Chassis 101 A quick rundown on chassis and choosing the right one for your bot Analyze Game Field and Elements
• Consider the terrain and obstacles – Chassis must be built to be able to climb or cross obstacles if needed – Chassis needs to be able to maneuver the field to pick up elements Designate a Certain Amount of Motors
• You are allowed a max of 8 motors – REV expansion hubs only have 4 motor ports • Designate based on mechanisms – More mechanisms = less drivetrain motors • Designate based on importance – If you want to focus more on pushing and possible defense you may want more motors Different Types of Chassis
• Tank Drive • Mecanum • Holonomic/X-Drive • H-Drive/Slide • Alternative Drives Wheel Types
• Traction wheels
• Omni wheels – Have rollers to move sideways
• Mecanum wheels – Have angled rollers to drive themselves sideways Tank Drive
• Pros: Reliable, simple | Cons: Less maneuverable • Different types – West Coast: Three wheels on each side middle wheel is lower than the others • Pros: Sturdy, pushing, and turning Cons: More complex – Skid Steer: Uses two traction and two Omni wheels • Pros: Simple, easy turning Cons: Less maneuverability – Standard: Uses all four of the same type of wheels typically omni wheel • Pros: Turns on a point, simple | Cons: Can get pushed Mecanum Wheel Base
• Special wheels allow for strafing – Four mecanum wheels – Requires 4 motors – Wheels are wider and heavier • Pros: Can Strafe and leaves room in center • Cons: Less pushing power and heavier Holonomic/X-Drive
• Offers the ability to move in any direction. – Has four Omni-Wheels. – Doesn’t do well at driving over objects such as craters. • Pros: Can drive at any angle • Cons: Not high pushing ability, can't drive some objects. H-Drive/Slide
• Basic structure of tank drive – all omni wheels – adds one or two perpendicular omni wheels • Pros: Can strafe, pushes like tank drive • Cons: Uses one extra motor, takes space in center Alternative Drives (Examples)
• Challenge specific/unique – Bogie Wheel Drive – Swerve Drive Commercial Off-The-Shelf Chassis
Option COTS Team Built
Retailers Pros ● Saves ● More options to time meet certain • Andymark-Tilerunner ● High needs quality ● Adaptable to • Gobilda game • Servocity ● Saves money Cons ● Expensive ● Takes more time ● Limited ● May require options more trial and error Make Hand Drawings of the Chassis
• Creates a visible layout – Maps spaces for mechanisms – Includes multiple views – Possibly uses full scale drawings • Ensures that all measurements are aligned – Creates fewer issues when prototyping Example Drawing
This is an example hand drawing of a chassis Different Drivetrains
Type Gears Chain Belt • Gears
Pros ● Simple ● Durable ● Traction ● Easy to ● Very from change adjustable increased ratios length contact • Chain Cons ● Can ● Can come ● Low wear/break off clearance based on sprockets ● Greater material under high mass for ● Can become torque motors to unaligned ● Requires a move • Belt ● Takes up chain tool (slower) more space to change length Motor Placement
• Good motor placement is crucial – Needs to make room for other mechanisms – Evenly distribute weight across the robot for better drive consistency Structure
• A strong chassis has good motor placement and structural bar placement – These help make the chassis sturdy, fast, and maneuverable – C-channels are a strong option Design the Chassis with the Mechanisms in Mind
• Make sure the chassis c channels and cross beam are not in the way of other mechanisms. The mechanisms and chassis should fit well together. Electrostatic Discharge (ESD)
• Consider game elements and other robots – They can cause ESD, for example: legs of the lander – Any exposed metal can cause ESD – All wheels cause ESD, but wheel type and outer material of the wheels matters – ESD can disconnect your robot Center of Gravity
• Should be kept in low, middle to prevent tipping. • Important for balance (example: balancing stone in Relic Recovery). Speed and Torque
• Gear ratios – Motors can be geared to either increase torque or speed – Torque is necessary for pushing other robots and certain game obstacles – Using 4” wheels with a 40:1 gearbox produces a mix of speed and torque, while a 20:1 will produce very competitive speeds Summary
• Analyze the game • Consider different chassis types. • Consider the amount and placement of the motors • Hand drawings are very helpful • Create a strong structure and protect against ESD • Have a low center of gravity Resources
http://ftckickoff.allendalerobotics.com/wp-content/uploads/2017/09/2017- Allendale-Robotics-FTC-Components-and-Tips.pdf https://www.servocity.com/ https://www.gobilda.com/ https://www.pitsco.com/Competitions-Clubs-and-Programs/FIRST-Tech- Challenge https://www.firstinspires.org/resource-library/ftc/robot-building-resources https://team1640.com/wiki/index.php/Swerve_Central http://www.revrobotics.com/rev-41-1354/ https://www.vexrobotics.com/omni-wheels.html https://www.vexrobotics.com/mecanum-wheels-1529.html?akamai-feo=off Questions?