Mech Design Guides

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We have so much design flexibility in the mechanical realm that it's easy to get overwhelmed and have trouble figuring out where to start. Use these general design guidelines to help design your robot.

Weight

Tipping
  • Low center of gravity: A robot with weight close to the ground will be far more stable to drive. A low center of gravity (CG) will be nearly in-line with forces from the wheels, which minimizes tipping moment.
  • Push the limit: While we can't exceed the max weight in the rules, it's important to get as close as possible - especially if the game involves robots pushing each other at all. Pushing force is limited by weight and coefficient of friction. If your plaction-wheeled 80 lb robot has a coefficient of friction of 1.4 on carpet, then your pushing force never exceeds 80 lbs x 1.4 = ll2 lbs regardless of gear ratio. A 150 lb robot can do almost twice that with the right gearing.

Complexity

  • Use un-modified off-the-shelf parts. Preferably ones we already have on hand - barring that, ones we can buy locally or get in a couple of days from AndyMark, McMaster-Carr, Stock Drive Products, or others.
  • Keep it simple! Simpler designs are faster to design, build, and test than complex ones.
    • A design that takes too long to design and build usually doesn't get tested, and untested designs usually don't work.
  • Everything always takes longer than you think it will. At least when you haven't done it before, and sometimes when you have.

Calculations

  • Drive train speed vs gear ratio: A good rule of thumb is to assume the CIM motors spin 4,000 rpm at top speed. To get your robot speed, find the gear reduction between motor and wheel, find your wheel circumference, and figure out how far a dot on the wheel will move in 1 second. For example, if your robot has 10:1 gear reduction and 6" diameter wheels, the top speed will be: (4000 motor REV/Minute) x (1 minute / 60 seconds) x (1 wheel REV / 10 motor REV) x (6 in x 𝝅) x (1 ft / 12 in) = 10.47 ft/s.
  • Mechanism Lifting torque & speed: