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Standalone RoboRio Testing with the Tethered Rover

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Kevin Lam edited this page Nov 20, 2018 · 14 revisions

Introduction

We have a lot of students who want to learn robot code development, and only a couple of existing FRC robots to work with. Some teams, especially rookies, don't even have that. We follow the good advice of building a robot control system laid out on a piece of plywood (we call ours Plyboy), but even this is expensive if you're setting up the entire FRC control system with a RoboRio, a PDP, VRM, access point, motor controllers, etc.

Fortunately it is possible to do simple robot code and training work using only a bare RoboRio and a few other inexpensive parts. This page describes our "Tethered Rover" development and experimentation platform, which uses low-powered continuous-rotation micro servos to stand in for PWM-controlled motors, gearboxes, and motor controllers! We power it off a 12V wall supply which means no batteries or chargers to deal with.

Parts List

  1. RoboRio - from AndyMark
  2. 12V, 2A or greater power supply - This $14.99 one from Amazon includes a mating barrel connector with screw terminals which is convenient.
  3. A standard USB A-B cable
  4. Four continuous-rotation 9g micro servos - $6.57CAD ea from RobotShop
  5. Four micro servo wheels - $1.83CAD ea from RobotShop
  6. (optional) Four PWM extension cables - such as these 24" ones from RobotShop
  7. 18 gauge stranded wire
  8. Material for a rover chassis, such as Lexan, acrylic, plywood - ours is Lexan approx. 3"x5"
  9. Double sided foam tape or adhesive Velcro

Assembly

  1. We used a barrel connector with screw terminals that mates with the 12V power supply we acquired (from Princess Auto). We cut two short (about 3") lengths of red and black 18 gauge stranded wire, and attached them from the barrel connector to the plug-in power supply connector from the RoboRio. Use a multimeter and verify the polarity before powering up the RoboRio!

  2. Press-fit a wheel to the spline (the white output gear) of each micro servo, and use a screw (included with the wheel) to secure it in place. Alternately, attach a round horn (included with the servo) to the spline, screw it in place, and then attach a wheel to the horn.

  3. Using double-sided tape or Velcro, attach the servos to the chassis. We covered the sides of our chassis with Velcro strips so we can reposition the servos as needed, for example to make a 2WD versus 4WD drivetrain, to make room for a sensor, or to reconfigure the chassis entirely.

  4. Attach servo extension cables, if desired, to each servo to extend the reach of the "tether".

  5. Label each servo (e.g. "A", "B", "C", "D") and the cables so they're easy to keep track of.

References

Other teams have done similar work with bare RoboRios. See: https://www.chiefdelphi.com/forums/showthread.php?threadid=163335

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