• aditya mehrotra.

2.12 gripper design - wheel gripper [2.12 Design Notebook]

So Alex came into the lab today with this super cute gripper with two spinny wheels on it on two arms connected by a rubber band. This FRC-inspired design was able to pick up all the water bottles and almost the crushed ones. So honestly, I think that's the design we want to try. I've got some free time - so I'm going to try to build my own version of the gripper. Simple, but maybe add some Arduino control and see what I can do with Alex's initial design. Plus I kinda just want to make one!

So we made an arm roughly 4 inches long with wheels on the end. We're honestly basing this all off the fact that the gripper needs to hold water bottles that are between 2.5in and 3.5in in diameter. We're using the guess-and-test method to size everything. This LOOKS like it'll work.

So here's what the gripper design looks like finally. The two wheels are 2" diameter wheels I would prefer if they were driven by belts from a single motor at the back of this robot gripper. If we do decide to do something like this for the gripper (which is looks like we might) we also may want to add some extra degrees of freedom to the wrist itself so we can maybe even shoot out the water bottle. Or we can use the arm trajectory which would be even more fun. This gripper will probably have to be angled up while shooting as well.

Now the thing is I know there were some few issues with Alex's gripper like it being hard for it to hold crushed bottles and then there was issue of the motor stalling. But to fix those we need to build this prototype first. I also added some holes to add rubber bands and wheel shafts and etc. The first gripper we'll just last cut and hot glue out of wood. Then we can talk about more advanced gripper designs.

So let's build it! Out of wood first.

While I'm doing this I'm watching Adam Savage examine the props on Hamilton :)

So the way we're going to put this together is with Hot Glue for now. I'd use Wood Glue but its a mess and I don't want to deal with it right now. Besides, it's a prototype we'd design it better later.

Okay so this is a jigsaw we need to put together. Here we go.

So in this case, I used a bolt, two washers, and a lock nut. The washers acted as spacers and the lock-nut allows us to tension the arms to the amount of "looseness" or "firmness" we want them to have. I kept them loose right now.

So I found these wheels and these motors, they might the same ones (motors) Alex used. I'm going to use this for the prototype. Had to do some modifications because of this.

Okay so now we need to solder some wires on and test. It's a 6V motor remember. The rubber bands is one standard rubber band looped around both arms, and one standard rubber band twisted once and stacked around the screws. That should give it enough tension if not too much.

So this gripper has a dual forward/reverse switch which allows us to spit out and take in, not that we'll need it on the actual robot arm. This gripper also only runs on 6V and at 105 RPM, Alex's was running a lot faster. The next steps is to try this gripper with different wheel speeds but also different amounts of tension on that rubber band, and different GRIPS on the wheels we might need more grip on the wheels. Those are the next steps. We also want. to try this on crushed bottles and on other kinds of bottles so we can get an idea of what we need to add to this prototype, add those things to the prototype, and then get the workings of a final design.

#robotics #two_twelve #robot #omgrobots #gripper_design

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