Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Welding is not a requirement for a competitive FRC robot. I would personally try to learn to work with Aluminum as well as plastics. Both materials have strengths and weaknesses and having more options in your arsenal means you can build the best robot you possibly can.

(And I hope I am not being too transparent about ignoring these puns, they clearly don't add anything to the discussion)

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Loving the polycarbonate, it's fun to see a team make a crab module out of something other than the usual aluminum. I'm really interested to see how this holds up after your next modifications are made with the wider belts and everything else you mentioned. I really like the idea of using the belt for both traction purposes and motion. Please keep us posted on your development process as I'd like to see video of your drive system with the usual 130 lbs involved.

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

While I agree with you for many potential components (I'd think making an AL swerve module would probably be a much safer option), a lot of times for our team there would be little benefit to building the robot out of aluminum when our resources for building that component out of polycarbonate are significantly greater. Take this year's robot, not a single structural failure, and we fabricated the robot faster this way than we would have if we used aluminum. In some cases it's better for our team to use polycarbonate only then. The tricky part is when we come across a game that basically requires a very strong, light part that isn't protected by foam bumpers...

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

I agree entirely, if you have better resources for working with a material and a part can be made out of that material without impacting its performance then by all means make it out of that material. I was merely remarking on a general concept that I see too often, people assume that one material is "better" than another. For example, a lot of times people will assume metal > wood. This is wrong, metal > wood in some applications in others the converse is true. In engineering, as in life, everything is a tradeoff. For example this component, while making it out of Aluminum may be safer and lighter (may or may not be the case but this is just an example so it doesn't really matter) you can fabricate the Polycarb easier. Which one you decide is based on certain criteria. As I said, just a general statement geared more towards a general audience than your specific design.

I do like the fact that you guys are finding limits of polycarb with PolyCrab. I just would like to see how it holds up compared to Aluminum. Perhaps do some tests (either in CAD or on the actual thing) to see how it holds up. This is the off season, why not take the time to find where you can cut weight out or where you need more material?

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

questions
1. How big is that lower pulley?
2. What diameter is that lower disc

niftyness

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

pully = ~ 7/8 (real one will be a bit bigger)
disk = ~ 3in

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

by "lower pulley" i meant what your using as a wheel
by "bottom disc" i meant the side support disc diameter

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

The lower pulley is roughly 3in, and the bottom disc is 5.5in.