DIY Lawnmower 2023

From wikiluntti

Introduction

My tobe biodiversity destroyer.

2 wheel drive using kids ATV chassis with 3" wheels without differential but with steering, 2x350W motor; speed controller. The grass cutter is a part from an old lawn mower. The ATV is steerable, thus a rotation measurement device is needed so that the motor will not burn.


https://www.kuldnebors.ee/search/search.mec?pob_action=search&search_O_string=atv&search_source=kwc

Arduino + GPS + IMU (Differential GPS).


Consider also

Theory

Steering

Use distance sensor to detect the angle
Gray code with rotary disk
Gray code; the thumbnail gets rendered wrong. However, the svg image is correct. width = 4, diff = 10, diff_center = 10, radius_center = 20 #mm
Gray code, in png format. width = 4, diff = 10, diff_center = 10, radius_center = 20 #mm

The angles needed are:

The motion of steering is restricted, thus the angle need to be measured. Two easy options:

  1. Use distance sensor (HC-SR04), or
  2. Use rotary encoder (single or multi track gray code)

Add the limit sensors to both.

Distance sensor HC-SR04

Gray code

Include the most significant bit (varies most) to outer circle.

Mechanics.

The position where the rotation angle measurement device is to be inserted.

Python code

Python code to generate the gray code image 

#
# Use sxiv to continously display the image 
#
#

import drawsvg as draw
import math as math

def outline(r1, width, t1, t2):
    #Use degrees
    pi = 3.14159
    r2 = r1 + width
    d.append(draw.ArcLine(0, 0, r1, t1, t2,
            stroke='black', stroke_width=1, fill='none', fill_opacity=0))
    d.append(draw.ArcLine(0, 0, r2, t1, t2,
            stroke='black', stroke_width=1, fill='none', fill_opacity=0))

    #Convert to rads
    t1 = -t1*2*pi/360
    t2 = -t2*2*pi/360
    d.append(draw.Lines( r1*math.cos(t1), r1*math.sin(t1),
                        r2*math.cos(t1), r2*math.sin(t1),
                        close=False, fill='none', stroke='black'))
    d.append(draw.Lines( r1*math.cos(t2), r1*math.sin(t2),
                        r2*math.cos(t2), r2*math.sin(t2),
                        close=False, fill='none', stroke='black'))


maxAngle = 60

# Draw multiple circular arcs
width = 4          # mm
diff = 10          #
diff_center = 10   #Extra difference from the center hole
radius_center = 20 #mm

d = draw.Drawing(400, 400, origin=( -2 -radius_center, -400 +1 + radius_center))


#Draw the center hole
d.append(draw.ArcLine(0, 0, radius_center, 0, 360,
        fill='nore', stroke='black', fill_opacity=0))


#
# 1st row
#
period = 2 #(one black strip, one white strip)
phaseshift = 0
r1 = radius_center + diff_center + diff
t1 = 0
t2 = maxAngle/period
outline(r1, width, t1, t2)

#
# 2nd row
#
period = 2 #(one black strip, one white strip)
phaseshift = maxAngle/(2*period)  ##90 degrees
r1 = r1 + width + diff
t1 = phaseshift
t2 = maxAngle/period + phaseshift
outline(r1, width, t1, t2)

#
# 3rd row
#
period = 4 #(one black strip, one white strip)
phaseshift = maxAngle/(2*period)                    
r1 = r1 + width + diff
for i in range(0, 4, 2):
        phaseshift = maxAngle/(2*period) + i*maxAngle/(period)           
        t1 = phaseshift
        t2 = maxAngle/period + phaseshift
        outline(r1, width, t1, t2)

#
# 4th row; 
#
period = 8 #(one black strip, one white strip)
r1 = r1 + width + diff
for i in range(0, 8, 2):
        phaseshift = maxAngle/(2*period)+i*maxAngle/(period)
        t1 = phaseshift
        t2 = maxAngle/period + phaseshift
        outline(r1, width, t1, t2)

#
# Print it
#

d.set_pixel_scale(2)  # Set number of pixels per geometry unit
#d.set_render_size(400, 200)  # Alternative to set_pixel_scale
d.save_svg('gray.svg')
d.save_png('gray.png')

# Display in Jupyter notebook
#d.rasterize()  # Display as PNG
d  # Display as SVG

print( 'Total width: ', r1 + width, ' mm' )

Borderline only

Wheels and tires

Using an old kids ATV; 3" wheels; too small for pushing the snow, but perhaps enough for the first project.

