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2019 Manufacturing run

After SP2018, it was decided that we should expand the summer school. Due to this, and also having had boards fail since the 2017 run, it was decided that we should do a manufacturing run.

The goals for the manufacturing run were to get us to the following quantities of kit:

Board Desired qty Qty we already had Qty to be manufactured
SR v4 Power Board 25 8 17
SR v4 Motor Board 25 9 16
SR v4 Servo Board 25 0 25

After the low yield rates of the 2017 run, along with lack of volunteers to manufacture in-house sustainably, we decided that we wanted to manufacture externally.

Putting together a quote pack

A quote pack was put together and sent out to a number of manufacturers. This quote pack contained (for each board):

  • The rendered gerber and drill files, for fabricating the PCBs.
  • A bill of materials, listing every component on the board and the supplier it is to be bought from.
  • The coordinates of each component, for configuring the manufacturer's pick-and-place machine.
  • Diagrams showing the name and orientation of each component, for aiding the manufacturing engineers in configuring the pick-and-place machine.
  • A schematic diagram of each board.
  • Human-readable notes describing the request for manufacture.

Generating the bill of materials

The BOMs we sent to the supplier were programmatically compiled from the original BOMs provided by Student Robotics and a human-curated file describing precisely what to replace out-of-stock components with. A Python application named bomtool was written to achieve this, but due to time constraints it ended up so full of special cases for this manufacture run that it would need major rework if we were to use it for manufacturing other boards in the future. Kier is working on pcbkit, a successor to bomtool.

Choosing a supplier

We reached out to six suppliers of PCB assembly services:

  • MyRO (recommended by Tyler)
  • Express Circuits (found by google search)
  • Circuitworx (a representative expressed interest in helping us at the UoS Careers Fair)
  • Beta Layout (the university's standard supplier for small quantity PCBs)
  • Soumac (recommended by Chris M)
  • Garner Osborne (manufactured all of SR's v4 boards and might still have the designs on file)

Three of these got back to us and were able to provide quotes:

Beta Layout MyRO Garner Osborne
Power board x 17
PCBs: £406.88 £223.02 (no breakdown given)
Assembly: £970.48 £804.62 (no breakdown given)
Components: £982.94 £1,678.64 (no breakdown given)
Subtotal: £2,360.30 £2,706.28 £2,501.50
(per board): £138.84 £159.19 £147.15
Motor board x 16
PCBs: £293.69 £208.68 (no breakdown given)
Assembly: £813.56 £655.70 (no breakdown given)
Components: £673.44 £830.83 (no breakdown given)
Subtotal: £1,780.69 £1,695.21 £1,938.76
(per board): £111.29 £105.95 £121.17
Servo board x 25
PCBs: £326.32 £218.92 (no breakdown given)
Assembly: £846.97 £761.27 (no breakdown given)
Components: £837.50 £1,219.98 (no breakdown given)
Subtotal: £2,010.80 £2,200.17 £2,415.50
(per board): £80.43 £88.01 £96.62
Total: £6,151.79 £6,601.67 £6,855.76
With vat £7,382.15 £7,922.00 £8,226.91

The decision was made to go with Beta Layout at the manufacturer.

Submitting the orders

The orders were placed via ECS Purchasing. Due to a miscommunication regarding the budget, the first order we placed only contained the power and motor boards. We later attempted to place a second order for the servo boards; however, at the time of writing (2019-10-23) it doesn't look like this order has reached the supplier.

The order instructions that we sent to ECS Purchasing can be found in the kit-manufacture-2019 repo. There are also some "special instructions" files that get sent to the manufacturer directly by copying their contents into a form as part of the order process.

Supporting the manufacture process

The supplier sent us a number of queries after the orders had been placed:

  • Informing us that they are unable to buy from one of the suppliers listed in our BOM and confirming whether they can buy the same part from a different supplier.
  • Asking for clarification on some notes in our BOM.
  • Asking us to review their shopping lists for components before they go ahead and buy them.
  • Asking us for clarification on the component orientation diagrams. They pointed out that the polarity markings are ambiguous or even missing on some components. Ultimately it was easier to just redraw the diagrams in a clearer way.
  • Confirming the number of through-hole components on the board - it turned out it had been entered incorrectly when placing the order.
  • Informing us that they cannot guarantee the quality of the mounting of the SMD components that are obscured by the buzzer on the power board.

Receiving the boards

The power and motor boards were received on the 23rd September 2019. As mentioned earlier, manufacture of the servo boards has not yet begun.

Finishing electronic assembly of the boards

The boards are recieved from Beta Layout with all surface-mount and through-hole soldered components attached; however there are still a number of steps to be completed before the boards are ready for use.

Power boards: mounting the fuse and captive cables

The power boards need three connectors (Farnell 1821273) to be mounted to the PCB. These are not soldered - instead they are pushed into the board with a press.

These connectors support a 40A midi fuse (Mouser 576-0498040.M) and the two captive battery cables, each of which is terminated with an M5 ring terminal (Farnell 2310102) at the power board and a male XT60 connector (Hobbytronics PRT-10474) at the battery.

The fuse and captive cables are secured to the connectors with three M5x6mm machine screws (Farnell 149483) and three M5 spring washers (Farnell 2506046).

Power boards: mounting the fan

Each power board needs a fan (e.g. Mouser 670-OD4010-12HSS, but any standard 40mm fan will do). It is mounted to the board with:

  • two M3x16mm machine screws (Farnell 7071000)
  • two M3 nylon washers (Farnell 2472664)
  • two M3 nuts (Farnell 7016943)
  • two M3x8mm bushings (Farnell 891435)

Power boards: mounting the button caps

The power button needs a red cap (Mouser 611-PVRD), and the start button needs a black one (Mouser 611-PVBK).

Flashing firmware onto the boards

The microcontroller needs to have its firmware uploaded onto it.

The tools repo has some docs on doing this for the power and motor boards. There are some further docs on doing this for the power board here.

Testing the boards

The boards need to be fully tested. It is advised to use the procedures provided by Student Robotics.

Manufacturing and fitting cases

Each board has a case made from laser-cut acrylic. Designs for these can be found in the respective hardware repositories. In the past we've been able to get time on ECS's laser cutting facilities to manufacture these.

Assembling the cases requires some screws and fixings etc. TODO: specifically what screws and fixings are needed?

Adding the boards to the inventory

We should ensure the boards are in our asset tracker.