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Weedinator

An autonomous roving CNC weeding/cultivating machine guided by GPS and coloured markers.

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Two years ago I initiated the Weedinator Project to fight back against the onslaught of weeds which threatened to dominate the leeks that I was growing. In the meantime, the weeds seem to have adapted to my mechanised approach and the war is far from over.

I am now ready to take the fight to a higher level with an autonomous GPS/Objects guided roving CNC machine that will destroy every living organism (except for the leeks) on the surface of the earth with powerful 25Kw butane fuelled flame throwers with localised temperatures of over 1200 degrees C.

Last year's efforts resulted in a tractor mounted weeding machine which worked reasonably well except for the fact that it was not accurate enough and sometimes ended up destroying the leeks as well as the weeds. The video below shows the results:

Since then I have been exploring CNC, GPS and GPRS technology and feel 97.2% confident that I can create a roving weeding machine that can also perform other tasks such as cultivating (digging) and mowing with the right attachments. Think 'Moon buggy' or the 'Mars Rover' and that will be what I'm aiming for. Actually, there is already an open source project for the CNC part - the Farm Bot.

The machine will carry it's own electric generator running on gas/diesel and be propelled forwards/backwards/sideways with stepper motors/servos. Coloured markers, detected by an object recognition system, will be placed in the soil to create grids for the Weedinator to work within as GPS is not accurate to the scale of 1 mm which will be necessary to avoid killing the crops. GPS will be used to navigate to particular fields or seed beds.

As time goes on a more intelligent object recognition system will be incorporated to detect individual weeds:

The flame thrower will be mounted on a normal CNC frame with 3 axis of movement and the nozzle itself will be shrouded by metal sheet to prevent damage to the crops themselves. Individual weeds could be zapped by a small gas powered butane torch as used by a chef when making crème brulee.

This may seem like a very ambitious project, but the actual chances of achieving success are quite high. Much of it depends on the quality of the code written for reading the GPS data and transforming that into real-time steering and motion. It all just seems like great fun to me!

Programming new coordinates into the Weedinator via the cell phone network is not going to be difficult as much of the task of handling GPRS data has already been covered in my weather station project.

There is a risk that as the project evolves we will run out of programming space or computing power on the MCU ...... So ....... Just add another one and get them talking to each other via the I2C bus, which I also had up and running on the weather station project, although my code for this communication does now seem a little bit 'clunky'.

The greatest 'risk' is due to the cost involved in buying all the components - the GPS system is expensive and it currently requires 12 stepper motors just for the steering, suspension and wheel drives. Each stepper motor needs it's own controller which, although homemade, are still a bit pricey. When I say risk, I'm really referring to 'How useful is this thing actually going to be when it's finished?' Yes, there's a very good chance that we can build it and it will work, but how well will it work? For example, it might be incredibly slow.

Current overall chances of success = 85%.

Components list 01.xlsx

Electronic components

sheet - 11.12 kB - 08/28/2017 at 09:07

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weedinator 01.wav

The next Weedinator video is going to need a sound track. Here's a snapshot of what it might comprise.

Waveform Audio File Format (WAV) - 8.93 MB - 05/20/2017 at 09:45

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  • Photos of the Old Tractor Mounted Weedinator

    TegwynTwmffat08/31/2017 at 16:09 0 comments

  • Side view of Mechanism

    TegwynTwmffat08/28/2017 at 09:09 0 comments

  • New Stepper Motor PCB ready for Fabrication

    TegwynTwmffat08/09/2017 at 17:15 0 comments

    Having given up on the STM L6482H stepper driver chip, for lack of software, the TI DRV8711 has now been laid out in PCB design software with it's associated MOSFETS. The design features attachment holes for two large aluminium heat sinks and a small 12 volt fan.

    Each of these boards has it's own Nano MCU which can be programmed for acceleration and torque characteristics and each motor has it's own board resulting in semi-autonomous motors. The boards will be stacked vertically on another PCB and individually controlled by a Master MCU via the I2C bus. Sounds complicated? Will this machine really have over 12 MCUs in it? ...... All will be made clear in future updates!

