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4DoF robot arm

Introduction

Repo for this 15$ 4DoF robot arm.

Work in progress ... here some teaser animations:

die.anim.gif fast.anim.gif

Construction

There are no instructions for building the robot arm in packet received, nor on product website. But building was possible by looking at the many photos of robot arm shown on product website.

I had to do a lot of sandpaper work in order to get movable gripper parts slide on the board screwed onto top servo motor.

What was really bad is that the diameter of the gearwheel connector did not fit into the hole of 3D printed robot arm ground plate. I did cut the one arm of gearwheel connector, then did put it on ground servo gearwheel, and screwed it with small screw. Then I took out my Dremel and removed material as long as needed to be able to press the robot arm ground plate on the prepared gearwheel connector. For seeing details of 5MP photo you have to right click:

Even really firmly screwing the big 3D printed gripper gearwheel onto the small top servo gearwheel leaves too much play for recreatable big gearwheel position wrt servo motor position. I solved that issue by putting two drops of superglue onto big 3D printed gearwheel before connecting with small servo gearwheel -- not perfect, but works.

Wiring diagram

A colleague told me to use powerrail in order to avoid voltage drop problems:
https://youtu.be/qc0d_gW480I
SG90.powerrails.yt.png

This is connection diagram:
SG90.powerrails.png

Tools

tools/gamepad

Tool tools/gamepad allows to control 4DoF robot arm with (SNES) gamepad.
All 8 buttons as well as all 4 axis buttons have functions.
Delta 1000/100/10 does 90°/9°/0.9° changes to servos:

pigpio pigs scripts

Hard coded sample scripts can be easily done using pigpio library's pigs command, especially:

...
S/SERVO u v - Set GPIO servo pulsewidth

This command starts servo pulses of v microseconds on GPIO u.  
...

Setting of 500/1500/2500 corresponds to 0°/90°/180° for servo motor.

Pi GPIO8/9/10/11 controls robot arm gripper/top/bottom/pan servo.

die picker

This is the script executed for die picking demo:

pi@raspberrypi3Bplus:~ $ cat doit
#!/bin/sh
pigs s 11 1500; pigs s 8 2100; sleep 0.5
pigs s 10 2500; pigs s 9 1900; sleep 0.5
pigs s 8 1500; sleep 0.5
pigs s 9 1500; pigs s 10 1500; sleep 0.5
pigs s 9 2500; pigs s 11 2500; sleep 0.5
pigs s 8 2200
pi@raspberrypi3Bplus:~ $

https://www.youtube.com/watch?v=iwZIn6fQfMk
die.anim.gif

4 servos moving simultaneously

These are the pigs commands for what you see in below animation:

...
pigs s 11 2000; pigs s 10 2000; pigs s 9 2000; pigs s 8 2000; sleep 0.6
pigs s 11 1000; pigs s 10 1000; pigs s 9 1000; pigs s 8 1000; sleep 0.6
pigs s 11 1500; pigs s 10 1500; pigs s 9 1500; pigs s 8 1500; sleep 2
pigs s 11 1000; pigs s 10 1000; pigs s 9 1000; pigs s 8 1000; sleep 0.3
pigs s 11 1500; pigs s 10 1500; pigs s 9 1500; pigs s 8 1500; sleep 0.3
pigs s 11 2000; pigs s 10 2000; pigs s 9 2000; pigs s 8 2000; sleep 0.3
pigs s 11 1000; pigs s 10 1000; pigs s 9 1000; pigs s 8 1000; sleep 0.3
pigs s 11 1500; pigs s 10 1500; pigs s 9 1500; pigs s 8 1500
...

https://www.youtube.com/watch?v=qc0d_gW480I
fast.anim.gif

Adding camera near gripper

Options are v1 mini camera sensor (that connects to Pi Zero only)
v1 mini camera

or v2 repair replacement camera sensor that needs a working original v2 camera board (for crypto chip)
v2 repair replacement camera

TBD

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stuff for 4DoF robot arm, construction, demos, tools, ...

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