How do you build telescopes/forklifts?

[Kevin Kolodziej]

Team 1675 has built a telescoping lift twice: 2005 and 2008. Both years we used a pair of three nesting aluminum tubes (two stage lift). We did it a little bit different from a traditional telescope though where we had the largest diameter tube on the outside. The smallest diameter tube was our rigid tube welded to the frame. I believe we used 2", 2.5" and 3" tubes, all 3/16" wall (the first year we ordered the wrong thickness and actually had to lathe four of the tubes!!). Depending on your use, 1/8" or maybe even .090" would be sufficient. The first year we simply lubed the tubes and didn't have too many friction problems. The second time we used 1/8" delrin strips mounted to the outside of the inner two pipes 120 degree intervals. The sliding was extremely smooth and our lift was actually angled about 15 degrees.

Both systems were cascading. The first year we used a kit gearbox (essentially today's AM Toughbox) and CIM to drive a 3" drum. We used 1/4" sailing rope (very strong, very light, and quite colorful!) and machined pockets into the tube for the cables to run between stages. We also use Harkin Micro Pulleys. For 2008 we switched to spectra cable and tried to make our own pulleys but eventually installed the Harkin pulleys. This one used a 2" drum and used a dual FP winch. We only used our lift in competition once (at IRI) due to mechanism problems (not lift problems).

You can see a picture of our lift from 08 here. The brown stage is the outer stage and rides up on the gold stage. The gold stage also would raise up over a black stage (not visible) and have a total lift height of about 8'. The black stripes are the delrin slides. The wood was there for stability since we weren't using the lift (the gripper arm would keep stability normally).

Good luck to you!

[PAR_WIG1350]

From personal experience, don't try extending a telescoping fishing pole (or anything really) by pushing bicycle break cable sheathing or similar cable into it between two wheels (either both driven or with one idling).

I've seen a cool rolamite-like design using a chain as a rack, in a manner similar to the metal bands in rolamite bearings, and a driven sprocket paired with an idler sprocket/roller acting like the rollers in a rolamite bearing. I don't remember where I saw it, but I do believe it was on an FRC robot (which I saw in pictures only, so it was sometime between ~'93-'08). I'm not sure how well it worked then, but by using large chain, it could be made incredibly strong.

[PAR_WIG1350]

Originally Posted by PAR_WIG1350

From personal experience, don't try extending a telescoping fishing pole (or anything really) by pushing bicycle break cable sheathing or similar cable into it between two wheels (either both driven or with one idling).

I've seen a cool rolamite-like design using a chain as a rack, in a manner similar to the metal bands in rolamite bearings, and a driven sprocket paired with an idler sprocket/roller acting like the rollers in a rolamite bearing. I don't remember where I saw it, but I do believe it was on an FRC robot (which I saw in pictures only, so it was sometime between ~'93-'08). I'm not sure how well it worked then, but by using large chain, it could be made incredibly strong.

found the picture, didn't remember it as well as I thought I did, still a cool idea:

[pfreivald]

In Overdrive we used Bosch (similar to 80/20) and steel cable, and it worked very well (except that the cable would get tangled if something caused the lift to move too quickly, or bumped it upward -- which happened a few times).

Last year for our lift we used Bosch again, only this time we used a 3' four-start screw drive (direct-driven with a CIM, with a shaft coupler and thrust bearing from McMaster) along with aluminum carriages equipped with delrin sliders. This worked *extremely* well for us.

Indeed, it worked so terrifically well that I think that we'd have to have a very compelling reason not to use a similar setup again if required to do any heavy lifting over any real linear distance.

[Mike Schreiber]

On the cascading rig, how do you determine the diameter of the two pulleys. My guess was that it is determined by the ratio of lengths between the lifting cable and retracting cable, can someone confirm this?

