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8. Board Stack

The four boards in the board stack are shown here (not shown is the USB Sound Card and OTG cable for Command and Control):

You will need these tools:

• Safety glasses (to protect eyes while soldering or trimming leads)
• Soldering iron and solder (I use lead-free solder, but leaded solder is easier to work with)
• Small Philips screwdriver
• Small flathead screwdriver
• Needle nose pliers (to bend leads and hold parts)
• Side cutters (to trim leads)

Checklist

The BOM has a sheet "By Steps" which lists the parts needed for each step in order. If you have a Google account, you can make a copy of this spreadsheet ("File" then "Make a Copy") and check off each part as you install it.

Here is the checklist for this step:

8.2 Stacking the Boards

This step will stack the three boards and the Pi Zero.

Video

Here is a video of stacking the boards

In order to stack the boards, we will need a set of 2.5mm steel, brass, or nylon spacers and two GPIO stacking headers.

Standoffs are described by the thread size (M2.5 in this case), length of the standoff (6, 10, and 15mm), and length of the standoff threads if any (+6mm). Also M2.5 screws and nuts are used. Here are the standoff pieces needed for the three board stack along with their names in their correct order and orientation. On the left is if you order the individual pieces using the BOM. On the right is if you buy a standoff set such as https://www.amazon.com/gp/product/B08HS7MFYZ/ and combine them. These instructions will describe the BOM parts with the kit combined parts in parentheses. The photos may show the combined parts.

If you use the standoff kit, you will need 8x M2.5 screws, 10x M2.5 nuts, 12x 6+6mm, 8x 15+6mm, and 4x 10mm.

You will also need two stacking GPIO headers to give extra spacing between the boards. They are identical to the ones soldered onto the Battery and STEM Payload boards.

Start with the Pi Zero and two 11mm and 6+6mm standoffs (or wo 10mm and 6+6mm standoffs):

The 11mm goes on top, the 6+6mm goes on the bottom. They go in the holes closest to the GPIO header pins

Next, take the Battery board. You will use 4x 23+6mm standoffs, and 2x 18mm standoffs (from the kit, make two sets of 10mm and a nut and a 6+6mm, and four sets of 6+6mm and a nut and a 15+6mm standoff).

Plug the Pi Zero into the bottom of the Battery board. The two 18mm standoffs (10mm, nut, and 6+6mm standoffs) will go under the other two corners of the Battery board

Make sure the OTG cable to the USB Sound Card is plugged in:

Screw the four 23+6mm standoffs (6+6mm, nut, and 15+6mm standoffs) into the top of the Battery board

Next, put a stacking GPIO header onto the Battery board so the STEM Payload board can be plugged on top:

If you are building the tape measure antenna version, it will look like this:

Next, use four 23+6mm standoffs (make up four more 6+6mm, nut, and 15+6mm standoffs) and screw them into the top of the STEM Payload board. If the SMA antenna is in use, make sure the coax cables are screwed in.

Here's how it looks from the sides:

Another stacking GPIO header is plugged into the top of the STEM Payload board so that the Solar board can be plugged in on top

If you are building the tape measure antenna version, it will look like this:

If you have the v1.3.2.3 STEM Payload Board, make sure the 2.5mm audio jumper is plugged in:

Now plug the Solar board on top. Connect the JST cable from the Battery board and the JST cable from the STEM Payload board. It doesn't matter which connector you use.

Use four M2.5 screws to secure the board

If you are building the tape measure antenna version, here's how it looks:

Here's how it looks from the side with the SMA antennas:

Here's how it looks with the USB Sound Card on resting on top with the v1.3.2.3 version:

If you have an older version, here's how it looks:

You can test the CubeSatSim by removing the RBF pin. Unless the batteries are fully depleted (NiMH batteries normally come charged up), the green light on the Pi will flicker and the CubeSatSim will boot up and start running.

The green LED on the Main Board will be lit up after booting is complete and the software is running. The blue LED on the Main Board will be lit up when the CubeSatSim is transmitting. The red LED on the Main Board will be lit up when the battery is being charged by either the micro USB power supply.

The pushbutton on the Main Board can be used to reboot or shutdown the CubeSatSim. Pressing and releasing the pushbutton will cause the green LED to turn off and the Pi to reboot. Pressing and holding the pushbutton until the green LED flashes three times slowly then releasing will shutdown the Pi. Once it has shutdown, it is safe to plug the RBF pin back in. Pressing the pushbutton with the RBF pin inserted will not turn on the Pi.

8.3 Installing the Board Stack into the Frame

The Board Stack is now ready to go into the Frame.

Printing the CubeSatSim Frame

Frame Print

Here are the v2 Frame STL files: https://github.com/alanbjohnston/CubeSatSim/tree/beta/hardware/frame/v1.3.2

The frame has 4 parts. You need to print two of the top/bottom parts, and one of each side.

Frame Test Assembly with Solar Panels

In this step, we will do a Frame test assembly and mount some of the Solar Panels on the Frame.

Video

A video of this step is available here.

Note that the video and the photos here show velcro to attach the solar panels, the new recommendation is to use clear double stick tape https://www.amazon.com/dp/B00004Z4BU It is easier to remove with velcro, but with the double stick tape, the solar panels are held more securely.

