4 bar linkages are very commonly used in FRC to create mechanisms that are able to move from a "closed" position to an "open" position. Four bar linkages can be an alternative to traditional pivots, but come with their set of pros/cons. Virtual 4 bar linkages are different from traditional 4 bar linkages, but have the same behavior, hence the name. Virtual 4 bars use a tension member, such as a chain/belt in order to recreate the 4 bar behavior. Videos below will discuss what 4 bars are, how to design with them, and a 3D model of a 4 bar and a virtual 4 bar. Videos to be added in the future.

Whilst designing manipulators, you might need an actuator to move part of your manipulator from point a to point b, or pivot it up and down. In such simple, 2 position scenarios, using pistons can save a lot of mechanical complexity with gearboxes and motors and free up slots on the PDP (Power Distribution Panel). The following video covers how you can design with pistons, taking into account their sizes, location, and the force they will produce and how much force your manipulator would need to operate.

The MVRT Parts Library contains a lot of the parts that are commonly used for an FRC robot such as screws, bearings, motors, etc. But sometimes, parts required for a specific application are just not on the parts library, such as a unique size of a screw, special bearings, etc. CAD files for pistons are also not in the parts library, so in order to add these files to your CAD models, you need to download them off a website and then import them into your model. Additionally with pistons, whilst it's not required, it's a good idea to allow the piston to move like it would in real life, in order to check for possible collisions and interference. The first video will cover importing files from McMasterCarr, followed by a video covering how to convert these piston files into moving assemblies.

Most FRC games require teams to have bumpers on their robots. It is important to model bumpers to ensure that they do not interfere with any mechanisms, as well as use them to your advantage (ex. over-bumper-intakes). The video below covers how to create a 3D model of bumpers in Inventor.

Whilst creating 3D models of a robot or its manipulators, often times a lot of parts are very similar are only differ with a few variables, such as length or thickness (ex. 2x1s, hex shafts, standoffs, spacers). In order to prevent the need to model these parts from scratch every single time, Inventor allows you to create custom templates. Templates will start at an initial state, such as an 1/8" 2x1 that's 5 inches long. From there, you just have to edit the length and the thickness to match your needs and add any other features. The video below will cover the creation of templates. It is important to make your templates robust so that you can change the variables you need to and not cause any errors in the part file.

Inventor's iLogic allows user to create code that will automate some part of your 3D modeling. The iLogic suite also contains forms, which create an easy-to-use interface that you can use to quickly edit parts, instead of searching for dimensions that need to be edited. The video below creates a template for Hex Shafts, using iLogic and iLogic Forms. The template gives the user the ability to switch between hex, cluster, dual cluster, and round shafts. A future video will cover a template that gives additional ability to switch between regular and thunder hex, as well as supporting 3/8 hex shafts.

FRC robots generally have a maximum weight limit, and the lighter the components are, the better robots perform. That is because, mechanisms that are light are easier to manipulate with motors, pistons, etc. and are able to operate faster and more consistently. One way to reduce the weight of mechanisms, whilst retaining strength, is to use pocketing or lightening. This process removes excess material from a part in a fashion that does not compromise the durability of the mechanism, but reduces the weight. Pocketing is usually done with Aluminum Plates and 2x1s, because other materials such as Polycarbonate are already extremely light and tend to become fragile with pocketing. Pocketing can be done in 2 distinct fashions, a free-form style useful for parts that do not have regular shapes such as gearbox plates, and a strict X pattern style that is useful for parts with regular shapes such as bellypans, side covers, etc. The video below covers the free-form style of pocketing. The video below will cover pocketing with the X pattern, useful for regular shapes.

Chain is very commonly used in FRC to transmit rotational energy from one place to another. Chains are extremely strong and easy to repair/replace when and if they do break. Although chains have an extremely high amount of backlash, higher than gears and timing belts, thus making them unfavorable for applications where precise control is required. The following video will guide you through creating a template that can be used to create a chain CAD. CADing chain is important as it allows you to check for interference and collisions.

