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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.

Software Pre-Requisites

To develop robot code (for the 2018-2019 season) and talk to the RoboRio you'll need to install the development tools. Follow the guidelines on this page.

Ensure the RoboRio has been imaged with the 2018 image.

Usage

Power up the RoboRio from the 12 volt wall power supply. Connect it to your PC via the USB A-B cable. This sidesteps the WiFi connection normally used to communicate with the RoboRio (hey, it's tethered anyway). If desired, you could set up a wireless AP and connect the RoboRio Ethernet port. You can then connect to the RoboRio via WiFi.

As long as you keep the current draw down, you can do a lot of testing and prototyping work on a bare RoboRio:

  • connect servos (either continuous rotation or traditional) to stand in for PWM-connected motor controllers, to the PWM ports
  • run basic 2WD or 4WD drivetrain code using the Tethered Rover platform
  • test simple timed autonomous drive modes
  • connect sensors, such as ultrasonic or infrared distance sensors, potentiometers, or contact switches, to the DIO or Analog Input ports
  • connect a webcam to the RoboRio's USB port
  • connect an MXP expansion board such as a RioDuino or NavX (you would need to move the RoboRio around to simulate robot movement)
  • connect to external devices like Raspberry Pi to test a vision pipeline via networktables
  • test logging to your driver station PC
  • test Dashboards on your driver station PC

DO NOT attempt to run "full size" motors (like CIMs). If you want to do this, install a bigger power supply (12 volts at 20-50 amps or even higher), or use a battery, and use a PDP with circuit breakers to prevent overloading.

Expansion

The idea behind this tiny Tethered Rover platform was to provide the lowest-cost and most minimal way to test and deploy robot code. We can transport the entire kit inside a small briefcase:

If you want to do more, you could turn this into a full FRC control systems trainer. See what we've done with Plyboy for ideas.

References

Other teams have done similar work with bare RoboRios. See: https://www.chiefdelphi.com/forums/showthread.php?threadid=163335 https://www.chiefdelphi.com/forums/showthread.php?t=140308

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