Let’s turn our attention to the base of the unit. A 1/4”-
20 nut allows the unit to be affixed to a tripod for support
and leveling. The nut is installed using a technique similar to
the threaded melt-in inserts that I’m so fond of for 3D
printed parts. The instructions recommend using a soldering
iron set to 382°C for installation, but I left mine at 345°C. It
took about 60 seconds to melt in, but the lower
temperature gave me more time to make sure it was
melting into the print straight.
I stopped when the top of the nut was flush with the
top of the print (Figure 20). In hindsight, that wasn’t deep
enough for a tripod to catch, so melt the nut to the bottom
of the pocket in the case. There’s enough metal that the
nut stays hot for some time, so give it a while to cool
Once everything is cool, snap the battery into the case
(make sure your orientation is correct) and double-check
that the 3D printed button turns the battery on. There is an
SLA printed light pipe that is installed with some double-stick tape. The light pipe’s performance coupled with the
not-so-bright LEDs on the battery make it difficult to see,
but you can make out the green lights from the outside of
The last electronics bit to install is the inertial
measurement unit (IMU) that will allow the sweep to
determine its orientation in space. Solder the headers onto
the breakout with pins facing upwards towards the
component side, and then connect the wires to the power
rails and communications as directed in the instructions.
I found it easiest to connect the wires to the IMU, then
install the IMU into the case with four self-tapping screws.
Next, connect the jumpers to the Pi. All the wires can tuck
nicely into the upper half of the case (Figure 21).
Finally, the upper and lower halves are joined with four
more self-tapping screws. We can then connect the Pi and
the HAT to the USB power pack with the provided stubby
USB cables. I found that I needed to fiddle a bit with the
Figure 19: Wires from the stepper motor connect to the screw
terminals on the HAT and leads from the micro-switch push onto
headers. Cutting the wires slightly longer would have been
Figure 20: The 1/4”- 20 nut melts into the bottom housing. I didn’t
melt mine in deep enough initially and the tripod mount didn’t
reach the threads.
Figure 21: Install and connect the IMU in the pocket at the top
left. The wiring compartment gets pretty crowded!
22 SERVO 09.2017