Tuesday 12th April 2016, 8pm
Present: Alan D, Al B, Benjie G, Bracken D, James B, Mark H, Paul D, Richard G, Step S, Tyler W
Apologies: Jem G, Stephen C, Chris S
First we attempted to outline some of the issues the Dalek has and what we'd like to improve about him. These included things such as (in alphabetical order...):
- Accessibility to children (e.g. letting them control sound effects)
- Cosmetics - fix scaling issues, make him more accurate
- Decrease weight - decrease motor strain, increase stability, increase battery life
- Dome light brightness
- Dome light design
- Easier charging (preferably without having to remove the batteries)
- Easier assembly and wiring - anyone should be able to put him together
- Eyestalk camera - dalek vision
- Lack of motion - base - replace motor controller
- Lack of motion - dome rotation
- Lack of motion - eyestalk up and down
- Lack of motion - weapons XY and some action
- Replacing caster wheel - maneuverability and stability
- Safer electrics - fuses, better connectors, harder to get wrong, etc.
- Under-skirt lighting - late night safety/visibility when on the road/pavement
Next we decided that the most important thing to do was to get him moving around under his own steam again by replacing his motor controller.
First we evaluated using the existing motor controller, but confirmed that both Bracken and Benjie had found it to be broken (giving some very strange readings) and felt that it would not be safe to continue to attempt to resuscitate this heavily modified and tortured board.
Next Tyler was asked to fill us in on the work he'd been doing with Jeremy R on the various electronics; however Tyler was only able to tell us about the power distribution boards (which I'll come back to later).
Bracken told us that after Dave's initial attempts at building a motor controller design, he had had a go at doing so using the high power FETs we already have in the space. However, after doing a design and costing it out he said that the total cost for a safe solution capable of dealing with Alan's high current and high voltage motors would likely be in the region of £80.
With the amount of effort that had gone into researching (and dismissing) alternatives, it was unsurprising that we all agreed unanimously to spend up to £120 of our budget on a commercial H-Bridge circuit (expecting the cost to be in the region of £105). Task: Bracken to choose specific motor controller board and email to Benjie
It was also decided that we'd continue to use a shrimp (arduino) to control the motor controller for now since that enables us to maintain the hardware cut-off in the event of the 'brain' (Raspberry Pi) crashing.
Further it was decided that we would be consolidating the switch, breaker, motor controller, shrimp, and 12V accessory regulator into one ventilated enclosure which Step has offered to laser cut for us, including design time adding labels to all the relevant ports to make it very easy for anyone to put the Dalek together. It was decided not to progress on this enclosure until the various parts and connectors had arrived.
Next it was clear that we would need good connectors and wire to prevent any further incidences of melting.
The wire needs to carry the current easily, and to this end Bracken suggested somewhere between 12AWG and 8AWG wire and all agreed to leave it to him to decide. Task: Bracken to choose specific wire and email to Benjie
We had a lot of discussion around connectors and decided:
- the connectors should be easy to mount
- the connectors should have suitable current carrying capabilities
- different connectors should be used for different purposes to make it extremely challenging to incorrectly connect them
- the battery leads should be permanently affixed to the batteries with suitable connectors - they can be plugged into the motor controller box to run, or unplugged and plugged into a charger to charge
- the battery leads should have inline fuses, most likely automotive style, and we will have to purchase fuse holders capable of significant current
- Neutric SpeakON connectors were recommended
The connectors we will need on the motor controller box are:
- 2x 12V battery inputs (interchangeable) good for 50A+
- 2x 24V motors outputs (use lead length to prevent confusion) good for 25A+
- 1x 12V accessory feed (powers remainder of Dalek) good for up to 10A
- 1x rugged USB socket (perhaps type B?) to allow connection from the 'brain'
Task: Mark and Bracken to discuss suitable connectors given the above, and send a shopping list to Benjie
Next we moved onto discussion of the Dome. Initial fears about a fibreglass dome sustaining damage by children were quickly allayed by Richards salient point that children are in fact generally quite small, and Alan is quite tall. We discussed various ways of constructing the dome, and the lead plan is to attempt to build a hexagonal framework via 3D printer or laser cutter and to fill this with foam and then sculpt to a suitable shape. No full conclusion was made yet, so more ideas are still welcome.