Timing belts work in a similar way to chains, except there are pros/cons that make them more useful for certain applications than others. Below are some pros/cons for timing belts. First of all, belts come in 2 main varieties, there are GT2 belts, and HTD belts. Basically, the HTD variety of belts is a little bit bigger in size and is able to handle more load. Most applications, such as intakes, rollers, etc., work well with either choice. Some HTD sources are lower priced though, so that can factor into the decision. In order to design with belts, first decide if you want a reduction from the belts. It works the same way as a chain, a smaller pulley to a larger pulley would reduce the speed and increase the torque. A lot of pulley sizes are available on vex/wcp/andymark, but for cases where you need a specific size, it is possible to make your own pulley and 3d print it. The custom pulley template file is here: https://drive.google.com/open?id=1V20gBSk1BTdx9tJyBxouhtSXlx6qvgTi . The file to make your own timing belt is here: https://drive.google.com/open?id=1dbGXd2BMeDrgdHg2dY48rRe5V3ZfEOs3 . Once you know your pulleys, you can find the center distance and what belt you would need to use. Use the belt center distance calculator below to find the center distance as well what size belt you would need. Link to belt center distance calculator: https://www.technobotsonline.com/timing-pulley-distance-between-centres-calculator.html WCP page with belts and pulley information: GT2: https://www.wcproducts.com/belts-chain-gears/belts-pulleys/gt2-timing-belts-and-pulleys/gt2-timing-pulleys?___SID=U HTD 9mm: https://www.wcproducts.com/belts-chain-gears/belts-pulleys/htd-timing-belts-9mm/htd-timing-belts-9mm-width?___SID=U Sample images of using the above calculator:

West Coast Drivetrains are the simplest yet one of the most robust and common drivetrains present in FRC. They're commonly referred as WCD's and utilize a tank drive, which means the wheels are parallel to each other on both sides of the robot. Differences in the speed of either side allow the drivetrain to turn. Versions without omni-wheels at the edges use a "drop-center" in order to ease turning (the center wheel is slightly lower than the others). Follow the guidelines and videos below to create a WCD! Links to use: JVN Calculator: https://docs.google.com/spreadsheets/d/1jKvegQ52v2o2tBl1QVohmnE2E6etftGUg3plpFB1f3A/edit?usp=sharing Chain Calculator: http://www.botlanta.org/converters/dale-calc/sprocket.html West Coast Drive Design Use JVN Calculator to determine gearbox Free speed of ~14 fps is good, faster/slower based on game Games with distinct sprints/defense would prefer shifting gb Current draw can be above 40A since it’s stall draw, but anything around 60-65A would cause brownout/lag whilst playing against defense (problem in 2019) Less reductions = less friction = more power Keep in mind sizes of gears, and how gearbox can look with various gear combinations Chain should be calculated using botlanta chain calculator Even number of links to remove the need for half links Chain pitches #25-0.25, #35-0.375 Use center to center distance, not horizontal Add an extra 0.018 to botlanta center to center distance to account for tolerance issues with chain Chain CAD is mainly aesthetic, but a simple loop would still allow to check for interference Drivetrain width/length Based on game requirements Try to never use maximum dimensions allowed Long robot = better turning, square robot = better stability Consider possible designs of other manipulators as well as maneuverability thru the field 2x1 Tubing Choice and Pattern Various combinations are possible, 0.125" tubing with regular bearings or 0.0625" tubing with versa bearing blocks (the numbers are the thickness of the tubing) Bearing blocks + 0.0625" tube is lighter, 0.125" tubing is stronger Regular 2x1 pattern is 5/32" holes, 0.5" from corner of tube, 0.5" spacing Bumpers Various ways to mount bumpers, one effective way is to use 1x1 tube on top of wheels (2019) and regular bumper brackets The 1x1 tube can be mounted with 2x1 supports on either end of the drivetrain or supports in between wheels depending on other manipulators Bellypan Pocketing belly pan with the diamonds is a big manufacturing pain An alternative is to use 3/32 or 1/16 sheet metal without any pocketing These sizes can become really weak if pocketed Gussets Full width gussets make alignment and assembly easier Should have diagonal supports Gearbox mounting Try to use 2x1 hole pattern or another VexPro Cots Pattern (patterns found on vexpro gearboxes) to make replacement easy if necessary, also requires less manufacturing/replacement time A common VexPro Cots pattern is 1.875” radius circular set of six holes around the bearing, with top and bottom ones removed DO NOT use large screws to mount the gearbox and hold the gearbox together, gearbox should be able to come out as a separate assembly without any hassle Encoders Falcon 500 and NEO motors have an encoder built in If encoder is needed, make sure it has a 1:1 ratio with the wheel otherwise encoder resolution is lost (applies to all manipulators) Encoders can be placed directly on the shaft or have a connecting gear Gearbox Design (Assuming ratios are known from previous steps) Gear Mesh Use VexPro chart on gears to find pitch diameter for all the gears (alternatively, you can take the number of teeth and divide it by the Diametral Pitch of the gear, ex. 36/20 = 1.8" pitch diameter) Create circles of pitch diameter and tangent them in order to get the center of each gear/shaft/motor. Add 0.003 to one of the pitch diameters in each gear interaction in order to prevent excess friction Overall shape and main holes in one sketch, pocketing in a separate sketch Try to use similar shape for both gearbox plates (derive the first plate to create similar shape without memorizing dimensions or copy/paste the sketch) Create all required parts, assemble, check for any interference, make any changes, then pocket VexPro Hex gears have bosses on either side of the gear, so gears can be flush with each other and bearings without a need for spacers All standoffs are 0.500 OD, irrespective of screw size For mounting motors, try to use 2 opposing holes in order to have maximum strength DO NOT using large screws for mounting everything, make the gearbox a standalone assembly that can be mounted to the rest of the drivetrain with relative ease Try to place screws so that they can be easily accessed, generally gearbox screws should be accessible from the inside of the robot so that changes can be made without removing wheels CIM Pinion gears can be assembled with 0.0625 distance from the face of the motor, no need to CAD the key or the retaining ring Standoffs should not interfere with the path of the chain since that will mess up the chain calculations

