Quote:
Originally Posted by DampRobot
Could someone (Adam?) go into a bit more detail about rigging the cabling in an elevator? For example, what type of cable is best, how do you deal with tensioning and stretching, and how do you tie it off the best? What are good ways to attach the cable to the drum, how do you keep it from getting tangled, and what are good ways to do pulleys?
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The last time I designed a real elevator was in 2011 when I was a college mentor for 228. My main goal was a really fast (<2 sec) and reliable lift, so I chose to avoid drums altogether. There are a bunch of photos of this setup online here:
http://team228.org/media/pictures/20...eason-week-six
I used fixed loops of 25p roller chain that I interspaced tension springs into to maintain tension in the chain due to stretching/wearing in. Make sure all the tension springs work on the downward pull, because if they work on the upward stroke you might get a slingshot effect (we learned this one the hard way). On a really fast elevator, the tension spring will stretch before the inertia of the carriage gets moving, so it will then slingshot upwards. If you put it on the downward stroke, gravity helps prevent this slingshot effect.
To fix the roller chain to the elevator stages, I simply
ran #4-40 bolts through the holes in the roller chain.
Quote:
Originally Posted by DampRobot
I'm also not 100% clear on how to do the Constant Force Springs. What's the best way to mount a CFS, and what are some of the better suppliers for CFSes? Also, I've had mentors try to dissuade me from using a CFS because it's basically a razor blade under 40 lbs of tension. Are CFSes safe to use, and what's some advice about setting them up safely?
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You do have to be careful with CF springs, but if used properly they work great. To use them just bolt the end with the mounting holes to your object then provide a loose clearance fit inside the spool on the other side. I'm pretty sure last time I used them I used a piece of 1" ish PVC pipe to act as the internal bushing for the curling half of the CF spring. Just let this side free spin on the ID.
Be careful with elevators with CF springs when in the pits. If you balance the elevator right, when you tip the robot sideways to work on it, the lack of gravity fighting the CF springs will cause the elevator to shoot outwards to fully elevated. Which when sideways, means you may hit someone standing several feet away.
As for a source, I've always used McMaster. Also, avoid kinking them at all costs, as you may begin to tear through the spring if you bend/kink it.