Cheap axis:

Ulkohalkaisija täynnä noin 36cm (6")

Current

Heat Dissipation

Motor

First prototype of the motor bed.
First prototype of the motor bed.

Motor Bed plan: keep is as simple as possible. Note that no welding machine, and other metal tools are scarce.


Torque, Speed, Duty Cycle

The gear is standard 410-9T bicycle chain (9 teeth). Thus, the gears from bicycles will be used for steering and driving. The wheel diameter is 3" (18 cm?), and the front gear is 9 spokes and the maximum rpm is 300. Thus, we have for the back gear

410 Roller Chain Dimension (see https://www.nitrochain.com/410-non-standard-roller-chain-10ft)

  • Pitch 12.7 mm (1/2")
  • Inner width 3.175 mm (1/8")
  • Roller diameter 7.747 mm (0.305")
  • Overall width 9.271 mm (0.365")
  • Pin diameter 3.6068 mm (0.142")
  • Link plate height 9.906 mm (0.390")



Vevor 24V 350W Nennstrom: 18,4A Brushed Permanentmagnetmotor Gear Reduction Packungsgröße: 22 x 19 x 17 cm (8,66 x 7,48 x 6,69 Zoll) Bruttogewicht: 3,05 kg

Older idea: https://www.ebay.de/itm/354278930033?hash=item527cab7671:g:NcAAAOSwrQNjIXA8&amdata=enc%3AAQAHAAAAsMHTOr42GQrvrE2i3wCdqI2r5jjEv1Xs%2BiBNogN2wRUiTlV4oLKSZLa9D8iT9KRAftUAsueGPYsgt1wNozci7go5zGnmZBCTHTE%2FBg2kQv04EJubQSPv9UXCipRa6pBzGubI%2B5RJl9PVJZdOm%2B2MaNdAeKMCMpAT5vLeXDPcrm0rR88Buo1sV4Q0l%2B9JTswzo5Qq5QxHEeGmWyUQU4NN4EgYsJ4TaD6%2BwVnMTwp2sTW%2B%7Ctkp%3ABk9SR8anh5a_YQ

Chain

9 Zahnrad für Kette Nr. 410, Teilung 12,7 mm. Besonders gut für Heimwerker geeignet, da der Antrieb mit Standard-Fahrradketten (1/2 Zoll Teilung) kompatibel ist.

Shimano: 114L or 116L depicts the number of links, length, of the chain.

Chains are identified by the number of rear sprockets they can support, anywhere from 3 (why not 1?) to 13. The following list enables measuring a chain of unknown origin to determine its suitability.

  • 10 speed – 6.0 to 7.0 mm (1⁄4 to 9⁄32 in) (Shimano, Campagnolo)
  • 10 speed (Narrow) – 5.88 mm (7⁄32 in) (Campagnolo, KMC)
  • 10 speed (Narrow, Direction) – 5.88 mm (7⁄32 in) (Shimano CN-5700, CN-6700, CN-7900)

Chains come in 3⁄32 in (2.4 mm), 1⁄8 in (3.2 mm), 5⁄32 in (4.0 mm), or 3⁄16 in (4.8 mm) roller widths, the internal width between the inner plates.

Chain widths

  • 3⁄32 in (2.4 mm) chains are generally used on bikes with derailleurs such as racing, touring, and mountain bikes.[17] (Fixed sprockets and freewheels are also available in 3⁄32 in (2.4 mm) widths, so fixed-gear and single-speed bikes can be set up to use the narrower and lighter 3⁄32 in (2.4 mm) chains.)
  • 1⁄8 in (3.2 mm) chains are typically used on bikes with a single rear sprocket: those with coaster brakes, hub gears, fixed gears such as track bicycles, or BMX bikes.
  • 5⁄32 in (4.0 mm) chains are used on cargo bikes and tricycles.


Shimano cn-nx10 1s suits.

Motor Speed Controller BTS7960

We use BTS7960 based speed controller IBT-2 with max 43 Amps current. The datasheet is available at https://electropeak.com/learn/download/bts7960-43a-motor-driver-datasheet/

Example code from Electropeak or Hessmer

Pins

  • VCC: 5V
  • GND: Ground
  • IS-R: Input signal for detecting high current – Straight rotation
  • IS-L: Input signal for detecting high current – Inverse rotation
  • EN-R: Output Signal for controlling motor direction – Straight rotation
  • EN-L: Output Signal for controlling motor direction – Inverse rotation
  • WM-R: PWM Signal for controlling motor speed – Straight rotation
  • PWM-L: PWM Signal for controlling motor speed – Inverse rotation

Motor pins (High current):

  • M+: Motor Positive; M-: Motor negative
  • B+: Battery positive; * B-: Battery negative


Some instructions:


Extra things and older thoughs.

