Robot Exhaust and Power Distribution

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Another in the series of building a robot for outdoor use. In this chapter we will install an exhaust fan, make shelves for the battery, motor control/primary Raspberry Pi and power converters. The goal is a fully autonomous robot to perform chores outside.

As with all my work, a big shout out to DroneRobotWorkShop, truly the giant shoulders I am standing upon. Without ServoCity and about a hundred folks on the web, I would be nowhere.

The exhaust fan will vent out the top, drawing air from the bottom of the weather tight box holding electronics. The shelves hold the battery and equipment and top shelf hold power distribution, Ethernet switch and likely another Raspberry Pi for OpenMV

Step 1: Create Holder for Fan

Using 3 1/2" square piece of 1/4 ply, I drilled a 1" hole in the middle. Gluing two 1/4 square strips plexiglas together gave me a method to attach to the top of the case. I clamped them to the ply frame edges and drilled four mounting holes using 3mm screws. By placing bolts near the frame to keep adequate spacing, I was able to glue the strips to the top, I found an adjustable pole quite handy to keep in place till glue dried.

The 1 inch fan was glued to the frame using a silicon glue and the frame was reattached to the plexiglass strips.

Step 2: Shelving

I need three shelves for now, possibly a fourth. Lower level is the battery, I found these 1/4 x 4" x 12" plexiglass shelves that fit perfectly. I first installed the battery shelf, marked the next height, glue the 1/4 plexiglas strips, temporarily installed the motor control and raspberry pi, marked the height and installed the top shelf. These shelves are not glued but will drill and tap a 3 mm screw to allow for easy removal

Step 3: Attaching Electronics to Shelves

I started with the power converters, 12v coming in from the battery but I need much 5v and some 3.3v so I have three 5v converters and one 3.3 v converter. These allow adjustment so I can change if needed. My Ethernet switch will connect the Raspberry Pis (2-4).

I marked the location of the boards, estimated the location of the holes, drilled and tapped for a 3mm risers. I did the same for the motor controller and raspberry pi.

Step 4: Attach Jumpers to the Buck Step Down Converters

The 12v in and specified out voltage jumpers where created, I tried to keep them long enough to allow removal of the shelf if needed but the out voltage jumpers were not long enough. The Buck Step Down Converters have a small screw that allows you to choose the out voltage.

Step 5: Wire Battery Switch and Protective Diode

This was a very hard step but with planning, it is working great.

This wiring harness connects the battery to a relay instead of to the switch as the battery could have more amps than the switch could handle. I'm likely going to need a larger battery with time so this is a future proofing step.

The relay will be switched on and off by this switch, waterproof and with a 12v LED. I would like the LED to be illuminated when on, the default option.

The 40A diode allows current to get back to the battery when the switch is turn off or fuse is blown. This will protect your electronics and is a must.

I spent about a week getting the wiring correct and was quite happy it worked the first time!

Step 6: Testing

You need to test each output and busbar individually before attaching any electronics. I found a reversed polarity on the 3.3v busbar that would have fried an Arduino or servo so take care in double checking.

Next I will complete the motor wiring and get the motor control fired up. Let's make this robot move!

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