Here's the frame parts with the ten Solar panels, plastic screws and nuts, and tape/velcro to secure the panels to the frame:

Here's the frame when it is put together:

The 1U frame of the CubeSatSim has solar panels on each face, which are labeled by the Cartesian axes X, Y, and Z. For the sides that face in the direction of the axes (see https://en.wikipedia.org/wiki/Cartesian_coordinate_system#/media/File:Coord_system_CA_0.svg), they are labeled +X, +Y, and +Z. For the sides that face in the opposite direction, they are labeled -X, -Y, and -Z. The CubeSat Design Specification (CDS) standard also has drawings showing the X, Y, and Z sides of a 1U CubeSat https://www.cubesat.org/cds-announcement. Here is a figure from that document:

On the CubeSatSim, the +Z side is the top of the CubeSatSim, the +X side has the pushbutton, micro USB connector, and the LEDs. The Main printed circuit board has the axes labeled on it as well.

Start with the top and bottom of the frame (the +Z and -Z sides). One solar panel is mounted on each. Cut four strips of velcro or double stick tape. Peel the backing on one side and stick them on the ribs on the frame:

Peel the backing on the other side and stick the solar panels onto the frame, making sure the JST connectors go to the inside of the frame. Here's how they look when mounted:

You can use a small amount of hot glue to mount the nuts in the top and bottom frame as you attach them. This prevents the screws from falling out when you disassemble the frame later in this step. However, be careful not to get glue in the threads.

Attach the two sides to the frame bottom. Don't tighten the four screws since you are going to be taking the frame a part at the end of this step.

We will start with the -X side. Cut four pieces of velcro and peel one side of the backing and attach to the rows of the frame piece with the camera mount. Don't stick to the frame bottom, just the side frame:

Then peel the other backing and attach the solar panels, again making sure the JST cables go the inside of the frame:

Video

Here is a video of the next part of the frame assembly

To build the frame, we will now attach the board stack to the bottom frame, then attach the two sides, then the top.

Four screws mount the bottom of the board stack to the frame bottom. In this photo, the LEDs and other connectors are facing to the left. The Pi Camera ribbon cable is routed as shown here:

Place the -Z frame on top and secure with four screws:

Flip it so the -Z frame is on the bottom. Here's how it looks from the +X side, the side with the LEDs and connectors.

The Pi Camera should face outward on the -X side opposite the LEDs and switches as shown here:

The solar panel JST connectors plug into the Solar board on the top of the stack. Start by plugging in the JST connector from the bottom frame into the -Z solar panel connector on the Solar board.

If you are using the SMA antennas, make sure the SMA coax cables are screwed into the STEM Payload board.

The first frame side to be mounted is the -X side which has the Pi Camera mount. We will mount the Camera using two M2 nylon screws and two M2 nylon nuts (Note: the photos show 4 screws and nuts, but you do not need the other two):

Here's how the Camera looks from inside and outside the frame when it is mounted (Note: again, although four screws are shown, you only need the bottom two screws):

Carefully stand up the frame, being careful not to stress the Pi Camera ribbon cable and snap into position on the bottom frame. Here's how it looks from the outside:

Here's how it looks from the top:

Secure the -X frame with two nylon screws and two nuts to the -Z bottom frame.

Here is how it looks from the the -X side:

Plug in the two -X solar panel JST cables into the Solar board.

The next frame side to be mounted is the +X side. We will use the frame without the camera mount and two nylon screws and two nylon nuts.

Snap the side frame onto the bottom frame and secure the side frame to the bottom frame with the two screws and nuts. Secure two solar panels to the frame, making sure there is room to see the LED and to access the USB-C and push button:

Plug in the two +X JST cables into the Solar board. Here's how it looks from the top with both sides attached and the solar panels plugged in:

Next, we will connect the top frame +Z, but we won't secure it with screws until all the solar panels have been plugged in:

If you are using the SMA antennas, remove the nuts from the coax and insert the coax through the frame, then put the nut on the other side to secure the coax. Plug in the +Z JST cable into the Solar board:

Then, carefully bend the coax so that you can put the top frame in place:

The two SMA antennas can now be screwed on:

Don't secure the top frame to the sides until all the solar panel connections have been made.

Note that the video and the photos here show velcro to attach the solar panels, the new recommendation is to use clear double stick tape https://www.amazon.com/dp/B00004Z4BU It is easier to remove with velcro, but with the double stick tape, the solar panels are held more securely.

Now we will attach the -Y solar panels with three pieces of tape/velcro for each panel:

Stick the tape/velcro to the frame as shown:

Plug the two -Y JST solar panel connections to the Solar board. If you need to, you can raise the top frame since it isn't secured yet:

Stick the two solar panels onto the frame:

Now do the same thing for the +Y solar panels. First stick the tape/velcro to the frame. Then connect the +Y JST connectors to the Solar board. Then stick the panels onto the frame.

Now you can secure the top frame using four plastic screws and four nuts

Here's how it looks:

Your CubeSatSim is complete and ready for Step 9. Final Testing