  • Artist's Impression of the Weedinator

    TegwynTwmffat08/04/2017 at 08:40 0 comments

  • Testing Weedinator Suspension Stepper Motor Driver

    TegwynTwmffat07/20/2017 at 17:08 0 comments

    The Weedinator uses a novel stepper motor driven system for it's 'suspension':

    I've deliberately avoided the normal spring type suspension as the machine must not wobble about when the cultivating / weeding mechanism is working and the overall machine needs to be effectively 'rigid' in relation to the ground, although there will be some 'give' in the tyres.

    The technical name for the motor is 'Non Captive Stepper Motor' and the one I'm using is a Nema 34 with a rated linear holding torque of 3500 N, so it was on planet earth and operating in parallel with the earth's core, it would hold still a massive 350 kg!

    In the test I set the motor to 16 steps and maximum torque using an Arduino Mega and put about 500 N force on the motor BEFORE turning it on. As can be seen in the video below, the motor accelerated up to speed and moved up the spindle reasonably quickly:

  • Weedinator Transmission Mechanism

    TegwynTwmffat07/16/2017 at 12:00 0 comments

    During the design process, initially there is rapid progress and the design changes very noticeably. As time goes on the rate of change decreases and there comes a point where it's ok to actually build the mechanism.

    Using 3D software such as Fusion 360, we can model the mechanism with incredible ease and view it as an animation to check that components mesh with each other properly and don't bump into each other either. I think that currently the design is at about 95% 'finished' and I aim to create the first prototype at 98%, so there's a bit more work to go in Fusion 360:

  • Testing Texas Instruments DRV8711 with Nema 34 Stepper Motor

    TegwynTwmffat07/15/2017 at 15:27 0 comments

    I was not having much success with the STM 6482 due to lack of good software examples so switched to the DRV8711 chip which has a few less functions, but much easier to get up and running. There's no SPI acceleration / deceleration control, but managed to write this into code fairly easily using the good old 'millis and previous millis' trick:

      tone(24,i*10);
      digitalWrite (DIRpin, dir) ;
      unsigned long currentMillis = millis();
        if (currentMillis - previousMillis >= interval) 
        {
        previousMillis = currentMillis;
        i++;
          if(i>600){i=600;}
        }

    The Tone library gives really nice smooth motor operation and I can gently ramp up the speed and torque quite nicely, preventing sudden current inrush.

    Next job is to create a PCB for each of the 12 motors. The current idea is to stick an Arduino Nano on each PCB and link all the PCBs together via the I2C bus - this seems to be the only way to get good simultaneous control of all 12 of them! Hopefully, most of the acceleration and torque profiles can just be uploaded onto the Nanos and then (mostly) forgotten about.

    The image above also shows the gearboxes, which currently are being selected as 100:1. Sometime soon I'll be able to actually build one of the wheel/steering/suspension modules.

  • Direct drive

    TegwynTwmffat07/15/2017 at 14:08 0 comments

    I managed to get rid of all the belts and pulley wheels by using direct drive through the gearbox.

  • Setting up STM 6482 stepper motor driver chip

    TegwynTwmffat07/09/2017 at 13:46 0 comments

    I really thought that this was going to be relatively easy, but soon a bit of a nightmare started to unfold.

    Since we've got quite a few motors running at the same time, doing various different jobs, we want really good control options so that means using the SPI bus with one MCU pin to shift the registers on each motor PCB. Speed, acceleration, torgue, current sensing has to be done via SPI and not PWM or else we'd soon run out of MCU pins. The STM 6482 seems to be the best chip for the job, but it's quite complicated to set up.

    After buying the STM 6482 discovery board and playing around on it with a swanky GUI I managed to convince myself that it would be ok. Next stage was to try and get the STM Eval board up and running.

    First problem: No software available! Fortunately, after emailing STM, they fixed the broken download link and now I've got a shed load of files to compile into a working system.

    Next problem: After literally an hour of arranging the files in the Mbed software the compiler throws out an error: 'Please select your Nucleo board' ...... Very polite but it turns out that the software only supports a narrow range of nucleo boards and my F072Rb aint one of them! Eventually I work out that I need a STMF103RB with 128k of flask to be defined in the software as 'Medium Density, Non Value Line'. Fortunately the boards are not expensive and they're in stock at RS supllies. Meanwhile, my test rig awaits patiently:

    The 'build' for the compilation looks quite well documented:

