Mk.2 build log

Summer 2008 to present: Major construction is complete, the chassis is assembled, motors mounted, Arduino mounted, terminal strips, GPS, and wiring all complete. Relay based motor controller ordered.

12-7-08: Cut out the third and uppermost deck. Installed 15 superbright LED’s around the perimiter. Not for any special reason, but just because I like flashing LED’s. The LED’s are made to flash using a simple 555 based timer, connected to the main 12vdc supply. No microcontroller pins used, the LED’s will simply flash whenever the robot is powered up. –picture coming soon–

12-8-08: Mounted the upper deck and installed the main power switch and LCD display on the upper deck.

12-28-08: The relay based motor controller arrived and worked great until a code error on my part energized the forward and reverse pins at the same time. Smoke released. Darlington chip went to electronics heaven. Trip to St. Louis planned.

12-30-08: When I removed the motor controller to repair it, I found a burned solder trace on the underside of the board. I repaired the solder trace with a bit of wire, and everything appears to be ok. So now I have three spare darlingtons and a socket!

12-31-08: Disaster! Well, kind of. All my testing of the PowerWheels motors and relay motor controller have been with the motors free-wheeling. As soon as the robot is on the ground, pow! a solder trace blows on the motor controller. I have measured the running amp draw for the PowerWheels motors at between 5 and 6 amps, and thought that a 10 amp motor controller would do the trick. Wrong-o. So now I am looking for a way to limit the current to the motors…I have put up a call for help to one of our club members. I’ll keep you posted. In the meantime, if you have a solution, please let me know!

1-2-09: Limiting the current that the motors draw is not going to work easily, so I am going to salvage the relays from the motor controller board I bought and reuse them on a home made board. I have found a circuit that will be much heavier duty and allow PWM control of the mechanical relays. I will post the results after tonight’s build session.

2-2-09: Building and or finding a suitable relay based motor controller has been a real show stopper. For now I am abandoning plans to use a relay based motor controller and instead will be using this one from Pololu that I got for my birthday. Things should progress rapidly now…the motor controller was a major stumbling block. The PowerWheels motors really do draw a whole heck of a lot of current!

2-28-09: Installed and tested the Pololu motor controller, so far so good. Running a variety of PWM speeds I did not detect any heat at all under no load. Further testing soon. Now that the motor controller problem appears to be solved, the next step will be to give the Mk.2 some “eyes”…Sharp infrared sensors, a Parallax Ping ultrasonic sensor, and the Garmin eMap GPS unit.

Planned for the next build session: Sensors, sensors, sensors! And hopefully some code to post here.

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