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WEEDINATOR 2025

The WEEDINATOR is back!

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The WEEDINATOR is back!
It's been 5 years since the last iteration and there's going to be same major changes.
The mission remains the same: KILL THE WEEDS !!!
..... but rather than build from scratch, we're now using a donor vehicle, an ISEKI SG15, featuring:

• 3 cylinder 15KW diesel engine
• Full hydraulic transmission
• 4 wheel drive
• Front mounted PTO

It's a tiny tractor but easy to work on. The ultimate aim is to provide a flexible control system that will allow others to create their own farm robots.

Sponsored by PCBWay https://www.pcbway.com/

Objectives:

• To provide an open source control system for farm robots on small farms.

Solutions:

• After many iterations, we decided to make most of the circuits in the control system user configurable, rather than having too many inflexible PCB traces on the PCBs. This has the added advantage that prototyping is easier and faster as otherwise one wrongly routed PCB trace could ruin the whole board. The main MCU is the largest STM Nucleo we could find, with 144 pins, the NUCLEO-H723ZG, and is fully laden with masses of features, including the ability to run at least 3 quadrature encoders (there's probably more available).

• Keep the components as modular as possible so, for example, we use the whole Nucleo plug in board without attempting to solder STM chips on our own boards.

• The PCBs are stackable, so more  NUCLEO-H723ZG modules can be added, for example. The motor controllers are on their own separate PCBs, which are also stackable.

Main Features of Control System:

• Control at least 3 DC motors / linear actuators with in-built quadrature encoders for positioning simultaneously.

• Switch at least 16 40A automotive relays for fuel pump, starter motor, glow plugs, hydraulic cylinder solenoids etc.

• Monitor at least 4 high ampage channels to provide 'digital fuses' and protect motors etc from becoming overloaded.

• Provide at least 10 conventional fuses for motors etc.

• Four x 16 bit Resistor divider circuits for sensing battery voltage, for example.

• Eight boolean Resistor divider circuits for sensing 12V positioning induction sensors, for example.

• Each of the above modules are stackable so, for example, there could be 8 or even 12 digital fuses.

• Cm level GPS.

• 4G modem.

Build Itinerary:

Stage 1:

• Make the steering and the throttle radio controlled using the onboard quadrature encoders in the motor and linear actuator in combination with inductive sensors to provide 'homing' locations at the mid point of the steering and the neutral position of the throttle. Since the machine is hydro-static, the throttle moves seamlessly from reverse to forward with a neutral position somewhere in the middle for 'stop' - trying to operate normal manual gears would be much more challenging!

Stage 2:

• Build up a super structure for protecting the internals from the weather and provide mounting points for the various antennae required.

Stage 3:

• Design and build an 'implement' to be positioned on the tractor's 3 point hitch which will have both x and y axis cultivation. The implement probably needs to be shrouded from external sun light to prevent strong shadows interfering with cameras.

Stage 4:

• Add cameras and extra control system for crop position detection to enable y axis cultivation.

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  • Current Sensor PCB (Digital Fuse)

    Capt. Flatus O'Flaherty ☠2 days ago 0 comments

    Featuring 4 channels of 16 bit 15A current sensing and 4 channels of 16 bit voltage sensing via voltage divider, this gadget can act as a digital fuse, protecting the motor driver and actuator from damage due to stalling. The steering actuator is particularly prone to this problem, even though it has an induction sensor at the mid position to reset encoder values - it's just too easy during development and commissioning of the machine to make a small mistake and blow up £200 worth of equipment. The resistor bridge can be used for accurately sensing battery voltage and anything else that crops up in the future.

    The underside of the board has some heavy duty copper lugs soldered in to connect the current sensing TMCS1123 chips to the large Wago connectors. PCBWay could have supplied extremely heavy 8oz boards, but I chose this option to save cash. BTW, the boards from PCBWay are great quality and the service is superb. They also check with me on the more esoteric features of the board before sending to the press, which guarantees there are no mistakes in interpreting the Gerber files. The chips themselves come in various sensitivity ratings and the ones currently installed are good for +-15A on a 3V3 power supply. The maximum range seems to be +-92 A with the TMCS1123A1A.

    This current sensor PCB sits on top of another PCB that has no electrical connections, just accurately placed mounting holes for 3 main modules - the current sensor, an analogue fuse box and a stack of motor controllers. The large white PCB can also be stacked up and there are large holes in the redundant space for cable routing. Mounting of the 3 modules has been checked and everything fits perfectly and the whole thing fits well in the main enclosure box with all the connections in sensible places. Phew !!

  • Relay Boards

    Capt. Flatus O'Flaherty ☠4 days ago 3 comments

    Featuring 16 channels with 40 amp automotive relays (relays not plugged in yet) and 2 experimental 4 amp high side switches, this board should be more than capable of illuminating the engine glow plugs (20 amps) and engage the starter motor solenoid (40 amps) for starting the engine. The DIP chips shown in the photo below are ST Stepper Motor Control/Driver L293D chips which can also be used for driving LEDs and relay coils as in this case. There must be some surface mount equivalents somewhere, but not found them yet. The connectors are all by the manufacturer Wago and were selected because of their solid mountings to the PCB and high spring clamping forces. The larger ones could easily break a finger if used wrongly. There's also a SMT 5v regulator for powering the driver chips with 470uF capacitor on the input. The relays could easily have been soldered directly onto the PCB, but using the mounts enable easy replacement if something goes wrong on the machine. The wiring of the relay high current terminals is not connected to the ground plane so a live feed can come out of the analogue fuse box, into the digital fuse box, if required, and then to the glow plugs, for example, which then connect to the machine's common earth.

    On the reverse side, as below, there are giant lugs of copper soldered to the relevant relay pins and large grey Wago connectors to carry the 40 amps of current. The relays themselves have fly back protection and are the Durakool 'DR' type. If the 'D' type was used by mistake, there would be plumes of magick smoke emitted from the relays and melting of wire insulation. The PCB, acquired from PCBWay, is 2 oz in weight, which is double the normal thickness and this weight was used to ensure solid connections with the large Wago connectors and no damage to the traces when soldering with a 450 watt soldering iron.

  • Steering, Engine Throttle and Hydro-static Throttle Installed

    Capt. Flatus O'Flaherty ☠11/22/2024 at 11:47 0 comments


    The main systems to enable the machine to drive around on remote control have been installed - steering and the two throttle motors. Yes, this machine has 2 throttles, one to control the engine speed like a normal throttle and another to control the hydrostatic transmission with forwards, reverse and neutral. There are no gears and there is a theoretical infinite range between neutral and 'fast'. In the past we struggled to get fine control and very low speeds and in this version we've installed a 'slow' actuator with a large travel distance (150mm) to get the best out of the in built quadrature encoders. We did tests on the steering with a 300kg spring balance to assess what kind of forces were involved if the wheels were to get stuck in a rut or such like. The balance was attached to the main lever which actuates the Ackerman steering mechanism and we recorded a good 300kg by jamming up the wheels by hand. We maybe should have put an actuator straight onto this lever but instead chose to attach a pulley wheel to the steering column gearbox which would have been a better solution if there was hydraulic assisted steering, of which there is none on the machine. There's a bit of back lash in the gearbox so it will be interesting to see if the machine can still travel in a straight line when using GPS positioning. If it's just too much hassle, we can swap out the pulley wheels and steering column and attach a linear actuator to the main lever instead. 

    We were worried about burning out the actuator motor by stalling the steering so installed a fuse box and also a custom made circuit board for sensing currents of about 20A which will provide a 'digital fuse' to help prevent damage.

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