After you have created your CAM profile and post-processed it, it's time to actually machine the part! The following text will cover the operation of the OMIO CNC. Important: The CNC is capable of cutting thru metal, and so it is possible to seriously injure yourself and others if it is operated incorrectly. Do not operate the CNC if Mr. Shinta is not present in the room (unless he has specified otherwise). Safety glasses are a must, and you are responsible for your safety as well as anyone around the machine (So make it clear that everyone needs glasses). Supervision is required unless you have been approved to operate the CNC alone. With that, read through to learn how to use the OMIO CNC! Using Mach3: Mach 3 is the controller software that can be used with the OMIO. You can choose to install it on your computer or use Mr. Shinta’s Computer #15. It has Mach3 installed and configured. If you would like to install and use Mach3 on your computer, please follow the instructions in https://drive.google.com/open?id=156mGQnoUq6unnkvuyV_lM1_QziWi2jcA. Once Mach3 has loaded, you can use the interface to control the cnc or use the USB receiver in order to use the wireless remote. In order to run an operation, use the File tab in Mach3 to Load G-Code. It will prompt you to select a file and then it will load that file. If using Mr. Shinta’s computer, you can use a USB to transfer the .tap files to the computer. The Reset button on Mach3 and the controller is the emergency stop in case anything goes wrong. Running the OMIO: It is very similar to the Laguna, but there are minor differences in the setup. The stock must have holes in the corners (at least as of now) so that it can be held in place on the CNC using screws. The endmills and collets for the OMIO can be found in the toolbox near the OMIO. Before running the machine, make sure the enclosure isn’t touching the stepper motors and/or any other moving parts.