Use PWM. Feedback? Arduino L298N H-bridge.

Arduino pwm motor controller 300W 36V 20Amps


https://electropeak.com/learn/interfacing-bts7960-43a-high-power-motor-driver-module-with-arduino/

High power dc motor speed controller

Radio controller

How to connect the receiver to Arduino

We chose Flysky FS-i6X RC Radio Sender & FS-IA10B Set 10-Kanal 2,4 GHz AFHDS unit to send and receive data. 

// https://medium.com/@werneckpaiva/how-to-read-rc-receiver-signal-with-arduino-54e0447f6c3f
#define CH1 3
#define CH2 5
#define CH3 6
#define CH4 9
#define CH5 10

// Read the number of a given channel and convert to the range provided.
// If the channel is off, return the default value
int readChannel(int channelInput, int minLimit, int maxLimit, int defaultValue){
  int ch = pulseIn(channelInput, HIGH, 30000);
  if (ch < 100) return defaultValue;
  return map(ch, 1000, 2000, minLimit, maxLimit);
}

// Red the channel and return a boolean value
bool redSwitch(byte channelInput, bool defaultValue){
  int intDefaultValue = (defaultValue)? 100: 0;
  int ch = readChannel(channelInput, 0, 100, intDefaultValue);
  return (ch > 50);
}

void setup(){
  Serial.begin(115200);
  pinMode(CH1, INPUT);
  pinMode(CH2, INPUT);
  pinMode(CH3, INPUT);
  pinMode(CH4, INPUT);
  pinMode(CH5, INPUT);
}

int ch1Value, ch2Value, ch3Value, ch4Value;
bool ch5Value;

void loop() {
  ch1Value = readChannel(CH1, -100, 100, 0);
  ch2Value = readChannel(CH2, -100, 100, 0);
  ch3Value = readChannel(CH3, -100, 100, -100);
  ch4Value = readChannel(CH4, -100, 100, 0);
  ch5Value = redSwitch(CH5, false);
  
  Serial.print("Ch1: ");
  Serial.print(ch1Value);
  Serial.print(" Ch2: ");
  Serial.print(ch2Value);
  Serial.print(" Ch3: ");
  Serial.print(ch3Value);
  Serial.print(" Ch4: ");
  Serial.print(ch4Value);
  Serial.print(" Ch5: ");
  Serial.println(ch5Value);
  delay(500);
}


Gear ratios

Gear ratio


Cutted parts and files

Dimensions

Inkscape's G Code generator, or use JsCut

Rotation detector. Plasma cutter.

  • Center hole: diameter 20 mm.
  • Width: 14 cm.


Steering gear plate:

  • Just two holes
  • Distance between hokes 56 mm.


Driving gear plate

  • Just some holes.

Cutting the grass

RPM, tip speed,

Tip speed. The faster the blades move the sharper, more define the cut... impact energy

  • Anything over 90 m/s is fine.
  • 84 m/s (16,500 fpm) blade tip speed
  • WB mfg are up near 86 m/s or 91 m/s (17k or 18k fpm). Husqvarna WB with a tip speed of 81 m/s (15.9k).
  • blade tip speed with 94 m/s


  • the design of the deck.


Blades available from a shop

  • 32cm
  • 33cm
  • 38cm veitsiterä
  • 42cm
  • 43cm veitsiterä (bio)
  • 46cm veitsiterä (akkukäyttöinen)
  • 48cm veitsiterä (bio, akku)
  • 49cm
  • 50cm
  • 51cm
  • 53cm (myös 2x, eli 107 cm) 42"
  • 56cm (bioleikkaava)


For example (at 97 m/s blade speed, 3.5 m/s ground speed, running single blades--so you get two "cuts" per revolution):

  • 30.5cm blade: 6048 rpm (!), 1.8 cm of ground travel between cuts (in/cut)
  • 42cm blade: 4398 rpm, 2.5 cm
  • 46cm blade: 4032 rpm, 2.7 cm
  • 53cm blade: 3455, 3 cm
  • 61cm blade: 3023, 3.5 cm

The blade should spin at approximately 3000 RPM (revolutions per minute) to cut grass efficiently. ANSI standards: the tip of the blade should spin at a speed no greater than 97 m/s.


Trimmer mower or field and brush mower for a very long grass

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