Raspberry PI Spiderbot

OsProject
id	PI-Q-Robot
state
owner	BITPlan
title	Raspberry PI controlled Quadruped Robot with 3D Simulator
url	https://github.com/BITPlan/PI-Q-Robot
version	0.0.1
description
date	2019-08-07
since
until

Click here to comment see Self Driving RC Car

Inspired by the Arduino Project below we'd like to create a Raspberry PI version as in https://github.com/yasaspeiris/aragog

Simulator

• http://pi-q-robot.bitplan.com/
• Simulator documentation

Calibration

Restful interface

http://<baseurl>/servo/<servoid>/<angle> will set the angle of a single servo

Servo numbering scheme

This is the default numbering schema as configured in the software. If your servos are mounted or cabled differently you might want o adjust the code a accordingly

ServoId	Leg	Extrimity	Inverted
0	1	Coxa
1	1	Femur	x
2	1	Tibia	x
3	2	Coxa
4	2	Femur	x
5	2	Tibia	x
6	3	Coxa
7	3	Femur
8	3	Tibia
9	4	Coxa
10	4	Femur
11	4	Tibia

Calibration Range

Extremity	Servo Angle	Position	Direction	Range
Coxa	90	45°	left to right	0°-180°
Femur	90	Flat	up to down	0°-180°
Tibia	90	Flat	down to up	0°-180°

Relevant source code

class Spider:
    """ I am a quadruped spider with four legs consisting of coxa, femur and tibia each"""
    def __init__(self):
        self.fl = Leg(0, 0,  1,  2)
        self.fr = Leg(1, 3,  4,  5)
        self.rl = Leg(2, 6,  7,  8)
        self.rr = Leg(3, 9, 10, 11)

...
class Leg:
    """ I am a single leg of the spider consisting of coxa, femur and tibia"""
    def __init__(self, legId,coxaId, femurId, tibiaId):
        self.legId=legId
        self.coxa = Extremity('coxa', coxaId)
        self.femur = Extremity('femur', femurId,legId<2)
        self.tibia = Extremity('tibia', tibiaId,legId<2)

...
class Servo:
    """ I am a single Servo motor """
    def __init__(self, id,inverted=False):
        self.id = id
        self.inverted=inverted

    def setAngle(self, angle):
        self.angle = angle
        trueAngle=180-angle if self.inverted else angle
        if kit is not None:
            kit.servo[self.id].angle = trueAngle
        return trueAngle

Links

• Spider robot(quad robot, quadruped)-MG90 regishu 2017
• https://github.com/regishsu/SpiderRobot
• https://www.hackster.io/yasaspeiris/raspberry-pi-powered-quadruped-bbb68b
• https://github.com/yasaspeiris/aragog
• https://engineering.tamu.edu/media/4247823/ds-servo-mg90s.pdf

Other

• https://github.com/topics/quadruped
• https://github.com/anoochit/arduino-quadruped-robot

Parts

#	picture	part	example sources	documents	~ price
1		Raspberry PI 3 B+	Raspberry PI 3 B+	en	35 €
2		microSD Card	SanDisk 16 GB		7 €
3		Raspberry PI Camera	1080 p Camera Module		23 €
4		DC/DC Converter 12 V-> 5V	12 V->5 V Converter Module		7 €
5		Micro USB Connector	Delock USB 2.0 Micro USB		6 €
6		3D Printed Parts: Coxa, Tibia, Femur, Hinge	parts from regishu's design
7		Adafruit PCA9685 16 channel PWM controller	PCA9685		6.5 €
8		set of small screws	set of small screws		8.5 €
9		12 x MG90S	12 x MG90s		42 €
				Total	~ 135 €
a		Breadbord Kit	MB102 Breadbord Kit		7 €
b		Ulrasound Sensor	5 x HC-SR04 + Cables		10 €

Printing

You might want to make sure that you print your parts with sufficient infill - I used 75%.

Example for broken part

This part was printed with Cura's default infill and broke off:

Assembly

• Legs and hinges are connected with 1.4x5mm screws
• Legs and servos are connected with 1.7x6mm screws

We use the raspberry base from https://github.com/yasaspeiris/aragog/blob/master/3d%20printed%20parts/base.STL

Leg Test

sudo python3 testadafruit.py 0 1 2 3  0

sudo python3 testadafruit.py 0 1 2 3  90

sudo python3 testadafruit.py 0 1 2 3  180

testadafruit.py

# Test Adafruit 
# WF 2019-07-09
import sys
import time
from adafruit_servokit import ServoKit
kit = ServoKit(channels=16)

# 
# set the given angle for the given servos
#
def setAngle(servos,angle):
  print (angle)
  for id in servos:
    kit.servo[id].angle=angle
  time.sleep(0.3)

# Test Servo Software
servos=[]
args=len(sys.argv)
fromangle=0
toangle=180
step=1
if args>1:
  for port in range(1,args-1,1):
    servos.append(int(sys.argv[port]))
  anglestr=sys.argv[args-1]
  if "-" in anglestr:
    parts=anglestr.split("-") 
    fromangle=int(parts[0])
    toangle=int(parts[1])
  else:
    fromangle=int(anglestr)
    toangle=fromangle
else:
  servos.append(0)
  servos.append(1)
  servos.append(2)

if fromangle!=toangle:
  try:
    while True:
      for setangle in range(fromangle,toangle+step,step):
        setAngle(servos,setangle)
  except KeyboardInterrupt:
    print("Keyboard interrupt")
else:
  setAngle(servos,fromangle)

Evolution of Base

Since we'd like to use a Raspberry PI we couldn't use the orignal Base by regishu. Trying the one from https://github.com/yasaspeiris/aragog also did not work since our raspberry PI case had a different size. So incrementally a new design was created:

The problems mentioned further below led to this design:

Legtest 2

The three parts of a leg have been connected to the ports 10,11 and 12 and then the test was started with:

sudo python3 testadafruit.py 10 11 12 60-120

Wiring

Breadboard - style wiring before designing a proper holder:

In this state of affairs:

1. the power input of the raspberry is blocked by a servo - needs to be moved by at least 13 mm
2. the corner hinges are to close to the corners of the servo holders
3. the pivots to be used for the next level are blocking e.g. the usb connectors

What Links Here

• BITPlan Self Driving RC Car