Building the Motor Controller

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Acquiring Parts

  • Purchase all of the components on the BOM File:Example.jpg from DigiKey. You can find the BOM under the 'bom' directory in the project: [1].
  • Purchase the AN22-F case from polycase: [2]
  • Order the PCBs. You will find the geber files under the 'hardware' directory: [3]. EasyEDA is an affordable choice for PCB fabrication. Ordering a top-side stencil (and some solder paste from Amazon, etc) will make assembly easier.


  • Machine the AN22-F case to the specifications in the Fusion 360 file.
  • Drill and tap the heatsink to the specifications in the Fusion 360 file (6 M3 holes).
  • Cut the busbars with a CNC machine. Be sure to use copper stock.

Electrical Assembly

Prep for reflow soldering

  • Get all of your components organized by type and the order in which you want to place them.
  • Apply solder paste to the PCB using the stencil and a paint scraper, then place each component using tweezers.
  • TIP: Work from the BOM and place all instances of a given part at a single time. Use 'CTRL-F' in KiCad to locate each component in Pcbnew.


Reflow solder the PCB. One option to do this is a toaster oven, with the following temperature profile (for 63Sn37Pb solder paste):

  • Preheat the oven to about 275F. Some cheap ovens have huge overshoot, so don't put the board in until you can confirm the temperature has stabilized.
  • Bake for about 2 minutes at 275F to gently bring all the components close to the reflow temp (this is the "soak" phase)
  • Set the temperature to about 400F. As soon as you observe all the solder joints becoming "shiny", turn off the oven and remove the board. It should only take about 10 seconds for the board to reflow once the temperature gets to about 380F or so. If you leave the board at this temperature for too long you risk damaging it.


Manual soldering:

  • Cleanup any solder bridges on the top side with solder wick and an iron.
  • Use an iron to solder through-hole components on the top of the board.
  • Use an iron to solder SMD components on the bottom of the board.

Solder the current sensor onto the PCB:

  • Place the current sensor into the PCB and solder the 3 small pins.
  • Solder the large pins. It will take a very long time to heat up these pins, so be patient.
  • Do not put excessive amounts of solder on the large pins -- doing so can make it harder to solder the adjacent busbars in the next step.

Solder the busbars onto the PCB:

  • Apply flux to all of the high-current traces, then use an iron to put a large amount of solder on them.
  • Preheat the busbars to about 400F.
  • Solder one busbar at a time by placing it on the PCB with pliers, then reflowing with a hot air gun. Be careful with busbar placement; they may shift position during reflow.
  • It's OK if the MOSFET through holes get covered up by solder; you can drill through the through it later. However, mis-alignment of the busbar with the PCB's through holes will be a problem.


Solder the MOSFETs (part 1):

  • Bend all of the MOSFET pins upwards at 90 degree angles, so that the pins will stick through the board when the drain of the FET is placed against the heatsink. Consult IRF Application note AN-1031 if you are unsure of how to bend the pins without damaging the device.
  • Place the MOSFETs on the bottom side of the board, so that their pins stick out through the top of the board and the drain tab will be flush with the heatsink.
  • Mount the PCB onto the heatsink using 7mm M4 standoffs (or a 5mm standoff and 2 M5 washers).
  • Gently screw the MOSFETs into the heatsink using M3 screws.
  • Solder the two pins of each MOSFET which are not connected to a busbar on the top of the board. Do not attempt to solder the MOSFETs to the busbars yet.
  • Unscrew the MOSFETs and remove the heatsink to proceed to the next stage.


Solder the MOSFETs (part 2):

  • Heat up a busbar with the hot air gun.
  • Apply solder to a MOSFET drain or source pin
  • Continue heating the busbar and applying solder to the pin until you see a proper solder joint form between the MOSFET pin and the busbar. You may find that much of the solder is sucked onto the other side of the board, forming a large mount on the top of the MOSFET pin. You can clean this up later with solder wick.
  • Do not mistake solder beaded up on a pin as a proper solder joint. Your solder joint should have a concave fillet of solder extending from the pin to the busbar. If you can't achieve this, the busbar is not hot enough for soldering.


Temperature sensor installation:

  • It is best to get a 2-wire jumper cable with male or female 2.54mm pitch connectors (of the standard type found on Arduino, etc), and opposite polarity connector on the PCB, so that the temperature probe can be unplugged from the PCB. If you don't do this, you will need to desolder the probe connection on the PCB if you ever want to remove the PCB from the heatsink (for maintenance, etc).
  • Separate and strip about 1.5" from a 2-conductor cable, or from 2 individual wires. Place heatshrink tubing on both wires.
  • Splice each lead of the thermistor to a wire. Use a heat gun to shrink the heatshrink tubing over the splice, so that it is covered.
  • Place a small bead of thermal paste on the heatsink.
  • Place the bead of the thermistor onto the thermal paste. Secure the thermistor onto the heatsink with several pieces of high temperature HVAC tape.



NOTE: Ignore the thermal pads in the picture. You do not need to have the thermal pads on the heatsink at this point.

Heatsink assembly:

  • Place all of the thermal pads on the heatsink.
  • Carefully position the PCB (with soldered MOSFETs and busbars) over the heatsink.
  • Gently screw the MOSFETs into their mounting holes on the heatsink. During this process, the thermal pads may be rotated by the screw torque. You must carefully watch the thermal pads and use tweezers to keep them in the correct position.
  • Gradually tighten each MOSFET screw. Don't tighten any one screw all at once. Don't tighten any of them to the point where you feel significant resistance.
  • Make sure the MOSFETs are completely flush against the heatsink, as in the picture below.
  • Tighten the screws a little bit past the point where you feel significant resistance. Don't be too aggressive or you risk damaging the MOSFETs.


Final Assembly

  • Insert the long standoffs into the mounting holes on the fin side of the heatsink. Screw the short standoffs onto the studs from the long standoffs, on the copper side of heatsink. If you aren't able to find 7mm standoffs, you will need to use 2 M5 washers between the heatsink and the short standoffs.
  • Mount the PCB onto the heatsink. Gradually tighten the M3 screws for the MOSFETs and the M4 screws for the PCB and heatsink.
  • Position the heatsink over the countersunk holes in the case and screw it in.
  • Attach fan wires and I/O connectors.