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FarmBot Genesis V2

A project log for FarmBot - Open-Source CNC Farming

FarmBot is an open-source CNC farming machine and software package built for small scale, hyper local, DIY food production.

Rory AronsonRory Aronson 08/19/2014 at 01:070 Comments

There are many design changes from Genesis V1 to V2 that make this version a huge improvement:

Tracks

Rendering of the track mounting plates, gantry plate, and gantry endstops.

There were two major issues with V1 tracks:

V2 tracks solve both of these issues by changing the orientation of the track pieces and the mounting bracket design. The brackets are larger and placed at the end of each track section so that one rigid bracket connects two extrusions. This keeps them from buckling or shifting, minimizes the number of brackets needed, allows for wheels to roll on the top and the bottom of the tracks, and allows for connection to a support post or another extrusion.

Gantry

V2 uses a belt and pinion style system to move the gantry along the tracks. The belt goes over the top of this pinion and then under each of the solid V-wheels at the tracks, and then to the end of the tracks where it is fastened. The motor also has a shaft going across the gantry to synchronize with an identical belt and pinion system on the other side.

The Gantry has seen significant change in V2. The most notable is the switch from a looped belt drive system that ran the full length of each track to a belt and pinion style system. Feeding the belt through the extrusions in V1 was hard for 1.5m length tracks and nearly impossible for 3m length tracks. The belt and pinion system uses half of the belt length and greatly simplifies installations and tightening of the belt. It also eliminates the need for pulleys and mounting plates at the end of the tracks.

Genesis V2 prototype plates cut out of MDF with a CNC router

In addition, the belt and pinion system allows the drive motor to be positioned on the gantry, allowing it to move with the other electronics, thereby simplifying wiring as all electronics move together. Also, a single drive motor in combination with a driveshaft allows for synchronized movement between both sides of the gantry along each track.

The other major improvement is the use of custom brackets which greatly simplifies the construction while making the Gantry more rigid. In V2, 1 base bracket and 4 wheels at the track/gantry interface replaces the 1 extrusion, 3 brackets, and 8 wheels for this same interface in V1. The base plates also provide locations for the endstops to be mounted.

Cross-Slide

Cross-slide endstops and belt and pinion drive system

Z-axis connection to the cross-slide and endstops

The Genesis V2 cross-slide saw a lot of improvement and change from V1. This version is constructed from three custom 3mm plates that have only the necessary holes to accommodate the needed hardware. The cross-slide moves along the gantry with a belt and pinion style drive system which saves on belt length, and is easier to install and tighten the belt. Endstops for the cross-slide and the z-axis are mounted onto the plates and are actuated by small plates that can be easily repositioned along the gantry for a different ending position. The leadscrew block for the z-axis is also mounted to one of the plates, which is hugely important because that block did not even exist in V1 hardware. The expensive eccentric spacers are replaced with angled slots for wheel adjustment and tightening. And the number of wheels for each axis of movement is reduced from four in V1 to three. Lastly, the Tee shaped plates are identical, making installation and manufacturing easier.

Z-Axis

Weight of Z-axis torquing the Cross-Slide.

The Z-axis of Genesis V2 is not any different from V1 other than the fact that we actually assembled the leadscrew into a real prototype rather than just designing it in the computer. The leadscrew is an 8mm diameter ACME screw thread that connects to the cross-slide via a delrin block. The system is smooth and reliable and all components are available from OpenBuilds.

Not shown in the renderings on this page but in the photo to the left is the delrin block being originally located far from the main gantry beam, attached onto the Tee shaped plate. This configuration created a large moment force on the cross-slide, attempting to torque it off of the main gantry beam. This torque can be seen in the photo to the left as the Z-axis becoming significantly angled. This configuration was modified so that the block is on the plate closer to the main gantry beam in order to reduce the induced moment force acting on the cross-slide by reducing the length of the moment arm the weight of the leadscrew was acting on.

Universal Tool Mount System

Universal Tool Mounting system

Tools can be interchanged and placed back into the tool bay

The Universal Tool Mount system was introduced in V2 hardware as a way to allow FarmBot to switch tools in an automated way so that it does not have to carry all of the tools at once. In addition, whichever tool is being used, generally has to be the "lowest" in Z-height so that it can reach the soil or plant. With all tools being mounted to the Z-Axis at the same time as in V1 hardware, all tools were competing to be the lowest. The Universal Tool Mount solves this issue.

The Universal Tool Mount system consists of five components:

  • A 3D printed tool mount
  • A 3D printed (or modified PVC pipe) tool "blank" that can be filled with electronics, motors, or anything else that defines the tool
  • A solenoid operated "door locker" that locks a tool into place when inserted into the tool mount
  • Four sets of spring loaded 5mm screws that allow power and data to be passed between the tool mount and the tool
  • A "tool bay" that is a 3mm plate for unused tools to be stored on

Using the FarmBot Web App, the user will define which tools are in which bays. FarmBot can then move to that position to pick up a tool, and load the necessary software "driver" to be properly use that tool. This system allows others to create new tools and drivers for any type of operation they can dream up, as long as it fits into the Tool Mount and incorporates the same four power and data screw configuration.

Issues with V2 and Proposed Solutions

Cable Management

Issue: There is no way to manage cables and water tubing.

Proposed Solution: Integrate cable carriers or another solution.

Universal Tool Mount

Issue: A few of the features are not optimized for 3D printing

Proposed Solution: Avoid cliff hangers with tapers and chamfers

Issue: Very little clearance between the screws that pass power and data

Proposed Solution: Decrease screw size from 5mm to 3mm screws

Issue: Tight fit of solenoid dead bolt in the tool mount hole, creating unnecessary tolerance requirements and friction

Proposed Solution: Increase size of hole in the tool mount

Issue: Tools are not inline with the leadscrew, creating a greater moment force on the Z-axis and Cross-Slide

Proposed Solution: Flip the orientation of the Universal Tool Mount so that the solenoid locker and tool are switched

Issue: Tool mount and tool are very tall

Proposed Solution: Optimize the tool and mount to be shorter

Track Belts

Issue: The track belts have an interference with the screws and tee nuts of the gantry corner brackets

Proposed Solution: Reconfigure the gantry to accomodate

Endstops

Issue: The small plates/brackets used to actuate the endstops are not necessary

Proposed Solution: Replace these components with just a screw and a tee nut to reduce number of custom components. Reconfigure the endstops if needed

Cross-Slide

Issue: The tee shaped brackets are not necessary and add complexity to the assembly of the cross slide

Proposed Solution: Remove them and mount the endstops on the main cross-slide plate

Number of Screws

Issue: There is an unnecessary number of screws holding the tracks together and the gantry together. This is more costly and increases assembly time significantly

Proposed Solution: Reduce the number of screws

3D CAD Files

FarmBot Genesis V2 was designed natively in SolidWorks 2014. Using SolidWorks 2014 or a newer version will provide the most seamless experience if you are interested in viewing or modifying the 3D part files. For those without access to SolidWorks, we have converted the files to other commonly used file formats.

Files can be downloaded here.

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