We got this put together yesterday to test some dimensions for the gripper before we send off the final sheet metal parts to our machine shop sponsor. Let me know if you have any questions, ect. 
Nice.
Does it grab the small part of the triangle?
Is it spring loaded?
Yes it does, we just did not have that object in the shop at the time. We found the wider the roller is, it can suck the corners in nice and deep. It is not spring loaded. We have a lot of compression, but the urethane belting adds a spring-like element when it stretches.
Sounds like you canât handle deflated tubes though. You should take some air out of one and see what happens.
The gripper compresses the tubes down anywhere from 2-3 inches. The rules state that all the tubes will be kept from 7-8" in diameter. With the tubes at any inflation in this range, our gripper can handle them.
Our triangle piece is as shallow as 5.5 inches in the middle fully inflated. Are the specs going to be kept that tight at competition?
This design compresses all objects to well below 5", and handles the triangles with no noticeable difference as the other two shapes. Also, the two belts run at approaching angles, compressing the shapes more as they are pulled in.
I guess Sean wasnât able to convince yall to go over to wood.
santosh, i know we have had our differences, but targeting your old team in a public enviroment is not the route to go. if you have a problemâŚcome talk to me in the publix parking lot @6:00 today. but we need to be done by 8 because thats when the game is. we are sorry it didnt work out with usâŚ
Nah, they just do it backwards of most teams. Instead of prototyping with plywood and machining metal for the final version, they make their prototypes out of sheet metal and machine the final robot out of wood. 
[/joke post]
The thing would have stopped running. Iâve done this kind of prototyping for nearly a decade now and never had anyone hurt by a drill âpopping offâ. In fact, using a system with a clutch and that loses power if someone drops it is significantly safer than using a motor with connectors into a battery or with exposed leads as I see quite frequently. Additionally all the gears are encased in a nice plastic shell so they canât catch fingers. Honestly, for prototypes drills are a pretty nice way to test. They have variable speeds, stop really quick, and have a clutch so you probably wonât destroy your mechanism if it hits a hard stop. It also probably wonât destroy a person if your mechanism hits them before you let go of the trigger.
2415, thanks for sharing. We have a couple roller claw prototypes out of Vex parts but I think I might get busy with a router and some plywood tonight to see if the shape of the back has a large impact.
A few questions:
What is your compression? You say you are compressing to less than 5" thickness. Does the drill seem to be struggling at all?
Have you tried other widths? 5", 7", 9"? Did this have an impact?
Have you tried not having rollers in the middle and instead grabbing from two points on the side?
Have you tried pulling your tubes out by hand both while the motors are running and while they arenât? Perhaps use a cable tied to the piece with a force gauge to measure your grip strength.
Have you tried grabbing at an angle? Both relative to the floor and relative to the tube.
What is your compression? You say you are compressing to less than 5" thickness. Does the drill seem to be struggling at all?
Drill does not seem to struggle at all. We will be using a 550 and a 1:16 banebots transmission.
Have you tried other widths? 5", 7", 9"? Did this have an impact?
We were satisfied with this result enough to not try any other amounts of compression. Much less (~6" or greater) would have probably struggled to maintain grip.
Have you tried not having rollers in the middle and instead grabbing from two points on the side?
Yes. It is effective to an extent (pretty much as long as you are going fairly straight and the roller tries to grab the tube it will work.
Have you tried pulling your tubes out by hand both while the motors are running and while they arenât? Perhaps use a cable tied to the piece with a force gauge to measure your grip strength.
We have not measured the grip strength with a force gauge but we do plan to turn off the motors once we have control and rely on the friction of the system (both the gearbox, the chain, and the belt) to hold the tube.
Have you tried grabbing at an angle? Both relative to the floor and relative to the tube.
Works just as well, although we plan to be grabbing straight on most of the time as it is easier to line up.
How well does that keep the tubes from rotating once it has held them. Can it rotate the tubes in place to adjust angle while placing??
No, in the final design it will all be powered by 1 motor. We thought it would be too hard to accurately rotate with 2 rollers. Instead, our design rotates the entire claw, giving the same effect and making it easier to fit inside starting dimensions.
It seems that rollers wonât be able to handle deflated tubes. Have you tried that yet?
We basically donât care about fully deflated tubes. If there happens to be a popped one we will move on to the next.
Is that polycord or urethane belting? How is the grip? My team is opting for surgical tubing like this for the grippiness of it.
polycord. grip is pretty good actually. we are spacing the cords apart and wrapping nitrile between the cords so they dont slide side to side. we are also going with thicker nitrile potentially on the real robot.
honestly i donât see why people do