After you have created your CAM profile and post-processed it, it's time to actually machine the part! The following text will cover the operation of the Laguna CNC. Important: The CNC is capable of cutting thru metal, and so it is possible to seriously injure yourself and others if it is operated incorrectly. Do not operate the CNC if Mr. Shinta is not present in the room (unless he has specified otherwise). Safety glasses are a must, and you are responsible for your safety as well as anyone around the machine (So make it clear that everyone needs glasses). Supervision is required unless you have been approved to operate the CNC alone. With that, read through to learn how to use the Laguna CNC! Preparation: The Post Processes should be in a folder which can be transferred into a USB disk Clear the CNC table of tools and any junk Grab the tools that will be used during the whole cut as well as find the proper collets Find a space large enough for the cut on the material, clamp the material down with clamps and screws to make sure it doesn’t move in the area that will be cut Plug in the USB into the handheld controller Change the tool to the correct one if needed on the CNC spindle Select the correct file (located in "UDisk") on the controller Handheld Controller Usage: Here's the link to a spreadsheet with the recommended CNC speeds: https://docs.google.com/spreadsheets/d/1h5xuGp8lyXH_XhM3Qpnia36MObEhu2rZI8jA7tbsC8w/edit?usp=sharing Procedure for Aluminum/Polycarb Plate: Set Origin (DO NOT USE ORIGIN 8 OR 9, THOSE ARE FOR THE 2x1 JIG) Navigate to a corner above the material and make sure you have enough room to cut the pieces Make sure the axes on the CNC are in line with the axes that were set in the CAM Zero the x-y at that point Slowly lower the spindle and check with a piece of paper when the tool hits the paper and it can’t move Zero the z Go to origin Running the operation Navigate to the desired operation and change the speeds if needed Start the vacuum cleaner with the red remote Check to make sure the table is clear, the material is clamped, the correct tool is in place, the spindle is zeroed correctly, and begin the operation Pause the operation immediately if something seems wrong. A pause will stop the operation and can be continued, whereas a break will break the operation and ask the user if it needs to be saved. If saved, the operation can be resumed at a later time. Wait until the operation is done and move the spindle to its absolute zero to change tools. Remember to zero the z again if the tool is changed since it can vary from tool to tool Move the spindle out of the way if screws need to be added Changing Speeds-Spindle Locate the control panel located in the front of the CNC (facing Mr. Shinta’s desk) Locate the control box and set the frequency to the correct speed (take frequency * 60 to get RPM) Changing Speeds- Work You can only change this when you resume a break or start a new process Note: If resuming from pause, you can change the percentage of speed (keep this at 1) Press the edit Important Information: CAM is instructions to turn a representation of 3d model into the physical part CAM software turns CAD file into g-code which can be used with machining For plates and batches, it is recommended to use nesting to combine various plates at once and then cam the whole assembly while for individual parts just CAM the part file. Procedure for Aluminum Tubes (2x1s, 1x1s, etc.): Set up the piece Clear the 2x1 jig of any dust/excess material with brush/compressed air Make sure the 2x1 piece has been squared off on one side (if not do it or have someone do it on the mill) Place the squared off side of the 2x1 against the screw and rail of the jig If it’s in a horizontal orientation, add the shim (golden strip) and tighten the allen screws with a ⅜ allen key If it’s in a vertical orientation, add a 1x1 tube to the side and then add the shim and tighten everything Softly hammer down the 2x1 with the head of the allen key to make sure it rests flat and check for any undesired movement Set Origin Select preset 9 on the CNC controller and navigate to the origin (it should be the corner of the 2x1 where the origin was set in the CAM) Make sure to move the spindle to be slightly over the 2x1 so that the z zero can be properly set Slowly lower the spindle and use a piece of paper to check when the spindle is right above the 2x1 and zero the z Go back to the origin Running the operation Navigate to the correct operation and change any speeds if desired Start the vacuum cleaner with the red remote Check that the table is clear, the 2x1 is properly in place and held securely, the correct tool is in place, the spindle is zeroed in the correct position (X, Y, Z), and finally, begin the operation Pause the operation if something seems wrong, and either discard or save the break For symmetric operation, loosen the screws and flip the 2x1 and begin the previous operation. Note: Recommended to mark the sides after you cut them to make it easier to remember which side was cut Depending on the length of the endmill, the parting operation might leave a small section of the 2x1 uncut Use the manual mill to cut the 2x1 to the correct length, or use the bandsaw for unusual parting shapes Remember to zero the z after tool changes

