Instructables
Picture of Froggy World 5 The Coffee Gripper


In Froggy World, the amusement park for adventurous plastic frogs, it became necessary to to move the frog from a train car back to the catapult.  Because I couldn't know whether the frog would be upright or sideways--and in what orientation--the gripper was a challenge.

I read about the "coffee gripper" developed at Cornell and used that technique for transporting the frog.

In the video, I cut out the "20 seconds of vacuum time--caused by my low cost pump" to keep from boring the viewers.

Step 1:

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What do we need to build this?

Arduino
Arduino motor shield
(2) Hitec HS-645MG ultra torque servo motors (amazon.com)
Vaccum pump  https://www.sparkfun.com/products/10398
Coffee (I used Maxwell house, original roast)
12" round balloon
Lazy Susan bearings  http://www.amazon.com/gp/product/B002TIKEQ6/ref=oh_details_o02_s00_i00?ie=UTF8&psc=1
Cast Acrylic tube  http://www.amazon.com/gp/product/B0070ZQGRE/ref=oh_details_o02_s00_i01?ie=UTF8&psc=1
Two feet of 3/8 inch OD, 1/4 inch ID tubing
Breadboard

Various 3D printed parts, design and print files at:
http://www.thingiverse.com/thing:68316

12 volt 1 amp power supply
5 volt 1 amp power supply

Step 2:

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To make this work, the coffee filled gripper must be pushed down onto the target.

The more it surrounds the target and the greater the vacuum, the greater the chances for a successful grip.

Since we are working with minimum "push" (servo motor 10 inches away) and low vacuum (low cost pump)--we have to do everything possible to help the system.

Reducing the thickness of the balloon wall is a first step.  Blow up a "12 inch" balloon and clamp it in the inflated position overnight.  It will stretch.

Step 3:

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Cut off the lip of the balloon.

Step 4:

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Weigh the balloon (around 3 grams) then attach a funnel.

Step 5:

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Add 20 grams of coffee.  I started with 47 grams and worked my way down--don't know what the absolute best situation would be.

Step 6:

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Insert the tube of the coffee filled balloon through the hole in the printed gripper and wrap it around the top edge of the gripper.

Insert one end of the plastic tube into the top of the printed gripper--it should just press in.
 
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fozzy131 year ago
These grippers are awesome! I first read about them in Popular Science I believe, and I like how so many people on Instructables have put it to use! Great job!
MikeTheMaker (author)  fozzy131 year ago
Thank you--I wanted to share what I learned so that it would be a little easier for the next person :)
hertzgamma1 year ago
Very nice! And I see you've got lots of 3D printed parts. You must be enthusiastic!
MikeTheMaker (author)  hertzgamma1 year ago
Thank you--I am enthusiastic! With the 3D printer, imagination is given freedom from many construction limits . . .