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.
Froggy World 5 The Coffee Gripper

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:

Major Components in Project

What do we need to build this?

Arduino motor shield
(2) Hitec HS-645MG ultra torque servo motors (
Vaccum pump
Coffee (I used Maxwell house, original roast)
12″ round balloon
Lazy Susan bearings
Cast Acrylic tube
Two feet of 3/8 inch OD, 1/4 inch ID tubing

Various 3D printed parts, design and print files at:

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

Step 2:

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:

Cut off the lip of the balloon

Cut off the lip of the balloon.

Step 4:

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

Step 5:

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:

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.

Step 7:

Drill a 1/2 inch hole in the printed head through the snout (I couldn’t figure out how to make the snout hole go all the way into the head when I designed it–so you have to drill about 1/2 inch of plastic).

Step 8:

Insert the gripper into the snout.  Drill two small holes and attach the two pieces together with screws.

This will allow removal of the gripper if the balloon fails or if you want to change the amount of coffee contained.


For more detail: Froggy World 5 The Coffee Gripper 

This Post / Project can also be found using search terms:

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