Posts Tagged ‘ minibot ’

Raiderbot X, 23 Days to Robot Ship: Lego Minibot!

Minibot proof of concept out of old Lego parts. The purple arms push against the pole, which angles the wheels into the pole to create a horizontal vector just strong enough to keep the bot on the pole. Took about two hours to make.

The bot is climbing up a 40 inch metal pole that is embedded in the concrete floor of our garage (for reasons beyond my imagination). Climb speed is about 6 in/s. Power is provided by a 13-year-old 9V Lego motor that is the wimpiest of the wimpiest Lego motors out there. It is being run on 12V.

The TETRIX motor we will be using in our actual minibot has 21.7 kg-cm of torque. This motor exerts no more than 200 g-cm of torque.

This is the first time in six or seven years I’ve put anything together with Legos. I think I’ve lost one of my tubs—I made this robot out of what few parts I could find. I need more gears!

Credits to my mother for taking the videos!

Raiderbot X Meeting 5, 38 Days to Robot Ship

Meeting time: 10:00 to 18:00
Hours logged: 36.74


The idea this year is to overload the bots with sensors of all kinds. Current sensors on every wheel, arm joint, and main circuit breaker to graph power consumption. Proximity sensors to avoid collision with other bots and facilitate scoring (automate entire process!). Encoders, gyro, and accelerometer for inertial measurement. And of course, line trackers for line following. I foresee lots of debugging, though it should help that the programmers have switched to Java+Netbeans that allows for serial communication with the cRIO.

Team 955 will now be using Git for version control. Git repository created here on Github.

Rockwell Automation Photoswitches

There is a wiring diagram on the back of the sensor box. L.O. and D.O. are light output and dark output, respectively. Power supply should be between 10.8 V and 30 V. See this Chief Delphi thread for more information. In the end, hooking it up to the cRIO is as simple as soldering brown to positive, blue to ground, and either white or black to signal of a PWM cable (which is true when either is light/dark?) and connecting the combination to Digital I/O. It is NOT necessary to hook up bleeder resistors from the signal lines to VCC as it says in the datasheet.

The datasheet is very useful:

  • Green LED on: sensor powered.
  • Green LED off: sensor not powered, output active, SCP* active.
  • Yellow LED on: output on.
  • Yellow LED off: output off.
  • Yellow LED flashing: output SCP active
  • Orange LED on: margin** > 2.5.
  • Orange LED off: margin < 2.5

* Short-Circuit Protection
** The orange LED shows that the signal strength is at least 2.5 times that needed to trigger an output. Signal strength is greater with higher voltages (obviously). This can be useful to overcome dust on the lens. The sensor’s sensitivity can be adjusted also by turning the knob on the front panel of the sensor. With an oscilloscope, I found that at maximum sensitivity, the photoswitch is triggered by almost anything (e.g., the table, paper, my red 955 sweater, my jeans) even at 10.8 V. We will need to test and calibrate the photoswitches so they trigger only over the reflective tape.

The datasheet recommends that the distance from the sensor to target to be at least 6 mm.

Standardized ordering process

Blanket POs from Will and Mr. A. Co-PMs and division leaders are the only ones authorized to order. Use order form on team website.


TETRIX parts list:
2 – Motor Mount, W739089
1 – Motor Shaft Hub, W739079
2 – DC Motor, W739083
1 – Gear Hub Spacers, W739090
1 – Tetrix Resource Kit*, W731900
1 – Battery Charger, W739059
1 – 12V NiMH Rechargeable Battery, W739057
1 – Power Switch, W739129

* The Tetrix Resource Kit contains the parts shown here. Unfortunately, I haven’t found a detailed list containing only the Resource Kit parts, so we have to use the detailed parts list we found earlier here to identify the kit parts.

The default kit seems to have enough parts in it for one minibot. Once the minibot team has a reasonably complete idea of how they want to build their two minibots, they’ll let me know of any additional parts they’ll need. We’ll see exactly what parts we have when the kit arrives (hopefully) later this week.

Sent an email to PHRED about the possibility of exchanging FTC parts for FRC parts. They apparently no longer plan to build a minibot.