Once you have created a CAM profile, the CAM needs to be converted into gcode, the programming language that is used by the CNCs in order to run the machine. This "translation" is called Post Processing, and there are a few minor difference when working with the OMIO CNC (small one) versus the Laguna CNC (big one). Follow the steps below to correctly post-process your CAM. Try to organize the operations so that multiple operations requiring the same tool are consecutive. Any operation that creates holes should be first in order to allow the user to add screws to the part and prevent it from moving under further operation Select all the operations that use the same tool and also meet the screw-down-the-part requirement Click Post Process, and make sure the configuration is set to Laguna CNC or CNC Router Parts (OMIO). (These post-processors can be found in the MVRT Parts Library, inside the CNC folder) Change the file path as needed Rename the file to reflect the operation and the tool used, commonly used format: For example: A196drill, B25adaptive, C6mmcontour, etc. MAKE SURE units are in millimeters since our CNCs uses millimeters Save the file with a PRG (Laguna) or TAP (OMIO) extension OMIO-specific Details: - The Omio will use the speeds and feeds from the first tab in the CAM, so while it wasn’t necessary to adjust those values when working with the Laguna, it is necessary to adjust those speeds when working with the Omio. For now, use the same speeds as the Laguna (such as polycarb endmill (laguna) - 300Hz; in cam for omio - 18000 rpm (1 Hz = 60rpm)). After further use a table with the values for the Omio will be available.

In order to machine Aluminum 1x1s, 2x1s, and 2x2s, a CAM profile must be made first. The idea is the same, but for Aluminum Tubing we use a custom-made jig that speeds up the machining process. The following text outlines the procedure on creating a CAM for Aluminum tubes. Create a new setup for any new orientation (vertical, horizontal, different horizontal from previous) Remove additional stock Set origin and axes according to 2x1 jig Z-axis: vertical and positive is up Y-axis: horizontal and along the jig (same as aluminum plate/polycarb) X-axis: horizontal and perpendicular to the jig (same as aluminum/polycarb) The origin for the 2x1 jig is on the left side (from Mr.Shinta’s desk view) so in CAM the X-axis should be perpendicular to the 2x1 and facing away from it Add Operations Use MVRT template for 2x1 and select correct operation Drill: select one of the holes and it should automatically select all the holes along the 2x1 Contour: select for bearing holes/ any other geometry, select the appropriate geometry Parting: use this for cutting the 2x1 to length, press ALT key and select one edge of the 2x1 Symmetrical 2x1s allow one CAM profile to be used for both sides; be careful and make sure that the 2x1 geometry is symmetrical and if not, duplicate the previous setup, and edit the operation that needs to be changed

The first step in machining Aluminum/Polycarbonate plates on the CNC is to create a CAM profile. The CAM serves as a set of instructions for the CNC to follow in order to achieve the desired part. Follow the instructions and images below to learn how to CAM these plates. Note: Inventor CAM must be installed in order to create CAM profiles. Create a new setup Remove additional stock Set origin and axes according to our CNC Z-axis: vertical and positive is up Y-axis: perpendicular to 3D printer table, towards Shinta’s desk is positive X X-axis: parallel to 3D printer table, towards the bandsaw is positive Y Add Operations Use MVRT template for aluminum or polycarb and select appropriate size and operation Drill: it should automatically select all holes of the respective size, click Ok Adaptive: Select individual pockets of the part(s) and after Ok is clicked, it will calculate the path and display it. Contour: select outer perimeter of the part(s) and after Ok is clicked, it will calculate the path and display it If you are doing a contour on aluminum, check Multiple Depths under the Passes tab and change the Maximum Roughing Stepdown to .04" for 6 mm (or 0.25 in) endmills, and 0.02 for 4 mm (or 0.125 in) endmills.

The very first step in creating 3D and realistic models of the robot is to create individual parts. The general workflow of CAD is to create a few parts, begin an assembly, create more parts or make modifications to existing ones, and finish your assembly. Create a new part and begin a new sketch on an appropriate plane. For the most part, it won’t make a large difference on what planes you use but it’s advised to stay consistent. Create a 2D sketch of your part. Make sure that you use the correct sizes such as bearing hole diameters, screw hole diameters, etc. Once done with the sketch, you will most likely use the extrude command to create a 3Dprofile of the sketch. For some parts, you may need to use the revolve command. There are other 3Dcommands but they are mostly unused in FRC CAD. Make sure that your 3Dfeatures are symmetrical about the planes as it will help you when assembling your CAD. Depending on the complexity of your part, you might need to make additional sketches and add 3D features such as fillets and chamfers. You may find it helpful to rename your features and sketches to a name that is easy to remember such as base, mounting holes, etc. Once done, save the file with the appropriate name (refer to the naming convention document).

