that. 980 has been the masters of telescoping arms since 2003. In 2003 it was a series of probably 6 or so metal tubes that all slid inside each other. OD of one is the same (slightly smaller actually) as the ID as the next one up. It was mounted at the top of the robot and tilted down stowed. Then when you lift it up byt the time it reaches level, gravity has fed it all the way out. Check out some videos on this page http://www.team980.com/Team980_2003.html

Their telescoping arm this year is a serpentine driven uinit powered by a window motor. They milled a slot through one side of round tube and then they attach a timing belt to one end of the tube, pass it over a large toothed pulley on the motor, and then run it to the other end of the tube and attach it there so it is powered both ways. This tube with the belt inside slides inside of a tube just larger than it. There are a couple idler pullies to keep the whole system running tight.

[Arefin Bari]

Team 108 SigmaC@ts made a telescoping arm like that back in 1997? I wasn't on the team at that point, but I did see the robot and the telescoping arm. It was 3 stage telescoping with cylinders. It was a basic pulley system. There were slots on the aluminum tubing which was made for the cable. The telescoping arm also used a turn spring to bring it back down. Unfortunately I dont have any drawings or pictures of that arm with me right now.

[EricH]

Originally Posted by sanddrag

A servo (at least the ones in the kit) is far to small for any task like that. 980 has been the masters of telescoping arms since 2003. In 2003 it was a series of probably 6 or so metal tubes that all slid inside each other. OD of one is the same (slightly smaller actually) as the ID as the next one up. It was mounted at the top of the robot and tilted down stowed. Then when you lift it up byt the time it reaches level, gravity has fed it all the way out.

I remember that one, they held it just slightly extended at the start (so it wouldn't latch). When start came, the arm would sweep up and around, extending as it went. After dealing with the boxes, it went to vertical and slid back in and latched. Nearly creamed people before it was brought under control by the programmers, which didn't take terribly long...

[dubious elise]

269 used a triangular telescoping arm last year (2004) with loads of success. Ask Ricky Q. or Robby if they have any plans for it or a more coherent explanation of how it works.

[Jeff Rodriguez]

RAGE had a square telescoping arm this year.

[Meyerman]

in 1999 team 153 used one im pretty sure its been a while scine ive seen the bot but im pretty sure they used one, but they are dead now soo i dont think thats gunna help much.
R.I.P. Team 153- Somerset County Vo-Tech-"Smokey" 1998-2001

[ArmoredFairy698]

You guys are so awesome! Thank you so much for the ideas and the tips, they are very, VERY helpful. I look foward to trying to build this thing.

Thanks again to all of you! Your replies were a HUGE help to me!!!

[Meyerman]

we maybe trying to get some stuff from 153 for a summer camp we might run if we do go there and got that bot i will get you pictures.

[ArmoredFairy698]

Pictures would be great.

I think I am going to go with a sort of pulley mechanism, attached to a small winch that sits in the middle of all the cylinders. My telescope will be cylindrical. I will create a removable base that the motor/winch system is mounted too, so that it will be detachable for repairs.

My next question is....if I create the cylinders to be VERY low friction, would a servo motor contain enough power to turn the winch system in order to lift the cylinders? I know it would be alright to bring them back down, because gravity will play a large role in the job. The rest is just letting the winch out slowly enough so that the parts do not crash back into the base. I'm worried about those plastic gears that come in the small servos though...they are small and kind of fragile, and I've seen what happens to plastic gears... *SNAP* The teeth break off if too much strain is put on the gears, and sometimes they no longer mesh properly (which also causes teeth to snap off). So what do you think? Can a servo handle the power needed to bring the telescope out vertically? Or is something like a DC motor better for this job?

What do you all think?

(And thanks so much for the continued help, the links to the videos, and the pictures!) I'm very grateful.

[sanddrag]

Originally Posted by ArmoredFairy698

My next question is....if I create the cylinders to be VERY low friction, would a servo motor contain enough power to turn the winch system in order to lift the cylinders?

Most definitely not. Technically, you could pull a semi-truck with an electric toothbrush motor if it was geared low enough, but the amount of time it would take would increase drastically. A servo is definietly not the tool for this job. First of all, a servo is designed to go to a certain position and hold it, not continuously rotate. So I assume you mean a servo modified for continuous rotation more like a gear motor. You could gear it way down but by the time you got low enough to power the arm the efficiency in each stage being multiplied will have eaten up all your torque, plus you'd have to go get lunch and come back before you'd ever see the arm move.

If you could explain more specifically what you are trying to do I'd be more than happy to point you in the right direction as far as selecting a motor and actuating mechanism. I think you are on a good track by selecting cylindrical. It may be a little more difficult to actuate but it will be easier to slide. If you take a pair of calipers to your local metal store, you can find some tubing that fits good inside another one, perhaps for several stages.

PS. Everything I said above is reliant on the assumption that you are talking about a full size FRC bot. If it was a vex, a servo motor would probably work.

[ChrisH]

ArmoredFairy698

The basic question is how much WORK you want to do while extending the telescope. Work=Force*distance. So figure out what you want to pick up, how much it weighs and how high you want it to go. The next thing to think about is how fast you want the Work done. This tells you how much Power will be required, because Power=Work/time. Power is also equal to Torque*Rotational Speed. By using these simple relations you should get a good idea of what size and speed of motor will do the job you have in mind, and how much gear reduction will be required to get it to work.

A couple of other things to consider. Electric motors are happiest if they are running at 75% of free speed or 25% of stall torque (typically they are the same place on the torque/speed curve) . So you want to plan around those numbers. You also need to subtract a certain percentage of available torque to allow for losses in the sliding system. Once you have a rough idea of how much power you need and what the moments will be, it would also be a good idea to estimate the weight of your arm and include that in your work calculations.

Yes, I know you just calculated stuff, but remember "Design is an iterative process" get used to doing this sort of thing over and over again. I highly recommend learning to use a spreadsheet for this sort of thing. It makes it a lot easier.

If you give us a better idea of what you are trying to do, we can walk through the calculations here. Doing so will be a good learning experience for all.

[Not2B]

Originally Posted by sanddrag

PS. Everything I said above is reliant on the assumption that you are talking about a full size FRC bot. If it was a vex, a servo motor would probably work.

Ah good you note that. I used one of the Vex motors (looks like a little servo motor). I made a 3 stage extending arm with square channel and fishing line. It was painfully small to thread, but it worked - powered up and down.

Also depends on what kind of servo motor you are talking about. Hobby servo motor? Or an industral servo motor? The servo motors we use on Electric Injection Molding Machines are powerful - the ones I've played with generated 1000 tonns of clamping force in a second or so.

[David Guzman]

This might help you out a little bit.

http://www.chiefdelphi.com/forums/sh...298#post388298

When we prototyped this arm we first made a model with cylindrical PVC and a string. The power you are going to need depends on the weight, what you are lifting and the friction that there is going to be. I can also agree that the servo is not enough unless we are talkin about a small tyoe of VEX robot. No matter how much friction there is your motor has to at the least be able to lift the waight of the stages and whatever it will carry.

More informayion would be helful.
Dave