Untested Conveyor Claw Design

During the build season, one of our design ideas was to have an elevator lift attached to an extending ‘hypotenuse’ that would be fixed to the rear. This extender would be a track for our roller-claw to travel from one side of the robot to the other. A spool and 9.5ft cable would be responsible for pulling the claw from one end to the other, and would also mechanically pull the claw over whenever the elevator was raised. Gravity would pull the claw back down. The idea behind all this was to prevent the need to turn around after getting a tube.
Not having much knowledge in 3D CAD, I made a digital model the way I did know how, which was to make an executable ‘game’ that allows the user to ‘control’ the design in a scale environment. You can access it here:

However, we didn’t go this route, because it was getting too late in the season to prototype anymore, and we hadn’t much positive experience with spools anyway. So what are your thoughts on this, now that we’ve seen actual matches in play? Would this design have been a trouble-maker, or should it be kept in mind for future years?

Wow, that actually sounds really cool.

The problem would be getting the claw back down. You really don’t want to rely on gravity, and there isn’t really a spring that would provide a constant force from 8’ to 6"

You could have a second motor used to pull it down, and be very careful not to let the two out of synchronization.

It also doesn’t look like you’d need to be able to rotate the tube, although it may be helpful. The problem is that it’s a lot of motors on there – two to rotate the rollers and another to rotate the entire claw. Then another three for movement of the entire thing… that’s six motors, assuming you don’t have to double up on anything.

But again, it’s a really neat design, and it may just work.

How about a constant force spring?

I think he was referring to the difficulty in finding a constant force spring that works from 6 inches to 8 feet stretch, nevermind just finding a spring that stretched that much at all.

The program doesn’t work for me but a continuous loop or a 2nd cable counterwound onto the same axle can often be used to drive a cabled mechanism in both directions.

The problem with that is that the length of the loop changes, but there might be some way around that.

166 has an elevator style cable driven lift and we ran into the same problem. We ended up attaching rubber-bands on the downward cables to act as tensioner. They are cheap, simple, and light weight. They work very well and we have not had any issues with them (yet). And if the rubber-bands do break you NEED a back up so it doesn’t fail catastrophically.

I hope you would have found the solution by now. It is really an awesome design. If you had an idea of 3D CAD then it would have been great because you get a clear picture of the working of the conveyor. It is better to use another motor instead of relaying on gravity.


I gotta say, this is a really awesome design. I too hope you figured out a way to make it work. Awesome entertaining little game too! Nice work.

Niiice, that’s definately my new favorite game!!

Team 1515 had a simple elevator design, gravity returned, and it worked fluidly and effectively. However, I think that running a second wire rope line the other way on the same drive-shaft would be a simple solution to that problem. Continuous loops tend to be difficult in pullied lift systems.
Also, Can someone please post a screenshot of the game?

Definitely a cool design! It looks like it would make hanging tubes easy because you can rotat the claw AND the tube, which is pretty awesome. Doesn’t exactly look easy to pull off, but hey, this is FRC! Also, it’s a great little game of catch the tube from the feeder station and hang it! :slight_smile:

This is an interesting design. The one big advantage it has over the elevators (which, I think, were largely dominating in this game) is the ability to hang on the opposite side of pickup. However, this then brings up the question: is this design better than the various arm designs that could hang on both sides?

The only thing I can think of that might make it better than the alternate arm design is a closer center of gravity. I think this is a big reason why elevator designs worked so well. We ended up just using a plain arm design, and speaking as the driver, the CoG of an arm makes fine control tricky when the arm is up. (of course, if your arm is fast enough, it wouldn’t need to be up very long) Also, a different distance is needed to hang on different heights when using an arm.