Need some help with forklifts

[Tom Line]

We used size 25 chain to drive our first stage, with spectra pulling the second up and down.

We used bungee cord to counterbalance the stages the motors didn't have to lift the weight of the them.

One thing to note about using any time of spectra or other line - tieing a knot in it will reduce the strength on the order of 40%. So, for instance, if you had a piece of line with a breaking strength of 500 pounds, and tied a knot in it, the break strength at the point of the knot will only be around 250 pounds. That sounds like a lot, but we managed to break a piece of spectra line with a break strength of over 1000 pounds when we were lifting a trackball and then got hit from the side by another robot (hard). If you can find a local rigger or a West Marine, they can splice the rope for you and eliminate the sharp bends that you'll create by tieing a knot. Or if you can "wrap" the spectra around whatever you're tieing it to several times then tie a couple half hitches, you'll eliminate that problem.

Shock loads are killer. Forces in a 10 mph collision have been measured at over 8 g's in the auto industry. We go a lot faster than that.

Another thing to note is that most spectra will not have a cover on it like your standard "West Marine" line, and that it is very susceptible to chafe. Vectran less so but you will certainly pay through the nose for vectran or any other high-tech line.

[camtunkpa]

222 has used 1/8" steel cable, 3/32" steel cable, 1/8" spectra cable, #25 chain and timing belts for extension devices. Out of everything we used I would say that I liked the chain and timing belt the best. You can't get much simpler. We used steel cable for years and that worked out well for us but many of us got tired of the frays on the steel cable making us bleed. So we eventually moved onto Spectra cable. I will utter the woes of the spectra cable creep. It gets very annoying. #25 chain is bullet proof for most FIRST lifts and can be as simple as a sprocket on a motor and a sprocket on a fixed member and an attachment block to the piece you want to extend. Timing belts can be used the same way the chain can, they are lighter and if tensioned correctly almost as strong. We used the timing belts for extension in our arm this year and we were impressed with how smooth the motion was. As far as chains and timing belts go your can find tons of sources. The timing belt and pulleys we used were supplied in the kit this year and they held up great! As far as a source for cables or other types of rope, here's a source I found that's got a little bit of everything.http://www.us-rope-cable.com/?gclid=...FQWAHgodgjYNWw

Hope this helps

[Dick Linn]

We've used 1/4" nylon rope before. It just happened to fit the groove in those ball-bearing sliding door rollers that are available at Home Depot: http://www.homedepot.com/webapp/wcs/...ctId=100200036

One team used some 1" wide nylon web strap, like you find on tie-down straps. That was nice because it would feed nicely on and off the winch mechanism. Plastic strapping used for shipping might work.

[IKE]

Originally Posted by AdamHeard

I'd advise against spectra cable. Yes it is strong, but it doesn't take shock very well at all.

We used it this year and it was good stuff once:

You have a friendly attachment as it can easily be cut by sharp edges
You have learned how to tie a good knot. Knots can reduced the strength rating by as much as 75%. Here is 1 link:
http://www.caves.org/section/vertica.../knotrope.html

You keep it relatively clean. (grease and filings can hinder flexibility and lengevity.
You have a good tensioner system.

These are a lot of provotionals, but once these are set, it works great.

Anecdote:
We bought our original stuff from Small Parts for $100 for 100 feet. We had to re-weld a part on our robot right before ship day and it partially fired one of our strings. It broke at our first regional in Chicago. We bought 300 feet in Chicago for $75. The purchase trasaction and pick was an interesting story in itself.

[EricH]

If you go with cable, make sure you have a good crimper. I don't mean a vise, I mean a cable crimper. 330 used to do lifts a lot (then discovered the joys of a single-joint arm), and when they did, they used cable, powered the lift both ways, and used a crimper used for aircraft cables. I don't think we broke any cable or crimps, though we once bent a lift by powering down while it was all the way down. Yes, bent.

[R.C.]

Originally Posted by EricH

If you go with cable, make sure you have a good crimper. I don't mean a vise, I mean a cable crimper. 330 used to do lifts a lot (then discovered the joys of a single-joint arm), and when they did, they used cable, powered the lift both ways, and used a crimper used for aircraft cables. I don't think we broke any cable or crimps, though we once bent a lift by powering down while it was all the way down. Yes, bent.

