Robot Arm

Hi everyone,

I am Bart Klijn, an engineering student from the Netherlands. For school I have made and programmed a robot arm which is able to pick up an object an bring it to the place around itself with the most light and then put it back on the floor. For this project I have only a limited time of nine weeks.

The robot arm has a range of 30 cm and will be controlled by an Arduino UNO microcontroller. My goal is that it can lift and move an object with a weight of 300 gram.

If you decide to make this instructable then be aware that you have to spend a lot of time and that this project definitely is not as simple as it looks like unless you already have made some projects and you are good at programming stuff.

In any case, good luck!

List of materials:

1. Housing

- 1 plate (130x130mm) 10mm pressed wood

- 1 plate (370x130mm) 10mm pressed wood

- 1 plate (135x130mm) 10mm pressed wood

- 5 plates (130x30mm) 10mm pressed wood

- 2 plates (95x30mm) 10mm pressed wood

2. Electronics

- Arduino UNO

- Breadboard

- 3x LDR (Light Dependent Resistor)

- 3x 10k ohm resistor

- 2x servo (FS5109M)

- 1x servo (1501MG)

- 1x micro servo (MG90S)

- USB cable

- Wires

3. Robot arm

- 1x 3D-printed (50x50mm) 5mm PLA

- 2x plate (120x35mm) 4mm plastic

- 2x plate (35x30mm) 10mm pressed wood

- 1x robot gripper

4. Tools & extras

- Screwdriver

- Drill

- Saw

- Glue gun

- 3D printer

- Soldering iron and tin

- Tie wraps

- Screws

For the first step you have to make the parts for the robot arm. For this we use two pieces of 120x35x4 mm made of plastic. You can make these parts with a laser cutter but I have made them by myself with a jig saw. These plates are quite easy to make and because of that I chose to do it by hand. In both of the plates there has to be drilled a hole of nine mm so the servo mount fits in it. Then there will come two holes of 1 to 2 mm in it on the basis of the servo mount. This ensures that the plate can be attached to the servomotor. By one of the plates there has to get drilled another four holes of 2 mm to attach two other blocks of 35x30x10 mm wood.

These wooden blocks I have also sawn but this time with an ordinary handsaw. After this the same holes has to be drilled in it so it can be attached to the plastic plate. In both blocks there has to be drilled another two holes so you can attach the robot gripper. In one block the two holes has to be drilled trough all and the other has to be drilled only 5 mm deep.

Then only the micro servo has to get attached to the robot gripper, but this won’t fit directly. Because of that I glued it all together with a glue gun. To make sure it won’t fell of I also tie wrapped it.

After you made all things it is wise to do a quick test fit because then you know if everything which you have made is good enough.

To make the housing for the electronics I used pressed wood which I have sawn by myself. The bottom plate is made of 370x130x10 mm pressed wood. As wall I used five plates of 130x30x10 mm and two plates of 95x30x10 mm pressed wood. On top of that there will come one plate of 130x130x10 pressed wood with a hole in the shape of a servo motor so the servo can be screwed together with the plate. There are also four holes in it for the screws for the servo. Beside that there will come another plate on it of 135x130x10 mm. In all of the pieces there has to be drilled holes to screw all things together.

Because I have to use at least one part which is made by a 3D-printer I have chosen an appropriate part for that. This part is a square plate of 50x50x5 mm PLA. This will be attached on the base servo which turns the whole arm. On top of this plate the servo which functions as a shoulder will be placed.

The robot arm is made so that it is able to function on its own power. At first it contains three LDR (Light Dependent Resistor) sensors to measure the luminous intensity. When there is a lot of light, the robot arm will pick up an object and move it to this place with the base servo. Then the object will be put back by using the three other servo’s. There are six options that the robot arm can do:

If the left LDR gets the most light the arm has to move to that place but it can come from the front or from the right side. If the LDR in the front gets the most light the object can be moved from the left or the right side. And finally there are the situations that the right LDR gets the most light. With this option the object can come from the left side or the front.

Because the servo’s can’t run on the power which is been given by the Arduino-board, I have applied an extra power supply. This power supply contains four batteries which deliver 6V and about 8000mAh.

Beside this it is essential that every servo is strong enough to turn the specific piece of the arm. Therefore I calculated how strong every servo has to be. The calculations can be found in the added file.

For every LDR I used a 10k ohm resistor because otherwise the LDR will break.

Step 1: Housing

To begin with, it is wise to screw the housing whole together. To do this it is necessary all the holes are already drilled. The size of the holes depends on which wood screws you decide to use. If you have made everything already it is not difficult to screw it all together.

Step 2: Robot arm

After that the robot arm itself has to be put together. Also with this there has to have drilled holes in every piece so it can be assembled without any troubles.

The first servo which functions as the shoulder of the robot arm is tied up on the square plate of 50x50x5mm which is 3D-printed. I did this with four tie wraps. After that I attached the first plate of the arm of 120x35x4mm on the servo mount which is fastened on the servo.

The servo which functions as elbow is glued on the end of this plat which has just been made. Then the second plate of 120x35x4mm is attached on the servo mount in the same way as the first one.

The next step is to fasten the two wooden blocks of 35x30x10mm onto the end of the last plate. When you got this the robot gripper can be attached with two screws on these blocks. But before you do this you have to glue the micro servo together with the gripper. To make sure the servo won’t fell off while it is turning I put a tie wrap around it.

After this the only thing you need to do is to fasten the base servo in the hole which is made for the servo in the square plate. And of course you have to put the whole robot arm on this servo so it can turn.

Step 3: Electronical board

The last step you got to do is to attach the Arduino-board and the breadboard on the base plate of the housing. This will prevent it from moving which can lead to the release of the wires. All the wires and LDR’s are connected according to the electrical schedule.

Of course this project can always be made so it functions better. For example to add some servo’s which can make the gripper also turn like a wrist. You can also add a servo which makes the gripper can rotate so it can pick up stuff that is skewed. But for this you need more power and thus more batteries.

Because of the lack of knowledge of programming and lank of time I didn’t made it to let the robot arm do what it should do.

But perhaps you guys will make it and let it work!

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I really appreciate it you read this instructable and maybe you even decide to make this or to improve it. If some of you succeed in this project it would be great that you also share your design in this open source.