Post #5: The Build Continues

My Proposed Layout for the bottom shelf

Monday and Tuesday, just not enough time in the day.  I took the platform apart so I can start laying out the mid layer boards.  I'm planning on the battery, the DC-DC Converter, the Motor Controller and my power conditioning board, all squeezed on the middle layer.  I'm hoping to keep enough room for a bigger battery some day, who knows what they will dream up at the school to put on this little bot, all taking power, so my little 1.3Ah battery may not be enough some day.  Unfortunately, all the parts I want to put on this layer are so big... but if this is all the space I have, so be it.  I actually laid out the parts, marked the holes and started drilling, even tapped a few!  But it got late so had to put it aside for the evening, too many season premiers starting :).

MISTAKE: forgot to account for assembly screws

The next day, having slept on this layout overnight, I decided to try something different. The side walls should be big enough to hold the two smaller boards, so this is what I did.  I now have some small unused holes in the bottom platform, but no big deal, they won't hurt anything. So today I laid out the smaller PCB's on the side panels and didn't forget to also drill/tap in the IR sensors for the front and back panel.  MISTAKE: I didn't account for the screws that hold the platform together, so I had to dremel out one of my nylon standoffs to make room for it (see pic).  Freeing up all that space where the 2 smaller boards are on the lower shelf will make lots of room for a bigger battery.

Front panel

Inside of Front panel

For the front panel, I chose to put the motor controller (the pic on the right).  If I place it near the top of the panel, that heat sink will fit nicely over top of my power conditioner board.  On the opposite side (the outside of the bot) I mounted an IR distance sensor, you can see the wires coming through a hole I drilled under the motor controller.

These PCB's can be pretty tall, so I did not mount one on the back riser as it would rob some space available for the bigger battery.

If you remember from this weekend, the left side of the robot has the power switches/fuses and power jack, so that leaves the right side of the robot for the DC-DC Converter.  You can see that in the MISTAKE picture above.  I wish I accounted for the mounting hole, would have saved me some time with the dremel tool, oh well.  It works.

Drill and Tap set

Electricians Tool (cuts screws too)

Takes quite a bit of time to drill the holes just perfectly (a small drill press from Harbor Freight is coming in handy to get the holes as close to perfect as possible.  You have a little wiggle room, but not much, the mounting holes on these PCB's are so small.  I picked up a drill and tap set from Lowes yesterday to make the tapping easy.  To keep your screws from standing out on the other side of your platform, an electricians tool comes in real handy to cut the screws down to size!

mark the adjusting resitor

adjust to 7.2v and test

Now that these little guys are mounted, we better check them and make sure we didn't do anything bad to them during the mounting process.  Before mounting the DC-DC Converter, I set it up to output about 7.2 volts (just a bit higher than the 7 needed to allow the onboard voltage regulator on the Arduino to work.  Once set up, I took a little marker and marked the variable resistor so I know where it is supposed to be.  After mounting, I tested it again, sure enough, the voltage was a bit low, so adjusted it back into shape.

Motor Controller

I also hooked up the motor controller and tried to figure out what the jumpers do.  There is an ENA (2) and ENB (1) jumper that leads to the 5 volt copper trace. We are going to take this jumper off and drive these pins with a PWM output from the Arduino to allow us to change the speed of the motor. There is another jumper (3) on the board, tracing and experimenting, I found out that it feeds the incoming 12 volts to the onbard voltage regulator that converts it to 5 volts.  This board won't use much current so we just may allow the regulator here to keep working instead of feeding 5 volts from the Arduino, saves me a wire too.  After hooking it up to 12 volts and using the onboard 5 volts to pull pins high, I verified that I got +12 and -12 on the motor hookups depending on which pin I pulled high.  Good to go, both motor controllers are working properly.

Now to finish up the bottom shelf.... work for Wednesday.... (PS, i'm going to have to figure out what the red/white/black wires do on the IR sensors, nothing comes with documentation!).