How do you build telescopes/forklifts?

[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.