Task: Step to send details of this method to the Dalek committee for further discussion
The Dome will need to rotate - suggestions for this included running a track around the lower part to support the weight and guide the Dome and having a stepper motor in the middle to rotate it. It was suggested that using strong magnets to connect to the stepper motor assembly would be a good way of making Alan both easy to assemble and resistent to shaking apart over bumpy terrain. It was also mentioned that keeping the weight off of the motor shaft where possible might be wise.
The Dome will also be equipped with an Eyestalk capable of pivoting up and down, the end of which will be equipped with blue LEDs and a Raspberry Pi camera. It's likely that we will want to buy another Pi 2 or even a Pi 3 to live in the Dome and perform the OpenCV or similar computer vision tasks to enable the Dalek to track faces, not to mention streaming Dalek vision. This Pi would most likely be connected to the 'brain' via Ethernet.
Many ideas were forwarded for an easier way to put the Dalek together, but nothing was concluded. It was clear however that no-one saw the current system of reaching all the way inside the Dalek to do the front bolts up as suitable.
On the wiring front, Tyler made an excellent suggestion that we have a dedicated connection area in each section of the Dalek with permanently fastened (and labelled!) connectors. This would enable us to plug in each connector in turn (preferably colour coded) just before placing the sections on top of each other and be sure that we haven't missed anything and further that it's unlikely they would come loose during Dalek operation.
Step suggested that having an "Alan box" inside of the skirt where we can keep relevant items, tools and spares (e.g. microphone, Wii Remote, Raspberry Pi, SD cards, bluetooth dongle, batteries for remotes, etc) essential to the running of the Dalek would be wise, and further offered to make one for us once the various parts had been agreed on. Further he suggested that it should come with an army-style inventory so that each item could be easily checked off before going to an event and before returning from one.
Ideas of what would go in Alan's box are welcome.
Tyler was keen to encourage us to adopt standards early in the development of the Dalek (inspired by his work on the Erica the Rhino project). He suggested that DMX is a good way to control lighting and similar things. Also it was generally agreed that we would standardise on the Autodesk suite of tools (since the 'space has licenses for these) for any 3D design work.
The Project Dalek plans were examined and it was made clear what the issues were with Alan's current design (and why those decisions were made). We evaluated the option of purchasing a pre-made fiberglass hull, but it was decided that that would be "cheating" - we are a Makerspace after all! General consensus was that laser cutting would be a good way of constructing the new shoulders, allowing for accuracy and speed and relatively low cost. No specific plans were made, however, since Chris S was not able to make it to the meeting and has some thoughts in this area.
A plan was hatched to have removable weapons modules of a known fixed size mounted onto some form of simple rail with a backplan connector somewhere supplying 12V and data connections. The modules should be self securing - once inserted they should not come out without the use of a tool or button. There should be a hollow behind the modules to allow for counter weights or liquid reservoirs.
Adopting this plan would give us the ability to work on weapons modules before the work on the shoulders is completed and fit them together at the end. The key thing to enable this would be committing to exact dimensions and then physically building a number of identical weapons boxes that can be used during the rest of the build to ensure compatibility. Laser cutter accuracy may be key here!
This also enables us to give Alan weapons upgrades, or to switch a water squirter for a bubble blower depending on the event.
Task: Tyler to look into servos for the weapons
One of the Dalek members may be able to get discounts at CPC/Farnell, so unless we have a better option placing orders (over £5) via them may be wise.
Task: Tyler to look into acquiring two lead acid battery chargers that may be able to be installed inside the Dalek
The main priority at this time is to get the Dalek moving again, so the first thing is to select the controller, wire and connectors, order them and get them installed. We will also be organising another meeting for roughly a months time, though hopefully by then other work will have taken place!
We'll be arranging another meeting for roughly a months time, there is contention over whether it should be on a Tuesday or not (pros: greater availability, cons: potentially in the way of other space users); if you have strong feelings either way then please get in touch.
The main topics for the next meeting will probably be an update on progress for the motor controller and beginning to commit to a plan for rebuilding the "shoulders" and dome - we're waiting to hear back from other contributors to the project on what their plans are so that we don't waste time reinventing the wheel.
If you would like to contribute to the Dalek project, please get in touch with Benjie; the more the merrier - there's plenty of work to go around!