telescoping arm
 

I am wondering if anyone has ideas for actuating a telescoping arm made of say square tubing. I am assuming that filling it full of air pressure would be illegal. How could three or more pieces reach 10 foot to hang a hook on the horizontal bar?http://www.chiefdelphi.com/forums/ne...ewthread&f=22#
http://www.chiefdelphi.com/forums/ne...ewthread&f=22#

Re: telescoping arm
 

My team built a telescopic arm for last year's Stack Attack, also made out of square material..

http://www.chiefdelphi.com/forums/sh...&highlight=843

:]

Re: telescoping arm
 

My team has built them in the past (shudder) and they are "extremely complex to build" not that I would say that but I trust the 4-5 engineers who almost collapsed into fits when we said moving arm to know what they are doing. plus if you work it right you might not need a telescoping arm to begin with....

Re: telescoping arm
 

you could make a pulley system with cables running through the telescoping components with a few motors. my team was contemplating on doing that.

Re: telescoping arm
 

ahmed: Nice photo of your bot from last year. How did the arm extend?

did it use cables and pulleys? how many stages did it have?

Re: telescoping arm
 

Actually, quite sadly, it's my first year on the team. I *almost* certain though it used cables and pulleys :]

I'll try and check with my teacher

Re: telescoping arm
 

that works pretty well as long as there is NO WAY for the cable to jump off the pulley - it has to be covered or the cable must have no where else to go.

this is how fork lifts raise way up BTW. same idea

Re: telescoping arm
 

http://www.valleytech.k12.ma.us/robo...1Robot2001.jpg

this has five stages half of the 1/8" cable is inside of the machine. This was a push pull system. 2 different cables. one to pull out and one to pull in. This is not hard to do at all. the hardest thing was to make the squares out of thin alum. we went 14' with this machine. we went 9' the year before.


we were only 17"when the machine was completely closed. this kept our center of gravity pretty low.

Re: telescoping arm
 

We had a non functioning telescoping arm for our 2002 robot. It would extend to almost half the field but it would always jam. We did it just by stringing it and then using the motor to wind up the wire.

Re: telescoping arm
 

For the Canadian teams, see if you guys can get the engineers who worked on the arm for the Space Shuttles to help you guys. :)

I'm sure they'll provide the best input.

In fact, how can I get ahold of them?!

Re: telescoping arm
 

That arm was designed over 25 years ago (Space Shuttle)

those guys are all walking around in florida now wearing white shoes and polyester sports jackets :c)

Re: telescoping arm
 

Hey Guys I'll shed a little light on our arm from 2003

It took 4 solid weeks to work out all the bugs in the telescoping mechanism. No pulleys or cables in that arm either. We used "fish tape" which is commonly used for running electrical wires thru conduit. it's like a 15' long piece of spring steel about 1/4" wide that we moved with two rollers. When retracted the tape was wound up inside the big brass ring that you see on the side of the mechanism. To tell the truth that thing was a pain in the $@#$@#$@#, it worked really well but only 60% of the time. That is until the bot fell on the mech in the first practice heat, from that point on it worked so well we could shoot the smallest extension like a spear, Almost lost my head the first time it happened!

Re: telescoping arm
 

My old team (442) built an arm that was 30' long in 2002. They used it to reach over all the other bots and goals and back to the home zone area. It used strings/pulleys/cables whatever. I'm not sure what kind of string material they used, but I know pulleys were involved.

Although I never really approved of building it, the few times it worked were kind of impressive. That is, until the top snapped off, swung by the string, and almost killed a referee. But, eh, it's all the same. ;)

Re: telescoping arm
 

In 99' Team 384, used an elevator to achieve the play. It was our first year, and I wasn't on the team because I was in 8th grade, but it used a pully system to achieve a 7 foot gain I believe. You could use the same system of pullies to get the height. But I would worry if you were to use the pullies to lift the bot as well, the cable could snap with that much weight on it... I'm not sure. I'm beginning to think that the bar is somewhat like stacking of last year, really great if you can do it, and it helps, but you can easily win with out it...
If you are using the device for grabbing the multiplier balls, don't go up and down, stay in a fixed location with an arm that moves from a stationary elevated point. It makes it so there is less to break.
Ivey

Re: telescoping arm
 

I was curious about this too, and saw many teams doing it successfully in 2000. There is a pretty good white paper powerpoint at ChiefDelphi by ChrisH on different ball lifts that shows how wires/chain could be used for a telescoping lift. So I built one out of Lego in a few hours to learn more about them.

