It is possible to control a robotic arm without a microcontroller, using simple electronic circuits. This post shows how.
The electronic circuit
The servomotor
Before building the electronic circuit, must be defined which servomotor to use on the robotic arm. Was chosen the microservo 9g SG90 of Tower Pro.
This servo’s datasheet can be accessed in this link.
Building the electronic circuit
Each servomotor can be controlled by a 555 circuit that generates a square wave signal and control this signal’s wavelength.
Click in the button below to access the Pulse Width Modulation post.
The electronic board that will control the 4 servos of robotic arm.
The DC power source emits interference signals that make the servos trembles during motion. To avoid that, were put capacitors in parallel with supply terminals (the Cp capacitor in schematics). The minimum value must be 220 μF. I put 3 of 220 μF and 1 of 470 μF. Are 4 capacitors in total, because are used 4 circuits, one for each servomotor.
Complete list:
- 4 555 chips.
- 4 10 kΩ potentiometers.
- 8 1N4148 diodes.
- 4 1.5 kΩ resistors.
- Wires.
- 4 1 μF x 50 V electrolitic capacitors.
- 4 220 μF x 16 V electrolitic capacitors.
- Printed circuit board 15 x 3.7 cm.
Assembling the robotic arm
Robotic arm is made of acrylic and has 4 degrees of freedom. In this post, I show step by step how to assemble it.
Base
The pieces to assemble the base.
Assembling the pieces.
The servo must be put in the rectangular space above, using this part.
In addition to the first 4, this kit has other 3 types of screws.
For each hole, must use the screw of right length to hold one or more parts. The screw’s tip must not be exposed.
Mobile box
Each SG90 servo comes with 3 screws and 3 plastic flanges as shown in the figure below.
The piece below is the mobile box’s base which must be linked to base’s servo.
Longer screws that come with the servo must be used to connect the flange to acrylic parts.
Assembling one of the sides.
The shorter screw that comes with SG90 serve to fix the flange to servomotor’s shaft.
The other side isn’t so different.
Assembling the middle part.
Uniting the parts of mobile box.
The long screws and nuts fit the side pieces.
The mobile box must be like this.
Articulation
To build the articulation, must use this part first.
Connecting it to long pieces with long screws and nuts.
Assembling the pieces and how to install on the robotic arm.
In this part you must use a nut.
Frontal vision showing the arrangment of pieces in the articulation’s last part.
Claw
First, you must put these pieces on the servomotor.
Parts that link the servo to claw.
The flange must be attached to this part with a screw that comes with the SG90.
Finishing the claw.
Linking the claw to the articulation.
Using medium length screws for side fitting.
Using the last two rings.
