In our last adventure we soldered a bunch of stuff onto our little PCB and got it more or less doing what we need, so now the time has come to mount our creations on the truck itself. This actually went a lot quicker and smoother than I’d planned.
The first step was to figure out how to mount the Arduino and our PCB in such a way that the truck would still be able to do monster truck-ish things without various bits of electronics flopping around and potentially flying off. Thankfully, most of the stuff in the Carnivore’s passenger compartment that would’ve gotten in my way was easily removable. Sans dashboard and seats, there was more than enough room to mount what we needed in a more or less secure fashion.
From a hardware perspective, everything is held in place with 3mm nuts and bolts. The floor of the Carnivore had a couple ridges for aligning the seats before screwing them in, but they weren’t incredibly tall and 7mm spacers provided more than enough clearance.
Rather than spend time with a ruler making barely visible markings, I held the boards more or less where I wanted them to go and used an awl to make dents wherever I’d need to drill. After finding a drill bit which fit comfortably through the spacer, I turned down the drill and went very slowly to avoid burring or messing up the plastic. After I’d done the passenger side, I mounted an empty PCB and did a dry fit to ensure we’d be okay:
You’ll notice in the picture above that the bolts I chose are much too long. I did this deliberately as it gives me a way of mounting the additional hardware I’m sure will spring up as I move along.
The Arduino itself is mounted in exactly the same fashion on the driver’s side. While I did my best to center my PCB, the Uno I chose to mount closer to the back so there’d be plenty of room for the power and USB connectors. This also makes it much easier to connect and reconnect the various wires.
Before I buttoned it up for good, I did another quick dry fit to ensure there’d be sufficient clearance between the bottom of the truck’s floor pan and the various bits of the chassis. This was especially important as directly beneath is the enclosure which contains the circuit board that makes the whole thing go.
A little bit of fun
As previously mentioned, for those playing along at home the LED chaser lights on the front aren’t really required for anything, but I feel I should warn you that whatever you’re building just won’t look as cool without them.
Earlier on, I’d decided I didn’t want the chaser to look like a bunch of lights stuck in holes on the front, so the search began for something that was translucent enough to diffuse the diodes slightly and small enough to fit on the grill. My first thought was the spine from the ghetto report covers (which they apparently only make coloured now) or the front page off a newer cover, but everything I had on hand was completely transparent.
Just when things were looking down, I happened across the plastic weight from an old set of blackout blinds we had kicking around. Not only was it just the right size, it also had rounded edges and does a great job of diffusing the LEDs when running off the 9v battery.
A utility knife was more than sufficient for removing the strip of plastic from the truck’s body, but cutting out the middle of the grill would’ve taken forever. As luck would have it, the area in question was the same width as the tip on my soldering iron so I used it to very carefully burn the middle out then went over it with the utility knife to clean up the edges.
To mount the diodes, I simply cut off a length of the weight, slit the back and slid the diodes in. I had to do some additional cutting to get around a support for the body, but it worked out that all 6 LEDs are fairly evenly spaced across the front and a few minutes with a hot glue gun ensured they’d stay that way.
I cut the length of cat5 that was previously connected to the breadboard to the length I needed, stripped off the outer plastic then cut the wires for each diode allowing for a little bit of flex.
To attach them, I stripped a little off each then tinned and sweated them directly to the anodes. For the cathodes, I bent them slightly and insulted them from the anodes with a couple layers of electrical tape. To connect them to ground via the 1k resistor on the board, I stripped enough off the ground wire to run the entire length of the diodes and attached it to each with a dollop of solder.
Connections made, I protected the whole mess as neatly as I could with a few layers of electrical tape because, when it’s all said and done, I’d like to be able to send the truck careening through puddles and snowbanks with its former aplomb.
We’re almost at the fun part, folks: We have the basic hardware built and working, so the only thing between us and breaking out the sensors are the libraries we’re going to need to control the truck through software. As usual, my geekery remains a step ahead of my blogging about my geekery, so expect a post outlining the simple scripting system used in the video above [ed - video fell down the memory hole long ago] very shortly.