Motorized Lego Telescoping Lift

Photo Contracted

Photo Extended

If you exclude the hook at the top, the structure doubles it length with three segments, going from 6.5" to 13".

The design certainly taught me some lessons about these lifts. Here they are:

1 ) There is a lot of tension in the plastic lego chain, so much that the chain pulls apart before the structure can actually lift itself up the bar, though the motor/gearing has enough torque for that. I would not use chain for a mechanism like this. Instead, I would use flexible steel cable and pulley. At the base, instead of a driving gear from the motor, the motor would turn a spool. The spool would have enough extra wire to move in both directions without running out of wire. Don't forget a tensioner... with cable or a non-continous chain (it can be fixed in place, like the locked gear, on the top segment) tensioning may be pretty easy.

2 ) Side loads. Just like overhanging a wheel can be bad, overhanging the shafts with the chain in the model (the ones you see moving, closest to the camer) is bad. It caused a side torque that jerked twist the assembly toward the side, almost breaking it, when the model reached the top of its travel. To fix this, I would route the chain/wire in the middle of the extension segments, via a hollow extension segment or extension segments on each side of the chain/wire.

3 ) Related to #2: The distance between the bottom-most two gears (the ones on the base) causes a FORWARD torque on the assembly. The longer this distance is, the more twisting force on the linear bearings, and the higher the chance of binding. The solution to this one is keeping that distance tiny, or doing the same solution to #2.

4 ) Adjustable speed. The first time I set this up, it was way too fast. Adjust the gearing from 1:1 to 5:1 helped quite a bit! Two sprockets and some chain could do the same thing. Make sure your motor is running at about half the no-load speed when it's lifting the robot up! This is where DC motors make the most power.

5 ) Overtravel. It breaks when you keep tellling the motors to pull up. The easy solution: limit switches that prevent the motors from moving when the thing's just about to hit a physical stop.

6 ) Your linear bearings MUST be super-smooth. The lift would bind when I had a bunch of 2-stud lego plates against 8-long lego slides. Bad! I replaced the 2-stud plate with 8-stud plates and the binding was less frequent, but still happened. If the plates weren't pressed ALL the way in, a tiny gap would catch.

7 ) Your linear bearings must have sufficient overlap (In my case, 6 out of 16 studs overlap). The greater this overlap, the less each segment can rotate with respect to another. This is an engineering tradeoff between reduced chance for binding and extra extension length.

8 ) I would consider using stretched rubber tubing between segments to reduce the torque the motor is required to produce.

9 ) Exposed chain when the lift is fully extended; may be vulnerable. Left as an exercise to the reader ;-)

The designs that used 80/20 or other aluminum extrusion in 2000 for hanging seemed by far the easiest lifts to construct. It can be done with entirely off-the shelf Al extrusion, linear bearings, pulleys and cable. A preliminary pricing from 80/20 showed a price on the order of $500 for the assembly, which would weigh about 20 lbs.

If anyone listening can chime in about their teams' experience with a lift like this, it'd be appreciated!

Thanks,
Brandon Heller
449 Alum / 931 Mentor

Re: telescoping arm
 

Awesome video and comments....

Re: telescoping arm
 

This is a helpful little tidbit, maybe:

The less telescoping pieces, the better. Two would be enough to reach the bar. As my team discussed; more than 2 would be impossibly difficult. Rmeember; it gets stronger and weaker as each telecoping piece size decreases.

Re: telescoping arm
 

Roccobot 2K

Roccobot 2K2

We used a two piece telescoping tower that is able to tilt all the way down. The good thing about Roccobot 2K was that it had a nice base, and it was able to evenly distribute weight even when extending to retrieve the big round balls. But it was not very strong, but did its job well. On Roccobot 2K2, we improved the arm design, but we were unable to maintain stability and balance when using the arm. Note that it had three wheels. But we made sure that if Roccobot 2K3 tipped over (which it has during competition) that it was able to right itself up easily using the arm.

Re: telescoping arm
 

WOW no one mentioned us team 25 in this artical i though we built one of the best telescoping arms ever made for first. Well if you need to see what we did get a hold of wayne.

Re: telescoping arm
 

Our telescoping arm made use of a pully system with extruded aluminum attatched by plastic sliders. We used pistons to extend. Very effective.

Re: telescoping arm
 

thats right, if i remember correctly, we (team 25) built a telescoping arm that reached about 12 feet out in order to steal the black balls from the other teams bin and then put into ours (2000 game), im suprised as well that no one has mentioned us....

