Micro:bit robotic drawing arm - Stardraw Megalink

StardrawMegalink - Robotic drawing arm

Introduction

The project aims to create an experimental prototype of a drawing arm with a base. It is designed to test inverse kinematics. The software part is provided by a Micro:bit microcomputer with a library actually written for the digital servos controlling the arms.

Equipment needed and price

• 3D printer with filament (recommended PLA) of about 400 grams with a print area of at least 18×18 cm(price about 2 USD)
• Nuts to load (12 nuts M14)
• 8 magnets (4 smaller: diameter 6 mm, thickness 1.3 mm, 4 larger: diameter 6 mm, thickness 2.6 mm)(price approx. 2 USD)
• Soldering iron
• Instant glue
• 5× thread inserts(price approx. 1 USD)
• 2× SG90 servo(price approx. 1.25 USD)
• 2× Plastic handle for attaching the arm to the servo (included with the servo)
• Drobné lineární mikroservo(cena cca 8.5 USD)
• Micro:bit(price approx. 34.5 USD)
• Expansion board for microbit(cena cca 11 USD)
• Micro USB cable(price approx. 1 USD)
• Micro USB adapter(price approx. 2.1 USD)
• Power cable extension tool and extension cable for microserv0o

*Total price: around 64.5 USD with micro:bit*

Similar screws and bolt must be obtained for assembly. Dimensions are given in width/length ratio (milimeters). The silver screw (second from the left) is supplied in the package with the servos.

Assembly and printing

Printing

Print the components below on a3D printer.

The recommended material for printing all components isPLA.

Arms

Links to download the arms in .STL format: 1st arm, 2nd arm.

If you need to customize the arms, they are also available in .SLDPRT format: 1st arm, 2nd arm.

Pen holder

Link to download the pen holder in .STL format: Pen holder.

If you need to customize the holder, the holder is also available in .SLDPRT format: Pen holder.

Base with lid and cube for holding USB

Download links for base with lid and cube in .STL format: Base, Lid, Cube.

If you need to customize the arms, components in .SLDPRT format are also available: Base, Lid, Cube. Beware! it is necessary to set the breakpoint in your program controlling printing on the 3D printer to the position just before pressing the magnet insertion point and pressing the nut insertion point during printing.

Assembly

Once you have all the components printed, magnets and nuts embedded in the base, and all the parts secured, you can proceed to assembly.

1. Soldering the threaded inserts

Heat the soldering iron to about 220 °C. Take the base and pen holder. Insert the threaded inserts into the holes in the base. One by one, place the tip of the soldering iron on each insert, waiting until the filament begins to melt slightly and the insert begins to embed. At this point, remove the soldering iron and push the insert into an aligned position using a blunt object (such as the end of a marker). Follow the same process for inserting the liner into the pen holder.After embedding, wait at least 5 minutes to allow for setting

2. Inserting the micro USB adapter

Insert the micro USB adapter into the hole on the inside of the base. Then take the printed cube, apply hot glue to the sides and slide the cube behind the micro USB adapter to fix the micro USB adapter in the hole.

3. Screwing in the micro:bit expansion board

Take the appropriate screws and screw the micro:bit expansion board to the base with them into the recessed inserts.

4. Screw the servos into the base and arm

Take your servo motors and use the screws provided to screw one into the hole in the base. Screw the other servo motor into the hole in the arm 1.

5. Screwing in the linear motor

Take the linear motor and use the screws to screw it to the pen holder from the back side. Make sure that it is screwed in the direction shown in the picture.

6. Screwing on the servo handles

Screw the servo handles into the arm sockets using the screws provided.

7. Screw the arms together and to the base and add the pen holder

Screw the second arm to the servo on the first arm first using the included servo screw. Then screw the first arm to the servo in the base.

Also, add the pen holder to the second arm and drip hot glue between the tip of the linear servo and the second arm.

*Voila you have folded the robotic arm*

Software

The software part is provided by the microsoft makecode environment for micro:bit https://makecode.microbit.org/.

An external pxt-smooth-servo library written inTypescript was created for this project. The library provides servo and microservo control.

The library has its own documentation in the main.ts code file.

The way to add this extension to the project's macrocode is described in readme.md.

Implementation of this class:

basic.forever(function () { basic.pause(50); smoothServo.SmoothServo.update(); });

let servo1 = smoothServo.SmoothServo.createServo(AnalogPin.P0); let servo2 = smoothServo.SmoothServo.createServo(AnalogPin.P1);

input.onButtonPressed(Button.A,() => { servo1.moveTo(2000); console.log(servo1.buffer()); console.log(servo1.toString()); });

Category: Mechanical Toys