Plastic Chain
 

Were are a 42 point stacking robot and can do 1 1/2 to 2 per match. We were picked by the #1 alliance in both of our districts. At this point we weight 119.5 pounds and use a elevator to raise the 6 totes , can and litter.
One of our mentors wants to add a can puller from the step. To do this we must lose weight and he wants to install plastic chain where we use metal chain now (lifting approx. 75 pounds). I feel that being a very high scoring robot it is not worth the risk of installing plastic chain. What are other teams experience using plastic chain ?

Re: Plastic Chain
 

Have you done the math on the stress on your chain, to see if the proposed chain is adequate?

Re: Plastic Chain
 

No. Unless you have access to something special, plastic 35 chain usually isn't meant for more than 60 lbs of working load. It won't hold up under the rigors of competition.

Risk versus rewards. You are risking your primary scoring mechanism while trying to make something that is not going to contribute to your score in every match.

Re: Plastic Chain
 

I will ask for that to be calculated.

Re: Plastic Chain
 

Im not that familiar with plastic chain. But are you sure that you will even have enough weight to make a decent can grabber. Our bots can grabbers are rather heavy as we have 2 of them and they each have 2 pneumatic pistons. Just something to think about. How effective a can grabber can you make with the limit you are placing on weight?

Re: Plastic Chain
 

The canburglar will not be used during Qualification only eliminations if used at all.

Re: Plastic Chain
 

Instead of plastic chain consider switch to timing belt. It should be a decent reduction in weight if you are currently running #35 chain.

Re: Plastic Chain
 

We are running 35# chain 4 of them approx. 12 feet long each so timing belt out of the question. Only 6 feet of each chain will be changed over to plastic. I see problems. What is that old line "Do not change horses in mid stream". PNW championships are in 5 days.

Re: Plastic Chain
 

Do you have photos of your current robot anywhere? That would help us identify places you can lose weight by swapping out materials.

Re: Plastic Chain
 

Our robot has two chains, each nearly six foot tall--pretty hard to find timing belts that long.

But that adds up to like 23 feet of chain. Heavy.

I know little about plastic chains, but if you're using #35 chain, you can switch to #25. Or even bicycle chain. Or lose the weight elsewhere. Switch to mini-cims. Canburgulars are very valuable and will make people want you.

We designed one that weighed in at about 4 lbs.

I think you can find four pounds.

Re: Plastic Chain
 

So you're running 4 12' lengths of #35 chain?

It requires new sprockets, but switching to #25 chain would provide HUGE weight savings and still be plenty strong.

Re: Plastic Chain
 

IIRC #25 chain is less than 1/4 the weight of #35 chain.

Re: Plastic Chain
 

We installed Minn-cims and found out with the weight of the bot we had problems doing zero point turns. We did a lot of drilling larger holes to reduce weight to return to regular cims.

Re: Plastic Chain
 

A little more than half, according to these guys. Still, at 0.23#/ft for 35 and 0.10#/ft for 25, that's 6# less of chain by switching to 25.

Also, you actually could switch to belts, you'd just have to use open length belting with a clamp to close it up. As long as you're running your lift a short enough distance that you don't have to run the clamp over a pulley, it'd be fine.

Re: Plastic Chain
 

#25 chain is the way to go. It's great stuff. #35 chain is OVERKILL on all mechanisms except chain driven arm pivots in my opinion.

McMaster lists a working load of 88 lbs for #25 chain and 200! for #35. Acetal #35 chain is listed as 45 lbs working load.

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