Re: Plastic Chain
 

Consider also that you can allow yourself to use weaker material by decreasing the load applied. Adding a spring will add some weight, but it may allow you to save some weight elsewhere (chain weight, motors, and gearbox for example).

Also, if you are having trouble with belts as an alternative to chain, you can also try a simple string winch. You can find cord and wire in long lengths for cheap that are very strong for their weight.

Re: Plastic Chain
 

Alternatively you could use a Constant Force Spring such at what McMaster sells.

http://www.mcmaster.com/#constant-force-springs/=whvq22

Re: Plastic Chain
 

This is what we are doing. with the spring our lift has a maximum load of about 35 pounds up and 20 pounds down.

Re: Plastic Chain
 

Speaking of lightweight RC Pullers, our team recently built and implemented one with only about four pounds of weight left to spare at the end of bag day. The entire subsystem weighs in at about three pounds (motor controller and wiring included), and uses a spool to retract. It can pull two RC's in auto within about five seconds, and could probably be sped up to pull within three seconds. I'm happy to provide further details if anyone is interested.

Here's a very preliminary video of the system in use at the Montreal Regional. It has become much faster since, and we now use it in autonomous mode. Skip to 1:15 to see it in action.

https://www.youtube.com/watch?v=pnUju-lFhRE