Re: telescoping arm
 

I don't mean to be rude, but why not mention yourselves? If you'll notice, most teams are mentioning mechanisms they built themselves. I'm not sure why you see it as everyone else's duty to talk about your team (and I'm not just referencing this thread. Another memeber of your team has been posting "Well we did this, why didn't anyone say anything about that?" on other threads, too)? I know you're a very old and respected team (25 is a very low number haha), but honestly, not everyone is going to know you built some (apparently) amazingly fancy mechanism. If you want it to be known, then say so.

I've located some pics and videos of 442's arm from 2002 and I'll be posting those soon (hopefully).

Re: telescoping arm
 

Our team built two 4 staged telescoping arms in 2001 which could put the balls on top of the goals while the goals were on the ramp. Here are some pics

Practicing capping goals

Don't really need 4 stages

Oops ... the red one ended up on the floor

Kinda see how they work … best pic I could find

Under the bar

In the Easter spirit

Here are some of my memories of the arms that might help

-Globe motor was used to extend arms
-Surgical hose was used to "assist" the globe motor
-Window motor was used to lift arm (about 6" moment arm with 1" hub) … arm had to fit under bar
-Seat motor was used for turret
-Spectra string was used to "pull" things
-An Eagle Scout tied all of our knots … pretty frustrating when a knot lets go.
-First stage was pinned to turret
-Globe motor "pulled" second stage into place (up or down … did not depend on gravity)
-Third stage strings were attached to second stage ... not directly to motor
-Likewise, fourth stage was attached to third stage
-The cross section was a triangle with flat corners
-Delrin blocks (Teflon was cost prohibitive) were used as anti-friction blocks and "pulleys"
-The aluminum used for the arms was 0.032" sheet
-Bending the triangular sections is definitely an art but can be mastered with a good sheet metal break

Although the structure of the arm was very strong, the actuators were all fairly weak (using all of the strong ones on the base and balancing mechanism). This was okay because it was a 4 team alliance with no defense. This year, you need to have more powerful positioning actuators; thus, this year we are thinking about simply using our base to point the arm or go to a very strong turret.

All in all these arms performed very well even though our main strategy that year was to balance both of the goals. Telescoping is a good way to go and if you go this way, try to leave yourself a solid week to get out all of the kinks & binds.

Good luck,
Lucien

Re: telescoping arm
 

All these telescoping arms are SWEET. I think I have the general idea of how they work, but does anyone have any specifics? A design sketch would be great.

Re: telescoping arm
 

I don't know if this helps but this is the way we did it for three years 2000, 2001, and 2002 this is the 2002 one inch version, It drives whith chain or cable. and except for 2000 (cable) it is very reliable and compact.

Re: telescoping arm
 

Acutally I saw 25's arm on another thread. It was very impressive. I don't remember which thread. You would have to search.

Re: telescoping arm
 

By any chance do you remember how much the 2 pieces weighed?

Re: telescoping arm
 

I'm afraid I do not remember how much the two pieces weigh, but I could ask my teammates and find out. But before I do, which robot you would like to know the weight of those two pieces?

Re: telescoping arm
 

The 2000 robot arm

Re: telescoping arm
 

Maybe a totally inovative method is required , we have a secret method that might stun you at its simplicity :yikes:
How about the parraleelagram method?

Re: telescoping arm
 

Are you refferring to a 4-bar linkage?
This is a perfectly viable solution to a "tall arm".

For some prime examples of 4-bar linkage systems check out the robots from 1997, 1998.

4-bar linkages also made appearances last season as well
(25, 461, 233, others)

Check this one out:
http://www.firstrobotics.net/03galle...0513-1_jpg.htm

John

Re: telescoping arm
 

I was just thinking about how to extend a telescoping arm, and it just came to me!

last year teams built arms that they wanted to extend in auton mode to hit the wall quickly

but this year, the arms would be for manipulating the 2X ball, or hooking the bar

but they dont need to extend by themselves

how do you extend the telescoping antenna on a portable radio or TV?

(you PULL it out, and it stays there)

all you need to do is design a telescoping arm that locks when extended

and to extend it, hook the end on the lip of the mobile goal, or on your alliace bot (or anywhere else you are allowed to grab something on the field)

and then backup your bot to pull the arm all the way out.

I dont think it could be any simplier than that! :c)

Re: telescoping arm
 

For Roccobot 2K, the entire arm design (minus the battery) was about 67 pounds (more or less). Towards the bottom part of the arm, is where we kept the battery. So overall, it would weigh about 75 to a maximum of 80 pounds (which includes 6 big 30" balls). These are rough estimates from what the team could remember.

