Introduction: Robot Arm With Coffee Gripper

About: I am a former English teacher turned Interactive Media Instructor turned STEM teacher turned computer science teacher. I like to make, fix, and take apart. Few things are more fun than taking something apart t…
My idea for this project came from the video below. After watching it I had to build my own version.

My version does not work nearly so well. Being strapped for cash at the moment I decided to see what I could build with odds and ends around the house and parts left over from other projects. This was really fun to make and I hope to improve on it later. 

Step 1: Tools/Materials

Soldering iron
Scroll saw (Any method to cut wood would work)
Hot Glue Gun

Reynolds Vacuum sealer
Futaba Servos (modified)
Gears - from old remote controlled car
12" latex balloon
Spindle - from hard drive
Controller - from Erector set
1/4 inch clear tubing
Loctite repair putty
Steel wire
Zip ties
Hot glue sticks
Wooden Shim
Wire mesh strainer
Alligator clips

Step 2: Modify Servos

Modifiy your servos using this instructable as a guide. I left the original wiring intact however and used my soldering iron to melt two holes for my wires to come out. I did not modify anything else on these servos.

I wanted to use an old OOpic microcontroller to set up my servos, but I no longer have a compiler for it and cannot find one.

Step 3: Build Base

You will need a square piece of wood for the base. Sand it with a 60 grit sandpaper to smooth the edges.

Build the vertical arm. Remove the plastic from the center of the gear by melting it with a soldering iron, note this is not safe. If you have a Dremel or a drill then use that to remove the plastic. The gear should fit onto the spindle from the hard drive. Attach the gear with Loctite epoxy putty. Let the putty cure overnight so that you have a good fit.

Now you need to attach a gear to the other servo. Take the other gear and remove the center with a 1/4th inch bit. Now remove the cross from the motor and use it to mark holes for where you will attach it to the servo. You will need two holes for each arm of the cross. Use a 1/8th inch bit to drill the holes. Then feed some wire in through the cross and the gear to attach the two. Then screw the cross back to the servo.

Take two smaller pieces of scrap wood and screwed them into the base to hold the servo that controls the horizontal motion. Then select some scrap wood so that the gear on the servo hits the gear on the hard drive. Attach the hard drive spindle to the base with nails. Use zip ties to keep pressure on the gears. 

Finally drill four 1/8th inch holes into the top of the vertical arm. These are for the servo to be attached to. Attach the second servo to the top of the bamboo using steel wire and twisting it around the servo. Attach the bamboo to the base gear with a generous amount of epoxy putty. Let it cure for overnight. 

Step 4: Build Arm

Take the bamboo you will be using for the horizontal arm and cut slots for the servo. Use a scroll saw to cut a 2 inch section off half the bamboo. Then cut two notches for the cross to fit firmly. Then cut a shim up to brace the cross from the servo. Use epoxy putty to set the shims in the bamboo. Then place the cross for the servo in the notches and marked it. Drill two holes where you marked. Then attach the cross with some steel wire. 

Step 5: Build Coffee Gripper

Cut a small section of wire mesh to fit over the hose. Hot glued it to the end of the hose. This is to prevent the coffee from being sucked up the hose by the vacuum sealer. 

To fill the balloon with coffee you can use a spoon. You will want the balloon full, but not too tight. To get the balloon full you will need to fill the balloon up into the neck and then blow it up. The coffee in the neck will fall into the body. You can do this until the balloon is full. 

Now place the hose into the neck of the balloon mesh end first. Secure it with a zip tie. Then use some hot glue to fill the neck. Finally twist the neck and place another zip tie. 

Cut the neck off a ballon. Use this on the other end of the hose to attach it to the vacuum. Secure the neck in the same way you secured the coffee filled ballon.

Finally attach the hose and coffee filled balloon to the arm with zip ties. 

How the gripper works: If you have ever bought coffee from the store packed in vacuum sealed bag you know that it is hard. Once you open the package it becomes loose. That same principle is at work here. The coffee acts like tiny little gears and when the air is taken out they lock into each other. This is what allows the gripper to work.

Step 6: Controlling the Arm

To control the arm I using the control from an old erector set I found. It has two switches on it that allow me to change the direction of the servo or leave them off.

For the base servo attach the wire directly. For the horizontal arm attach a potentiometer between the leads. This allowed you to put enough current into the arm so that it would lift only enough to hold what it is picking up. You need that kind of find control or the servo will lift the item too quickly. You can use alligator clips to make the connections. If you want the item more permanent solder them.

Step 7: Problems and Solutions

The final arm worked better than I thought. It moves with no problems, but it is not capable of applying the pressure I need to firmly grip most objects. Part of the problem is the size of the balloon I am using and the other is I am limited by the materials I had available. Look below for some video of the arm in action. 

This is a video of it not working well.

This is a video of it gripping with some help.

This is a video of it in action and working pretty well.

If I win I will use the shop bot to improve on my gripper arm design, by fabricating pieces specifically for it rather than modifying parts I have lying around. I also would use it to improve on my other projects and create new things with it. 

ShopBot Challenge

Participated in the
ShopBot Challenge

Coffee Challenge

Participated in the
Coffee Challenge

Toy Challenge 2

Participated in the
Toy Challenge 2