DIY Lawnmower 2023: Difference between revisions

Latest revision as of 22:43, 17 June 2025

Introduction

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

ArduPilot https://ardupilot.org/rover/docs/gettit.html
Cube Orange https://ardupilot.org/copter/docs/common-thecubeorange-overview.html
OpenMower

Theory

Rotary Encoders or a Shaft Encoder

Two main types of rotary encoder: absolute (angle transducer) and incremental.

Mechanical (eg potentiometer)
Optical (sensitive to dust)
Capacitive
On-axis magnetic ()
Off-axis magnetic

Rotary pulse encoder; Eg 600 ppr (pulses per rotation).

Gray code 3d STL files

Caption1
Caption2
Caption2
Caption2
Caption2

3d design with Blender

60 degree limit; 16 segments.

Create a cylinder with 16x6 = 96 vertices; Radius 35; Depth 3.
Edit mode; extrude radially; scale s using the following numbers (which makes the difference of the radii the same). The data is found on File:Gracode percentages.ods. The difference $d={\frac {R-r_{1}}{4}}$

Caption text
Radii	Subtraction (d=0.825)	Coeffiecient
R_max	7
R	6.6	0.943
r₄	5.775	0.875
r₃	4.95	0.857
r₂	4.125	0.8333
r₁	3.3	0.8

Make the cylindrical object which is to be attached to the axis. The angle is 100 deg.
Interesting but not working method: Cube; Hole; Simple Deform; Array

The blend file: File:Gray disc.zip

Sizes

Diameter of the axis: 25 mm
Width: 10 cm
Length: 7 cm (4.5 cm)
Height: Less than 26 mm
Diameter of the LDR is 0.51 mm

Four + two (4+2) radii.

7 / 6 = 1.1 cm

Steering

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:

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

Add the limit sensors to both.

Distance sensor HC-SR04

Dependent on ambient temperature.
Ping rarely so that no echoes.
Tests on accuracy

Gray code

In a gray code the bit distance between two consecutive words is exactly one (mono-difference).
Accuracy:
Absolute Position Coding Method for Angular Sensor—Single-Track Gray Codes
The Structure of Single-Track Gray Codes
Finding Single Track Gray Codes with SAT

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

Mechanics.

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:

125cc 835 mm, 55.90€: https://www.tuontitukku.fi/pienkone-vene-ja-varaosa/monkija-125cc-taka-aksila-835-mm-taka-aksila-monkijaan-83-5-cm/p/6419773800559/
Takanapa 4x110 Mikilon Pentora 125cc; 32.90€: https://www.tuontitukku.fi/pienkone-vene-ja-varaosa/takanapa-4x110-mikilon-pentora-125cc-taka-akselille-jossa-19-os-20mm-boori/p/9977000025276/

Ulkohalkaisija täynnä noin 36cm (6")

Current

Heat Dissipation

Motor

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 $in$

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

https://www.ebay.de/itm/134260101005?hash=item1f42868f8d:g:t1kAAOSwf0ljOTPG&amdata=enc%3AAQAIAAAA8Ao6wUUoT1WDjHCODdl3m2xH255xL30h99ZcuqQSUjSyt7JvM02btIHsmHAXNg8FOqT0oIQPQ1KEC%2BnLal19zabXO%2FLykrgs0JxbSzZ8Wn4lngUubdhcxlNQ9op1Sb4uRV9cEiDEpRE8FClxXNuuwthOD1ZohDHUaSX2pwc4qnR15VhyL%2BrjcdeHNSCwr5vR7opzR4d5lTXLmMAF%2F4N%2BAWB1l1EexFKuGxqAR7dT0KqQ6pl9WV44uaR0jWWJPDtfi3zOEBwXzrODyMSYV3K71T23rYouoCzlAZCzlSftYSI9QHaSTRe6hc%2F%2FqWAFoGA42A%3D%3D%7Ctkp%3ABk9SR5qVyrn6YQ

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

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);
}

https://medium.com/@werneckpaiva/how-to-read-rc-receiver-signal-with-arduino-54e0447f6c3f

Gear ratios

Gear ratio

${\begin{aligned}N_{2}&=2\pi rN_{1}{\frac {n_{1}}{v}}\\&=2\pi 18cm9{\frac {51/s}{20km/h}}\\&=2\pi 0.18m9{\frac {51/s}{20/3.6m/s}}\\&=18\pi 0.18{\frac {5\times 3.6}{20}}\\&=18\pi 0.18{\frac {5\times 3.6}{20}}\\&=9\end{aligned}}$

Cutted parts and files

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

Anonymous

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DIY Lawnmower 2023: Difference between revisions

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Contents

Introduction