Re: telescoping arm
 

i didn't mean like that but we have made a lego model here :rolleyes:
basically it consists of a main section with some pulleys and you have a parralellagram which when the main internal part gets to the top extends outwards.
Without being rude , i find it incredably hard :confused: working in inches and stuff and all the stuff is confusing me as in the uk we are metric, hence our name is systemetric :ahh:

Re: telescoping arm
 

there is another way to extend a telescoping arm

power car antennas push a still wire up the center to extend it, and pull it back to retract it.

Re: telescoping arm
 

I was in the process of suggesting a couple of alternatives or variations to implementing the arm, then thought the better of it. Not for competitive reasons, but because you will feel so much better if you come up with it yourselves.

We've seen some sophisticated arms and lifting mechanisms in the past, but I'm convinced that there are some very simple and effective (read inexpensive) ways to at least reach the bar and lift off.

If you're stuck for ideas or just want to know what I'm rambling on about about, I'd be happy to discuss it.

Dick Linn
Mentor - Team 975

Re: telescoping arm
 

Though, for it to work by latching onto a mobile goal, there'd have to be less resistance in pulling out your telescoping arm than there is making the goal roll -- otherwise your telescoping arm will be nothing more than a fancy goal latch.

Re: telescoping arm
 

I'm interested in finding out your idea. We are currently toying with 3 concepts for extending arms. Using the forklift type, the folding pneumatic type, and the telescoping arms. We have not been able to come up with the "simple" method of telescoping an arm between 10-12'.

Re: telescoping arm
 

ok then, lift you arm so its horizontal, and do a victory spin

centripital force will extend it for you

dont demo it in the pits!

Re: telescoping arm
 

OK. Lacking a sketch, try this. Think of 3 sections of tubing, say 3", 2", 1 inch, or whatever nests relatively nicely. Between each of the two junctions, place either a length of surgical tubing or, outside the junction between successive section of tubing, place a coiled clock spring on the outside, business end pointed down. When you collapse the tubing, it will tend to want to spring out to it's former position because of the "springs" placed in the tubing. At the far (top) end, you attach a cable, which is routed straight down through the tube to a winch at the base. The only function of the spring or surgical tubing is to allow the relatively light cable and PVC pipe to extend to the desired height. Reversing the direction of the winch will pull the beastie up. If the PVC tubing is flimsy, so much the better, as it will not interfere with the upward lifting.

A variation of this is to put a small pulley at the top of the base tube on the outside, one on the bottom of the second tube and so forth. Sort of like a Sine wave propagating itself up and down throughout each successive layer of tubing. Retracting the cable will at first extend the tubing then, when at full extent, pick the whole thing up. Having very weak, flimsy tubing might help when lifting, as you only have to lift a foot or so. You won't have to worry about how (or if) the tubing nests back in again. PVC pipe is cheap! Change it if it breaks or bends.

A sketch would be a lot better than my explanation...email me at rlinn@wrsystems.com if you want something you can see.

Re: telescoping arm
 

The springs and surgical tubing could work if the design conforms to the requirements laid out by FIRST for stored energy devices, as well as being safe.

I am not following you on the variant of that with the pulleys installed on the outside of the various sections of tubing. With a pulley installed on the outside bottom of the 2nd stage tubing, how will it slide and retract into the 1st (base) stage tubing.

My variant of that is to use a combination of what was mentioned in a previous thread here, and and your coiled spring suggestion. I'll send you a simple PDF file of the concept I have in mind.

Re: telescoping arm
 

you can make a arm very easy with extruded aluminum 30m x 30m. We put one together in 10 minutes today. it goes out 14 feet. it comes in at 7 1/2 lbs. and only takes up 7" X 3' of space in our robot. I will have pictures up in a day.

Re: telescoping arm
 

for our telescoping arm we just went down to our local boat shop and bought a telescoping boat hook. Its extremely light (less than a pound), strong, and very long. Plus it already has a hook on the end. it was a very easy solution to a very hard problem.

Re: telescoping arm
 

We just put one together today that extends out about 14 feet in about 30 minutes. I think that it works great. All of our hard problems have been solved now we just have to build the drive train.
Drew Hopman
Team 801

Re: telescoping arm
 

Our team decided against it after...incidents...from two years ago. Cable isn't fun to keep tensioned and stuff =( We did contemplate it for a while though...the thing with telescoping is, it's relatively easy for just two pieces, but once you get into three it starts getting screwy...

Re: telescoping arm
 

14 feet in 30 minutes. wow that is fast