After creating individual components, it is time to join the components into a manipulator that can go on a robot! Multiple part files can be combined into a single assembly in Inventor, and these assemblies can further be combined into a larger main assembly. The video below covers assembly in Inventor, along with the rest of the text. Create a new assembly and place the first few parts of your assembly. (For a drivetrain that could be the 2x1s, on an intake that could be the plates on the sides, etc.) You will use the constrain command to join your parts. The command itself had multiple tabs that will allow you to make a variety of joints. Watch the assembly video to see the different constraints in action. Make sure your assembly is symmetrical to the planes of the assembly file. This will make the large robot assembly easier to work with as your mechanism will be symmetrical about its planes. Use the planes in your parts do add constraints on parts that need to be symmetrical. Adding motion constraints isn’t required but it will add an aesthetic touch to your CAD. Make sure that your assembly is complete with all the parts. Do not forget to add screws, nuts, bearings, spacers, washers and any other parts that will be on the actual robot. This will allow you to be certain that there won’t be any surprising interference when you assemble the robot in real life. Check to make sure nothing is interfering. Once done, save the file with the appropriate name (refer to the naming conventions document).

Projects are used in Autodesk Inventor to allow the program to quickly find all the files you are working with. This also allows us to use a separate library for common parts, such as Screws, Washers, Bearings, etc. It is extremely important that you setup your project before starting the season or offseason or even a CADathon. 1. Make sure you download at least the “MVRT2020.ipj” file from GrabCAD before starting this. (You don’t need to download the other files for now) 2. Click on the Projects button on the top-left corner of Inventor when you start it up. (Make sure no files are open in inventor otherwise it won’t allow you to change your projects!) 3. In the Projects pop-up box, click on the Browse button near the bottom of the window. 4. Navigate to the folder “MVRT 2020” (you need to download at least the “MVRT2020.ipj” file from GrabCAD for this step) 5. Select the “MVRT2020.ipj” file in the folder (the one with the orange logo as seen in picture below) 6. In the options below, open (click the plus sign) Libraries and right-click the long line so that you see the option to edit 7. Click Edit 8. You should now see a folder and magnifying glass symbol to the right of the file path. Click on this symbol. 9. Now browse to the GrabCAD folder and select the “Parts Library” folder (as shown) and click Ok. 10. Now make sure that the file path under libraries shows a location on your computer, and hit Save and that’s it! This allows other users to open your files without errors since everyone’s using a common library.

Whilst CADing a robot, a lot of off-the-shelf parts are commonly used, such as Screws, Washers, Bearings, etc. In order to prevent the need to create these models from scratch each time, MVRT uses a Parts Library for common items. This Library can be downloaded through GrabCAD. The video below along with the text will go over the usage of the Parts Library. Note: DO NOT upload any accidental changes made to the parts library since these changes can cause problems when another person uses the parts library. Make sure your computer’s parts library is updated so that you have access to all parts. The parts library can only contain so many parts and it is possible for you to need to download parts that aren’t available. But make sure to first look through the library since it allows anyone in the MVRT GrabCAD to view your entire CAD without problems. The parts library is organized into electronics and pneumatics, hardware, and motion. You will most likely not have to access the CNC and iParts folders when creating your own designs. The electronics and pneumatics folder contains electrical components that will mostly be used to create the electrical bellypan. It will also be used for any sensors that your mechanisms may require. The hardware folder contains screws, nuts, spacers, versa gussets, standoffs, and shaft collars. Most of the common sizes of screws we use are in the parts library. If your mechanism requires a specific size that isn’t available in the parts library, refer to https://www.mcmaster.com/standard-socket-head-screws and navigate to Socket Head -> Alloy Steel Socket Head Screws and browse through the catalog to find your specific screw. The motion folder of the parts library contains parts such as bearings, gears, hubs, gearboxes, motors, sprockets, and wheels. These folders contain the most commonly used parts by our team. If your design requires a part not available in these folders, try to search the website of that specific part for CAD files. VexPro Parts contain downloadable CAD files at the bottom of the web page. When using the parts library, remember to create CAD models that are as similar to the real life version as possible since it allows you to check for any collisions, interference as well as gauge the parts required to build your mechanism. This will ensure that you aren’t missing parts when you build your mechanism and there aren’t any surprises about the mechanical design.