[Tom Line]

The diameter of the pulleys in a pulley system have absolutely no effect on the reduction of that system. Also, you do NOT want to use drawer slides. They have to much friction, don't extend far enough, and aren't nearly strong enough. I'll have a couple cad sketches up of systems of bearings and cascades in a bit (once I get done with a work issue..)

Edited to add:

That's a picture of the 254/968 setup from a while back (the blue tube in the picture below). It works well if you want only 1 stage. If you want multiple stages (per the PDF) you can make rectangular frames, then use C-channel with some bearings in them at the tops and bottoms of each frame to guide them.

In '08 we used IGUS slides to do it. It worked remarkably well, however the slides were certainly not meant for that application and we had to do pretty regular maintenance on them. Video of that robot here:

http://www.youtube.com/watch?v=jOJmiPAcZt4

In addition, many hi-lo setups have counterweights to counteract the weight of each stage. That year, we used bungie cord and pulleys so that each stage effectly weighed "nothing" - in fact the motor had to keep the stages down because we decided to also counteract some of the weight of the ball.

[buildmaster5000]

AM has a lot of good info on their manipulators powerpoint presentation here. It explains some of the math behind the designs which is good as well

[,4lex S.]

One thing my old team used to do a lot was build telescoping sections by interfacing 8020 with a delrin slider (you can see the result relatively well here). Overall, it was simple to implement and mounting pulleys was easy.

If someone optimized the weight, and figured out how to reduce binding more, this design could work pretty efficiently.

[blayde5]

Originally Posted by ,4lex S.

One thing my old team used to do a lot was build telescoping sections by interfacing 8020 with a delrin slider (you can see the result relatively well here). Overall, it was simple to implement and mounting pulleys was easy.

If someone optimized the weight, and figured out how to reduce binding more, this design could work pretty efficiently.

Whenever our team has made elevators, we have used 80/20 like material and delirin sliders as well. It's generally very east to set up albeit a little on the heavy side.

[Mike Schreiber]

Does anyone have detailed pictures of Hammond from '07? That is probably one of the best examples I can think of, but I can't seem to find any close up pictures of their elevator on here or their website.

[lbarger]

Others have addressed cable/chain routing so I will not. Besides when my team did it we used something close to 22 ft of chain for an 8 ft lift. (Not at all efficient routing.)

What I will bring to the discussion is full extension draw slides. They are on the heavy side but made for extending. Nothing to build, just drill holes and mount. What they cost in weight is made up for in simplicity, availability of spares and speed of assembly. Think about side loads and getting hit with them up when looking at load ratings.

Also think about how you will determine full extension or retraction. Our system had a shuttle that ran up and down a tract on the top stage and two sets of draw slides on aluminum tubing to get to 8 feet. With binding, any stage could move or stick during the lift. We counted stripes on the drive axle to determine amount of motion. This was great accept we could not get the controller to remember the position between restarts. This was solved with a home switch in the lowest possible position for the upper stage of the lift.

[Tom Line]

Originally Posted by lbarger

Others have addressed cable/chain routing so I will not. Besides when my team did it we used something close to 22 ft of chain for an 8 ft lift. (Not at all efficient routing.)

What I will bring to the discussion is full extension draw slides. They are on the heavy side but made for extending. Nothing to build, just drill holes and mount. What they cost in weight is made up for in simplicity, availability of spares and speed of assembly. Think about side loads and getting hit with them up when looking at load ratings.

Also think about how you will determine full extension or retraction. Our system had a shuttle that ran up and down a tract on the top stage and two sets of draw slides on aluminum tubing to get to 8 feet. With binding, any stage could move or stick during the lift. We counted stripes on the drive axle to determine amount of motion. This was great accept we could not get the controller to remember the position between restarts. This was solved with a home switch in the lowest possible position for the upper stage of the lift.

That sounds very similar to what we considered. We could have used an encoder in the toughbox (relative) with a home switch at the bottom of travel, however we opted for a 10-turn potentiometer riding on the bottom chain so that we had an absolute value and could minimize wiring.