Do you know where to get a really good one? Will this work?

7424K88 - McMaster Carr

[EricH]

Originally Posted by rc_cola1323

Do you know where to get a really good one? Will this work?

7424K88 - McMaster Carr

I'm not sure. We borrowed ours from a mentor...

But what you have is NOT steel cable crimpers.

You want something more like what McMaster calls "wire rope". The 3633T group of crimps and crimpers, to be more exact.

[R.C.]

3633T16, is this it? McMaster Carr

[EricH]

Originally Posted by rc_cola1323

3633T16, is this it? McMaster Carr

Yeah, that's about it. 330 used 3/32 (with sheath, 1/8), so that's more like a 3633T14.

[R.C.]

Thanks EricH, I really needed that.

[ChrisH]

By the way, the sheath is important. It helps keep the cable well behaved and greatly reduces kinking. If a cable kinks you are better off to get rid of it and build a new one than to try and get it to follow the intended path.

You will however need to strip the sheath around crimps and thimbles. Otherwise the crimps won't work properly

ChrisH

[sgreco]

Another thing you can use is seatbelt material. It is woven in such a way that it is very strong and durable. Depending on how you build your lift, you may need to modify it a little to use seatbelt material, because it is wider than a cable.

[Dick Linn]

Here's a typical selection of webbing material: http://www.strapworks.com/webbing_an...brics_s/20.htm

In particular: http://www.strapworks.com/Polyester_s/60.htm

If you can get by with 12-15 feet, just buy 1" cargo tie-down straps or lashing straps. They are about $3. each at Harbor Freight.

[Jon Jack]

We've built 3 different lifts in 4 years. Here's some of the things we've learned from each:

2005
In 2005 we used a cable (3/32" core, 1/8 OD) driven lift. Each side of the lift had a cable, this was to prevent racking and for redundancy. The cables were tensioned with two turn buckles. It was power up, gravity down using an old van door motor. We used no encoders for position sensing.

Pros:
The cable never broke. The turn buckles provided a quick and off the shelf method for cable tensioning.

Cons:
When the motor stalled we would lose the spool of cable and be out for the rest of the match.

2007
In 2007 we used a chain driven lift. A single 25 chain gave us the ability to power up and down. We used a single fisher price motor -> AM Planetary -> BaneBots Planetary to drive the lift. We added an encoder to simplify the control on the lift. We also used 80/20 extruded aluminum and 80/20 slides for the structure of the lift. The motor assembly was on a slide so tensioning the chain was as easy as loosening a couple screws and sliding the motor our.

Pros:
We were power up and power down. The single fisher price motor was plenty of power to move the lift up and down. We were able to go from ground to the top row of the rack in just a couple seconds. The encoder allowed us to maintain our height without a lot of driver finesse.

Cons:
The chain was very heavy, however once it was on we never had to mess with it again. I think we calculated something between 20-25 ft. of chain being used. Between our competition and practice robot we used about 75ft. of 25 chain at $162/ 50ft. spool. Obviously not a cheap solution.

2008
This year we used a 968/254 style lift. The lift was driven by two cables (1/16, no coating) and two fisher price motors running into a custom gearbox. We used to cables for redundancy and to prevent racking. Once again an encoder was used for position sensing. The cables were looped into two eye bolts. By tightening the nut on the eyebolt we could tension the cable.

Pros:
Power up and down, again. Fairly inexpensive to build. Lighter than the 2007 lift. The cables never broke, however we did lose a crimp because someone over tensioned the cables. The encoder allowed us to easily set and maintain positions.

Cons:
In our first competition we had some minor racking problems due to spacing and alignment, which is critical for a lift of this type. By Atlanta we had fixed all of our racking problems.

Overall lessons to be learned:

• Do not power up/gravity down. This can become a major headache at competitions.
• 1/16 steel wire rope is plenty strong enough.
• Tensioning should not be over looked on any lift system. Not mater what you're using it's going to stretch over time and stretching can end up killing your lift if you don't have a tensioner.

[David Guzman]

Originally Posted by techtiger1

The motors were the small and big banebot if my memory serves me corretly and don't quote me on this rs 440 and 550 combined in a custom gearbox.

We used the RS540 and RS550 motors. Also the cable we used was 1/16" stainless steel.

Our spool was 3" diameter rotating at around 400 RPMs.