    /**
    @page cSPIN_Example cSPIN

    @verbatim
    /**
    ******************************************************************************
    * @file cspin/readme.txt
    * @author IPC Rennes
    * @version V2.1
    * @date November 4, 2013
    * @brief Description of the cSPIN Example.
    * @note (C) COPYRIGHT 2013 STMicroelectronics
    ******************************************************************************
    * @copy
    *
    * THE PRESENT FIRMWARE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS
    * WITH CODING INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE
    * TIME. AS A RESULT, STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY
    * DIRECT, INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING
    * FROM THE CONTENT OF SUCH FIRMWARE AND/OR THE USE MADE BY CUSTOMERS OF THE
    * CODING INFORMATION CONTAINED HEREIN IN CONNECTION WITH THEIR PRODUCTS.
    *
    * <h2><center>&copy; COPYRIGHT 2013 STMicroelectronics</center></h2>
    */
    @endverbatim

    @par Example Description

    This example shows how to use cSPIN firmware library. Main program starts with
    clock configuration (system clock config SYSCLK to 24MHz).
    The SYSCLK frequency is selected by user in clock.h file.

    All used peripherals are then initialized, cSPIN chip is configured (registers are
    set with requested parameters).

    Different commands are then shown to perform requested operation.


    @par Directory contents

    - cspin/inc/stm32f10x_conf.h Library Configuration file
    - cspin/src/stm32f10x_it.c Interrupt handlers
    - cspin/inc/stm32f10x_it.h Header for stm32f10x_it.c
    - cspin/inc/clock.h System clock setup related header
    - cspin/src/clock.c System clock source file
    - cspin/inc/cspin.h cSPIN definitions header
    - cspin/src/cspin.c cSPIN routines source file
    - cspin/inc/cspin_config.h cSPIN configuration parameters (this file can be generated by the GUI)
    - cspin/inc/main.h Main header file
    - cspin/src/main.c Main program
    - cspin/src/pre_include.h First header file included by the preprocessor

    @par Hardware and Software environment


    - This example has been tested with :
    EVAL6480H-DISC board
    EVAL6482H-DISC board.


    @par How to use it ?

    In order to make the program work, you must do the following :
    - Create a project and setup all project configuration
    - For the DISCOVERY board :
    - Device : ST STM32F105xB
    - Library low-level interface: Semihosted. stdout/stderr Via SWO. Use CMSIS library
    - Preprocessor defined symbols :
    - STM32F10X_CL
    - USE_STDPERIPH_DRIVER
    ...

    Read more »

  • Stepper motors with gearboxes allow nice slow, controlled movement

    TegwynTwmffat06/08/2017 at 18:47 0 comments

    The wheel modules start to take shape. Stepper motors with gearboxes allow nice slow, controlled movement with the option to apply electric brakes to stabilise the machine when it is doing actual weeding / cultivating, otherwise it would move around slightly due to inertial forces acted by the cultivating equipment.

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mark wrote 4 days ago point

Hi TegwynTwmffat.  The cost of your project could be justified if you have hectares of leeks.  

An alternative to fire is soil injected steam.  Safer for some fire prone environments.  The downside is the weight of the water.

  Are you sure? yes | no

Galane wrote 08/28/2017 at 06:31 point

You're re-inventing the Sizz-Weeder. That goes back at least to the late 1940's. It mounted to the back of a tractor and used thin flame jets to burn *really close* to the crop plants. For more mature plants and tougher crops like corn, the flames could be run across the crop plants to get the small weeds between them in the row - when the tractor was run fast enough so the flame would barely warm the larger plants.

The Sizz-Weeder seems to have fallen out of use with the rise of chemical herbicides.

  Are you sure? yes | no

K.C. Lee wrote 05/04/2017 at 16:25 point

"I say we take off and nuke the entire site from orbit. It's the only way to be sure."  :)

  Are you sure? yes | no

TegwynTwmffat wrote 05/04/2017 at 16:35 point

Yeah ..... We should colonise Mars ....... But you can bet that some weeds will find a way to stow-away onto the space rocket :(

  Are you sure? yes | no

Emach00 wrote 05/04/2017 at 16:15 point

After watching your video, never before have I become so emotionally invested in the success of another man's leek patch. :)

  Are you sure? yes | no

TegwynTwmffat wrote 05/04/2017 at 16:23 point

He he ....... Yes it's quite a dramatic video. The music is from Terminator Salvation by Danny Elfman.

  Are you sure? yes | no

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